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Swift-XRT follow-up of IGR J05511-1218, IGR J07072-1227 and IGR J17259+2603

ATel #10363; A. Malizia, R. Landi, L. Bassani, N. Masetti (IASF/INAF Bologna), A. Bazzano, M. Fiocchi, P. Ubertini (IAPS/INAF Rome), A. J. Bird (University of Southampton)
on 10 May 2017; 14:41 UT
Credential Certification: Angela Malizia (malizia@iasfbo.inaf.it)

Subjects: X-ray, Gamma Ray, AGN

In this telegram we report X-ray follow-up observations performed with Swift-XRT on 3 unidentified INTEGRAL sources, namely IGR J05511-1218, IGR J07072-1227 and IGR J17259+2603.
All 3 sources are reported as new persistent detections in the latest INTEGRAL/IBIS survey by Bird et al. (2016 ApJS, 223, 15). For the search of X-ray counterparts we used the 90% IBIS positional uncertainty unless otherwise stated.

IGR J05511-1218
XRT performed 4 pointings towards this source for a total exposure of 6045 sec. Within the IBIS error circle, XRT detects only one X-ray source located at R.A.(J2000) = 05h 51m 13.05s and Dec.(J2000) = -12d 14m 39.54s (5.11 arcsec 90% positional uncertainty). The XRT detection is around 5 sigma in the 0.3-10 keV band with the majority of counts above 3 keV. Inside the XRT error circle there is the galaxy 2MASX J05511312-1214419 (also LEDA 148076) at z=0.035028.
The XRT spectrum is well fitted with an absorbed power law having a photon index fixed at 1.7, an intrinsic column density of NH = 8.6 [+9.3, -4.9] x 1022 cm-2, and a 2-10 keV flux of 0.8 x 10-12 erg cm-2 s-1.

IGR J07072-1227
XRT performed 7 pointings towards this source for a total exposure of 4786 sec. Also in this case within the IBIS positional uncertainty we find a single source detected at 6 sigma level over the 0.3-10 keV band again with most counts above 3 keV. The XRT position is at R.A.(J2000) = 07h 07m 11.43s and Dec.(J2000) = -12d 28m 00.2s with a 90% positional uncertainty of 4.74 arcsec. This is consistent with the position of the galaxy 2MASX J07071126-1227560 of unknown redshift.
The XRT spectrum is well fitted with an absorbed power law having a fixed photon index of 1.7, an intrinsic column density of NH = 5.1 [+13.5, -2.8] x 1022 cm-2, and a 2-10 keV flux of 1.1 x 10-12 erg cm-2 s-1.
Neither of the above sources is reported in the NVSS survey (Condon et al. 1998, AJ 115, 1693) with an upper limit to the 20 cm flux of 2 mJy. The presence of intrinsic absorption suggests that both IGR J05511-1218 and IGR J07072-1227 are likely type 2 AGN.

IGR J17259+2603
XRT performed 10 pointings towards this source for a total exposure of 6183 sec. Within the IBIS error circle, XRT detects only one X-ray source with a significance of around 6 sigma in the 0.3-10 keV band, but no detection above 3 keV. This X-ray source is located at R.A.(J2000) = 17h 25m 48.01s and Dec.(J2000) = +25d 55m 34.90s (5.05 arcsec 90% positional uncertainty) and is therefore associated to the QSO candidate SDSS J172547.98+255531.3 (photometric z=0.635). The XRT spectrum is well fitted with a power law absorbed by the Galactic column density of 4.8 x 1022 cm-2 and having a photon index of 2.26 [+0.75, -0.65] and a 2-10 keV flux of 17.5 x 10-14 erg cm-2 s-1. The source weak flux and no detection above 3 keV casts some doubts about its association with INTEGRAL. We note also that a harder and brighter source is present in the XRT image but outside the 99% IBIS error circle (8.7 arcmin distance); the source is located at R.A.(J2000) = 17h 25m 30.05s and Dec.(J2000) = +25d 50m 44.89s (5.53 arcsec 90% positional uncertainty) and is associated to a more distant QSO candidate SDSS J172529.89+255043.2 (photometric z=1.285). The X-ray spectrum is a simple power law with Γ=1.47 [+0.89, -1.12] and a 2-10 keV flux of 1.2 x 10-13 erg cm-2 s-1.