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arXiv:0706.2784 (astro-ph)
[Submitted on 19 Jun 2007 (v1), last revised 21 Jun 2007 (this version, v2)]

Title:BeppoSAX observation of 4U 1705-44: detection of hard X-ray emission in the soft state

Authors:S. Piraino, A. Santangelo, T. Di Salvo, P. Kaaret, D. Horns, R. Iaria, L. Burderi
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Abstract: 4U 1705-44 is one of the best studied type I X-ray burster and atoll sources. Since it covers a wide range in luminosity (from a few to 50 x 10^{36} erg s^{-1}) and shows clear spectral state transitions, it represents a good laboratory to test the accretion models proposed for atoll sources. We analysed the energy spectrum accumulated with BeppoSAX observations (43.5 ksec) in August 2000 when the source was in a soft spectral state. The continuum of the wide band energy spectrum is well described by the sum of a blackbody (kT_{bb}~0.56 keV) and a Comptonized component (seed-photon temperature kT_W~1 keV, electron temperature kT_e~2.7 keV, and optical depth ~11). A hard tail was detected at energies above ~25 keV. The latter can be modeled by a power law having a photon index ~2.9 which contributes ~11% of the total flux in the range 0.1-200 keV. A broad emission line, possibly from a relativistic accretion disk, models the feature in the Fe K line region of the spectrum. This is the first time that a high energy tail has been observed during a soft state of the source.
Comments: 4 pages,3 figures. Accepted for publication as a Letter to the Editor in A&A
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0706.2784 [astro-ph]
  (or arXiv:0706.2784v2 [astro-ph] for this version)
  https://doi.org/10.48550/arXiv.0706.2784
Related DOI: https://doi.org/10.1051/0004-6361%3A20077841

Submission history

From: Santina Piraino [view email]
[v1] Tue, 19 Jun 2007 13:09:31 UTC (85 KB)
[v2] Thu, 21 Jun 2007 14:12:15 UTC (70 KB)
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