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ATEL # 2830; R. Landi, L. Bassani, A. Malizia (INAF/IASF Bologna), A. Bazzano, P. Ubertini (INAF/IASF Rome), A.J. Bird (Univ. Southampton), N. Gehrels (NASA/GSFC), J.A. Kennea, D.N. Burrows (PSU)
on 6 Sep 2010; 16:04 UT
Password Certification: Raffaella Landi (firstname.lastname@example.org)
Subjects: X-ray, Gamma Ray, Request for Observations
Referred to by ATEL #: 2839
We report the results of the X-ray follow-up observations obtained with Swift/XRT of the unidentified INTEGRAL source IGR J20450+7530 listed in the 4th IBIS Survey Catalog (Bird et al. 2010, ApJS, 186, 1).
XRT pointed at the IBIS source position on 2010, July 20, 21, 23, 30, and August 16 for a total exposure of ~19.4 ks. There are three sources detected by XRT which are compatible with the IBIS position: namely source #1 and #2 are well located within the IBIS uncertainty, while source #3 is just at its border.
Source #1: this source, located at RA(J2000) = 20h 45m 22.10s and Dec(J2000) = +75d 30m 53.37s (5.76 arcsec uncertainty), is detected at 3.6 sigma c.l. in 0.3-10 keV energy band (3 sigma c.l. in 0.3-3 keV) and is not detected above 3 keV. The XRT position is compatible with a USNO-A2.0 objects with magnitudes R ~18.9 and B ~19.1. No infrared counterpart is found for this object. From the X-ray data we can estimate a 2-10 keV flux in the range (0.3-1.3) x 10-13 erg cm-2 s-1 during the various XRT observations, with an average value of 0.9 x 10-13 erg cm-2 s-1, assuming a power law model with photon index 1.8.
Source #2: this object is located at (RA(J2000) = 20h 44m 34.47s and Dec(J2000) = +75d 31m 56.97s, 4.69 arcsec uncertainty). It is detected at 6.8 sigma c.l. in 0.3-10 keV energy range (5.7 sigma c.l. in 0.3-3 keV) and it is still detected above 3 keV at 3.4 sigma c.l.. The XRT position is compatible with a USNO-A2.0 object having magnitudes R ~16.6 and B ~17.9, also listed in the 2MASS catalogue with magnitudes J ~15.8, H ~14.7, and K ~14.0. It is also a 2MASS Extended object (2MASX J20443451+7531588) classified in NED as a galaxy. In each observation the X-ray data are well described by a simple power law with Gamma ~1.7-2.0 and a 2-10 keV flux in the range (2.9-7.1) x 10-13 erg cm-2 s-1. The average spectrum requires an intrinsic absorption (NH(intr) ~0.2 x 1021 cm-2) in excess to the Galactic one and provides a Gamma ~2.2 and a 2-10 keV flux of 3.2 x 10 -13 erg cm-2 s-1.
Source #3: this source is located at RA(J2000) = 20h 44m 41.16s and Dec(J2000) = +75d 35m 07.85s (4.57 arcsec uncertainty) and is detected at 7.6 sigma c.l. in 0.3-10 keV energy range (7.3 sigma c.l. in 0.3-3 keV), and is not detected above 3 keV. This object has a counterpart in the USNO-A2.0 catalogue with magnitudes R ~8.6 and B ~8.9, also listed in the 2MASS survey with magnitudes I ~8.1, H ~7.8, and K ~7.8. Its position is also compatible with the ROSAT Faint object 1RXS J204440.6+753006. The XRT data are fitted with a bremsstrahlung model with a kT ~0.36-0.54 keV and a 2-10 keV flux in the range (0.17-1.10) x 10-14 erg cm-2 s-1. The average temperature and 2-10 keV flux are ~0.51 keV and ~0.8 x 10-14 erg cm-2 s-1, respectively.
In view of the above information we suggest that source #2, which is the only hard object detected by XRT, is the likely counterpart of the IBIS hard X-ray source and encouraged further observations of the source in order to assess its real nature.
XRT image of IGR J20450+7530