Multiwavelength observations of 1RXH J173523.7-354013: revealing an unusual bursting neutron star
D'Avanzo, P.; de Luca, A.; Degenaar, N.; Wijnands, R.; Rea, N.; Esposito, P.; Novara, G.; Israel, G. L.; Lo Curto, G.; Cackett, E. M.; Torres, M. A. P.; Krimm, H.; Holland, S. T.; Trap, G.; Jonker, P. G.; Patruno, A.; Kaur, R.
Netherlands, United States, Spain, Italy, France
Abstract
On 2008 May 14, the Burst Alert Telescope onboard the Swift mission triggered on a type-I X-ray burst from the previously unclassified ROSAT object 1RXH J173523.7-354013, establishing the source as a neutron star X-ray binary. We report on X-ray, optical and near-infrared observations of this system. The X-ray burst had a duration of ~2 h and belongs to the class of rare, intermediately long type-I X-ray bursts. From the bolometric peak flux of ~3.5 × 10-8ergcm-2s-1, we infer a source distance of D <~ 9.5 kpc. Photometry of the field reveals an optical counterpart that declined from R = 15.9 during the X-ray burst to R = 18.9 thereafter. Analysis of post-burst Swift/X-ray Telescope observations as well as archival XMM-Newton and ROSAT data suggests that the system is persistent at a 0.5-10 keV luminosity of ~2 × 1035 (D/9.5 kpc)2ergs-1. Optical and infrared photometry together with the detection of a narrow Hα emission line (full width at half maximum = 292 +/- 9kms-1, equivalent width = -9.0 +/- 0.4 Å) in the optical spectrum confirms that 1RXH J173523.7-354013 is a neutron star low-mass X-ray binary. The Hα emission demonstrates that the donor star is hydrogen rich, which effectively rules out that this system is an ultracompact X-ray binary.