Swift/XRT follow-up observations of unidentified INTEGRAL sources (1)
ATel #1322; R. Landi, N. Masetti, V. Sguera (INAF/IASF Bologna), M. Del Santo, A. Tarana (INAF/IASF Rome), A. B. Hill, A. J. Dean (Univ. Southampton), P. Caraveo, F. Senziani (INAF/IASF Milano)
on 8 Dec 2007; 15:30 UT
Credential Certification: Raffaella Landi (firstname.lastname@example.org)
Subjects: X-ray, Gamma Ray, Request for Observations
We report on X-ray follow-up observations performed with Swift/XRT of four
unidentified INTEGRAL sources in the third IBIS Survey Catalogue
(Bird et al. 2007, ApJS, 170, 175).
Within the IBIS uncertainty XRT detects two sources with a statistical significance of 22.5 and 22.3
sigma. The first brighter object is
located at RA(J2000) = 00h 33m 18.36s and Dec(J2000) = +61d 27m 42.4s (3.7 arcsec uncertainty) and is
associated with a 2MASS extended object (2MASX J00331831+6127433) positionally coincident with the
radio source NVSS J003318+612740.
The X-ray data analysis provides an absorbed (NH ~1022 cm-2) power law
spectrum with photon index ~1.8
and an observed 2-10 keV flux of 6.7 x 10-12 erg cm-2 s-1.
The second, fainter, source is detected at RA(J2000) = 00h 33m 57.82s and Dec(J2000) = +61d 26m 30.8s
(3.7 arcsec uncertainty) and coincides with a ROSAT Bright Survey object (1RXS J003357.9+612445).
The X-ray spectrum of this source is very soft with virtually no counts above a few keV and an X-ray flux
a factor of ~30 below the first source. On the basis of the available information, the first object is a more likely counterpart to the IBIS source.
Two objects are detected by XRT within the IBIS uncertainty. The first, detected at 3.3 sigma
is located at RA(J2000) = 17h 48m 47.0s and Dec(J2000) = -31d 24m 23.6s (6 arcsec uncertainty).
There are no USNO-B1.0 nor 2MASS counterparts to this object.
The second source, observed at 4.3 sigma confidence level, is located at RA(J2000) = 17h 48m 30.92s and
Dec(J2000) = -31d 24m 40.2s (4.8 arcsec uncertainty).
In this case, we find a counterpart in a USNO-B1.0 object, having magnitude
R ~16.8, which also belongs to the 2MASS survey.
The X-ray spectra can only provide an estimate of the 2-10 keV flux at
a level of 10-14 erg cm-2 s-1 for both objects.
XRT detects a source, within the IBIS error box, at RA(J2000) = 18h 48m 25.67s and
Dec(J2000) = -00d 46m 33.3s (4.9 arcsec uncertainty). This object has a counterpart in the
2MASS survey and it is likely associated with the radio source G31.89724+0.31680 in the
The X-ray spectrum indicates an absorbed (NH ~1023 cm-2) spectrum (Gamma = 1.8
fixed) with an observed 2-10 keV flux of 1 x 10-12 erg cm-2 s-1.
An X-ray source is detected within the IBIS uncertainty at RA(J2000) = 21h 27m 18.42s and Dec(J2000) = +42d 39m 08.6s (5 arcsec uncertainty).
Within the XRT error box there are two USNO-B1.0 sources
with magnitudes R around 17 and 18 respectively; only one of these two sources is also listed in
the 2MASS catalogue.
The XRT spectrum is well described by an unabsorbed power law with photon index ~1.9 and a 2-10
keV flux of 2.6 x 10-13 erg cm-2 s-1.