TITLE: GCN CIRCULAR NUMBER: 6019 SUBJECT: GRB 070110: Continued Detection and Request for Ground Followup DATE: 07/01/19 20:02:14 GMT FROM: Hans Krimm at NASA-GSFC H. A. Krimm (GSFC/USRA), D. N. Burrows (PSU), M. Chester (PSU), D. Grupe (PSU), V. Mangano (INAF-IASFPA), F. Marshall (GSFC), J. Nousek (PSU), B. Sbarufatti (INAF-IASFPA), N. Gehrels (GSFC) report on behalf of the Swift Team GRB070110 has been identified as a "Swift Burst of Interest" (Krimm et al, GCN 6014) due to the remarkable irregular light curve seen in X rays, and the long duration and slow fading of the optical emission. We report that the U band emission has now faded below the UVOT threshold of detectability (roughly 23rd magnitude), so the UVOT can no longer follow this GRB, but we project that the optical brightness will continue to slowly fade, making it a possible candidate for late-time optical detection. We are continuing observations with the XRT and we encourage ground-based observers to attempt measurements of the afterglow, if they are capable of detecting an afterglow to our estimate of V=22.7 over the next five days. The UVOT light curves (Figure 4 in GCN Report 26.3 http://gcn.gsfc.nasa.gov/reports/report_26_3.pdf ) show power-law decays with the following indices. V and B bands (T+1ksec to T+200 ksec): -0.5; U band (T+ 10 ksec to T+500 ksec): -0.7. Converting to magnitudes using the zero points for the filters yields the following fits: Vmag = 21.2 + 1.25*log10(t) Bmag = 21.9 + 1.25*log10(t) Umag = 21.8 + 1.75*log10(t). where the time, t, is measured in days from the trigger. For example at 7:00 UT on Jan. 20, 2007, the predicted V magnitude is 22.4. The X-ray light curve (see Figure 2 in GCN Report 26.3) is decaying very slowly and in fact the three most recent data points suggest a slight upward trend. Fitting the data after the steep drop in flux (from T+35 ksec to T+800 ksec), but excluding the big rise at around T+65 ksec, the best fit decay index is -0.6 +/- 0.1. If the source follows this decay law we predict a count rate in the XRT (0.3-10.0 keV) of 1.5 X 10^-3 cts/sec on Jan. 22, 2007. If it continues to decay at this rate, the source will continue to be bright enough to be observed with the XRT during the month of February 2007. We note that this source (RA/dec: 0h 03m 39.27s, -52s 58' 26.9", epoch 2000.0) is currently observable from an observatory at -29 degrees latitude and is currently above 30 degrees elevation for approximately 2 hours after astronomical twilight. This time will be only about one hour by the end of January.