{
  "bibcode": "2011GCN.12212....1G",
  "body": "D. Grupe (PSU), C.A. Swenson (PSU), J.L. Racusin (NASA/GSFC),\n& C. Wolf (PSU) report on behalf of the Swift team.\n\n\nWe report on the Swift follow-up observations of the field of the\nafterglow candidate reported by Greiner et al. (GCN Circ. 12192) of\nthe FERMI GBM/LAT detected burst GRB 110721A (Tierney & v. Kienlin,\nGCN Circ. 12187; Vasileiou et al., GCN Circ. 12188). Greiner et al.\nfound a faint X-ray source in one of the tiling Swift observations\n(Obs ID 20169, 1.8 ks) which was also detected by GROND.  This\nfield was observed by Swift again approximately 150 hours after\nthe FERMI trigger for 4.9  ks with the XRT in photon counting mode\n(Obs ID 20174). We did not detect any  source in the 0.3-10 keV\nband at the position reported by Greiner  et al. (GCN Circ. 12192).\nWe determined a 3 sigma upper limit of  2.5 e-3 counts/s. The\ncomparison of this new observation to the X-ray afterglow\ncandidate with a count  rate of (3.8+6.14-3.16)e-3 counts/s (in the\n1.8 ks observation 20169) is inconclusive as it could be\nconsistent with either a constant source or fading.\n\nBased on the source detection in Obs ID 20169, if we assume a\nstandard X-ray spectrum with Galactic foreground absorption and\nthe standard cosmology for a source at a redshift of z=0.382 as\nreported by  Berger (GCN Circ. 12193) the luminosity in the\n0.3-10 keV band is 2e43 ergs/s. This luminosity is consistent\nwith that of a low luminosity AGN.\n\n\nNote that some of the Swift observations of the fields around\nGRB 110721A were unusable because this region was difficult for\nthe star trackers to achieve lock. Therefore, no further\nobservations are planned.",
  "circularId": 12212,
  "createdOn": 1311994909000,
  "email": "grupe@astro.psu.edu",
  "subject": "GRB 110721A: Swift observations of afterglow candidate",
  "submitter": "Dirk Grupe at PSU/Swift-XRT  <grupe@astro.psu.edu>",
  "eventId": "GRB 110721A"
}