[ Previous | Next | ADS ]

Optical spectroscopy of putative counterparts of INTEGRAL sources in the Cassiopeia/Perseus region

ATel #941; N. Masetti, L. Bassani, A. Malizia (INAF/IASF, Bologna), A. J. Bird (Univ. Southampton) and P. Ubertini (INAF/IASF, Rome)
on 9 Nov 2006; 16:42 UT
Credential Certification: Nicola Masetti (masetti@iasfbo.inaf.it)

Subjects: Optical, X-ray, AGN, Star

Referred to by ATel #: 1326, 1375

On the night between October 1 and 2, 2006, under non-perfect sky conditions (seeing ~2.5 arcsec), we used the instrument BFOSC mounted on the `G.D. Cassini' 1.5m telescope of the Astronomical Observatory of Bologna located in Loiano (Italy) to acquire optical spectra of the putative optical counterparts of sources IGR J00335+6126 and IGR J00254+6822, reported in Kuiper et al. (ATel #939) and also present in the forthcoming 3rd INTEGRAL/IBIS survey (Bird et al., in prep.).
Total exposure times ranged from 5 to 60 minutes, depending on the object brightness.

In the following we report our results.

IGR J00335+6126: the error box of the ROSAT source 1RXS J003357.9+612645 within the INTEGRAL error circle encompasses two relatively bright and pointlike USNO-A2.0 objects: U1500_00600156 (RA = 00 33 57.34, Dec = +61 26 32.7 [J2000]; mag R ~ 10.7) and U1500_00600240 (RA = 00 33 57.60, Dec = +61 26 51.1 [J2000]; mag R ~ 13.6). Optical spectroscopy on both sources shows that they are galactic stars of intermediate spectral type with no peculiarities; in particular, neither Balmer nor helium emission lines are found in their spectra, making them unlikely counterparts of the hard X-ray emitting object.

IGR J00254+6822: the optical counterpart proposed by Kuiper et al. (ATel #939), galaxy LEDA 136991, shows a double nucleus morphology. Spectroscopy on both parts of the galaxy shows the following. The western nucleus has narrow [OIII], Halpha, [NII] and [SII] emission lines at redshift z = 0.012, superimposed on a reddened continuum. Line ratios are consistent with those of a Seyfert 2 nucleus. The eastern nucleus of the galaxy instead does not show any sign of activity. We thus conclude that the western part of galaxy LEDA 136991 is a viable optical candidate for INTEGRAL source IGR J00254+6822; this is also supported by its positional consistency with the IRAS source 00227+6805. As usual, we stress that pointed soft X-ray observations with satellites affording arcsecond localizations (such as Chandra, XMM-Newton or Swift) are conclusive to confirm this association.

We thank S. Bernabei for the night assistance at the telescope.