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- · arXiv e-print (arXiv:1004.3391)
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| Title: |
| The Energy Spectrum of Anomalous X-ray Pulsars and Soft Gamma-ray Repeaters |
| Authors: |
| Trümper, J.; Zezas, A.; Ertan, Ü.; Kylafis, N. D. |
| Publication: |
| eprint arXiv:1004.3391 |
| Publication Date: |
| 04/2010 |
| Origin: |
| ARXIV |
| Keywords: |
| Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Solar and Stellar Astrophysics |
| Comment: |
| 6 pages, 2 figures, minor corrections, accepted for publication in A&A |
| Bibliographic Code: |
| 2010arXiv1004.3391T |
Abstract
Assuming that AXPs and SGRs accrete matter from a fallback disk, we attempt to explain both the soft and the hard X-ray emission as the result of the accretion process. We also attempt to explain their radio emission or the lack of it. We test the hypothesis that the power-law, hard X-ray spectra are produced in the accretion flow mainly by bulk-motion Comptonization of soft photons emitted at the neutron star surface. Fallback disk models invoke surface dipole magnetic fields of $10^{12} - 10^{13}$ G, which is what we assume here. Unlike normal X-ray pulsars, for which the accretion rate is highly super-Eddington, the accretion rate is approximately Eddington in AXPs and SGRs and thus the bulk-motion Comptonization operates efficiently. As an illustrative example we reproduce both the hard and the soft X-ray spectra of AXP 4U 0142+61 well using the XSPEC package compTB. Our model seems to explain both the hard and the soft X-ray spectra of AXPs and SGRs, as well as their radio emission or the lack of it, in a natural way. It might also explain the short bursts observed in these sources. On the other hand, it cannot explain the giant X-ray outbursts observed in SGRs, which may result from the conversion of magnetic energy in local multipole fields.
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