Spectroscopy of six optical candidates to unidentified INTEGRAL sources
ATel #1033; N. Masetti (INAF/IASF, Bologna), L. Morelli (PUC, Santiago), S. A. Cellone (UNLP, La Plata), L. Bassani, A. Malizia (INAF/IASF, Bologna), A. Bazzano (INAF/IASF, Rome), A. J. Bird (Univ. Southampton), G. Galaz (PUC, Santiago), G. E. Romero (UNLP, La Plata), R. Walter (ISDC, Versoix)
on 27 Mar 2007; 16:01 UT
Credential Certification: Nicola Masetti (firstname.lastname@example.org)
Subjects: Optical, X-ray, AGN
We obtained optical spectra of the putative counterparts of six
unidentified INTEGRAL X-ray sources (Bird et al., astro-ph/0611493;
Krivonos et al., astro-ph/0701836) using the BFOSC instrument of the
1.5m 'Cassini' telescope of the Astronomical Observatory of Bologna in
Loiano (Italy) on 13 Jan 2007, the R-C spectrograph of the CTIO 1.5m telescope
in Cerro Tololo (Chile) on 18-19 Feb 2007, and the REOSC spectrograph of the
2.15m 'Jorge Sahade' telescope at CASLEO (Argentina) on 10-11 Mar 2007.
As usually performed, and as proven very effective in this investigation
(see e.g. Masetti et al. 2006, A&A, 459, 21), in order
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) within the INTEGRAL error box.
In a few cases we observed peculiar objects falling within the INTEGRAL
error circle of the X-ray source of interest. For these cases, we stress
once more that pointed soft X-ray observations with satellites affording
arcsecond localizations are essential to confirm the proposed
Exposure times ranged from 40 to 90 min, depending on the object brightness.
Notes on individual sources (coordinates refer to epoch J2000):
PKS 0611-663: the spectrum of USNO-A2.0 object U0225_02842370 (RA = 06 11
48.32, Dec = -66 24 34.0), the only optical source in the 6" radius X-ray
error circle of ROSAT source 1RXS J061148.5-662430, shows broad Balmer and
narrow [OIII] emission lines at redshift z = 0.230. The line shapes and
ratios indicate that this object is a Seyfert 1.5 AGN. We remark that this
source, which most likely is the optical counterpart of the INTEGRAL hard
X-ray emission, is actually not the object PKS 0611-663, lying more than
20" away and thus positionally inconsistent with the ROSAT source. Thus,
we suggest to change the name of this newly-identified INTEGRAL source to
IGR J06117-6625, following the usual naming convention for INTEGRAL
IGR J07437-5137: the optical spectrum of galaxy LEDA 21656, at z = 0.025
(at odds with the redshift z = 0.0086 from the Hyperleda catalogue, http://leda.univ-lyon1.fr/ ) shows narrow Halpha, [NII], and [OII] emission
lines superimposed on the stellar continuum of the galaxy. The
Halpha/[NII] line ratio is consistent with that of Seyfert 2 AGNs.
NGC 4180: from the nucleus of this radio-emitting galaxy (Condon et al.
1998, AJ, 115, 1693) we detect Halpha, [NII], [SII] and [OIII] lines in
emission at redshift z = 0.006 (consistent with the Hyperleda catalogue
value). Line ratios point to the fact that this most likely is a Seyfert 2
IGR J14561-3738: the spectrum of galaxy LEDA 53392, at redshift z = 0.025
(consistent with that in the Hyperleda catalogue), shows Halpha, [NII] and
[SII] in emission superimposed on the galaxy stellar continuum. Line
ratios are consistent with those of Seyfert 2 AGNs.
IC 4518a: we detect strong and narrow Balmer, [OI], [OIII], [NII] and
[SII] emission lines in the optical spectrum of the nucleus of this
radio-emitting galaxy (Mauch et al. 2003, MNRAS, 342, 1117), at redshift z
= 0.016 (coincident with the result of West et al. 1981, A&AS, 46, 57).
Line ratios confirm that this galaxy hosts a Seyfert 2 AGN.
IGR J16056-6110: spectroscopy of the galaxy LEDA 3079933 within the 8"
radius error box of ROSAT source 1RXS J160551.9-611142 shows that this
object has broad Balmer and narrow [OIII] emissions at redshift z = 0.025.
Line width and ratios allow us to identify this source as a Seyfert 1.5
We thank S. Galleti and S. Bernabei for the service mode observations made
in Loiano, C. Aguilera and A. Gomez for assistance at CTIO, and A. De
Franceschi for assistance at CASLEO.