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http://hdl.handle.net/20.500.12386/30275
Title: | NuSTAR and XMM-Newton broad-band spectrum of SAX J1808.4-3658 during its latest outburst in 2015 | Authors: | Di Salvo, T. Sanna, A. Burderi, L. PAPITTO, ALESSANDRO Iaria, R. Gambino, A. F. Riggio, A. |
Issue Date: | 2019 | Journal: | MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY | Number: | 483 | Issue: | 1 | First Page: | 767 | Abstract: | The first discovered accreting millisecond pulsar, SAX J1808.4-3658, went into X-ray outburst in 2015 April. We triggered a 100 ks XMM-Newton ToO, taken at the peak of the outburst, and a 55 ks NuSTAR ToO, performed 4 d apart. We report here the results of a detailed spectral analysis of both the XMM-Newton and NuSTAR spectra. While the XMM-Newton spectrum appears much softer than in previous observations, the NuSTAR spectrum confirms the results obtained with XMM-Newton during the 2008 outburst. We find clear evidence of a broad iron line that we interpret as produced by reflection from the inner accretion disc. For the first time, we use a self-consistent reflection model to fit the reflection features in the NuSTAR spectrum; in this case, we find a statistically significant improvement of the fit with respect to a simple Gaussian or diskline model to fit the iron line, implying that the reflection continuum is also significantly detected. Despite the differences evident between the XMM-Newton and NuSTAR spectra, the smearing best-fitting parameters found for these spectra are consistent with each other and are compatible with previous results. In particular, we find an upper limit to the inner disc radius of ∼12R_g. In all the cases, a high inclination angle (>50°) of the system is required. This inclination angle, combined with measurements of the radial velocity of the optical companion, results in a low value for the neutron star mass (< 0.8 M_☉), a result that deserves further investigation. | URI: | http://hdl.handle.net/20.500.12386/30275 | URL: | https://academic.oup.com/mnras/article/483/1/767/5159480 https://arxiv.org/abs/1811.00940 |
ISSN: | 0035-8711 | DOI: | 10.1093/mnras/sty2974 | Bibcode ADS: | 2019MNRAS.483..767D | Fulltext: | open |
Appears in Collections: | 1.01 Articoli in rivista |
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File | Description | Size | Format | |
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2019-DiSalvo-arxiv-1811.00940.pdf | 1.18 MB | Adobe PDF | View/Open | |
2019-DiSalvo.sty2974.pdf | pdf editoriale | 850.86 kB | Adobe PDF | View/Open |
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