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

¹ ISDC Data Centre for Astrophysics, Chemin d’Ecogia 16, 1290 Versoix, Switzerland
e-mail: enrico.bozzo@unige.ch
² INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica – Palermo, via U. La Malfa 153, 90146 Palermo, Italy
³ International Space Science Institute, Hallerstrasse 6, 3012 Bern, Switzerland
⁴ International Space Science Institute in Beijing, No. 1 Nan Er Tiao, Zhong Guan Cun, 100190 Beijing, PR China
⁵ Institut de Ciències de l’Espai (IEEC-CSIC), Campus UAB, carrer de Can Magrans, S/N 08193 Cerdanyola del Vallès, Barcelona, Spain
⁶ Center for Research and Exploration in Space Science and Technology (CRESST) and NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
⁷ Universities Space Research Association, 7178 Columbia Gateway Drive, Columbia, MD 21046, USA

Received: 21 March 2015
Accepted: 22 May 2015

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.