GRB 120528B

M. Morii, N. Kawai, R. Usui, K. Ishikawa (Tokyo Tech),
M. Serino, T. Mihara, M. Sugizaki, T. Yamamoto,
M. Matsuoka (RIKEN),
S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa (JAXA),
H. Negoro, M. Nakajima, N. Serita, M. Asada, H. Sakakibara (Nihon U.),
A. Yoshida (AGU),
H. Tsunemi, M. Kimura (Osaka U.),
Y. Ueda, K. Hiroi, M. Shidatsu, R. Sato (Kyoto U.),
Y. Tsuboi, M. Higa (Chuo U.)
M. Yamauchi, Y. Nishimura, T. Hanayama, K. Yoshidome (Miyazaki U.),
K. Yamaoka (Waseda U.)
report on behalf of the MAXI team:

MAXI/GSC triggered at 2012-05-28T18:12:08 UT on a bright uncatalogued
X-ray transient source.
The transient emission lasted at least for 20.0 seconds
within the 40.0 second long triangular transit response of
MAXI/GSC. We identify this event as GRB 120528B.

Assuming that the source flux was constant over the transit,
we obtain the source position at

(R.A., Dec) = (+77.59 deg, -37.80 deg) = (05 10 21, -37 47 50)(J2000)

with a rectangular statistical error box (90%C.L.) of the following corners:

(R.A., Dec) = (+77.23 deg, -37.92 deg) = (05 08 56, -37 54 60)(J2000)
(R.A., Dec) = (+77.56 deg, -38.12 deg) = (05 10 16, -38 07 15)(J2000)
(R.A., Dec) = (+77.96 deg, -37.71 deg) = (05 11 51, -37 42 47)(J2000)
(R.A., Dec) = (+77.63 deg, -37.51 deg) = (05 10 31, -37 30 36)(J2000)

There is an additional systematic uncertainty of 0.1 deg (90%
containment radius).

Without assumptions on the source constancy, we obtain a rectangular error
box for the transient source with the following corners:

(R.A., Dec) = (+76.80 deg, -37.54 deg) = (05 07 12, -37 32 34)(J2000)
(R.A., Dec) = (+77.09 deg, -37.25 deg) = (05 08 21, -37 15 0)(J2000)
(R.A., Dec) = (+78.38 deg, -38.05 deg) = (05 13 31, -38 02 57)(J2000)
(R.A., Dec) = (+78.09 deg, -38.35 deg) = (05 12 22, -38 20 42)(J2000)

The X-ray flux averaged over the scan was 285 +65/-58 mCrab (4-10 keV,
1 sigma error).

Follow-up observations are encouraged.

S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, P.
Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf of the Konus-Wind
team report:

The long GRB 120528B (MAXI/GSC detection and localization:
M. Morii et al., GCN 13346
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 ) was detected by Konus-Wind
in the waiting mode starting at T0(KW)= 65508 s UT (18:11:48),
~20s before the T0(MAXI).

The burst light curve shows a single pulse with a total duration of ~30s.

As observed by Konus-Wind, the burst had a fluence
of (2.9 � 0.8)x10-6 erg/cm2 (in the 20 - 1200 keV energy range).

Modelling the K-W 3-channel time-integrated spectrum
(from T0(KW) to T0(KW)+26 s)
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
yields alpha = -0.41 � 1.22, and Ep = 201 � 112 keV

All the quoted errors are estimated at the 1 sigma confidence level.

The K-W light curve of this burst is available at
http://www.ioffe.rssi.ru/LEA/GRBs/GRB120528B/