Broadband X-ray Imaging and Spectroscopy of the Crab Nebula and Pulsar with NuSTAR
Abstract
We present broadband (3-78 keV) NuSTAR X-ray imaging and spectroscopy of the Crab nebula and pulsar. We show that while the phase-averaged and spatially integrated nebula + pulsar spectrum is a power law in this energy band, spatially resolved spectroscopy of the nebula finds a break at ~9 keV in the spectral photon index of the torus structure with a steepening characterized by ΔΓ ~ 0.25. We also confirm a previously reported steepening in the pulsed spectrum, and quantify it with a broken power law with break energy at ~12 keV and ΔΓ ~ 0.27. We present spectral maps of the inner 100'' of the remnant and measure the size of the nebula as a function of energy in seven bands. These results find that the rate of shrinkage with energy of the torus size can be fitted by a power law with an index of γ = 0.094 ± 0.018, consistent with the predictions of Kennel and Coroniti. The change in size is more rapid in the NW direction, coinciding with the counter-jet where we find the index to be a factor of two larger. NuSTAR observed the Crab during the latter part of a γ-ray flare, but found no increase in flux in the 3-78 keV energy band.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 2015
- DOI:
- 10.1088/0004-637X/801/1/66
- arXiv:
- arXiv:1502.07765
- Bibcode:
- 2015ApJ...801...66M
- Keywords:
-
- pulsars: individual: Crab;
- stars: neutron;
- X-rays: individual: Crab;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 2015 ApJ 801 66