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he likely optical counterpart to the X-ray transient IGR J01363+6610

ATel #339; FORTH & University of Crete
on 8 Oct 2004; 12:55 UT
Credential Certification: Pablo Reig (pablo.reig@uv.es)

Subjects: Optical, X-ray, Binary, Neutron Star, Transient

Referred to by ATel #: 343

We report photometric and spectroscopic optical observations of the likely optical counterpart to the X-ray transient IGR J01363+6610 discovered by INTEGRAL (Grebenev et al., ATel 275). The photometric and red-end spectroscopic observations were made from the 1.3-m telescope of the Skinakas Observatory (Crete, Greece), while blue-end spectra were obtained using the NOT 2.56m telescope at El Roque de los Muchachos Observatory (La Palma, Spain).

The observations revealed that the star located at R.A.= 01h35m50s, Decl.=66d12m40s, consistent with the INTEGRAL uncertainty circle, shows a very strong Halpha emission. Measured photometric magnitudes are B=14.68+-0.02, V=13.29+-0.03, R=12.32+-0.03 and I=11.37+-0.04 (JD 2,453,214.55) and the Halpha equivalent width is -50+-2 amstrongs (JD 2,453,193.52). The classification spectrum (4000-5000 Amstrongs) shows the presence of Hbeta and Hgamma in emission and the metallic and HeI lines typical of an early B-type star of low luminosity. The spectral type is close to B1, typical of a Be/X-ray binary. This object is very probably identical with the catalogued emission line star [KW97] 6-30 (Kohoutek & Wehmeyer, 1999, A&AS, 134, 255), though the coordinates listed in this catalogue locate the source about 4 arcmin away and outside the INTEGRAL error circle.

If the identification is correct then the early-type optical companion, the presence of Balmer emission lines and the lack of radio emission (Pooley, ATel 276) suggests that IGR J01363+6610 is a new Be/X-ray binary. The detections of X-ray pulsations would provide the final proof of its nature.