GRB 100510A

M. Morii (Tokyo Tech), M. Nakajima (Nihon U.), S. Nakahira (AGU),
N. Kawai, K. Sugimori (Tokyo Tech), M. Matsuoka, K. Kawasaki, S. Ueno,
H. Tomida, M. Kohama, M. Ishikawa (JAXA), T. Mihara, Y.E. Nakagawa,
M. Sugizaki, M. Suzuki, T. Yamamoto, T. Sootome (RIKEN), A. Yoshida,
K. Yamaoka (AGU), H. Tsunemi, M. Kimura (Osaka U.), H. Negoro, H. Ozawa,
F. Suwa (Nihon U.), Y. Ueda, N. Isobe, S. Eguchi, K. Hiroi (Kyoto U.),
A. Daikyuji (Miyazaki U.), A. Uzawa, T. Matsumura, K. Yamazaki (Chuo U.)
report on behalf of the MAXI team

MAXI/GSC detected a bright X-ray transient at a scan transit from
2010-05-10T19:27:09 to 19:27:37 UT. The transient emission lasted at least
for 28 seconds within the 50 second long triangular transit response of
MAXI/GSC.
This event is temporary coincident with the Fermi-GBM Trigger #295212428 at
2010-05-10T19:27:06.97, thus we identify this event as GRB 100510A.

The best-fit position of the source is
(R.A., Dec) = (+355.8 deg, -35.6 deg) = (23 43 10, -35 37 25)(J2000),
with a rectangular statistical error box (90%C.L.) of the following corners:

 (R.A., Dec) = (+355.69 deg, -35.79 deg) = (23 42 45, -35 47  8)(J2000)
 (R.A., Dec) = (+355.58 deg, -35.55 deg) = (23 42 19, -35 32 49)(J2000)
 (R.A., Dec) = (+355.90 deg, -35.46 deg) = (23 43 35, -35 27 38)(J2000)
 (R.A., Dec) = (+356.00 deg, -35.70 deg) = (23 44  1, -35 41 56)(J2000).

There is additional systematic uncertainty of 0.2 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) = (+355.18 deg, -35.92 deg) = (23 40 43, -35 55 12)(J2000)
 (R.A., Dec) = (+355.08 deg, -35.68 deg) = (23 40 18, -35 40 49)(J2000)
 (R.A., Dec) = (+356.70 deg, -35.24 deg) = (23 46 47, -35 14 11)(J2000)
 (R.A., Dec) = (+356.81 deg, -35.47 deg) = (23 47 14, -35 28 27)(J2000).

The peak X-ray flux was at least 650 +- 70 mCrab (4-10 keV, 1 sigma error).

The position above is consistent with the Fermi-GBM flight position
on 2010-05-10T19:27:33 UT (record #58, RA=345.10, Dec=-20.03, error=18.37),
but outside of the ground position on 2010-05-10T19:27:40 UT (record #57,
RA=31.87, Dec=-31.55, error=19.12).

The all-sky image and the light curve will be shown at the MAXI web site
http://maxi.riken.jp/ at the "News" section.

P. N. Bhat (UAH), Vandiver Chaplin (UAH), Valerie Connaughton (UAH)
and Chip Meegan (USRA)
report on behalf of the Fermi GBM Team:

"At 19:27:06.97 UT on 10 May 2010, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 100510 (trigger 295212428 / 100510810),
which was also detected by the MAXI/GSC (Morii et al. 2010, GCN 10739
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The on-ground calculated location, using the GBM trigger
data, is RA = 355.05, DEC = -18.86 (J2000 degrees,
equivalent to 23 h 40 m, -18 d 52 '), with an uncertainty
of 5 degrees (radius, 1-sigma containment,
statistical only; The GBM on-ground location is subject to systematic
errors due to blockage by the solar panels at this orientation.)
 
The angle from the Fermi LAT boresight is 90 degrees.

The GBM light curve consists of a single FRED
with a duration (T90) of about 31 s (50-300 keV).
The time-averaged spectrum from T0-11 s to T0+54 s is
adequately fit by a power law function with an exponential
high energy cutoff.  The power law index is -0.97 +/- 0.18 and
the cutoff energy, parameterized as Epeak, is 70 +/- 6.8 keV

(C-stat value 553.2 for 242 d.o.f.).

The event fluence (8-1000 keV) in this time interval is
(2.68 +/- 0.08)E-06 erg/cm^2. The 0.256-sec peak photon flux measured
starting from T0 s in the 8-1000 keV band
is 0.8 +/- 0.03 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."