LOCATING THE MOST ENERGETIC ELECTRONS IN CASSIOPEIA A

Journal Article · Fri Mar 20 00:00:00 EDT 2015 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/802/1/15· OSTI ID:22522030

Grefenstette, Brian W.; Harrison, Fiona A.; Madsen, Kristin K.; Miyasaka, Hiromasa; Forster, Karl ^[1]; Reynolds, Stephen P. ^[2]; Humensky, T. Brian ^[3]; Boggs, Steven E.; Zoglauer, Andreas; Craig, William W. ^[4]; Fryer, Chris L. ^[5]; DeLaney, Tracey; Zhang, William W. ^[6]; Wik, Daniel R. ^[7]; Kitaguchi, Takao ^[8]; Lopez, Laura ^[9]; Nynka, Melania; Hailey, Charles J. ^[10]; Christensen, Finn E. ^[11]; Stern, Daniel ^[12]

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1. Cahill Center for Astrophysics, 1216 E. California Blvd., California Institute of Technology, Pasadena, CA 91125 (United States)
2. Physics Department, NC State University, Raleigh, NC 27695 (United States)
3. Physics Department, Columbia University, New York, NY 10027 (United States)
4. Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States)
5. CCS-2, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)
6. Physics and Engineering Department, West Virginia Wesleyan College, Buckhannon, WV 26201 (United States)
7. Astrophysics Science Division, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
8. RIKEN, 2-1 Hirosawa, Wako, Saitama, 351-0198 (Japan)
9. MIT-Kavli Institute for Astrophysics and Space Research, 77 Massachusetts Avenue, 37-664 H, Cambridge, MA 02139 (United States)
10. Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States)
11. DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby (Denmark)
12. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)

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.

• OSTI ID: 22522030
• Journal Information: Astrophysical Journal, Vol. 802, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ACCELERATION
EMISSION SPECTRA
FILAMENTS
GEV RANGE
HADRONS
KEV RANGE
LEPTONS
MORPHOLOGY
SUPERNOVA REMNANTS
TAIL ELECTRONS
TEV RANGE
X RADIATION