NuSTAR Observations of Hard X-ray Continuum from SN 1987A
Abstract
We present hard X-ray observations with the NuSTAR satellite of the remnant of Supernova 1987A in the Large Magellanic Cloud. We detect continuum emission up to at least 25 keV. The continuum spectrum between 3 and 25 keV can be described by a power-law (Gamma = 3.43 +/- 0.02) or by the tail of a synchrotron spectrum from electrons with a power-law distribution with exponential cutoff at some Emax, or, somewhat more poorly, by a purely thermal shock model with a temperature of 3.27 +/- 0.03 keV. For the cutoff model, the peak photon energy emitted by electrons with Emax is 0.19 +/- 0.01 keV. We also detect a weak Fe K alpha line with centroid 6.6 +/- 0.05 keV, indicating that at least some of the emission above 6 keV is thermal. The purely thermal shock model requires an iron abundance at least a factor of two lower than general LMC abundances. Unless much of the expected iron is in the form of dust grains, a substantial nonthermal contribution to the continuum is required. The spectrum we observe argues strongly against an attribution to a pulsar-wind nebula (PWN), requiring that any nonthermal component be produced by electrons accelerated in the remnant blast wave. In this case, however, the shock accelerating the electrons must be modified by cosmic-ray pressure, both to produce a concave-up spectrum from radio to X-rays, and to increase the magnetic field to at least 60 microG to allow shock acceleration to X-ray-emitting energies in only 27 years. Magnetic-field strengths of order 100 microG mean that Emax is between 10 and 100 TeV. Fluxes in both the 3 -- 8 keV and 8 -- 25 keV ranges are increasing, with a rate reasonably well described by an exponential with e-folding time about 5000 days, slower than earlier rates reported for either 3 -- 8 keV X-rays or for radio emission. The flux increase provides additional evidence against a PWN interpretation.
- Publication:
-
American Astronomical Society Meeting Abstracts #225
- Pub Date:
- January 2015
- Bibcode:
- 2015AAS...22514022R