The identification of the optical/IR counterpart of the 15.8-s transient X-ray pulsar XTE J1946+274

Verrecchia, F.; Israel, G. L.; Negueruela, I.; Covino, S.; Polcaro, V. F.; Clark, J. S.; Steele, I. A.; Gualandi, R.; Speziali, R. and Stella, L. (2002). The identification of the optical/IR counterpart of the 15.8-s transient X-ray pulsar XTE J1946+274. Astronomy & Astrophysics, 393(3) pp. 983–989.

DOI: https://doi.org/10.1051/0004-6361:20021087

Abstract

We report on the discovery of the optical/IR counterpart of the 15.8s transient X-ray pulsar XTE J1946+274. We re-analysed archival BeppoSAX observations of XTE J1946+274, obtaining a new refined position (a circle with 22" radius at 90% confidence level). Based on this new position we carried out optical and infra-red (IR) follow-up observations. Within the new error circle we found a relatively optical faint (B=18.6) IR bright (H=12.1) early type reddened star (V-R=1.6). The optical spectra show strong Hα and Hβ emission lines. The IR photometric observations of the field confirm the presence of an IR excess for the Hα-emitting star (K=11.6, J-H=0.6) which is likely surrounded by a circumstellar envelope. Spectroscopic and photometric data indicate a B0-1V-IVe spectral-type star located at a distance of 8-10kpc and confirm the Be-star/X-ray binary nature of XTE J1946+274.

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