The discovery of the optical/IR counterpart of the 12-s transient X-ray pulsar GS 0834-43

Abstract

We report the discovery of the optical counterpart of the 12.3-s transient X-ray pulsar GS 0834−43. We reanalysed archival ROSAT PSPC observations of GS 0834−43, obtaining two new refined positions, ∼14 and ∼18 arcsec away from the previously published one, and a new spin period measurement. Based on these results we carried out optical and infrared (IR) follow-up observations. Within the new error circles, we found a relatively faint (V=20.1) early-type reddened star (V−R=2.24). The optical spectrum shows a strong Hα emission line. The IR observations of the field confirm the presence of an IR excess for the Hα-emitting star (K′=11.4, J−K′=1.94), which is likely surrounded by a conspicuous circumstellar envelope. Spectroscopic and photometric data indicate a B0–2 V–IIIe spectral type star located at a distance of 3–5 kpc and confirm the Be-star/X-ray binary nature of GS 0834−43.