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Optical classification of 8 INTEGRAL sources

ATel #783; N. Masetti (INAF/IASF, Bologna), L. Morelli (PUC, Santiago), E. Palazzi, J. Stephen (INAF/IASF, Bologna), A. Bazzano (INAF/IASF, Rome), A. J. Dean (Univ. Southampton), R. Walter (ISDC, Versoix) and D. Minniti (PUC, Santiago)
on 30 Mar 2006; 21:06 UT
Credential Certification: Nicola Masetti (masetti@iasfbo.inaf.it)

Subjects: Optical, X-ray, Binary, Cataclysmic Variable

Referred to by ATel #: 2601

On 20-22 March 2006 we used the R-C spectrograph of the CTIO 1.5m telescope in Cerro Tololo (Chile) to get optical spectra of the putative counterparts of 8 X-ray sources discovered by INTEGRAL (see Bird et al. 2006, ApJ, 636, 765; Halpern 2005, ATel #572; Kuiper et al. 2006, ATel #684; Sazonov et al. 2005, A&A, 444, L37; Revnivtsev et al. 2006, Astron. Lett., 32, 145).

To reduce the X-ray error box size to a few arcsec at most, we selected sources with a single ROSAT Bright Source (Voges et al. 1999, A&A, 349, 389), and/or a single Swift/XRT archival X-ray source (available at http://www.asdc.asi.it ), or a single Chandra source within the INTEGRAL error box (which, according to Stephen et al. 2006, A&A, 445, 869, means that this is very likely the soft X-ray counterpart of the INTEGRAL source).
In one case (AX J1700.2-4220) we chose a known emission-line star in the INTEGRAL error box as the putative counterpart; for the caveats regarding this choice, we refer the reader to Masetti et al. (2006, A&A, in press [astro-ph/0512399]).
Exposure times ranged from 40 to 60 minutes, depending on the object brightness.

Notes on individual sources (coordinates refer to epoch J2000):

IGR J05007-7047: the presence of Halpha emission and the rest of the Balmer lines in absorption, at a redshift consistent with that of the LMC, suggests that this is likely a HMXB located in this galaxy.

XSS J12270-4859: the only object in the error boxes of 1RXS J122758.8-485343 and of the XRT observation, USNO-A2.0 source U0375_15949017 (RA = 12 27 58.77, Dec = -48 53 42.8), shows Balmer and HeI lines in emission at z = 0. Given the similarity with the optical spectrum of IGR J00234+6141 (Bikmaev et al. 2006, Astron. Lett., in press [astro-ph/0603715]) we classify it as a CV.

IGR J14536-5522: the brightest object in the XRT and ROSAT error boxes (Mukai et al. 2006, ATel #686), USNO-A2.0 source U0300_22436308 (RA = 14 53 41.16, Dec = -55 21 37.4), shows a spectrum which is similar to that of XSS J12270-4859. Thus we classify it as a CV.

IGR J15094-6649: as for the two previous cases, we classify the USNO source U0225_21896607 (RA = 15 09 26.00, Dec = -66 49 23.4), contained within the 1RXS J150925.7-664913 source error box, as a CV due to the emissions in its optical spectrum.

IGR J16167-4957: Balmer, HeI and HeII emissions at z = 0 observed in the only optical source within the XRT error circle, USNO-A2.0 object U0375_26829054 (RA = 16 16 37.78, Dec = -49 58 44.7), suggest that the spectrum is typical of a CV.

IGR J16207-5129: in the XRT error box, the USNO-A2.0 object U0375_27093111 (RA = 16 20 46.28, Dec = -51 30 06.3) shows an Halpha emission at redshift 0 superimposed on a reddened continuum. The optical spectrum is similar to that of 2RXP J130159.6-635806 (see Masetti et al. 2006, A&A, in press [astro-ph/0512399]); thus, the source is likely a HMXB. We also correct the identification of IGR J16207-5129 reported in the above paper, where this object was associated with star HD146803.

AX J1700.2-4220: our spectrum of star HD153295 within the INTEGRAL error box confirms its emission-line nature (e.g. Merrill & Burwell 1943, ApJ, 98, 153). The optical spectrum of this star points to a HMXB nature. However, as no arcsec-sized X-ray position is available, we consider the association as tentative.

IGR J17195-4100: the only object consistent with the error boxes of source 1RXS J171935.6-410054 and of the XRT pointing, USNO-A2.0 object U0450_27095307 (RA = 17 19 35.91, Dec = -41 00 53.7), shows Balmer and He emissions at z = 0, similarly to the CVs described above.

We thank C. Aguilera and A. Gomez for assistance at the telescope.