IGR J17503–2636: a candidate supergiant fast X-ray transient

¹ Department of Astronomy, University of Geneva, Chemin d’Écogia 16, 1290 Versoix, Switzerland
e-mail: carlo.ferrigno@unige.ch
² Dipartimento di Fisica, SP Monserrato-Sestu, Universitá degli Studi di Cagliari, km 0.7, 09042 Monserrato, Italy
³ National Space Institute, Technical University of Denmark, Elektrovej 327-328, 2800 Lyngby, Denmark
⁴ Dipartimento di Fisica e Chimica, Università degli Studi di Palermo, Via Archirafi 36, 90123 Palermo, Italy

Received: 31 January 2019
Accepted: 20 March 2019

Abstract

The object IGR J17503–2636 is a hard X-ray transient discovered by INTEGRAL on 2018 August 11. This was the first ever reported X-ray emission from this source. Following the discovery, follow-up observations were carried out with Swift, Chandra, NICER, and NuSTAR. Here we report on the analysis of all of these X-ray data and the results obtained. Based on the fast variability in the X-ray domain, the spectral energy distribution in the 0.5–80 keV energy range, and the reported association with a highly reddened OB supergiant at ∼10 kpc, we conclude that IGR J17503–2636 is most likely a relatively faint new member of the supergiant fast X-ray transients. Spectral analysis of the NuSTAR data revealed a broad feature in addition to the typical power-law with exponential roll-over at high energy. This can be modeled either in emission or as a cyclotron scattering feature in absorption. If confirmed by future observations, this feature would indicate that IGR J17503–2636 hosts a strongly magnetized neutron star with B ∼ 2 × 10¹² G.