[vsnet-grb-info 17967] GRB 160509A: MAXI/GSC refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19415
SUBJECT: GRB 160509A: MAXI/GSC refined analysis
DATE:    16/05/10 04:13:32 GMT
FROM:    H. Negoro at Nihon U.  <negoro at phys.cst.nihon-u.ac.jp>

H. Negoro (Nihon U.), S. Nakahira (JAXA),  T. Mihara (RIKEN),
S. Ueno, H. Tomida, M. Ishikawa, Y. E. Nakagawa, Y. Sugawara (JAXA), 
M. Sugizaki, M. Serino, W. Iwakiri, M. Shidatsu, J. Sugimoto, T. Takagi, M. Matsuoka (RIKEN), 
N. Kawai, N. Isobe, S. Sugita, T. Yoshii, Y. Tachibana, Y. Ono, T. Fujiwara (Tokyo Tech), 
A. Yoshida, T. Sakamoto, Y. Kawakubo, Y. Kitaoka (AGU), 
H. Tsunemi, R.Imatani (Osaka U.), M. Nakajima, K. Tanaka, T. Masumitsu, 
T. Kawase (Nihon U.), Y. Ueda, T. Kawamuro, T. Hori, A. Tanimoto (Kyoto U.), 
Y. Tsuboi, Y. Nakamura, R. Sasaki (Chuo U.), M. Yamauchi, K. Furuya (Miyazaki U.),  
K. Yamaoka (Nagoya U.) report on behalf of the MAXI team:

We reexamined the localization of GRB 160509A (Longo et al. GCN 19403; 
Ono et al. GCN 19404,19405) only using the GSC camera 7 (Bcam1), and
not using an uncalibrated GSC camera 0 (Acam0) which was also used in 
the previous analysis (GCN 19404, 19405).

We obtain the source position for a constant flux source at
(R.A., Dec) = (311.521 deg, 76.057 deg) = (20 46 05, +76 03 24) (J2000)
with a 90% C.L. statistical error of 0.12 deg and an additional systematic 
uncertainty of 0.1 deg (90% containment radius),
and a rectangular error box for a variable flux source with the following corners:
(R.A., Dec) = (310.806 deg, 76.105 deg) = (20 43 13, +76 06 16) (J2000)
(R.A., Dec) = (311.249 deg, 75.892 deg) = (20 44 59, +75 53 32) (J2000)
(R.A., Dec) = (312.671 deg, 76.056 deg) = (20 50 41, +76 03 21) (J2000)
(R.A., Dec) = (312.242 deg, 76.270 deg) = (20 48 57, +76 16 13) (J2000)

The Swift/XRT source position (Kennea et al. GCN 19408; Levan et al. GCN 19410;  
Alexander et al. GCN 19414) is 0.076 arc-degree from the refined best position, 
and also within the rectangular region.

A GSC spectrum is roughly represented by an absorbed power-law 
with a photon spectral index of 1.26 +/- 0.16, and the resultant 2-10 keV flux 
is 2.78e-08 ergs/cm^2/s. The absorption column is fixed to 4.6 x 10^21 cm^-2 
in the fit (Kennea et al. GCN 19408).

We also note that there was no significant excess flux in the next transit at 
10:37 UT on 2016 May 9 with an upper limit of 20 mCrab.
~