Broadband x-ray imaging and spectroscopy of the crab nebula and pulsar with NuSTAR

Kristin K. Madsen, Stephen Reynolds, Fiona Harrison, Hongjun An, Steven Boggs, Finn Erland Christensen, William W. Craig, Chris L. Fryer, Brian W. Grefenstette, Charles J. Hailey

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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.
Original languageEnglish
Article number66
JournalAstrophysical Journal
Volume801
Issue number1
Number of pages14
ISSN0004-637X
DOIs
Publication statusPublished - 2015

Keywords

  • Pulsars: individual (Crab)
  • Stars: neutron
  • X-rays: individual (Crab)

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