Swift-XRT follow-up of IGR J00486-4241 and IGR J21485+4306

ATel #10467; R. Landi, A. Malizia, L. Bassani, V. Sguera (IASF/INAF Bologna), A. Bazzano, M. Fiocchi, P. Ubertini (IAPS/INAF Rome), A. J. Bird (University of Southampton
on 6 Jun 2017; 13:35 UT
Credential Certification: Angela Malizia (malizia@iasfbo.inaf.it)

Tweet

We report on X-ray follow-up observations performed with Swift-XRT of 2 unidentified INTEGRAL sources, namely IGR J00486-4241 and IGR J21485+4306. Both sources are listed as new persistent detections in the latest INTEGRAL/IBIS survey by Bird et al. (2016 ApJS, 223, 15).

IGR J00486-4241
XRT performed only 2 pointings towards this source for a total exposure of 1449 sec.
Within the IBIS 90% error circle, XRT detects only one X-ray source located at R.A.(J2000) = 00h 49m 14.9s and Dec.(J2000) = -42d 46m 49.40s (6 arcsec 90% positional uncertainty). The XRT detection is around 3 sigma in the 0.3-10 keV band with no counts above 3 keV possibly due to the short exposure. This X-ray source is also reported as a bright Rosat object (1RXS J004913.8-424649, 14 arcsec positional uncertainty) with a 0.1-2.4 keV flux of 1.8 x 10^-12 erg cm^-2 s^-1.
Inside the XRT error circle, we only find the optical/infrared source 6dFGS J0049144-424649/WISE J004914.46-424649. The 6dF spectrum is of too poor quality for a reliable classification of the source, while the WISE IR colours are W1-W2=1.17 and W2-W3=3.0, i.e. typical of of AGN (Secrest et al. 2015 ApJS, 221, 12).
XRT data provide a 0.1-2.4 and 2-10 keV flux of 2 x 10^-13 and and 2.1 x 10^-13 erg cm^-2 s^-1 respectively; this is a factor of 10 below the Rosat flux, indicating substantial variability at soft X-ray energies.
Despite the lack of counts above 3 keV and the low XRT flux, we consider this association reliable given the Rosat previous detection.

IGR J21485+4306
XRT performed 11 pointings towards this source for a total exposure of 3982 sec.
Within the IBIS 90% positional uncertainty we find a single X-ray source detected at 4 sigma level over the 0.3-10 keV band, but with no counts above 3 keV. This source is located at R.A.(J2000) = 21h 48m 38.90s and Dec.(J2000) = +43d 06m 41.62s (5.40 arcsec 90% positional uncertainty) and is associated with the Tycho star TYC 3192-244-1.
Within the 99% positional uncertainty (6 arcmin) we find two other objects one of which is detected also above 3 keV and hence it is a more likely counterpart to the INTEGRAL source. This object is detected at 6.4 sigma in the 0.3-10 keV band and 4.5 sigma above 3 keV. Its XRT position is at R.A.(J2000) = 21h 48m 22.04s and Dec.(J2000) = +43d 01m 24.61s (4.61 arcsec 90% positional uncertainty). This is consistent with the position of the infrared source WISE J214821.72+430130.4 having colours W1-W2=0.96 and W2-W3=2.59. The XRT spectrum is well fitted with an absorbed power law having a fixed photon index of 1.7, an intrinsic column density of NH=6 x 10²¹ cm^-2 and a 2-10 keV flux of 0.7 x 10^-12 erg cm^-2 s^-1.
This likely association is not reported in the NVSS survey (Condon et al. 1998, AJ 115, 1693) with an upper limit to the 20 cm flux of 2 mJy. The Wise colours are however typical of AGN (Secrest et al. 2015 ApJS, 221, 12) suggesting an extragalactic origin.