//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17772 SUBJECT: GRB 150428C/MAXI J0400+678: MAXI/GSC detection DATE: 15/04/28 09:17:41 GMT FROM: H. Negoro at Nihon U. F. Honda, M. Fujita, H. Negoro (Nihon U.), M. Serino (RIKEN), S. Nakahira, S. Ueno, H. Tomida, M. Kimura, M. Ishikawa, Y. E. Nakagawa (JAXA) T. Mihara, M. Sugizaki, M. Shidatsu, J. Sugimoto, T. Takagi, M. Matsuoka (RIKEN), N. Kawai, T. Yoshii, Y. Tachibana, Y. Ono (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Kawakubo, H. Ohtsuki (AGU), H. Tsunemi, R. Imatani (Osaka U.), M. Nakajima, T. Namba, T. Masumitsu, K. Tanaka (Nihon U.), Y. Ueda, T. Kawamuro, T. Hori (Kyoto U.), Y. Tsuboi, S. Kanetou (Chuo U.), M. Yamauchi, D. Itoh (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Morii (ISM) report on behalf of the MAXI team: The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at 08:24:15 UT. Assuming that the source flux was constant over the transit, we obtain the source position at (R.A., Dec) = (60.247 deg, 67.818 deg) = (04 00 59, +67 49 03) (J2000) with a 90% C.L. statistical error of 0.29 deg and an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 161 +- 27 mCrab (4-10keV, 1 sigma error). Without assumptions on the source constancy, we obtain a rectangular error box for the transient source with the following corners: (59.061 deg, 67.515 deg) = (03 56 14, +67 30 54) (J2000) (58.970 deg, 68.084 deg) = (03 55 52, +68 05 00) (J2000) (61.826 deg, 67.549 deg) = (04 07 18, +67 32 57) (J2000) (61.794 deg, 68.119 deg) = (04 07 10, +68 07 09) (J2000) There was no significant excess flux in the previous transit at 06:51 UT with an upper limit of 20 mCrab. We note that no significant X-ray flux above 10 keV was detected, and the spectrum was represented by a blackbody model with the temperature of approximately 1 keV. Thus, the burst might be an X-ray burst from an unknown source. We tentatively name the source MAXI J0401+678. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17775 SUBJECT: GRB 150428C: Tiled Swift observations DATE: 15/04/28 13:01:17 GMT FROM: Phil Evans at U of Leicester P. A. Evans (U. Leicester) reports on behalf of the Swift team: Swift has initiated a series of observations, tiled on the sky, of the MAXI GRB 150428C. Automated analysis of the XRT data will be presented online at http://www.swift.ac.uk/xrt_products/TILED_GRB00043 Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. The probability of finding serendipitous sources, unrelated to the MAXI event is high: any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration. Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8). This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17782 SUBJECT: GRB 150428C: MASTER-net automatic optical inspection DATE: 15/04/28 17:12:31 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V.Yurkov, Yu.Sergienko, D.Varda, E.Sinyakov Blagoveschensk Educational State University, Blagoveschensk E. Gorbovskoy, V. Lipunov, N.Tyurina, V.Kornilov, P.Balanutsa, A.Kuznetsov,D.Kuvshinov, Lomonosov Moscow State University, Sternberg Astronomical Institute D.Buckley, S. Potter, A.Kniazev, M.Kotze South African Astronomical Observatory K.Ivanov, S.A.Yazev, N.M.Budnev, O.Gres, O.Chuvalaev, V.A.Poleshchuk Irkutsk State University A. Tlatov, A.V. Parhomenko, D. Dormidontov, V.Sennik Kislovodsk Solar Station of the Pulkovo Observatory V.Krushinski, I.Zalozhnih, A. Popov Ural Federal University, Kourovka Hugo Levato and Carlos Saffe Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE) Carlos Lopez, Claudio Mallamaci and Federico Podest Observatorio Astronomico Felix Aguilar (OAFA) MASTER II robotic telescope (MASTER-Net: http://observ.pereplet.ru) located in Blagoveschensk was pointed to the GRB150428C 12184 sec after notice time (after sun set) and 15390 sec after trigger time at 2015-04-28 12:40:45 UT. We did not find OT brighter then 17.4 mag . The message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17786 SUBJECT: GRB 150428C: Swift-XRT observations DATE: 15/04/29 13:06:40 GMT FROM: Kim Page at U.of Leicester K.L. Page and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the MAXI-detected burst GRB 150428C (Honda et al. GCN Circ. 17772) in a series of observations tiled on the sky. The total exposure time is 2.1 ks, distributed over 7 tiles; the maximum exposure at a single sky location was 819 s. The data were collected between T0+16.2 ks and T0+28.9 ks, and are entirely in Photon Counting (PC) mode. No real uncatalogued sources have been detected. Although a low-significance source was reported by the automatic software, we believe this is an artifact caused by high background emission. In addition, a previously-catalogued X-ray source has been detected, however because it is a catalogued object it is unlikely to be the afterglow. The 3-sigma upper limit in the field ranges from ~0.01 to ~0.05 ct s^-1, corresponding to a 0.3-10 keV observed flux of 4e-13 to 2e-12 erg cm^-2 s^-1 (assuming a typical GRB spectrum). The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at http://www.swift.ac.uk/xrt_products/TILED_GRB00043/