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Broad-band spectral analysis of the accreting millisecond X-ray pulsar SAX J1748.9-2021.
- Source :
- Monthly Notices of the Royal Astronomical Society; 4/11/2016, Vol. 457 Issue 3, p2988-2998, 11p
- Publication Year :
- 2016
-
Abstract
- We analysed a 115-ks XMM-Newton observation and the stacking of 8 d of INTEGRAL observations, taken during the raise of the 2015 outburst of the accreting millisecond X-ray pulsar SAX J1748.9-2021. The source showed numerous type-I burst episodes during the XMM-Newton observation, and for this reason we studied separately the persistent and burst epochs. We described the persistent emission with a combination of two soft thermal components, a cold thermal Comptonization component (~2 keV) and an additional hard X-ray emission described by a power law (г ~ 2.3). The continuum components can be associated with an accretion disc, the neutron star (NS) surface and a thermal Comptonization emission coming out of an optically thick plasma region, while the origin of the high-energy tail is still under debate. In addition, a number of broad (σ = 0.1-0.4 keV) emission features likely associated with reflection processes have been observed in the XMM-Newton data. The estimated 1.0-50 keV unabsorbed luminosity of the source is ~5 × 10<superscript>37</superscript> erg s <superscript>-1</superscript>, about 25 per cent of the Eddington limit assuming a 1.4 M☉ NS. We suggest that the spectral properties of SAX J1748.9-2021 are consistent with a soft state, differently from many other accreting X-ray millisecond pulsars which are usually found in the hard state. Moreover, none of the observed type-I burst reached the Eddington luminosity. Assuming that the burst ignition and emission are produced above the whole NS surface, we estimate an NS radius of ~7-8 km, consistent with previous results. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 00358711
- Volume :
- 457
- Issue :
- 3
- Database :
- Complementary Index
- Journal :
- Monthly Notices of the Royal Astronomical Society
- Publication Type :
- Academic Journal
- Accession number :
- 113655422
- Full Text :
- https://doi.org/10.1093/mnras/stw176