Swift/XRT follow-up observations of unidentified INTEGRAL sources

ATel #2975; E. Maiorano, R. Landi, P. Parisi, N. Masetti, L. Bassani, A. Malizia (INAF/IASF Bologna), A. Bazzano, P. Ubertini (INAF/IASF Rome), A. J. Bird (Univ. Southampton), E. Jimenez-Bailon (UNAM, Mexico City), V. Chavushyan (INAOE, Puebla), G. Galaz, D. Minniti (PUC, Santiago de Chile) and L. Morelli (Univ. Padua)
on 27 Oct 2010; 13:10 UT
Credential Certification: Elisabetta Maiorano (maiorano@iasfbo.inaf.it)

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We report on X-ray follow-up observations performed with Swift/XRT of 3 unidentified INTEGRAL sources listed in the fourth IBIS Survey Catalogue (Bird et al. 2010, ApJS, 186, 1).

IGR J08190-3835
Within the IBIS uncertainty XRT detects one source with a statistical significance of 5.8 sigma in the energy range 0.3-10 keV and 5.6 sigma above 3 keV. This object, located at RA(J2000) = 08h 19m 11.3s and Dec(J2000) = -38d 33m 09s (5 arcsec uncertainty), is associated with a 2MASS extended object (2MASX J08191136-3833104) classified as a galaxy in the NED archive and is positionally coincident with radio source NVSS J081910-383307. The X-ray data analysis provides an absorbed (NH(intr) ~ 13.6 x 10^22 cm^-2, in excess of the Galactic value of 9.6 x 10^21 cm^-2) power law spectrum with photon index of 1.8 (fixed) and an observed 2-10 keV flux of 1.49 x 10^-12 erg cm^-2 s^-1. The radio data analysis provides a flux of 2.7+/-0.7 mJy at 1.4 GHz. Optical spectroscopy acquired at the 1.5m CTIO telescope on 2010 Jan 18 shows that the source displays Halpha, [NII] and [SII] narrow emission lines at redshift z=0.009+-0.001 superimposed on a reddened continuum. The flux ratios among these emission features suggest that the object is likely a Type 2 AGN and thus the actual counterpart of the IBIS source.

IGR J17520-6018
The only X-ray source, detected at 4.1 sigma confidence level in the ranges 0.3-10 keV and above 3 keV by XRT within the IBIS uncertainty, is located at RA(J2000) = 17h 51m 56.2s and Dec(J2000) = -60d 19m 42s (6 arcsec uncertainty). It has a counterpart in the 2MASS extended survey (2MASX J17515581-6019430) and is also associated with the radio source SUMSS J175155-601943; the source is reported as a galaxy in the NED archive. The X-ray data analysis provides an absorbed (NH(intr) ~13 x 10^22 cm^-2 in excess of the Galactic value of 7.0 x 10^20 cm^-2) power law spectrum with photon index of 1.8 (fixed) and an observed 2-10 keV flux of 2.6 x 10^-12 erg cm^-2 s^-1. The radio data analysis provides a flux of 25.2+/-2.2 mJy at 843 MHz. Based on this information we propose that this object is the likely counterpart to the IBIS source and we further suggest that is a type 2 AGN.

IGR J21441+4640
Within the IBIS positional uncertainty of this source, there are two galaxies, UGC 11802 and UGC 11806, at the same redshift (z=0.011), which form a galaxy pair. Both galaxies are detected at radio frequencies in the NVSS catalogue (NVSS J214354+463705, NVSS J214413+463718) and are also listed in the 2MASS extended catalogue (2MASX J21435408+4637048, 2MASX J21441345+4637169). Within the IBIS uncertainty XRT finds only UGC 11806 at a statistical significance of 2.5 sigma in the range 0.3-10 keV; no signal is found above 3 keV. The object is located at RA(J2000) = 21h 44m 13.8s and Dec(J2000) = +46d 37m 20s (6 arcsec uncertainty). The XRT spectrum is well described by an unabsorbed power law with photon index of 1.8 (fixed) and an observed 2-10 keV flux of 1.2 x 10^-13 erg cm^-2 s^-1. The radio data analysis provides a flux of 11.0+/-1.1 mJy at 1.4 GHz. Optical spectroscopic observations secured with the 2.1m San Pedro Martir telescope on 2009 Sep 15 indicate that this object is a narrow emission-line galaxy with flat continuum and prominent Balmer, [NII], [OIII] and [SII] lines at a redshift consistent with that of the literature. The low significance detection in X-rays may be due to the variable nature of the source (Bird et al. 2010, ApJS, 186, 1) rather than to high absorption, which is not readily apparent from the optical spectrum.

We would like to thank the Swift Team for scheduling these observations, and J. Velasquez for service mode observations at the 1.5m CTIO telescope.