Swift/XRT follow-up of three unidentified INTEGRAL sources
ATel #2853; R. Landi, L. Bassani, P. Parisi, N. Masetti (INAF/IASF Bologna), A. Bazzano, M. Fiocchi (INAF/IASF Rome), A. J. Bird (Univ. Southampton), N. Gehrels (NASA/GSFC), J. A. Kennea (PSU)
on 22 Sep 2010; 12:07 UT
Credential Certification: Raffaella Landi (firstname.lastname@example.org)
Subjects: X-ray, Gamma Ray, Request for Observations
We report the results of X-ray follow-up observations performed with Swift/XRT of three unidentified
INTEGRAL sources listed in the 4th IBIS Survey Catalogue (Bird et al. 2010, ApJS, 186, 1) and in the
INTEGRAL/IBIS 7-year All-Sky Hard X-Ray Survey (Krivonos et al. 2010, arXiv:1006.4437).
In the following, the XRT error box radii are given at 90% confidence level (c.l.).
Within the IBIS error circle XRT detects one X-ray source at 3.2 and
2.1 sigma c.l. in the 0.3-10 keV energy range and above 3 keV, respectively. This object is located at
RA(J2000) = 09h 18m 58.65s and Dec(J2000) = -44d 18m 34.49s (7.3 arcsec uncertainty) and is
associated with the 2MASS extended object 2MASX J09185877-4418302 classified as galaxy in the NED
thus suggesting a probable AGN nature. This source has also a counterpart in the USNO-A2.0 catalogue
with magnitude R ~16.8.
Due to the short XRT exposure (965 s), we can only infer a 2-10 keV
flux of ~10-12 erg cm-2 s-1.
Within the IBIS error circle of this source, we find an X-ray source at
RA(J2000) = 17h 23m 22.83s and Dec(J2000) = -28d 37m 51.65s (4 arcsec uncertainty).
This object, which is detected at 11.7 sigma c.l. in the 0.3-10 keV energy range and still
observed at energies above 3 keV with a statistical significance of 8.5 sigma, coincides with a ROSAT
Faint source (1RXS J172323.7-283805). The XRT location is also compatible with the USNO-B1.0 source
(USNO-B1.0 0613-0535226) with magnitude R ~19.5.
The X-ray data are well described by an unabsorbed flat (Gamma ~0.98) power law
with a 2-10 keV flux of 2.1 x 10-12 erg cm-2 s-1.
There in an X-ray source, within the IBIS error circle, at RA(J2000) = 18h 29m 20.01s and
Dec(J2000) = -12d 12m 48.44s (5.3 arcsec uncertainty), which is detected at 5.4 sigma c.l. in the
0.3-10 keV energy range and is still detected above 3 keV at 4.5 sigma c.l..
The X-ray spectrum is fitted with an unabsorbed
power law having a flat (~0.35) photon index and a 2-10 keV flux of
2.3 x 10-12 erg cm-2 s-1.
No catalogued optical and infrared counterpart is found within the XRT uncertainty.
From a visual inspection of the DSS-II-red image of the region we, however, find a bright object
the XRT error box, which is listed in the USNO-B1.0 and 2MASS catalogues with magnitudes
R ~17.6-18.4 and I ~15.7, H ~15.0, K ~15.2, respectively. Two other fainter objects are
clearly seen in the DSS-II-red image inside the XRT uncertainty circle.
Optical observations of these objects are strongly encouraged in order to assess their nature and
determine which of them is the likely counterpart of the corresponding IBIS source.