//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 11980 SUBJECT: GRB 110426A: MAXI/GSC detection of a GRB DATE: 11/04/27 00:33:16 GMT FROM: Motoko Suzuki at RIKEN S. Nakahira (RIKEN), H. Negoro (Nihon U.), M. Matsuoka , T. Mihara, M. Sugizaki, M. Serino, T. Yamamoto, T. Sootome (RIKEN), S. Ueno, H. Tomida, M. Kohama, M. Ishikawa (JAXA), N. Kawai, M. Morii, K. Sugimori, R. Usui, T. Toizumi (Tokyo Tech), A. Yoshida, K. Yamaoka (AGU), H. Tsunemi, M. Kimura, H. Kitayama (Osaka U.), M. Nakajima, F. Suwa (Nihon U.), Y. Ueda, K. Hiroi, M. Shidatsu (Kyoto U.), Y. Tsuboi, T. Matsumura, K. Yamazaki (Chuo U.) report on behalf of the MAXI team: At the scan transit centered at UT 2011-04-26T15:08:36, MAXI/GSC detected a short X-ray transient lasting about 18 seconds within the 46 seconds triangular transit response of MAXI/GSC. Judging from its location and spectral hardness ratio, this transient is probably a gamma-ray burst. Since the emission was detected only for a fraction of the triangular transit response, the uncertainty of its position along the scan direction is large. Without assuming the source constancy, we obtain a rectangular error box (90%C.L.) with the following corners: (R.A., Dec) = (+219.64 deg,-9.51 deg) = (14 38 34, -09 30 36)(J2000) (R.A., Dec) = (+222.36 deg,-12.97 deg) = (14 49 26, -12 58 12)(J2000) (R.A., Dec) = (+222.57 deg,-12.77 deg) = (14 50 17, -12 46 12)(J2000) (R.A., Dec) = (+219.84 deg,-9.31 deg) = (14 39 21, -09 18 36)(J2000) There is additional systematic uncertainty of 0.2 deg (90% containment radius). The preliminary flux (2-20 keV) of the source was at least 200 mCrab. There was no significant detection at the transit location in the previous and following orbits (92 min before or after the detection) with an upper limit of 20 mCrab. There is no known bright X-ray source at the detected position. Follow-up observations are encouraged. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 11981 SUBJECT: GRB 110426A: MASTER synchronous with MAXI/GSC observations DATE: 11/04/28 08:09:19 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs O. Gres, K.Ivanov, V.A.Poleshchuk, S.Yazev, N.M.Budnev, O.Chuvalaev Irkutsk State University E. Gorbovskoy, V. Lipunov, V.Kornilov, D.Kuvshinov, A.Belinski, N.Tyurina, N.Shatskiy, P.Balanutsa, V.V.Chazov, P.V.Kortunov, A.Kuznetsov, D.Zimnukhov, M. Kornilov, A.Kuznetsov, D.Zimnukhov, M. Kornilov, A.Sankovich Sternberg Astronomical Institute, Moscow State University A. Tlatov, A.V. Parhomenko, D. Dormidontov Kislovodsk Solar Station of the Pulkovo Observatory V.Krushinski, I.Zalozhnich, T.Kopytova, A. Popov Ural State University, Kourovka V.Yurkov, Yu.Sergienko, D.Varda, I.Kudelina Blagoveschensk Educational State University, Blagoveschensk First we pointed to FERMI trigger N325523188 (ra=217.133 dec=-12.333 err=32.42) at 15:07:28 (62 sec after trigger time). We observed this area to 15:08:33, until the next more exact FERMI alert (ra=205.160 dec=-11.570 err=10.9) comes. Unfortunately, after that replacement, the part of MAXI error-box has left a FOV of ours widefield cameras. We observ this new place to 15:13:33. We coadd all wide field (500 square degrees) camera unfiltered images. There is no OT from automatical identification. So we have following results: T_start T_s-T_fermi T_s-T_maxi exptime limit Cover_MAXI 15:07:28 62 sec -68 sec 55 sec 13.0 100 % 15:08:33 126 sec -3 sec 250 sec 13.8 85 % First epoch image http://observ.pereplet.ru/images/evgeny/grb110426a1.jpeg Second epoch image http://observ.pereplet.ru/images/evgeny/grb110426a2.jpeg Black lines is MAXI error_box. The main MASTER telescopes (40 sm) also made observations in 2 polarizations, in the center of each of FERMI error-boxes, but them FOV (4 sq. degree) it has appeared not enough for observ at least parts MAXI error-box. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 11990 SUBJECT: GRB 110426A: Swift/XRT non-detection DATE: 11/05/03 13:51:45 GMT FROM: Hans Krimm at NASA-GSFC H. A. Krimm (GSFC/USRA),V. D'Elia (ASDC) and G. Stratta (ASDC), report on behalf of the Swift team: Swift XRT and UVOT instruments observed the center of the error rectangle for the MAXI-detected GRB 110426A (Nakahira et al, GCN Circ. 11980) on two occasions. The first observation was for 5 ks starting 7 ks after the MAXI trigger. In this observation four point sources were found. One is consistent with a source in the Digitized Sky Survey and the other three were of <3-sigma significance. The second observation, also 5 ks, began 250 ks after then trigger. In the second observation, the DSS source was detected without having faded and two other weak sources were seen at different locations. Since there is no evidence for a fading source in the XRT field of view, we conclude that we have not detected the afterglow of GRB 110426A. However, we note that the reported 90% error box for GRB 110426A (Nakahira et al, GCN Circ. 11980) is approximately eight times the size of the XRT field of view. Therefore, it is likely that the true GRB location is outside the observed field. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 12013 SUBJECT: GRB 110426A: Fermi GBM detection DATE: 11/05/09 23:47:06 GMT FROM: Alexander van der Horst at NASA/MSFC A.J. van der Horst and A. Camero-Arranz (USRA) report on behalf of the Fermi GBM Team: "At 15:06:26.61 UT on 26 April 2011, the Fermi Gamma-Ray Burst Monitor triggered on GRB 110426A (trigger 325523188 / 110426629). The on-ground calculated location, using the GBM trigger data, is RA = 219.9, Dec = -8.7 (J2000 degrees, equivalent to 14h40m, -8d43'), with an uncertainty of 2.1 degrees (radius, 1-sigma containment, statistical only; there is additionally a systematic error which is currently estimated to be 2 to 3 degrees). The angle from the Fermi LAT boresight is 88 degrees. This is most likely the same source as the one that MAXI/GSC reported in GCN 11980. Although MAXI/GSC triggered 130 seconds later than GBM on GRB 110426A, the locations obtained by both instruments are consistent. The GBM light curve consists of multiple peaks with a duration (T90) of 328 +/- 3 s (50-300 keV), indicating that the source was still active when MAXI/GSC detected it. The time-averaged spectrum from T0-4.1 s to T0+327.7 s is adequately fit by a simple power law function with index -2.28 +/- 0.01. The event fluence (10-1000 keV) in this time interval is (4.54 +/- 0.06)E-5 erg/cm^2. The 1-sec peak photon flux measured starting from T0+216.1 s in the 10-1000 keV band is 6.7 +/- 0.4 ph/s/cm^2. We note that there is bursting emission detected in GBM starting ~40 minutes before the trigger. This emission is significantly softer than the ~6 minute emission episode after the GBM trigger time. The start of the spectrally soft bursts is consistent with Sco X-1 coming out of Earth occultation. The GRB 110426A location, however, is not consistent with Sco X-1 and thus a separate source. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."