Swift/XRT localization of IGRJ02045-1156 and IGRJ02574-0303

ATel #4345; C. Ricci, E. Bozzo, R. Walter, S. Paltani (ISDC/University of Geneva, Switzerland), L. Stella (INAF-OAR, Italy)
on 29 Aug 2012; 06:23 UT
Credential Certification: E. Bozzo (enrico.bozzo@unige.ch)

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As part of our observational program aimed at searching for soft X-ray counterparts of faint unidentified INTEGRAL sources detected in the direction of the Galactic poles (Atel #4102), we report here on the Swift/XRT localization of two new INTEGRAL sources: IGRJ02045-1156 and IGRJ02574-0303.

IGRJ02045-1156 is detected in the 17-80 keV IBIS/ISGRI mosaic at a significance level of 5.6 sigma (on source exposure time ~740 ks) and a flux of 1.1+/-0.2 mCrab (i.e. ~1.6E-11 erg/cm^2/s). The ISGRI spectrum is well described (chi^2_red/dof=1.0/5) by a power-law model with photon index 2+/-1 (all uncertainties are given at 90% c.l.). The best determined INTEGRAL position of IGRJ02045-1156 is at
RA=31.133
DEC=-11.944
(J2000), with an associated 90% c.l. uncertainty of 4 arcmin.

Within the ISGRI error circle a single faint source is detected with Swift/XRT (total exposure time 5.5 ks). The best determined XRT position is at:
RA=31.15306,
DEC=-11.99501
(J2000), with an associated 90% c.l. uncertainty of 2.1 arcsec (here and for the other source below we used the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalog, see http://www.swift.ac.uk/user_objects and Evans et al. 2009, MNRAS, 397, 1177). The XRT position is consistent with that of the Seyfert 1 6dFGS gJ020436.8-115943 and that of the X-ray source 1RXS J020436.8-115941.

The XRT spectrum is well described (C-statistics/dof=15.8/16) by using a power-law model. We fixed the absorption column density at the Galactic value in the direction of the source (N_H=1.8E+20 cm^(-2)) and measured a photon index of 1.6+/-0.3. This is compatible with that estimated in the ISGRI energy band and with values usually observed in AGN. The observed 0.5-10 keV X-ray flux is 9.3E-13 erg/cm^2/s.

IGRJ02574-0303 is detected in the 17-80 keV IBIS/ISGRI mosaic at a significance level of 5.8 (on source exposure time ~445 ks) and a flux of 1.5+/-0.3 mCrab (i.e. ~2E-11 erg/cm^2/s). The ISGRI spectrum is well described (chi^2_red/dof=0.6/5) by a power-law model with photon index 0.6+/-0.9. The best determined INTEGRAL position of IGRJ02574-0303 is at
RA=44.3722
DEC=-3.060
(J2000), with an associated 90% c.l. uncertainty of 4 arcmin.

Within the ISGRI error circle a single faint source is detected with Swift/XRT (total exposure time 5.3 ks). The best determined XRT position is at:
RA=44.34122,
DEC=-3.10622
(J2000), with an associated 90% c.l. uncertainty of 2.5 arcsec. No obvious catalogued counterparts in the optical and IR domain are found within the XRT error circle.

Given the relatively poor statistic of the data, a meaningful XRT spectrum could not be extracted. The estimated source count-rate from the XRT data was of (1.7+/-0.3)E-2 cts/s. Assuming a power-law spectrum with photon index 1 and an absorption column density equal to that expected in the direction of the source (N_H=4E20 cm^(-2)), this count-rate would translate into a 0.5-10 keV X-ray flux of ~1E-12 erg/cm^2/s.

We thank the Swift team for having performed these observations.