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.
Stars, Interstellar Medium and the Galaxy
Degenaar, N., Jonker, P. G., Torres, M. A. P., Kaur, R., Rea, N., Israel, G. L., Patruno, A., Trap, G., Cackett, E. M., D'Avanzo, P., Lo Curto, G., Novara, G., Krimm, H., Holland, S. T., de Luca, A., Esposito, P., Wijnands, R. 2010. Multiwavelength observations of 1RXH J173523.7-354013: revealing an unusual bursting neutron star. MNRAS 404(3), 1591-1602.