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Identification of the nature of sources IGR J17404-3655 and IGR J18173-2509

ATEL # 1620; N. Masetti, P. Parisi, E. Palazzi, R. Landi (INAF/IASF-Bologna), L. Morelli (Univ. Padua), G. Galaz, D. Minniti (PUC, Santiago), A.J. Dean (Univ. Southampton) and P. Ubertini (INAF/IASF-Rome)
on 18 Jul 2008; 15:36 UT
Password Certification: Nicola Masetti (

Subjects: Optical, X-ray, Binaries, Cataclysmic Variables

On the night of July 2, 2008, we used the R-C spectrograph of the CTIO 1.5m telescope in Cerro Tololo (Chile) to perform optical spectroscopy on sources inside the 90% confidence level Swift/XRT X-ray error boxes (Landi et al., ATels #1539 and #1437; see also Ibarra et al., ATel #1397) of the unidentified INTEGRAL sources IGR J17404-3655 and IGR J18173-2509 (Bird et al. 2007, ApJS, 170, 175).
The optical objects were selected by overlapping the XRT error boxes on the relevant DSS-II-Red survey archive images (

The following results were obtained (coordinates refer to epoch J2000):

IGR J17404-3655: two optical spectra of source USNO-A2.0 0525_28851523, with coordinates RA = 17 40 26.85, Dec = -36 55 37.6 and magnitude R ~ 17.3, were acquired for a total exposure time of 4800 s.
The object shows a red continuum, possibly absorbed by the Galactic dust along the line of sight (this field lies at a Galactic latitude b = -3.3 deg). A single narrow emission line, at a wavelength consistent with that of restframe Halpha and with equivalent width ~17 Angstrom, is readily detected.
From the above optical characteristics, we conclude that this object is a Galactic X-ray source, and that is likely a Galactic Low-Mass X-Ray Binary.

IGR J18173-2509: two 2400-s spectra of an optical source lying at RA = 18 17 22.25, Dec = -25 08 42.9 (according to the DSS-II-Red survey astrometry) show a number of Balmer (up to Hdelta at least), HeI and HeII emission lines at z=0, superimposed on a rather blue continuum.
The optical spectral appearance of this source, by analogy with other cases identified in the past (see e.g. Masetti et al. 2006, A&A, 459, 21; 2008, A&A, 482, 113) allows us to identify this object as a Galactic Cataclysmic Variable.

We thank E. Cosgrove and M. Hernandez for assistance at the telescope.

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