研究者業績
基本情報
研究キーワード
1経歴
6-
2023年11月 - 現在
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2018年4月
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2016年4月 - 2018年3月
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2013年4月 - 2016年3月
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2015年4月 - 2015年8月
学歴
4-
2010年4月 - 2012年9月
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2008年4月 - 2010年3月
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2004年4月 - 2008年3月
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2000年4月 - 2003年3月
委員歴
1-
2019年4月
論文
82-
Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray 92-92 2024年8月21日
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The Astrophysical Journal Letters 969(2) L30-L30 2024年7月1日Abstract We present the first X-ray spectropolarimetric results for Cygnus X-1 in its soft state from a campaign of five IXPE observations conducted during 2023 May–June. Companion multiwavelength data during the campaign are likewise shown. The 2–8 keV X-rays exhibit a net polarization degree PD = 1.99% ± 0.13% (68% confidence). The polarization signal is found to increase with energy across the Imaging X-ray Polarimetry Explorer’s (IXPE) 2–8 keV bandpass. The polarized X-rays exhibit an energy-independent polarization angle of PA = −25.°7 ± 1.°8 east of north (68% confidence). This is consistent with being aligned to Cyg X-1’s au-scale compact radio jet and its parsec-scale radio lobes. In comparison to earlier hard-state observations, the soft state exhibits a factor of 2 lower polarization degree but a similar trend with energy and a similar (also energy-independent) position angle. When scaling by the natural unit of the disk temperature, we find the appearance of a consistent trend line in the polarization degree between the soft and hard states. Our favored polarimetric model indicates that Cyg X-1’s spin is likely high (a * ≳ 0.96). The substantial X-ray polarization in Cyg X-1's soft state is most readily explained as resulting from a large portion of X-rays emitted from the disk returning and reflecting off the disk surface, generating a high polarization degree and a polarization direction parallel to the black hole spin axis and radio jet. In IXPE’s bandpass, the polarization signal is dominated by the returning reflection emission. This constitutes polarimetric evidence for strong gravitational lensing of X-rays close to the black hole.
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The Astrophysical Journal 968(2) 76-76 2024年6月1日Abstract We report on an observational campaign on the bright black hole (BH) X-ray binary Swift J1727.8–1613 centered around five observations by the Imaging X-ray Polarimetry Explorer. These observations track for the first time the evolution of the X-ray polarization of a BH X-ray binary across a hard to soft state transition. The 2–8 keV polarization degree decreased from ∼4% to ∼3% across the five observations, but the polarization angle remained oriented in the north–south direction throughout. Based on observations with the Australia Telescope Compact Array, we find that the intrinsic 7.25 GHz radio polarization aligns with the X-ray polarization. Assuming the radio polarization aligns with the jet direction (which can be tested in the future with higher-spatial-resolution images of the jet), our results imply that the X-ray corona is extended in the disk plane, rather than along the jet axis, for the entire hard intermediate state. This in turn implies that the long (≳10 ms) soft lags that we measure with the Neutron star Interior Composition ExploreR are dominated by processes other than pure light-crossing delays. Moreover, we find that the evolution of the soft lag amplitude with spectral state does not follow the trend seen for other sources, implying that Swift J1727.8–1613 is a member of a hitherto undersampled subpopulation.
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The Astrophysical Journal Letters 967(2) L38-L38 2024年5月30日Abstract Supernova remnants (SNRs) provide insights into cosmic-ray acceleration and magnetic field dynamics at shock fronts. Recent X-ray polarimetric measurements by the Imaging X-ray Polarimetry Explorer (IXPE) have revealed radial magnetic fields near particle acceleration sites in young SNRs, including Cassiopeia A, Tycho, and SN 1006. We present here the spatially resolved IXPE X-ray polarimetric observation of the northwestern rim of SNR RX J1713.7–3946. For the first time, our analysis shows that the magnetic field in the particle acceleration sites of this SNR is oriented tangentially with respect to the shock front. Because of the lack of precise Faraday rotation measurements in the radio band, this was not possible before. The average measured polarization degree (PD) of the synchrotron emission is 12.5% ± 3.3%, lower than the one measured by IXPE in SN 1006, comparable to the Tycho one, but notably higher than the one in Cassiopeia A. On subparsec scales, localized patches within RX J1713.7–3946 display a PD of up to 41.5% ± 9.5%. These results are compatible with a shock-compressed magnetic field. However, in order to explain the observed PD, either the presence of a radial net magnetic field upstream of the shock or partial reisotropization of the turbulence downstream by radial magnetohydrodynamical instabilities can be invoked. From comparison of PD and magnetic field distribution with γ-rays and 12CO data, our results provide new inputs in favor of a leptonic origin of the γ-ray emission.
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The Astrophysical Journal 963(2) 133-133 2024年3月1日Abstract We present the first X-ray polarimetric study of the dipping accreting neutron star 4U 1624−49 with the Imaging X-ray Polarimetry Explorer. We report a detection of polarization in the nondip time intervals with a confidence level of 99.99%. We find an average polarization degree (PD) of 3.1% ± 0.7% and a polarization angle of 81° ± 6° east of north in the 2–8 keV band. We report an upper limit on the PD of 22% during the X-ray dips with 95% confidence. The PD increases with energy, reaching from 3.0% ± 0.9% in the 4–6 keV band to 6% ± 2% in the 6–8 keV band. This indicates the polarization likely arises from Comptonization. The high PD observed is unlikely to be produced by Comptonization in the boundary layer or spreading layer alone. It can be produced by the addition of an extended geometrically thin slab corona covering part of the accretion disk, as assumed in previous models of dippers, and/or a reflection component from the accretion disk.
MISC
2講演・口頭発表等
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the Fourth Annual Symposium of the Innovative Area "Gravitational Wave Physics and Astronomy: Genesis 2021年2月
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Gravitational wave physics and astronomy: Genesis: The Third Annual Area Symposium 2020年2月
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2nd CORE-U conference: Cosmic Polarimetry from Micro to Macro Scales 2017年2月
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NuSTAR Science meeting 2016 2016年11月
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1st CORE-U conference : Intense fields and Extreme Universe 2016年2月
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PLASMA2014（招待講演） 2014年11月
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The Energetic Cosmos: from Suzaku to Astro-H 2009 2009年6月
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Frontiers of Space Astrophysics: Neutron stars & Gamma Ray Bursts 2009年3月
共同研究・競争的資金等の研究課題
6-
日本学術振興会 科学研究費助成事業 2024年4月 - 2027年3月
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日本学術振興会 科学研究費助成事業 2020年4月 - 2022年3月
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2016年4月 - 2019年3月
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日本学術振興会 科学研究費助成事業 2015年4月 - 2017年3月
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日本学術振興会 科学研究費助成事業 2013年4月 - 2016年3月