{
  "bibcode": "2007GCN..6019....1K",
  "body": "H. A. Krimm (GSFC/USRA),  D. N. Burrows (PSU), M. Chester (PSU),\nD. Grupe (PSU), V. Mangano (INAF-IASFPA), F. Marshall (GSFC),\nJ. Nousek (PSU), B. Sbarufatti (INAF-IASFPA), N. Gehrels (GSFC)\nreport on behalf of the Swift Team\n\nGRB070110 has been identified as a \"Swift Burst of Interest\"\n(Krimm et al, GCN 6014) due to the remarkable irregular light curve\nseen in X rays, and the long duration and slow fading of the optical\nemission.  We report that the U band emission has now faded below\nthe  UVOT threshold of detectability (roughly 23rd magnitude),\nso the UVOT can no longer follow this GRB, but we project that the\noptical brightness will continue to slowly fade, making it a possible\ncandidate for late-time optical detection.  We are continuing\nobservations with the XRT and we encourage ground-based observers\nto attempt measurements of the afterglow, if they are capable of\ndetecting an afterglow to our estimate of V=22.7 over the next five days.\n\nThe UVOT light curves (Figure 4 in GCN Report 26.3\nhttp://gcn.gsfc.nasa.gov/reports/report_26_3.pdf )  show\npower-law decays with the following indices.  V and B bands\n(T+1ksec to T+200 ksec): -0.5; U band (T+ 10 ksec to T+500 ksec):\n-0.7.  Converting to magnitudes using the zero points for the\nfilters yields the following fits:\nVmag = 21.2 + 1.25*log10(t)\nBmag = 21.9 + 1.25*log10(t)\nUmag = 21.8 + 1.75*log10(t).\nwhere the time, t, is measured in days from the trigger.  For example\nat 7:00 UT on Jan. 20, 2007, the predicted V magnitude is 22.4.\n\nThe X-ray light curve (see Figure 2 in GCN Report 26.3) is decaying\nvery slowly and in fact the three most recent data points suggest a\nslight upward trend.  Fitting the data after the steep drop in flux\n(from T+35 ksec to T+800 ksec), but excluding the big rise at\naround T+65 ksec, the best fit decay index is -0.6 +/- 0.1.  If the\nsource follows this decay law we predict a count rate in the XRT\n(0.3-10.0 keV) of 1.5 X 10^-3 cts/sec on Jan. 22, 2007.  If it\ncontinues to decay at this rate, the source will continue to be bright\nenough to be observed with the XRT during the month of February 2007.\n\nWe note that this source (RA/dec:   0h 03m 39.27s, -52s 58' 26.9\",\nepoch 2000.0) is currently observable from an observatory at\n-29 degrees latitude and is currently above 30 degrees elevation\nfor approximately 2 hours after astronomical twilight.  This time\nwill be only about one hour by the end of January.",
  "circularId": 6019,
  "createdOn": 1169236934000,
  "email": "krimm@milkyway.gsfc.nasa.gov",
  "subject": "GRB 070110:  Continued Detection and Request for Ground Followup",
  "submitter": "Hans Krimm at NASA-GSFC  <krimm@milkyway.gsfc.nasa.gov>",
  "eventId": "GRB 070110"
}