X-Ray Measurements of the Particle Acceleration Properties at Inward Shocks in Cassiopeia A
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Author
Sato, Toshiki
Katsuda, Satoru

Morii, Mikio
Bamba, Aya

Hughes, John P.

Maeda, Yoshitomo
Ishida, Manabu
Fraschetti, Federico

Affiliation
Univ Arizona, Dept Planetary Sci & AstronIssue Date
2018-01-22Keywords
acceleration of particlesISM: supernova remnants
supernovae: individual (Cassiopeia A)
X-rays: ISM
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IOP PUBLISHING LTDCitation
X-Ray Measurements of the Particle Acceleration Properties at Inward Shocks in Cassiopeia A 2018, 853 (1):46 The Astrophysical JournalJournal
The Astrophysical JournalRights
© 2018. The American Astronomical Society. All rights reserved.Collection Information
This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu.Abstract
We present new evidence that the bright nonthermal X-ray emission features in the interior of the Cassiopeia A supernova remnant are caused by inward-moving shocks, based on Chandra and NuSTAR observations. Several bright inward-moving filaments were identified using monitoring data taken by Chandra in 2000-2014. These inward-moving shock locations are nearly coincident with hard X-ray (15-40 keV) hot spots seen by NuSTAR. From proper-motion measurements, the transverse velocities were estimated to be in the range of similar to 2100-3800 km s(-1) for a distance of 3.4 kpc. The shock velocities in the frame of the expanding ejecta reach values of similar to 5100-8700 km s(-1), which is slightly higher than the typical speed of the forward shock. Additionally, we find flux variations (both increasing and decreasing) on timescales of a few years in some of the inward-moving shock filaments. The rapid variability timescales are consistent with an amplified magnetic field of B similar to 0.5-1 mG. The high speed and low photon cut-off energy of the inward-moving shocks are shown to imply a particle diffusion coefficient that departs from the Bohm regime (k(0) = D-0/D-0,D-Bohm similar to 3-8) for the few simple physical configurations we consider in this study. The maximum electron energy at these shocks is estimated to be similar to 8-11 TeV, which is smaller than the values of similar to 15-34 TeV that were inferred for the forward shock. Cassiopeia A is dynamically too young for its reverse shock to appear to be moving inward in the observer frame. We propose instead that the inward-moving shocks are a consequence of the forward shock encountering a density jump of 5-8 in the surrounding material.ISSN
1538-4357Version
Final published versionSponsors
Japan Society for the Promotion of Science (JSPS) KAKENHI [16J03448, 16K17673, 17K05395]; CREST; NASA [NNX15AJ71G, NNX15AK71G]; Simons Foundation; Leading Initiative for Excellent Young Researchers, MEXT, JapanAdditional Links
http://stacks.iop.org/0004-637X/853/i=1/a=46?key=crossref.b8218d398297bed36904b6b512c61327ae974a485f413a2113503eed53cd6c53
10.3847/1538-4357/aaa021