TITLE: GCN CIRCULAR NUMBER: 10188 SUBJECT: GRB 091120: MAXI GSC detection DATE: 09/11/24 11:19:53 GMT FROM: Atsumasa Yoshida at Aoyama Gakuin U M.Nakajima (Nihon U.), S.Nakahira (AGU), M.Sugizaki, M.Kohama(RIKEN), M.Suzuki (ISAS/JAXA), A.Yoshida, K.Yamaoka (AGU), N.Kawai, M.Morii(Tokyo Tech), H.Negoro (Nihon U.), M.Matsuoka, H.Tomida, S.Ueno(ISAS/JAXA), Y.Ueda, S.Eguchi (Kyoto U.) and H.Tsunemi (Osaka Univ.) on behalf of the MAXI team report: The Gas Slit Camera (GSC) of MAXI detected a bright hard X-ray transient at 04:34:56 on 20 November 2009 (UT). This event should correspond to a GRB detected by Fermi-GBM, INTEGRAL SPI-ACS andKonus-Wind. The location of the source derived from the GSC data is (R.A.,Dec.)=(226.81 deg, -21.79 deg)=(15:07:14.40, -21:47:24.0)(J2000) with an uncertainty of about 0.5 degree. This is consistent with that reported by Gruber (GCNC10187) within an error. The GSC FOV scanned over the source from 04:34:56 (UT) (16 seconds after the GBM trigger) for about 40 seconds. The average X-ray flux over the observation is 4.9x10^-8 erg/cm2/s in 3-15 keV. Significant intensity variation was clearly seen in the light curve. MAXI is currently under the commissioning phase and the systematic uncertainty in localization will be significantly improved with the progress of the alignment calibration. This message may be citable.