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Locating the Most Energetic Electrons in Cassiopeia A

Grefenstette, Brian W. and Reynolds, Stephen P. and Harrison, Fiona A. and Humensky, T. Brian and Boggs, Steven E. and Fryer, Chris L. and Delaney, Tracey and Madsen, Kristin K. and Miyasaka, Hiromasa and Wik, Daniel R. and Zoglauer, Andreas and Forster, Karl and Kitaguchi, Takao and Lopez, Laura and Nynka, Melania and Christensen, Finn E. and Craig, William W. and Hailey, Charles J. and Stern, Daniel and Zhang, William W. (2015) Locating the Most Energetic Electrons in Cassiopeia A. Astrophysical Journal, 802 (1). Art. No. 15. ISSN 0004-637X. doi:10.1088/0004-637X/802/1/15.

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We present deep (>2.4 Ms) observations of the Cassiopeia A supernova remnant with NuSTAR, which operates in the 3–79 keV bandpass and is the first instrument capable of spatially resolving the remnant above 15 keV. We find that the emission is not entirely dominated by the forward shock nor by a smooth "bright ring" at the reverse shock. Instead we find that the >15 keV emission is dominated by knots near the center of the remnant and dimmer filaments near the remnant's outer rim. These regions are fit with unbroken power laws in the 15–50 keV bandpass, though the central knots have a steeper (Γ ~ −3.35) spectrum than the outer filaments (Γ ~ −3.06). We argue this difference implies that the central knots are located in the 3-D interior of the remnant rather than at the outer rim of the remnant and seen in the center due to projection effects. The morphology of >15 keV emission does not follow that of the radio emission nor that of the low energy (<12 keV) X-rays, leaving the origin of the >15 keV emission an open mystery. Even at the forward shock front we find less steepening of the spectrum than expected from an exponentially cut off electron distribution with a single cutoff energy. Finally, we find that the GeV emission is not associated with the bright features in the NuSTAR band while the TeV emission may be, suggesting that both hadronic and leptonic emission mechanisms may be at work.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Grefenstette, Brian W.0000-0002-1984-2932
Harrison, Fiona A.0000-0003-2992-8024
Boggs, Steven E.0000-0001-9567-4224
Fryer, Chris L.0000-0003-2624-0056
Madsen, Kristin K.0000-0003-1252-4891
Miyasaka, Hiromasa0000-0002-8074-4186
Wik, Daniel R.0000-0001-8952-676X
Forster, Karl0000-0001-5800-5531
Lopez, Laura0000-0002-1790-3148
Nynka, Melania0000-0002-3310-1946
Christensen, Finn E.0000-0001-5679-1946
Stern, Daniel0000-0003-2686-9241
Zhang, William W.0000-0002-1426-9698
Additional Information:© 2015 American Astronomical Society. Received 2014 September 16; accepted 2015 January 14; published 2015 March 16. B.G. thanks Una Hwang for the Chandra 4–6 keV band image. This work was supported under NASA contract NNG08FD60C and made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by NASA. We thank the NuSTAR Operations, Software, and Calibration teams for support with the execution and analysis of these observations. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS), jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA). Facilities: Chandra, Fermi, HESS, NuSTAR, VERITAS, VLA
Group:NuSTAR, Space Radiation Laboratory
Funding AgencyGrant Number
Subject Keywords:acceleration of particles; ISM: individual objects (Cassiopeia A); ISM: supernova remnants; radiation mechanisms: non-thermal; X-rays: ISM
Issue or Number:1
Record Number:CaltechAUTHORS:20150424-140813411
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:56965
Deposited By: Ruth Sustaita
Deposited On:24 Apr 2015 22:19
Last Modified:10 Nov 2021 21:06

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