Follow-up observations of TXS 1530-131 (PMN J1532-1319) using Fermi/LAT and Swift/XRT
ATel #3629; P. H.T. Tam (NTHU, Taiwan), H. F. Yu (HKU), A. K.H. Kong, J. H.K. Wu (NTHU, Taiwan)
on 5 Sep 2011; 11:11 UT
Credential Certification: Albert Kong (akong@phys.nthu.edu.tw)
Subjects: Optical, X-ray, Gamma Ray, >GeV, Blazar, Quasar, Transient
We report observations of TXS 1530-131 (PMN J1532-1319) following the Fermi/LAT detection of a new gamma-ray transient coincident with the source (ATel #3579). Our analysis of the Fermi/LAT data between 2010 September 1 and 2011 September 4 shows that the source has undergone several flaring periods since 2011 June, before which the source was undetected by LAT. The source can be detected daily with TS > 25 from 2011 August 30 to September 4, indicating that the source is still flaring in gamma-rays. Using data from 2011 May 23 to Aug 23, we derived the best-fit gamma-ray position of R.A. = 233.16 deg, Decl. = -13.34 deg (J2000) with a 95% containment radius of 3'.2, much smaller than that (i.e., 0.32 deg) reported in ATel #3579.
A total of 3ks Swift observations of the source were performed on 2011 August 31, 19:54 UT. There is one bright X-ray source in the XRT field-of-view. By using the UVOT images taken simultaneously with the XRT image, we find an astrometrically corrected X-ray position at R.A.=15h32m45.4s, Decl.=-13d19'11.9" (J2000) with a 90% error circle of 2.2 arcsec in radius (Goad et al. 2007; Evans et al. 2009), consistent with the radio position as in Healey et al. (2008). The source is the only X-ray source within the above Fermi error circle. The X-ray spectrum can be described with an absorbed power-law model with a photon index of 1.4(+0.6,-0.4) and N_H=1(+4,-1)e21 cm^-2. The unabsorbed 0.3-10 keV flux is 1.85e-12 erg/s/cm^2.
SDSS lists a very faint (g=22.66) galaxy-like object at the radio position. We find that this source has increased in brightness in the last few months.
We would like to thank the Swift team for their prompt response of our ToO request.
