Swift/XRT follow-up observations of unidentified INTEGRAL sources (3)
ATel #3273; R. Landi, L. Bassani , N. Masetti (INAF/IASF Bologna), A. Bazzano (INAF/IASF Rome), A. J. Bird (University of Southampton)
on 11 Apr 2011; 17:17 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 2 unidentified
INTEGRAL sources listed in the INTEGRAL all sky survey (Krivonos et al. 2010, A&A, 523, 61).
The XRT observation indicates 3 possible counterparts to the INTEGRAL source, two of which
are inside the IBIS error circle and one just at its border.
The position of source #1 and #3 are consisted with those reported by Krivonos et al. 2010
(A&A, 519, 107).
Source #1 is detected at 3.3 sigma confidence level (c.l.) in the 0.3-10 keV energy band and is
located at R.A.(J2000) = 11h 20m 27.15s
Dec.(J2000) = +45d 34m 53.5s (6.0 arcsec uncertainty). Within this positional error we find two
faint galaxies in the SDSS catalogue: SDSS J112027.30+453453.5 (g ~22.0) and
SDSS J112027.33+453449.5 (g ~23.2).
The X-ray data indicate a fit with a power law having index of ~1.7 and a 2-10 keV flux of
~5 x 10-14 erg cm-2 s-1.
Source #2 is detected at 3.2 sigma c.l. (0.3-10 keV) and is located at R.A.(J2000) = 11h 20m
Dec.(J2000) = +45d 29m 12.2s (5.6 arcsec uncertainty). Within this positional error we find a faint
object in the SDSS catalogue (SDSS J112028.37+452912.5, g ~24.0) most likely associated to a star.
The 2-10 keV flux is ~3 x 10-14 erg cm-2 s-1 by assuming a power law with
photon index 1.8.
Source #3 is detected at 4.4 sigma c.l. (0.3-10 keV) and is located at R.A.(J2000) = 11h 20m 34.29s
Dec.(J2000) = +45d 28m 15.2s (5.4 arcsec uncertainty). Within this positional error we find again two
faint galaxies in the SDSS catalogue: SDSS J112034.21+452815.4 (g ~21.5) and SDSS J112034.53+452818.2
The X-ray data, fitted with a power law having index 1.8, provides a 2-10 keV flux of ~8 x 10-14
erg cm-2 s-1.
It is difficult to state at this stage which of the 3 sources is the most likely counterpart given that
none is detected above a few keV and all are very weak in X-rays.
XRT detects an X-ray source whose location is compatible with the IBIS uncertainty.
This object, detected at ~7 sigma c.l. in the 0.3-10 keV energy band and above 3 keV, is located at
R.A.(J2000) = 17h 42m 40.82s and Dec.(J2000) = -30d 22m 36.2s (4.4 arcsec uncertainty).
This position is also compatible with that of the unidentified ASCA source AX J1742.6-3022 (Sakano et
al. 2002, ApJS 138, 34), and with a radio source (NVSS J174240-302239, 1LC 358.439-0.211, GPSR
358.440-0.210) reported in various catalogues at a 20 cm flux in the range 12.5-43 mJy and a flat
radio spectrum (Nord et al. 2004, AJ, 128, 1646); this object is compact and has been proposed to be an
extragalactic source seen through the Galactic Center (Lazio & Cordes 1998, ApJS, 118, 201). Neither
optical nor infrared counterpart is associated to this radio source.
The X-ray spectroscopy provides a 2-10 keV flux of 1.8 x 10-12 erg cm-2
s-1, assuming an absorbed (NH ~8 x 1022 cm-2) power law with
photon index fixed at 1.8.
The authors acknowledge the use of public data from the Swift data archive.