Optical spectroscopic follow-up of INTEGRAL sources

ATel #10447; N. Masetti, A. Malizia, R. Landi, L. Bassani, (INAF/IASF, Bologna), V. Chavushyan (INAOE, Puebla), A. Bazzano, M. Fiocchi, P. Ubertini (INAF/IAPS, Rome), A. J. Bird (Univ. Southampton) and E. Jimenez-Bailon (UNAM)
on 31 May 2017; 12:34 UT
Credential Certification: Nicola Masetti (masetti@iasfbo.inaf.it)

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As a follow-up work of the identification of the soft X-ray counterpart to selected INTEGRAL sources reported in ATels #10363 and #10364, we observed with two different telescopes, using mid-resolution spectroscopy, some of their proposed optical counterparts. In the following, preliminary results on this campaign are reported.

IGR J05511-1218

The proposed counterpart, LEDA 148076 (ATel #10363), was observed on February 20, 2017 with the 1.5m "Cassini" telescope (equipped with BFOSC) in Loiano, Italy, for a total exposure time of 2400 s. The setup allowed a dispersion of 4.0 Angstroms/pixel.
The spectrum shows a smooth continuum with Balmer, CaII H+K, MgI absorptions at a common redshift z=0.035+-0.001, consistent with the one reported in the literature. Relatively faint (total EW ~ 4 Angstroms) narrow emission lines of the [NII] 6548/6583 complex are detected at the same redshift. The spectral appearance suggests that the source is a X-ray Bright, Optically Normal Galaxy (see e.g. Comastri et al., 2002, ApJ, 571, 771).

IGR J07072-1227

Three 1800-s spectra were acquired on March 30, 2017, with the 2.1m telescope (plus B&C spectrograph) of the San Pedro Martir (SPM) Observatory in Mexico on the counterpart reported in ATel #10363. A dispersion of 2.3 Angstroms/pixel was achieved.
Narrow Halpha, [NII] and [OIII] emission lines were detected at redshift z=0.071+-0.001, superposed on a low S/N, reddened continuum. Line ratios indicate that the source is a Seyfert 2 galaxy, as suggested in ATel #10363.

IGR J17259+2603

The object within the 90% INTEGRAL error circle was observed with the "Cassini" telescope on March 17, 2017, using the same setup reported above for this telescope.
Broad Hgamma and MgII emissions are seen at redshift z=0.597+-0.001 and are superimposed on a blue continuum. This allows us to identify this object as a Type 1 QSO. We suggest that source variability in X-rays, not unusual in QSOs, may at least in part explain the faintness of the high-energy emission detected with XRT from this object (see ATel #10363).

IGR J21095+4322

The northern of the two optical objects within the XRT error circle (ATel #10364), 2MASS J21092386+4319371, was observed at SPM on October 2, 2016, with the same setup described above for this telescope.
The spectrum shows several Balmer (up to Hepsilon), HeI and HeII emission lines at a redshift consistent with zero on a relatively flat continuum. This spectral appearance is thus typical of a (possibly magnetic) Cataclysmic Variable.
While we cannot conclusively state that this is the counterpart of IGR J21095+4322 until a spectrum of the other optical object positionally associated with it in ATel #10364 is available, the presence of a CV within the XRT error circle strongly points at this source as the actual responsible of the observed X-ray emission.


We thank the staffs of the Loiano and SPM observatories for their assistance during the observations reported here.