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Discovery of type-I X-ray bursts from the low-mass X-ray binary 4U 1708-40

S. Migliari·T. Di Salvo·T. Belloni·M. van der Klis·R. P. Fender·S. Campana·C. Kouveliotou·M. Méndez·W. H. G. Lewin
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Abstract

We report the discovery of type-I X-ray bursts from the low-mass X-ray binary 4U 1708-40 during the 100 ks observation performed by BeppoSAX on 1999 August 15-16. Six X-ray bursts have been observed. The unabsorbed 2-10 keV fluxes of the bursts range from ~ (3-9)x10^(-10) erg cm^(-2)s^(-1). A correlation between peak flux and fluence of the bursts is found, in agreement with the behaviour observed in other similar sources. There is a trend of the burst flux to increase with the time interval from the previous burst. From the value of the persistent flux we infer a mass accretion rate Mdot~7x10^(-11) Msun/yr, that may correspond to the mixed hydrogen/helium burning regime triggered by thermally unstable hydrogen. We have also analysed a BeppoSAX observation performed on 2001 August 22 and previous RXTE observations of 4U 1708-40, where no bursts have been observed; we found persistent fluxes of more than a factor of 7 higher than the persistent flux observed during the BeppoSAX observation showing X-ray bursts.

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S. Migliari, T. Di Salvo, T. Belloni, M. van der Klis, R. P. Fender, S. Campana, C. Kouveliotou, M. Méndez, W. H. G. Lewin. 2003-03-06. Discovery of type-I X-ray bursts from the low-mass X-ray binary 4U 1708-40. https://doi.org/10.1046/j.1365-8711.2003.06597.x

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