研究者業績
基本情報
受賞
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2022年2月
論文
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Physics of the Dark Universe 35 100912-100912 2022年3月 査読有り
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Monthly Notices of the Royal Astronomical Society 507(1) 1528-1545 2021年10月1日We report here on the first multiwavelength (MWL) campaign on the blazar TXS 1515-273, undertaken in 2019 and extending from radio to very-high-energy gamma-rays (VHE). Up until now, this blazar had not been the subject of any detailed MWL observations. It has a rather hard photon index at GeV energies and was considered a candidate extreme high-synchrotron-peaked source. MAGIC observations resulted in the first-time detection of the source in VHE with a statistical significance of 7.6σ. The average integral VHE flux of the source is 6 ± 1 per cent of the Crab nebula flux above 400 GeV. X-ray coverage was provided by Swift-XRT, XMM-Newton, and NuSTAR. The long continuous X-ray observations were separated by ∼9 h, both showing clear hour scale flares. In the XMM-Newton data, both the rise and decay time-scales are longer in the soft X-ray than in the hard X-ray band, indicating the presence of a particle cooling regime. The X-ray variability time-scales were used to constrain the size of the emission region and the strength of the magnetic field. The data allowed us to determine the synchrotron peak frequency and classify the source as a flaring high, but not extreme synchrotron-peaked object. Considering the constraints and variability patterns from the X-ray data, we model the broad-band spectral energy distribution. We applied a simple one-zone model, which could not reproduce the radio emission and the shape of the optical emission, and a two-component leptonic model with two interacting components, enabling us to reproduce the emission from radio to VHE band.
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ASTRONOMY & ASTROPHYSICS 647 2021年3月 査読有りContext. QSO B1420+326 is a blazar classified as a flat-spectrum radio quasar (FSRQ). At the beginning of the year 2020, it was found to be in an enhanced flux state and an extensive multiwavelength campaign allowed us to trace the evolution of the flare.Aims. We search for very high-energy (VHE) gamma-ray emission from QSO B1420+326 during this flaring state. We aim to characterize and model the broadband emission of the source over different phases of the flare.Methods. The source was observed with a number of instruments in radio, near-infrared, optical (including polarimetry and spectroscopy), ultraviolet, X-ray, and gamma-ray bands. We use dedicated optical spectroscopy results to estimate the accretion disk and the dust torus luminosity. We performed spectral energy distribution modeling in the framework of combined synchrotron-self-Compton and external Compton scenario in which the electron energy distribution is partially determined from acceleration and cooling processes.Results. During the enhanced state, the flux of both SED components of QSO B1420+326 drastically increased and the peaks were shifted to higher energies. Follow-up observations with the MAGIC telescopes led to the detection of VHE gamma-ray emission from this source, making it one of only a handful of FSRQs known in this energy range. Modeling allows us to constrain the evolution of the magnetic field and electron energy distribution in the emission region. The gamma-ray flare was accompanied by a rotation of the optical polarization vector during a low -polarization state. Also, a new superluminal radio knot contemporaneously appeared in the radio image of the jet. The optical spectroscopy shows a prominent FeII bump with flux evolving together with the continuum emission and a MgII line with varying equivalent width.
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ASTROPHYSICAL JOURNAL 908(1) 2021年2月 査読有りThe coincident detection of GW170817 in gravitational waves and electromagnetic radiation spanning the radio to MeV gamma-ray bands provided the first direct evidence that short gamma-ray bursts (GRBs) can originate from binary neutron star (BNS) mergers. On the other hand, the properties of short GRBs in high-energy gamma-rays are still poorly constrained, with only similar to 20 events detected in the GeV band, and none in the TeV band. GRB 160821B is one of the nearest short GRBs known at z = 0.162. Recent analyses of the multiwavelength observational data of its afterglow emission revealed an optical-infrared kilonova component, characteristic of heavy-element nucleosynthesis in a BNS merger. Aiming to better clarify the nature of short GRBs, this burst was automatically followed up with the MAGIC telescopes, starting from 24 s after the burst trigger. Evidence of a gamma-ray signal is found above similar to 0.5 TeV at a significance of similar to 3 sigma during observations that lasted until 4 hr after the burst. Assuming that the observed excess events correspond to gamma-ray emission from GRB 160821B, in conjunction with data at other wavelengths, we investigate its origin in the framework of GRB afterglow models. The simplest interpretation with one-zone models of synchrotron-self-Compton emission from the external forward shock has difficulty accounting for the putative TeV flux. Alternative scenarios are discussed where the TeV emission can be relatively enhanced. The role of future GeV-TeV observations of short GRBs in advancing our understanding of BNS mergers and related topics is briefly addressed.
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Proceedings Volume 11451, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation IV 114510G 2020年12月13日
MISC
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Proceedings of Science 395 787 2022年3月 査読有り
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Proceedings of Science 358 703 2019年7月 査読有り
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2017年9月12日List of contributions from the Cherenkov Telescope Array Consortium presented<br /> at the 35th International Cosmic Ray Conference, July 12-20 2017, Busan, Korea.
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ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES 232(1) 2017年9月Spontaneous breaking of Lorentz symmetry at energies on the order of the Planck energy or lower is predicted by many quantum gravity theories, implying non-trivial dispersion relations for the photon in vacuum. Consequently, gamma-rays of different energies, emitted simultaneously from astrophysical sources, could accumulate measurable differences in their time of flight until they reach the Earth. Such tests have been carried out in the past using fast variations of gamma-ray flux from pulsars, and more recently from active galactic nuclei and gamma-ray bursts. We present new constraints studying the gamma-ray emission of the galactic Crab Pulsar, recently observed up to TeV energies by the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) collaboration. A profile likelihood analysis of pulsar events reconstructed for energies above 400. GeV finds no significant variation in arrival time as their energy increases.. Ninety-five percent CL limits are obtained on the effective Lorentz invariance violating energy scale at the level of E-QG1 > 5.5 x 10(17) GeV (4.5 x 10(17) GeV) for a linear, and E-QG2 > 5.9 x 10(10) GeV (5.3 x 10(10) GeV) for a quadratic scenario, for the subluminal and the superluminal cases, respectively. A substantial part of this study is dedicated to calibration of the test statistic, with respect to bias and coverage properties. Moreover, the limits take into account systematic uncertainties, which are found to worsen the statistical limits by about 36%-42%. Our constraints would have been much more stringent if the intrinsic pulse shape of the pulsar between 200 GeV and 400 GeV was understood in sufficient detail and allowed inclusion of events well below 400 GeV.
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ASTROPARTICLE PHYSICS 94 29-41 2017年9月MAGIC, a system of two imaging atmospheric Cherenkov telescopes, achieves its best performance under dark conditions, i.e. in absence of moonlight or twilight. Since operating the telescopes only during dark time would severely limit the duty cycle, observations are also performed when the Moon is present in the sky. Here we develop a dedicated Moon-adapted analysis to characterize the performance of MAGIC under moonlight. We evaluate energy threshold, angular resolution and sensitivity of MAGIC under different background light levels, based on Crab Nebula observations and tuned Monte Carlo simulations. This study includes observations taken under non-standard hardware configurations, such as reducing the camera photomultiplier tubes gain by a factor similar to 1.7 (reduced HV settings) with respect to standard settings (nominal HV) or using UV-pass filters to strongly reduce the amount of moonlight reaching the cameras of the telescopes. The Crab Nebula spectrum is correctly reconstructed in all the studied illumination levels, that reach up to 30 times brighter than under dark conditions. The main effect of moonlight is an increase in the analysis energy threshold and in the systematic uncertainties on the flux normalization. The sensitivity degradation is constrained to be below 10%, within 15-30% and between 60 and 80% for nominal HV, reduced HV and UV-pass filter observations, respectively. No worsening of the angular resolution was found. Thanks to observations during moonlight, the maximal duty cycle of MAGIC can be increased from similar to 18%, under dark nights only, to up to similar to 40% in total with only moderate performance degradation. (C) 2017 Elsevier B.V. All rights reserved.
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2017年8月17日MAGIC (Major Atmospheric Gamma Imaging Cherenkov) is a system of two 17 m<br /> diameter, F/1.03 Imaging Atmospheric Cherenkov Telescopes (IACT). They are<br /> dedicated to the observation of gamma rays from galactic and extragalactic<br /> sources in the very high energy range (VHE, 30 GeV to 100 TeV). This submission<br /> contains links to the proceedings for the 35th International Cosmic Ray<br /> Conference (ICRC2017), held in Bexco, Busan, Korea from the 12th to the 17th of<br /> July, 2017.
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ASTRONOMY & ASTROPHYSICS 603 2017年7月Aims. We present an extensive study of the BL Lac object Mrk 501 based on a data set collected during the multi-instrument campaign spanning from 2009 March 15 to 2009 August 1, which includes, among other instruments, MAGIC, VERITAS, Whipple 10 m, and Fermi-LAT to cover the gamma-ray range from 0.1 GeV to 20 TeV; RXTE and Swift to cover wavelengths from UV to hard X-rays; and GASP-WEBT, which provides coverage of radio and optical wavelengths. Optical polarization measurements were provided for a fraction of the campaign by the Steward and St. Petersburg observatories. We evaluate the variability of the source and interband correlations, the gamma-ray flaring activity occurring in May 2009, and interpret the results within two synchrotron self-Compton (SSC) scenarios. Methods. The multiband variability observed during the full campaign is addressed in terms of the fractional variability, and the possible correlations are studied by calculating the discrete correlation function for each pair of energy bands where the significance was evaluated with dedicated Monte Carlo simulations. The space of SSC model parameters is probed following a dedicated grid-scan strategy, allowing for a wide range of models to be tested and offering a study of the degeneracy of model-to-data agreement in the individual model parameters, hence providing a less biased interpretation than the "single-curve SSC model adjustment" typically reported in the literature. Results. We find an increase in the fractional variability with energy, while no significant interband correlations of flux changes are found on the basis of the acquired data set. The SSC model grid-scan shows that the flaring activity around May 22 cannot be modeled adequately with a one-zone SSC scenario (using an electron energy distribution with two breaks), while it can be suitably described within a two (independent) zone SSC scenario. Here, one zone is responsible for the quiescent emission from the averaged 4.5-month observing period, while the other one, which is spatially separated from the first, dominates the flaring emission occurring at X-rays and very-high-energy (> 100 GeV, VHE) gamma-rays. The flaring activity from May 1, which coincides with a rotation of the electric vector polarization angle (EVPA), cannot be satisfactorily reproduced by either a one-zone or a two-independent-zone SSC model, yet this is partially affected by the lack of strictly simultaneous observations and the presence of large flux changes on sub-hour timescales (detected at VHE gamma rays). Conclusions. The higher variability in the VHE emission and lack of correlation with the X-ray emission indicate that, at least during the 4.5-month observing campaign in 2009, the highest energy (and most variable) electrons that are responsible for the VHE gamma rays do not make a dominant contribution to the similar to 1 keV emission. Alternatively, there could be a very variable component contributing to the VHE gamma-ray emission in addition to that coming from the SSC scenario. The studies with our dedicated SSC grid-scan show that there is some degeneracy in both the one-zone and the two-zone SSC scenarios probed, with several combinations of model parameters yielding a similar model-to-data agreement, and some parameters better constrained than others. The observed gamma-ray flaring activity, with the EVPA rotation coincident with the first gamma-ray flare, resembles those reported previously for low frequency peaked blazars, hence suggesting that there are many similarities in the flaring mechanisms of blazars with different jet properties.
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ASTRONOMY & ASTROPHYSICS 603 2017年7月Context. PKS 1510 089 is one of only a few flat spectrum radio quasars detected in the very-high-energy (VHE, > 100 GeV) gamma-ray band. Aims. We study the broadband spectral and temporal properties of the PKS 1510 089 emission during a high gamma-ray state. Methods. We performed VHE gamma-ray observations of PKS 1510 089 with the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescopes during a long, high gamma-ray state in May 2015. In order to perform broadband modeling of the source, we have also gathered contemporaneous multiwavelength data in radio, IR, optical photometry and polarization, UV, X-ray, and GeV gamma-ray ranges. We construct a broadband spectral energy distribution (SED) in two periods, selected according to VHE gamma-ray state. Results. PKS 1510 089 was detected by MAGIC during a few day-long observations performed in the middle of a long, high optical and gamma-ray state, showing for the first time a significant VHE gamma-ray variability. Similarly to the optical and gamma-ray high state of the source detected in 2012, it was accompanied by a rotation of the optical polarization angle and the emission of a new jet component observed in radio. However, owing to large uncertainty on the knot separation time, the association with the VHE gamma-ray emission cannot be firmly established. The spectral shape in the VHE band during the flare is similar to those obtained during previous measurements of the source. The observed flux variability sets constraints for the first time on the size of the region from which VHE gamma rays are emitted. We model the broadband SED in the framework of the external Compton scenario and discuss the possible emission site in view of multiwavelength data and alternative emission models.
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ASTRONOMY & ASTROPHYSICS 603 2017年7月Context. The extragalactic very-high-energy gamma-ray sky is rich in blazars. These are jetted active galactic nuclei that are viewed at a small angle to the line-of-sight. Only a handful of objects viewed at a larger angle are so far known to emit above 100 GeV. Multi-wavelength studies of such objects up to the highest energies provide new insights into the particle and radiation processes of active galactic nuclei. Aims. We aim to report the results from the first multi-wavelength campaign observing the TeV detected nucleus of the active galaxy IC 310, whose jet is observed at a moderate viewing angle of 10 degrees-20 degrees. Methods. The multi-instrument campaign was conducted between 2012 November and 2013 January, and involved observations with MAGIC, Fermi, INTEGRAL, Swift, OVRO, MOJAVE and EVN. These observations were complemented with archival data from the AllWISE and 2MASS catalogs. A one-zone synchrotron self-Compton model was applied to describe the broadband spectral energy distribution. Results. IC 310 showed an extraordinary TeV flare at the beginning of the campaign, followed by a low, but still detectable TeV flux. Compared to previous measurements in this energy range, the spectral shape was found to be steeper during the low emission state. Simultaneous observations in the soft X-ray band showed an enhanced energy flux state and a harder-when-brighter spectral shape behavior. No strong correlated flux variability was found in other frequency regimes. The broadband spectral energy distribution obtained from these observations supports the hypothesis of a double-hump structure. Conclusions. The harder-when-brighter trend in the X-ray and VHE emission, observed for the first time during this campaign, is consistent with the behavior expected from a synchrotron self-Compton scenario. The contemporaneous broadband spectral energy distribution is well described with a one-zone synchrotron self-Compton model using parameters that are comparable to those found for other gamma-ray-emitting misaligned blazars.
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MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 468(2) 1534-1541 2017年6月We present the first detection of the nearby (z = 0.084) low-luminosity BL Lac object 1ES 1741+196 in the very high energy (E > 100 GeV) band. This object lies in a triplet of interacting galaxies. Early predictions had suggested 1ES 1741+196 to be, along with several other high-frequency BL Lac sources, within the reach of MAGIC detectability. Its detection by MAGIC, later confirmed by VERITAS, helps to expand the small population of known TeV BL Lacs. The source was observed with the MAGIC telescopes between 2010 April and 2011 May, collecting 46 h of good quality data. These observations led to the detection of the source at 6.0 s confidence level, with a steady flux F(> 100 GeV) = (6.4 +/- 1.7(stat) +/- 2.6(syst)) x 10-12 ph cm(-2)s(-1) and a differential spectral photon index Gamma = 2.4 +/- 0.2(stat) +/- 0.2(syst) in the range of similar to 80 GeV-3 TeV. To study the broad-band spectral energy distribution (SED) simultaneous with MAGIC observations, we use KVA, Swift/UVOT and XRT and Fermi/LAT data. One-zone synchrotron-self-Compton (SSC) modelling of the SED of 1ES 1741+196 suggests values for the SSC parameters that are quite common among known TeV BL Lacs except for a relatively low Doppler factor and slope of electron energy distribution. A thermal feature seen in the SED is well matched by a giant elliptical's template. This appears to be the signature of thermal emission from the host galaxy, which is clearly resolved in optical observations.
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ASTROPHYSICAL JOURNAL 840(2) 2017年5月We perform simulations for future Cherenkov Telescope Array (CTA) observations of RX J1713.7-3946, a young supernova remnant (SNR) and one of the brightest sources ever discovered in very high energy (VHE) gamma rays. Special attention is paid to exploring possible spatial (anti) correlations of gamma rays with emission at other wavelengths, in particular X-rays and CO/H I emission. We present a series of simulated images of RX J1713.7-3946 for CTA based on a set of observationally motivated models for the gamma-ray emission. In these models, VHE gamma rays produced by high-energy electrons are assumed to trace the nonthermal X-ray emission observed by XMM-Newton, whereas those originating from relativistic protons delineate the local gas distributions. The local atomic and molecular gas distributions are deduced by the NANTEN team from CO and H I observations. Our primary goal is to show how one can distinguish the emission mechanism(s) of the gamma rays (i.e., hadronic versus leptonic, or a mixture of the two) through information provided by their spatial distribution, spectra, and time variation. This work is the first attempt to quantitatively evaluate the capabilities of CTA to achieve various proposed scientific goals by observing this important cosmic particle accelerator.
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ASTRONOMY & ASTROPHYSICS 601 2017年5月Context. We present the results of a multi-year monitoring campaign of the Galactic center (GC) with the MAGIC telescopes. These observations were primarily motivated by reports that a putative gas cloud (G2) would be passing in close proximity to the super-massive black hole (SMBH), associated with Sagittarius A*, located at the center of our galaxy. This event was expected to give astronomers a unique chance to study the effect of in-falling matter on the broad-band emission of a SMBH. Aims. We search for potential flaring emission of very-high-energy (VHE; >= 100 GeV) gamma rays from the direction of the SMBH at the GC due to the passage of the G2 object. Using these data we also study the morphology of this complex region. Methods. We observed the GC region with the MAGIC Imaging Atmospheric Cherenkov Telescopes during the period 2012-2015, collecting 67 h of good-quality data. In addition to a search for variability in the flux and spectral shape of the GC gamma-ray source, we use a point-source subtraction technique to remove the known gamma-ray emitters located around the GC in order to reveal the TeV morphology of the extended emission inside that region. Results. No effect of the G2 object on the VHE gamma-ray emission from the GC was detected during the 4 yr observation campaign. We confirm previous measurements of the VHE spectrum of Sagittarius A*, and do not detect any significant variability of the emission from the source. Furthermore, the known VHE gamma-ray emitter at the location of the supernova remnant G0.9+0.1 was detected, as well as the recently discovered VHE source close to the GG radio arc.
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A&A 602, A98 (2017) 2017年2月25日In this work we present data from observations with the MAGIC telescopes of<br /> SN 2014J detected in January 21 2014, the closest Type Ia supernova since<br /> Imaging Air Cherenkov Telescopes started to operate. We probe the possibility<br /> of very-high-energy (VHE; $E\geq100$ GeV) gamma rays produced in the early<br /> stages of Type Ia supernova explosions. We performed follow-up observations<br /> after this supernova explosion for 5 days, between January 27 and February 2 in<br /> 2014. We search for gamma-ray signal in the energy range between 100 GeV and<br /> several TeV from the location of SN 2014J using data from a total of $\sim5.5$<br /> hours of observations. Prospects for observing gamma-rays of hadronic origin<br /> from SN 2014J in the near future are also being addressed. No significant<br /> excess was detected from the direction of SN 2014J. Upper limits at 95$\%$<br /> confidence level on the integral flux, assuming a power-law spectrum,<br /> d$F/$d$E\propto E^{-\Gamma}$, with a spectral index of $\Gamma=2.6$, for<br /> energies higher than 300 GeV and 700 GeV, are established at<br /> $1.3\times10^{-12}$ and $4.1\times10^{-13}$ photons~cm$^{-2}$s$^{-1}$,<br /> respectively. For the first time, upper limits on the VHE emission of a Type Ia<br /> supernova are established. The energy fraction isotropically emitted into TeV<br /> gamma rays during the first $\sim10$ days after the supernova explosion for<br /> energies greater than 300 GeV is limited to $10^{-6}$ of the total available<br /> energy budget ($\sim 10^{51}$ erg). Within the assumed theoretical scenario,<br /> the MAGIC upper limits on the VHE emission suggest that SN 2014J will not be<br /> detectable in the future by any current or planned generation of Imaging<br /> Atmospheric Cherenkov Telescopes.
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ASTROPHYSICAL JOURNAL 834(1) 2017年1月Blazars are variable emitters across all wavelengths over a wide range of timescales, from months down to minutes. It is therefore essential to observe blazars simultaneously at different wavelengths, especially in the X-ray and gamma-ray bands, where the broadband spectral energy distributions usually peak. In this work, we report on three " target-of-opportunity" observations of Mrk 421, one of the brightest TeV blazars, triggered by a strong flaring event at TeV energies in 2014. These observations feature long, continuous, and simultaneous exposures with XMM-Newton (covering the X-ray and optical/ultraviolet bands) and VERITAS (covering the TeV gamma-ray band), along with contemporaneous observations from other gamma-ray facilities (MAGIC and Fermi-Large Area Telescope) and a number of radio and optical facilities. Although neither rapid flares nor significant X-ray/TeV correlation are detected, these observations reveal subtle changes in the X-ray spectrum of the source over the course of a few days. We search the simultaneous X-ray and TeV data for spectral hysteresis patterns and time delays, which could provide insight into the emission mechanisms and the source properties (e. g., the radius of the emitting region, the strength of the magnetic field, and related timescales). The observed broadband spectra are consistent with a one-zone synchrotron self-Compton model. We find that the power spectral density distribution at greater than or similar to 4 x 10(-4) Hz from the X-ray data can be described by a power-law model with an index value between 1.2 and 1.8, and do not find evidence for a steepening of the power spectral index (often associated with a characteristic length scale) compared to the previously reported values at lower frequencies.
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JOURNAL OF INSTRUMENTATION 11 2016年11月We describe and report the status of a neutrino-triggered program in IceCube that generates real-time alerts for gamma-ray follow-up observations by atmospheric-Cherenkov telescopes (MAGIC and VERITAS). While IceCube is capable of monitoring the whole sky continuously, high-energy gamma-ray telescopes have restricted fields of view and in general are unlikely to be observing a potential neutrino-flaring source at the time such neutrinos are recorded. The use of neutrino-triggered alerts thus aims at increasing the availability of simultaneous multi-messenger data during potential neutrino flaring activity, which can increase the discovery potential and constrain the phenomenological interpretation of the high-energy emission of selected source classes (e. g. blazars). The requirements of a fast and stable online analysis of potential neutrino signals and its operation are presented, along with first results of the program operating between 14 March 2012 and 31 December 2015.
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ASTRONOMY & ASTROPHYSICS 595 2016年11月Context. QSO B0218+357 is a gravitationally lensed blazar located at a redshift of 0.944. The gravitational lensing splits the emitted radiation into two components that are spatially indistinguishable by gamma-ray instruments, but separated by a 10-12 day delay. In July 2014, QSO B0218+357 experienced a violent flare observed by the Fermi-LAT and followed by the MAGIC telescopes. Aims. The spectral energy distribution of QSO B0218+357 can give information on the energetics of z similar to 1 very high energy gamma-ray sources. Moreover the gamma-ray emission can also be used as a probe of the extragalactic background light at z similar to 1. Methods. MAGIC performed observations of QSO B0218+357 during the expected arrival time of the delayed component of the emission. The MAGIC and Fermi-LAT observations were accompanied by quasi-simultaneous optical data from the KVA telescope and X-ray observations by Swift-XRT. We construct a multiwavelength spectral energy distribution of QSO B0218+357 and use it to model the source. The GeV and sub-TeV data obtained by Fermi-LAT and MAGIC are used to set constraints on the extragalactic background light. Results. Very high energy gamma-ray emission was detected from the direction of QSO B0218 +357 by the MAGIC telescopes during the expected time of arrival of the trailing component of the flare, making it the farthest very high energy gamma-ray source detected to date. The observed emission spans the energy range from 65 to 175 GeV. The combined MAGIC and Fermi-LAT spectral energy distribution of QSO B0218+357 is consistent with current extragalactic background light models. The broadband emission can be modeled in the framework of a two-zone external Compton scenario, where the GeV emission comes from an emission region in the jet, located outside the broad line region.
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2016年10月17日List of contributions from the Cherenkov Telescope Array (CTA) Consortium<br /> presented at the 6th International Symposium on High-Energy Gamma-Ray Astronomy<br /> (Gamma 2016), July 11-15, 2016, in Heidelberg, Germany.
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ASTRONOMY & ASTROPHYSICS 593 2016年9月Aims. We study the multi-band variability and correlations of the TeV blazar Mrk 421 on year timescales, which can bring additional insight on the processes responsible for its broadband emission. Methods. We observed Mrk 421 in the very high energy (VHE) gamma-ray range with the Cherenkov telescope MAGIC-I from March 2007 to June 2009 for a total of 96 h of effective time after quality cuts. The VHE flux variability is quantified using several methods, including the Bayesian Block algorithm, which is applied to data from Cherenkov telescopes here for the first time. The 2.3 yr long MAGIC light curve is complemented with data from the Swift/BAT and RXTE/ASM satellites and the KVA, GASP-WEBT, OVRO, and Metsahovi telescopes from February 2007 to July 2009, allowing for an excellent characterisation of the multi-band variability and correlations over year timescales. Results. Mrk 421 was found in different gamma-ray emission states during the 2.3 yr long observation period: The flux above 400 GeV spans from the minimum nightly value of (1.3 +/- 0.4) x 10(-11) cm(-2) s(-1) to the maximum flux, that is about 24 times higher, at (3.1 +/- 0.1) x 10(-10) cm(-2) s(-1). Flares and different levels of variability in the gamma-ray light curve could be identified with the Bayesian Block algorithm. The same behaviour of a quiet and active emission was found in the X-ray light curves measured by Swift/BAT and the RXTE/ASM, with a direct correlation in time. The behaviour of the optical light curve of GASP-WEBT and the radio light curves by OVRO and Metsahovi are different as they show no coincident features with the higher energetic light curves and a less variable emission. Overall, the fractional variability increases with energy. The comparable variability in the X-ray and VHE bands and their direct correlation during both high-and low-activity periods spanning many months show that the electron populations radiating the X-ray and gamma-ray photons are either the same, as expected in the synchrotron-self-Compton mechanism, or at least strongly correlated, as expected in electromagnetic cascades.
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A&A 591, A76 (2016) 591 2016年7月The gamma-ray binary LS I +61$^{\circ}$303 is a well established source from<br /> centimeter radio up to very high energy (VHE; E$>$100 GeV). Its broadband<br /> emission shows a periodicity of $\sim$26.5 days, coincident with the orbital<br /> period. A longer (super-orbital) period of 1667 $\pm$ 8 days was discovered in<br /> radio and confirmed in optical and high energy (HE; E>100 MeV) gamma-ray<br /> observations. We present a four-year campaign performed by MAGIC together with<br /> archival data concentrating on a search for a long timescale signature in the<br /> VHE emission. We focus on the search for super-orbital modulation of the VHE<br /> peak and on the search for correlations between TeV emission and optical<br /> determination of the extension of the circumstellar disk. A four-year campaign<br /> has been carried out by MAGIC. The source was observed during the orbital<br /> phases when the periodic VHE outbursts have occurred ($\phi$=0.55-0.75).<br /> Additionally, we included archival MAGIC observations and data published by the<br /> VERITAS collaboration in these studies. For the correlation studies, LS I<br /> +61$^{\circ}$303 has also been observed during the orbital phases where<br /> sporadic VHE emission had been detected in the past ($\phi$=0.75-1.0). These<br /> MAGIC observations were simultaneous with optical spectroscopy from the<br /> LIVERPOOL telescope. The TeV flux of the periodical outburst in orbital phases<br /> $\phi$=0.5--0.75 was found to show yearly variability consistent with the<br /> $\sim$4.5 years long-term modulation found in the radio band. This modulation<br /> of the TeV flux can be well described by a sine function with the best fit<br /> period of $1610\pm 58$ days. The complete dataset span two super-orbital<br /> periods. There is no evidence for a correlation between the TeV emission and<br /> the mass-loss rate of the Be star but this may be affected by the strong, short<br /> timescale (as short as intra-day) variation displayed by the H$\alpha$ fluxes.
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MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 459(3) 3271-3281 2016年7月The Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes observed the BL Lac object H1722+119 (redshift unknown) for six consecutive nights between 2013 May 17 and 22, for a total of 12.5 h. The observations were triggered by high activity in the optical band measured by the KVA (Kungliga Vetenskapsakademien) telescope. The source was for the first time detected in the very high energy (VHE, E > 100 GeV) gamma-ray band with a statistical significance of 5.9s. The integral flux above 150 GeV is estimated to be (2.0 +/- 0.5) per cent of the Crab nebula flux. We used contemporaneous high energy (HE, 100 MeV < E < 100 GeV) gamma-ray observations from Fermi-Large Area Telescope to estimate the redshift of the source. Within the framework of the current extragalactic background light models, we estimate the redshift to be z = 0.34 +/- 0.15. Additionally, we used contemporaneous X-ray to radio data collected by the instruments on board the Swift satellite, the KVA, and the Owens Valley Radio Observatory telescope to study multifrequency characteristics of the source. We found no significant temporal variability of the flux in the HE and VHE bands. The flux in the optical and radio wavebands, on the other hand, did vary with different patterns. The spectral energy distribution of H1722+119 shows surprising behaviour in the similar to 3 x 10(14)-10(18) Hz frequency range. It can be modelled using an inhomogeneous helical jet synchrotron self-Compton model.
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MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 459(3) 2286-2298 2016年7月The BL Lac object 1ES 1011+ 496 was discovered at very high energy (VHE, E > 100GeV) gamma-rays by Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) in Spring 2007. Before that the source was little studied in different wavelengths. Therefore, a multiwave-length (MWL) campaign was organized in Spring 2008. Along MAGIC, the MWL campaign included the Mets " ahovi Radio Observatory, Bell and Kungliga Vetenskapsakademien (KVA) optical telescopes and the Swift and AGILE satellites. MAGIC observations span from 2008 March to May for a total of 27.9 h, of which 19.4 h remained after quality cuts. The light curve showed no significant variability yielding an integral flux above 200GeVof (1.3 +/- 0.3) x10(-11) photons cm(-2) s(-1). The differential VHE spectrum could be described with a power-law function with a spectral index of 3.3 +/- 0.4. Both results were similar to those obtained during the discovery. Swift X-ray Telescope observations revealed an X-ray flare, characterized by a harder-when-brighter trend, as is typical for high synchrotron peak BL Lac objects (HBL). Strong optical variability was found during the campaign, but no conclusion on the connection between the optical and VHE gamma-ray bands could be drawn. The contemporaneous spectral energy distribution shows a synchrotron-dominated source, unlike concluded in previous work based on non-simultaneous data, and is well described by a standard one-zone synchrotron self-Compton model. We also performed a study on the source classification. While the optical and X-ray data taken during our campaign show typical characteristics of an HBL, we suggest, based on archival data, that 1ES 1011+496 is actually a borderline case between intermediate and high synchrotron peak frequency BL Lac objects.
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ASTRONOMY & ASTROPHYSICS 591 2016年7月The Geminga pulsar, one of the brighest gamma-ray sources, is a promising candidate for emission of very-high-energy (VHE > 100 GeV) pulsed gamma rays. Also, detection of a large nebula has been claimed by water Cherenkov instruments. We performed deep observations of Geminga with the MAGIC telescopes, yielding 63 h of good-quality data, and searched for emission from the pulsar and pulsar wind nebula. We did not find any significant detection, and derived 95% confidence level upper limits. The resulting upper limits of 5.3 x 10(-13) TeV cm(-2) s(-1) for the Geminga pulsar and 3.5 x 10(-12) TeV cm(-2) s(-1) for the surrounding nebula at 50 GeV are the most constraining ones obtained so far at VHE. To complement the VHE observations, we also analyzed 5 yr of Fermi-LAT data from Geminga, finding that the sub-exponential cut-off is preferred over the exponential cut-off that has been typically used in the literature. We also find that, above 10 GeV, the gamma-ray spectra from Geminga can be described with a power law with index softer than 5. The extrapolation of the power-law Fermi-LAT pulsed spectra to VHE goes well below the MAGIC upper limits, indicating that the detection of pulsed emission from Geminga with the current generation of Cherenkov telescopes is very difficult.
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ASTRONOMY & ASTROPHYSICS 591 2016年7月Context. 1ES 1011+496 (z = 0.212) was discovered in very high-energy (VHE, E > 100 GeV) gamma rays with MAGIC in 2007. The absence of simultaneous data at lower energies led to an incomplete characterization of the broadband spectral energy distribution (SED). Aims. We study the source properties and the emission mechanisms, probing whether a simple one-zone synchrotron self-Compton (SSC) scenario is able to explain the observed broadband spectrum. Methods. We analyzed data in the range from VHE to radio data from 2011 and 2012 collected by MAGIC, Fermi-LAT, Swift, KVA, OVRO, and Metsahovi in addition to optical polarimetry data and radio maps from the Liverpool Telescope and MOJAVE. Results. The VHE spectrum was fit with a simple power law with a photon index of 3.69 +/- 0.22 and a flux above 150 GeV of (1.46 +/- 0.16) x 10(-11) ph cm(-2) s(-1). The source 1ES 1011+496 was found to be in a generally quiescent state at all observed wavelengths, showing only moderate variability from radio to X-rays. A low degree of polarization of less than 10% was measured in optical, while some bright features polarized up to 60% were observed in the radio jet. A similar trend in the rotation of the electric vector position angle was found in optical and radio. The radio maps indicated a superluminal motion of 1.8 +/- 0.4 c, which is the highest speed statistically significant measured so far in a high-frequency-peaked BL Lac. Conclusions. For the first time, the high-energy bump in the broadband SED of 1ES 1011+496 could be fully characterized from 0.1 GeV to 1 TeV, which permitted a more reliable interpretation within the one-zone SSC scenario. The polarimetry data suggest that at least part of the optical emission has its origin in some of the bright radio features, while the low polarization in optical might be due to the contribution of parts of the radio jet with different orientations of the magnetic field with respect to the optical emission.
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ASTRONOMY & ASTROPHYSICS 590 2016年6月Context. During February-March 2014, the MAGIC telescopes observed the high-frequency peaked BL Lac 1ES 1011 + 496 (z = 0.212) in flaring state at very-high energy (VHE, E > 100 GeV). The flux reached a level of more than ten times higher than any previously recorded flaring state of the source. Aims. To describe the characteristics of the flare presenting the light curve and the spectral parameters of the night-wise spectra and the average spectrum of the whole period. From these data we aim to detect the imprint of the extragalactic background light (EBL) in the VHE spectrum of the source, to constrain its intensity in the optical band. Methods. We analyzed the gamma-ray data from the MAGIC telescopes using the standard MAGIC software for the production of the light curve and the spectra. To constrain the EBL, we implement the method developed by the H.E.S.S. collaboration, in which the intrinsic energy spectrum of the source is modeled with a simple function (<= 4 parameters), and the EBL-induced optical depth is calculated using a template EBL model. The likelihood of the observed spectrum is then maximized, including a normalization factor for the EBL opacity among the free parameters. Results. The collected data allowed us to describe the night-wise flux changes and also to produce differential energy spectra for all nights in the observed period. The estimated intrinsic spectra of all the nights could be fitted by power-law functions. Evaluating the changes in the fit parameters, we conclude that the spectral shape for most of the nights were compatible, regardless of the flux level, which enabled us to produce an average spectrum from which the EBL imprint could be constrained. The likelihood ratio test shows that the model with an EBL density 1.07 (-0.20, + 0.24)(stat+sys), relative to the one in the tested EBL template, is preferred at the 4.6 sigma level to the no-EBL hypothesis, with the assumption that the intrinsic source spectrum can be modeled as a log-parabola. This would translate into a constraint of the EBL density in the wavelength range [0.24 mu m, 4.25 mu m], with a peak value at 1.4 mu m of lambda F-lambda = 12. 27(-2.29)(+2.75) nWm(-2) sr(-1), including systematics.
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ASTRONOMY & ASTROPHYSICS 589 2016年5月Clusters of galaxies are expected to be reservoirs of cosmic rays (CRs) that should produce diffuse gamma-ray emission due to their hadronic interactions with the intra-cluster medium. The nearby Perseus cool-core cluster, identified as the most promising target to search for such an emission, has been observed with the MAGIC telescopes at very-high energies (VHE, E greater than or similar to 100GeV) for a total of 253 h from 2009 to 2014. The active nuclei of NGC1275, the central dominant galaxy of the cluster, and IC310, lying at about 0.6 degrees from the centre, have been detected as point-like VHE gamma-ray emitters during the first phase of this campaign. We report an updated measurement of the NGC1275 spectrum, which is described well by a power law with a photon index Gamma = 3.6 +/- 0.2(stat) +/- 0.2(syst) between 90GeV and 1200 GeV. We do not detect any diffuse gamma-ray emission from the cluster and so set stringent constraints on its CR population. To bracket the uncertainties over the CR spatial and spectral distributions, we adopt different spatial templates and power-law spectral indexes alpha. For alpha = 2.2, the CR-to-thermal pressure within the cluster virial radius is constrained to be less than or similar to 1-2%, except if CRs can propagate out of the cluster core, generating a flatter radial distribution and releasing the CR-to-thermal pressure constraint to less than or similar to 20%. Assuming that the observed radio mini-halo of Perseus is generated by secondary electrons from CR hadronic interactions, we can derive lower limits on the central magnetic field, B-0, that depend on the CR distribution. For alpha = 2.2, B-0 greater than or similar to 5-8 mu G, which is below the similar to 25 mu G inferred from Faraday rotation measurements, whereas for alpha less than or similar to 2.1, the hadronic interpretation of the diffuse radio emission contrasts with our gamma-ray flux upper limits independently of the magnetic field strength.
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ASTROPHYSICAL JOURNAL 819(2) 2016年3月We present coordinated multiwavelength observations of the bright, nearby BL Lacertae object Mrk 421 taken in 2013 January-March, involving GASP-WEBT, Swift, NuSTAR, Fermi-LAT, MAGIC, VERITAS, and other collaborations and instruments, providing data from radio to very high energy. (VHE).-ray bands. NuSTAR yielded previously unattainable sensitivity in the 3-79. keV range, revealing that the spectrum softens when the source is dimmer until the X-ray spectral shape saturates into a steep Gamma approximate to 3 power law, with no evidence for an exponential cutoff or additional hard components up to similar to 80. keV. For the first time, we observed both the synchrotron and the inverse-Compton peaks of the spectral energy distribution (SED) simultaneously shifted to frequencies below the typical quiescent state by an order of magnitude. The fractional variability as a function of photon energy shows a double-bump structure that relates to the two bumps of the broadband SED. In each bump, the variability increases with energy, which, in the framework of the synchrotron self-Compton model, implies that the electrons with higher energies are more variable. The measured multi band variability, the significant X-ray-to-VHE correlation down to some of the lowest fluxes ever observed in both bands, the lack of correlation between optical/UV and X-ray flux, the low degree of polarization and its significant (random) variations, the short estimated electron cooling time, and the significantly longer variability timescale observed in the NuSTAR light curves point toward in situ electron acceleration and suggest that there are multiple compact regions contributing to the broadband emission of Mrk 421 during low-activity states.
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ASTROPARTICLE PHYSICS 76 38-47 2016年3月We have developed a non-sequential ray-tracing simulation library, ROOT-based simulator for ray tracing (ROBAST), which is aimed to be widely used in optical simulations of cosmic-ray (CR) and gamma-ray telescopes. The library is written in C++, and fully utilizes the geometry library of the ROOT framework. Despite the importance of optics simulations in CR experiments, no open-source software for ray-tracing simulations that can be widely used in the community has existed. To reduce the dispensable effort needed to develop multiple ray-tracing simulators by different research groups, we have successfully used ROBAST for many years to perform optics simulations for the Cherenkov Telescope Array (CTA). Among the six proposed telescope designs for CTA, ROBAST is currently used for three telescopes: a Schwarzschild-Couder (SC) medium-sized telescope, one of SC small-sized telescopes, and a large-sized telescope (LST). ROBAST is also used for the simulation and development of hexagonal light concentrators proposed for the LST focal plane. Making full use of the ROOT geometry library with additional ROBAST classes, we are able to build the complex optics geometries typically used in CR experiments and ground based gamma-ray telescopes. We introduce ROBAST and its features developed for CR experiments, and show several successful applications for CTA. (C) 2015 Elsevier B.V. All rights reserved.
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JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS (2) 2016年2月We present the first joint analysis of gamma-ray data from the MAGIC Cherenkov telescopes and the Fermi Large Area Telescope (LAT) to search for gamma-ray signals from dark matter annihilation in dwarf satellite galaxies. We combine 158 hours of Segue 1 observations with MAGIC with 6-year observations of 15 dwarf satellite galaxies by the Fermi-LAT. We obtain limits on the annihilation cross-section for dark matter particle masses between 10 GeV and 100 TeV - the widest mass range ever explored by a single gamma-ray analysis. These limits improve on previously published Fermi-LAT and MAGIC results by up to a factor of two at certain masses. Our new inclusive analysis approach is completely generic and can be used to perform a global, sensitivity-optimized dark matter search by combining data from present and future gamma-ray and neutrino detectors.
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ASTRONOMY & ASTROPHYSICS 585 2016年1月Aims. We investigate the extension of the very high-energy spectral tail of the Crab Pulsar at energies above 400 GeV. Methods. We analyzed similar to 320 h of good-quality Crab data obtained with the MAGIC telescope from February 2007 to April 2014. Results. We report the most energetic pulsed emission ever detected from the Crab Pulsar reaching up to 1.5 TeV. The pulse profile shows two narrow peaks synchronized with those measured in the GeV energy range. The spectra of the two peaks follow two different power-law functions from 70GeV up to 1.5 TeV and connect smoothly with the spectra measured above 10GeV by the Large Area Telescope (LAT) on board the Fermi satellite. When making a joint fit of the LAT and MAGIC data above 10 GeV the photon indices of the spectra differ by 0.5 +/- 0.1. Conclusions. Using data from the MAGIC telescopes we measured the most energetic pulsed photons from a pulsar to date. Such TeV pulsed photons require a parent population of electrons with a Lorentz factor of at least 5x10(6). These results strongly suggest IC scattering off low-energy photons as the emission mechanism and a gamma-ray production region in the vicinity of the light cylinder.
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ASTROPARTICLE PHYSICS 72 61-75 2016年1月The MAGIC telescopes are two Imaging Atmospheric Cherenkov Telescopes (IACTs) located on the Canary island of La Palma. The telescopes are designed to measure Cherenkov light from air showers initiated by gamma rays in the energy regime from around 50 GeV to more than 50 TeV. The two telescopes were built in 2004 and 2009, respectively, with different cameras, triggers and readout systems. In the years 2011-2012 the MAGIC collaboration undertook a major upgrade to make the stereoscopic system uniform, improving its overall performance and easing its maintenance. In particular, the camera, the receivers and the trigger of the first telescope were replaced and the readout of the two telescopes was upgraded. This paper (Part I) describes the details of the upgrade as well as the basic performance parameters of MAGIC such as raw data treatment, linearity in the electronic chain and sources of noise. In Part II, we describe the physics performance of the upgraded system. (C) 2015 Elsevier B.V. All rights reserved.
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ASTROPARTICLE PHYSICS 72 76-94 2016年1月MAGIC is a system of two Imaging Atmospheric Cherenkov Telescopes located in the Canary island of La Palma, Spain. During summer 2011 and 2012 it underwent a series of upgrades, involving the exchange of the MAGIC-I camera and its trigger system, as well as the upgrade of the readout system of both telescopes. We use observations of the Crab Nebula taken at low and medium zenith angles to assess the key performance parameters of the MAGIC stereo system. For low zenith angle observations, the standard trigger threshold of the MAGIC telescopes is similar to 50 GeV. The integral sensitivity for point-like sources with Crab Nebula-like spectrum above 220 GeV is (0.66 +/- 0.03)% of Crab Nebula flux in 50 h of observations. The angular resolution, defined as the a of a 2-dimensional Gaussian distribution, at those energies is less than or similar to 0.07 degrees, while the energy resolution is 16%. We also re-evaluate the effect of the systematic uncertainty on the data taken with the MAGIC telescopes after the upgrade. We estimate that the systematic uncertainties can be divided in the following components: < 15% in energy scale, 11%-18% in flux normalization and +/- 0.15 for the energy spectrum power-law slope. (C) 2015 Elsevier B.V. All rights reserved.
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ASTROPHYSICAL JOURNAL LETTERS 815(2) 2015年12月The flat-spectrum radio quasar PKS 1441+25 at a redshift of z = 0.940 is detected between 40 and 250 GeV with a significance of 25.5 sigma using the MAGIC telescopes. Together with the gravitationally lensed blazar QSO. B0218 +357 (z = 0.944), PKS. 1441+25 is the most distant very high energy (VHE) blazar detected to date. The observations were triggered by an outburst in 2015 April seen at GeV energies with the Large Area Telescope on board Fermi. Multi-wavelength observations suggest a subdivision of the high state into two distinct flux states. In the band covered by MAGIC, the variability timescale is estimated to be 6.4 +/- 1.9 days. Modeling the broadband spectral energy distribution with an external Compton model, the location of the emitting region is understood as originating in the jet outside the broad-line region (BLR) during the period of high activity, while being partially within the BLR during the period of low (typical) activity. The observed VHE spectrum during the highest activity is used to probe the extragalactic background light at an unprecedented distance scale for ground-based gamma-ray astronomy.
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A&A 582, A67 (2015) 582 2015年10月Context. In the last five years the Fermi Large Area Telescope (LAT)<br /> instrument detected GeV {\gamma}-ray emission from five novae. The GeV emission<br /> can be interpreted in terms of an inverse Compton process of electrons<br /> accelerated in a shock. In this case it is expected that protons in the same<br /> conditions can be accelerated to much higher energies. Consequently they may<br /> produce a second component in the {\gamma}-ray spectrum at TeV energies. Aims.<br /> We aim to explore the very-high-energy domain to search for {\gamma}-ray<br /> emission above 50 GeV and to shed light on the acceleration process of leptons<br /> and hadrons in nova explosions. Methods. We have performed observations with<br /> the MAGIC telescopes of the classical nova V339 Del shortly after the 2013<br /> outburst, triggered by optical and subsequent GeV {\gamma}-ray detec- tions. We<br /> also briefly report on VHE observations of the symbiotic nova YY Her and the<br /> dwarf nova ASASSN-13ax. We complement the TeV MAGIC observations with the<br /> analysis of con- temporaneous Fermi-LAT data of the sources. The TeV and GeV<br /> observations are compared in order to evaluate the acceleration parameters for<br /> leptons and hadrons. Results. No significant TeV emission was found from the<br /> studied sources. We computed upper limits on the spectrum and night-by-night<br /> flux. The combined GeV and TeV observations of V339 Del limit the ratio of<br /> proton to electron luminosities to Lp<~0.15 Le.
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ASTROPHYSICAL JOURNAL 812(1) 2015年10月We report on simultaneous broadband observations of the TeV-emitting blazar Markarian 501 between 2013 April 1 and August 10, including the first detailed characterization of the synchrotron peak with Swift and NuSTAR. During the campaign, the nearby BL Lac object was observed in both a quiescent and an elevated state. The broadband campaign includes observations with NuSTAR, MAGIC, VERITAS, the Fermi Large Area Telescope, Swift X-ray Telescope and UV Optical Telescope, various ground-based optical instruments, including the GASP-WEBT program, as well as radio observations by OVRO, Metsahovi, and the F-Gamma consortium. Some of the MAGIC observations were affected by a sand layer from the Saharan desert, and had to be corrected using event-by-event corrections derived with a Light Detection and Ranging (LIDAR) facility. This is the first time that LIDAR information is used to produce a physics result with Cherenkov Telescope data taken during adverse atmospheric conditions, and hence sets a precedent for the current and future ground-based gamma-ray instruments. The NuSTAR instrument provides unprecedented sensitivity in hard X-rays, showing the source to display a spectral energy distribution (SED) between 3 and 79 keV consistent with a log-parabolic spectrum and hard X-ray variability on hour timescales. None (of the four extended NuSTAR observations) show evidence of the onset of inverse-Compton emission at hard X-ray energies. We apply a single-zone equilibrium synchrotron self-Compton (SSC) model to five simultaneous broadband SEDs. We find that the SSC model can reproduce the observed broadband states through a decrease in the magnetic field strength coinciding with an increase in the luminosity and hardness of the relativistic leptons responsible for the high-energy emission.
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2015年8月31日We have developed a non-sequential ray-tracing simulation library, ROot-BAsed<br /> Simulator for ray Tracing (ROBAST), which is aimed for wide use in optical<br /> simulations of cosmic-ray (CR) and gamma-ray telescopes. The library is written<br /> in C++ and fully utilizes the geometry library of the ROOT analysis framework.<br /> Despite the importance of optics simulations in CR experiments, no open-source<br /> software for ray-tracing simulations that can be widely used existed. To reduce<br /> the unnecessary effort demanded when different research groups develop multiple<br /> ray-tracing simulators, we have successfully used ROBAST for many years to<br /> perform optics simulations for the Cherenkov Telescope Array (CTA). Among the<br /> proposed telescope designs for CTA, ROBAST is currently being used for three<br /> telescopes: a Schwarzschild--Couder telescope, one of the Schwarzschild--Couder<br /> small-sized telescopes, and a large-sized telescope (LST). ROBAST is also used<br /> for the simulations and the development of hexagonal light concentrators that<br /> has been proposed for the LST focal plane. By fully utilizing the ROOT geometry<br /> library with additional ROBAST classes, building complex optics geometries that<br /> are typically used in CR experiments and ground-based gamma-ray telescopes is<br /> possible. We introduce ROBAST and show several successful applications for CTA.
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2015年8月25日List of contributions from the CTA Consortium presented at the 34th<br /> International Cosmic Ray Conference, 30 July - 6 August 2015, The Hague, The<br /> Netherlands.
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First study of Mrk 501 through the eyes of NuSTAR, VERITAS and the LIDAR-corrected eyesight of MAGIC2015年8月21日The blazar Mrk 501 is among the brightest X-ray and TeV sources in the sky,<br /> and among the few sources whose spectral energy distributions can be<br /> characterized by current instruments with relatively short observations<br /> (minutes to hours). In 2013, we organized an extensive multi-instrument<br /> campaign including Fermi-LAT, MAGIC, VERITAS, F-GAMMA, Swift, GASP-WEBT, and<br /> other groups and instruments which provided the most detailed temporal and<br /> energy coverage on Mrk 501 to date. This campaign included, for the first time,<br /> observations with the Nuclear Stereoscopic Telescope Array (NuSTAR), a<br /> satellite mission launched in 2012. NuSTAR provides unprecedented sensitivity<br /> in the hard X-ray range 3-79 keV, which, together with very high energy (VHE;<br /> >100 GeV) observations, is crucial to probe the highest energy electrons in Mrk<br /> 501. The campaign covered a few day long flaring activity in July 2013 which<br /> could be studied with strictly simultaneous NuSTAR and MAGIC observations. A<br /> large fraction of the MAGIC data during this activity was affected by hazy<br /> atmospheric conditions, due to a sand layer from the Saharan desert. These data<br /> would have been removed in any standard Cherenkov Telescope data analysis.<br /> MAGIC has developed a technique to correct for adverse atmospheric conditions,<br /> making use of information from the LIDAR facility at the MAGIC site, and<br /> applies an event-by-event correction to recover data affected by adverse<br /> weather conditions. This is the first time that LIDAR information has been used<br /> to produce a physics result with Cherenkov Telescope data taken during adverse<br /> atmospheric conditions, and hence sets a precedent for current and future<br /> ground-based gamma-ray instruments. In this contribution we report the<br /> observational results, focusing on the LIDAR-corrected MAGIC data and the<br /> strictly simultaneous NuSTAR and MAGIC/VERITAS data, and discuss the scientific<br /> implications.
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MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 450(4) 4399-4410 2015年7月PG 1553+113 is a very high energy (VHE, E > 100 GeV) gamma-ray emitter classified as a BL Lac object. Its redshift is constrained by intergalactic absorption lines in the range 0.4 < z < 0.58. The MAGIC telescopes have monitored the source's activity since 2005. In early 2012, PG 1553+113 was found in a high state, and later, in April of the same year, the source reached its highest VHE flux state detected so far. Simultaneous observations carried out in X-rays during 2012 April show similar flaring behaviour. In contrast, the gamma-ray flux at E < 100 GeV observed by Fermi-LAT is compatible with steady emission. In this paper, a detailed study of the flaring state is presented. The VHE spectrum shows clear curvature, being well fitted either by a power law with an exponential cut-off or by a log-parabola. A simple power-law fit hypothesis for the observed shape of the PG 1553+113 VHE gamma-ray spectrum is rejected with a high significance (fit probability P = 2.6 x 10(-6)). The observed curvature is compatible with the extragalactic background light (EBL) imprint predicted by current generation EBL models assuming a redshift z similar to 0.4. New constraints on the redshift are derived from the VHE spectrum. These constraints are compatible with previous limits and suggest that the source is most likely located around the optical lower limit, z = 0.4, based on the detection of Ly alpha absorption. Finally, we find that the synchrotron self-Compton model gives a satisfactory description of the observed multiwavelength spectral energy distribution during the flare.
講演・口頭発表等
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HIGH ENERGY GAMMA-RAY ASTRONOMY 2017年 AMER INST PHYSICSThe MAGIC telescopes are strongly involved in several multimessenger programs. One of them are follow-up observations of astrophysical neutrino events, to search for hadronic gamma-ray emission from the neutrino direction and identify potential neutrino sources. In 2013 the IceCube collaboration reported the first detection of astrophysical neutrinos and up to now 55 events, which interact inside the IceCube detector active volume, dubbed High Energy Starting Events (HESE), have been reported. These include 13 track-like events, caused usually by muon neutrino charge current interactions. The track-like events ( as opposed to cascade-like neutral current interactions) are characterised by a very good angular resolution of < 1 deg, which facilitates follow-up observations and potential source identification. The MAGIC telescopes performed follow-up observations of 4 HESE track-like events from the Northern hemisphere: HESE-37, HESE-38, HET (ATel #7856) and the GCN HESE alert from 27/04/2016 (GCN #19363). No signal was detected. Here we present the results of those observations and discuss the implications for the constraints on the density of the astrophysical neutrino sources.
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日本物理学会講演概要集 2014年8月22日 一般社団法人日本物理学会
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日本物理学会講演概要集 2014年8月22日 一般社団法人日本物理学会
共同研究・競争的資金等の研究課題
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日本学術振興会 科学研究費助成事業 2023年4月 - 2028年3月
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日本学術振興会 科学研究費助成事業 国際共同研究加速基金(国際共同研究強化(B)) 2020年10月 - 2025年3月
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日本学術振興会 科学研究費助成事業 研究活動スタート支援 2019年4月 - 2020年3月
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日本学術振興会 科学研究費助成事業 特別研究員奨励費 2006年 - 2008年