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Swift/XRT follow-up observations of two unidentified INTEGRAL sources

ATel #3065; R. Landi, N. Masetti (INAF/IASF Bologna), A. Bazzano, F. Capitanio (INAF/IASF Rome), A. J. Bird (Univ. Southampton), N. Gehrels (NASA/GSFC)
on 3 Dec 2010; 13:35 UT
Credential Certification: Raffaella Landi (landi@iasfbo.inaf.it)

Subjects: X-ray, Gamma Ray, Request for Observations

Referred to by ATel #: 3072

We report the results of X-ray follow-up observations performed with Swift/XRT of two unidentified INTEGRAL sources listed in the 4th IBIS Survey Catalogue (Bird et al. 2010, ApJS, 186, 1).

IGR J14466-3352

We detect one source in each of the two XRT pointings available located within the IBIS error circle: source #1 (1st observation) and source #2 (2nd observation).

Source #1, detected at 3.3 sigma c.l. (0.3-10 keV), is located at R.A.(J2000) = 14h 46m 37.4s and Dec.(J2000) = -33d 52m 29.6s (6 arcsec uncertainty). It has a counterpart in the radio source NVSS J144637-335234 having a 20 cm flux of 13+/-0.6 mJy. No optical or infrared counterpart is found; the 2-10 keV flux is 7.4 x 10-14 erg cm-2 s-1, assuming a power law with photon index 1.8.

Source #2 is at 2.7 sigma c.l. in the same energy band and is located at R.A.(J2000) = 14h 46m 31.1s and Dec.(J2000) = -33d 52m 37.6s (6 arcsec uncertainty). No counterpart at other wavelengths is found; the 2-10 keV flux is 4.9 x 10-14 erg cm-2 s-1.

The fact that IGR J14466-3352 is reported as variable in the IBIS catalogue and is located at high Galactic latitudes suggests that it could be a Blazar-type object, hence favouring the association with source #1, the one of the two with radio emission.

IGR J21565+5948

There are two sources detected by XRT whose positions are both compatible with the IBIS positional uncertainty:

Source #1: is detected, within the IBIS error circle, at 3 sigma c.l. (0.3-10 keV) with coordinates R.A.(J2000) = 21h 56m 27.3s and Dec.(J2000) = +59d 47m 40.9s (6 arcsec uncertainty). It has a counterpart in a USNO-A2.0 object (R ~7), and is also listed in the 2MASS survey (J, H, and K ~6.6). It also belongs to the UVOT Bright Star Catalog (V and B ~7). The 2-10 keV flux is 2.5 x 10-14 erg cm-2 s-1, assuming a power law with photon index 1.8. The counterpart of this object is most likely the star CCDM J21565+5948AB, of spectral type AO.

Source #2: is detected just at the border of the 99% IBIS error circle at 10.5 sigma c.l. in the 0.3-10 keV energy band; it is a hard source as it is still observed at E > 3 keV at 5.3 sigma c.l.. It is located at R.A.(J2000) = 21h 56m 04.29s and Dec.(J2000) = +59d 56m 01.66s (4.11 arcsec uncertainty). The XRT position coincides with a USNO-A2.0 object (R ~16 and B ~18), also listed in the 2MASS catalogue (J ~16, H ~15 and K ~14). The X-ray location is also compatible with the ROSAT Faint object 1RXS J215604.4+595607. The X-ray spectrum is well fitted with an unabsorbed power law (Gamma ~2) and provides a 2-10 keV flux of 1.2 x 10-12 erg cm-2 s-1.

Despite the fact that source #1 is located within the 90% IBIS error circle might suggest it as the possible IBIS counterpart, the nature of its optical counterpart and the X-ray characteristics of source #2 (brightness and hardness) lead us to propose the latter as the likely counterpart to the IBIS detection.