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Swift/XRT follow-up of the unidentified INTEGRAL source IGR J03564+6242

ATel #4025; M. Molina, R. Landi (INAF/IASF Bologna), A. Bazzano, M. Fiocchi (INAF/IASF Rome), A. J Bird, S. P. Drave (Univ. Southampton)
on 10 Apr 2012; 09:08 UT
Credential Certification: Manuela Molina (molina@iasfbo.inaf.it)

Subjects: Radio, X-ray, Gamma Ray, AGN, Blazar, Quasar

We report the possible association of the unidentified INTEGRAL source IGR J03564+6242 with the radio galaxy 4C 62.08, obtained through a Swift/XRT Target of Opportunity follow-up observation.

IGR J03564+6242 is listed in the 4th INTEGRAL/IBIS catalogue (Bird et al. 2010), at coordinates RA (J2000) = 59.099 and Dec (J2000) = 62.714, with a positional uncertainty of 4.6 arcmin. The source is flagged as Y in the catalogue, indicating that it is mildly variable; the peak flux in the 20-40 keV band of 11.35±3.08X10-12 erg cm-2s-1.

The XRT observed the source four times between April 2, 2011 and April 10, 2011. The combined images reveal one X-ray source at 4.4 sigma confidence level located at 5.4 arcminutes from the unidentified INTEGRAL source, i.e. just outside the 90% IBIS error circle, but well within the 99% one. The coordinates of the X-ray source are RA (J2000) = 03h55m41.79s and Dec (J2000) = +62d40m57.60s (0.09 arcmin positional uncertainty). The source 2-10 keV flux is 2.57x10-13 erg cm-2s-1, assuming a photon index of 1.8. Consistent with the X-ray position, we find the bright radio source 4C +62.08, classified in NED as an asymmetric double radio source, with a steep spectrum of -1.1 (where S&nu&prop&nu&alpha). It has been observed at various frequencies from 38 MHz with a flux of 1.9 Jy (8C survey) to 4.85 GHz (NRAO 1987 Green Bank radio survey) with a flux of 191 mJy.

Coincident with the radio and X-ray coordinates, we also find an optical counterpart in the USNO B-1 catalogue with magnitudes R=18.23, B=19.65 and I=18.07 and an IR counterpart in the 2MASS catalogue, with magnitudes J=16.71, H=16.12 and K=15.28. Since measurements at 4.85 GHz and in the B magnitude are available, we calculate the radio loudness of the source (i.e. a source is radio loud if RL= Log(F4.85GHz/FB)>1; Kellerman et al. 1989) and find that RL=3.5. The radio association as well as radio morphology, loudness and X-ray variability all point to an extragalactic nature for this source. More in-depth follow-up observations at other wavelengths, in particular in the optical, are desirable in order to further confirm the nature of this source.