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The likely optical counterpart to the X-ray transient IGR J01363+6610 (Resubmission of ATel#339)

ATel #343; Pablo Reig (FORTH & University of Crete), Ignacio Negueruela (University of Alicante, Spain), Antonis Manousakis (University of Crete), Amparo Marco (University of Alicante) and Giannis Papamastorakis (University of Crete)
on 12 Oct 2004; 09:47 UT
Credential Certification: Pablo Reig (pablo.reig@uv.es)

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

After the submission of ATel #339 a few formatting inconsistencies and some missing/incorrect information were spotted. This is the corrected version of ATel #339. It also contains new information concerning the association of the proposed counterpart with the Halpha emission line star [KW97] 6-30.

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 Anstrongs (JD 2,453,193.52). The classification spectrum (4000-5000 Anstrongs) 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 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 2 arcmin south-west of our proposed candidate and outside the INTEGRAL error circle. It was brought to our attention by Brian Skiff (Lowell Observatory) that the catalogued Halpha emission line star might as well be TYC 4043- 860-1 at R.A.= 01h36m06.79s, DEC=+66h13m02.6s (J2000), i.e, ~1.5 arcmin east of our observed star. This star has V=11.5 and was observed by Gonzalez & Gonzalez (1956, Bol. Obs. Tonantz. Tacub., 2, part no 15, 16-26). However, this star is not presently active. A slitless spectrum obtained with the NOT (JD 2,453,282.5) shows Halpha in absorption. Likewise, our photometric value through a narrow Halpha filter (JD 2,453,186.56) is comparable to those of other field stars.

If our 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.