Chandra, MDM, Swift, and NuSTAR Observations Confirming the SFXT Nature of AX J1949.8+2534

Abstract

AX J1949.8+2534 is a candidate supergiant fast X-ray transient (SFXT) observed in outburst by the International Gamma-ray Astrophysics Laboratory (IGR J19498+2534). We report on the results of six Neil Gehrels Swift-XRT, one Chandra, and one Nuclear Spectroscopic Telescope Array observation of the source. We find evidence of rapid X-ray variability on a few kilosecond timescales. Fortunately, Chandra observed the source in a relatively bright state, allowing us to confidently identify the optical/NIR counterpart of the source. We also obtained an optical spectrum of this counterpart, which shows an Hα emission line and He I absorption features. The photometry and spectrum of the source allow us to constrain its distance, ̃7-8 kpc, and reddening, A V = 8.5-9.5. We find that the star is likely an early B-type Ia supergiant, confirming that AX J1949.8+2534 is indeed an SFXT.