TITLE: GCN CIRCULAR NUMBER: 9135 SUBJECT: GRB 090417B: Swift detection of a burst DATE: 09/04/17 15:41:13 GMT FROM: Scott Barthelmy at NASA/GSFC B. Sbarufatti (INAF-IASFPA), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester), D. N. Burrows (PSU), P.A. Curran (MSSL-UCL), P. A. Evans (U Leicester), O. Godet (U Leicester), C. Guidorzi (U Ferrara), S. T. Holland (CRESST/USRA/GSFC), E. A. Hoversten (PSU), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), N. P. M. Kuin (MSSL), V. Mangano (INAF-IASFPA), J. Mao (INAF-OAB), R. Margutti (Univ Bicocca&OAB), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL), P. Romano (INAF-IASFPA), B. A. Rowlinson (U Leicester), M. H. Siegel (PSU), M. Stamatikos (NASA/ORAU) and T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team: At 15:20:03 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 090417B (trigger=349450). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 209.706, +47.000 which is RA(J2000) = 13h 58m 49s Dec(J2000) = +47d 00' 01" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The TDRSS BAT light does not show much for this 320-sec image trigger (as is typical for image triggers). The XRT began observing the field at 15:26:30.4 UT, 387.0 seconds after the BAT trigger. XRT found a bright, uncatalogued and fading X-ray source located at RA, Dec 209.6931, +47.0170 which is equivalent to: RA(J2000) = 13h 58m 46.34s Dec(J2000) = +47d 01' 01.2" with an uncertainty of 5.0 arcseconds (radius, 90% containment). This location is 68 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy. The initial flux in the 2.5 s image was 2.77e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 395 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The 3-sigma upper limit is white = 20.1 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.02. Burst Advocate for this burst is B. Sbarufatti (sbarufatti AT ifc.inaf.it). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.)