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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
Password Certification: Raffaella Landi (firstname.lastname@example.org)
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).
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.
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.