TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4608 SUBJECT: GRB 060123: Swift refined analysis of an unusual GRB DATE: 06/01/27 22:37:00 GMT FROM: Jay R. Cummings at NASA/GSFC/Swift J. Cummings (GSFC/ORAU), V. Mangano (INAF-IASFPA), L. Angelini (GSFC), L. Barbier (GSFC), S. Barthelmy (GSFC), D.N. Burrows (PSU), M. Chester (PSU), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (UMD), J. Kennea (PSU), H. Krimm (GSFC/USRA), V. La Parola (INAF-IASFPA), A. Levan (U. Leicester), C. Markwardt (GSFC/UMD), T. Mineo (INAF-IASFPA), J. Norris (GSFC), P. O'Brien (U. Leicester), D. Palmer (LANL) A. Parsons (GSFC), E. Rol (U. Leicester), P. Romano (INAF-OAB), T. Sakamoto (GSFC/ORAU), G. Sato (ISAS), J. Tueller (GSFC), on behalf of the Swift team: Using Swift-BAT survey data from T-23 to T+877 sec and target of opportunity (ToO) Swift-XRT observations, we report further analysis of Swift-BAT GRB 060123 (Palmer, et al., GCN 4584). T90 was 900 +- 100 seconds (estimated one-sigma error), with multiple peaks but an overall gradual profile. Peak flux was 0.04 +- 0.01 photons/cm2/sec in the 15-150 keV band. The prompt emission time-averaged spectrum is well fitted by a simple power law model. The power law index is 1.9 +- 0.6. The fluence in the 15-150 keV band was (3.0 +- 1.2) x 10^-7 erg/cm2. A Swift ToO observation started at 19:14:14 on Jan 24th, 2006 (75.1 ks after the event). XRT detected a point source within the BAT error box (Palmer et al, GCN 4584). Subsequent ToO observations revealed that, after an initially flat phase, this source is steadily decaying with a slope of -2.2 +/- 0.4. The initial flat phase extended to ~1.1 x 10^5 sec. Further observations are ongoing. The average XRT spectrum accumulated in the time interval from 75.1 ksec to 291 ksec after the event (20 ksec of net exposure) was fitted, using Cash statistics, with an absorbed power law. The best fit photon index is 2.1 +/- 0.2. The spectrum shows evidence of absorption at the level of (2 +/- 1)e21 cm^-2, in excess of the estimated Galactic value (1.6e20 cm^-2, Dickey & Lockman 1990). The average unabsorbed 0.2-10 keV flux is 7.0e-13 ergs cm^-2 s^-1. All the quoted errors are at the 90% confidence level except as noted. This was an unusual event. It was very long and very gradual, having the longest duration and weakest peak flux of any BAT burst. The GRB nature of the event would be uncertain on the basis of the BAT data alone, but is highly probable given the fading XRT light curve. The flat decay phase extends very late for a GRB. Followup observations are strongly encouraged.