SAX J1748.9-2021 is an accreting X-ray millisecond pulsar observed in outburst five times since its discovery in 1998. In early October 2017, the source started its sixth outburst, which lasted only ~13 days, significantly shorter than the typical 30 days duration of the previous outbursts. It reached a 0.3-70 keV unabsorbed peak luminosity of ~3 × 1036erg s-1. This is the weakest outburst ever reported for this source to date. We analysed almost simultaneous XMM-Newton, NuSTAR, and INTEGRAL observations taken during the decaying phase of its 2017 outburst. We found that the spectral properties of SAX J1748.9-2021 are consistent with an absorbed Comptonization plus a blackbody component. The former, characterized by an electron temperature of ~20 keV, a photon index of ~1.6-1.7 keV, and seed photon temperature of 0.44 keV, can be associated to a hot corona or the accretion column, while the latter is more likely originating from the neutron star surface (kTbb~ 0.6 keV, Rbb~ 2.5 km). These findings suggest that SAX J1748.9-2021 was observed in a hard spectral state, as it is typically the case for accreting millisecond pulsars in outburst. © 2018 The Author(s) Published by Oxford University Press on behalf of The Royal Astronomical Society.

Pintore, F., Sanna, A., Riggio, A., Di Salvo, T., Mereghetti, S., Bozzo, E., et al. (2018). A faint outburst of the accreting millisecond X-ray pulsar SAX J1748.9-2021 in NGC 6440. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 479(3), 4084-4090 [10.1093/mnras/sty1735].

A faint outburst of the accreting millisecond X-ray pulsar SAX J1748.9-2021 in NGC 6440

Di Salvo, T.;Iaria, R.
2018-01-01

Abstract

SAX J1748.9-2021 is an accreting X-ray millisecond pulsar observed in outburst five times since its discovery in 1998. In early October 2017, the source started its sixth outburst, which lasted only ~13 days, significantly shorter than the typical 30 days duration of the previous outbursts. It reached a 0.3-70 keV unabsorbed peak luminosity of ~3 × 1036erg s-1. This is the weakest outburst ever reported for this source to date. We analysed almost simultaneous XMM-Newton, NuSTAR, and INTEGRAL observations taken during the decaying phase of its 2017 outburst. We found that the spectral properties of SAX J1748.9-2021 are consistent with an absorbed Comptonization plus a blackbody component. The former, characterized by an electron temperature of ~20 keV, a photon index of ~1.6-1.7 keV, and seed photon temperature of 0.44 keV, can be associated to a hot corona or the accretion column, while the latter is more likely originating from the neutron star surface (kTbb~ 0.6 keV, Rbb~ 2.5 km). These findings suggest that SAX J1748.9-2021 was observed in a hard spectral state, as it is typically the case for accreting millisecond pulsars in outburst. © 2018 The Author(s) Published by Oxford University Press on behalf of The Royal Astronomical Society.
2018
Settore FIS/05 - Astronomia E Astrofisica
https://academic.oup.com/mnras/issue
Pintore, F., Sanna, A., Riggio, A., Di Salvo, T., Mereghetti, S., Bozzo, E., et al. (2018). A faint outburst of the accreting millisecond X-ray pulsar SAX J1748.9-2021 in NGC 6440. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 479(3), 4084-4090 [10.1093/mnras/sty1735].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10447/296909
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