Swift J1734.5-3027: a new long Type-I X-ray bursting source

Abstract

Swift J1734.5-3027 is a hard X-ray transient discovered by Swift while undergoing an outburst in September 2013. Archival observations showed that this source underwent a previous episode of enhanced X-ray activity in 2013 May-June. In this paper we report on the analysis of all X-ray data collected during the outburst in 2013 September, the first that could be intensively followed up by several X-ray facilities. Our dataset includes INTEGRAL, Swift, and XMM-Newton observations. From the timing and spectral analysis of these observations, we show that a long Type-I X-ray burst took place during the source outburst, making Swift J1734.5-3027 a new member of the class of bursting neutron star low-mass X-ray binaries. The burst lasted for about 1.9 ks and reached a peak flux of (6.0 ± 1.8) × 10^-8 erg cm^-2 s^-1 in the 0.5-100 keV energy range. The estimated burst fluence in the same energy range is (1.10 ± 0.10) × 10^-5 erg cm^-2. By assuming that a photospheric radius expansion took place during the first ~200 s of the burst and that the accreted material was predominantly composed by He, we derived a distance to the source of 7.2 ± 1.5 kpc.