GRB 050509C

E.S. Rykoff (U Mich), H. Swan (U Mich), R. Quimby (U Texas), T.A. McKay 
(U Mich), report on behalf of the ROTSE collaboration:

ROTSE-IIIc, located at the H.E.S.S. site at Mt. Gamsberg, Namibia, 
responded to GRB 050509c (HETE trigger 3751), producing images beginning 
6.4 s after the GCN notice time. An automated response took the first 
image at 22:46:19.6 UT, 25.7 s after the burst, under excellent 
conditions. We took 10 5-sec, 10 20-sec and 120 60-sec eposures. These 
unfiltered images are calibrated relative to USNO A2.0 (R).  The final 
error box reported by Prigozhin et al. (GCN 3402
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 ) was entirely contained 
within the ROTSE-IIIc field of view of the initial response.

Comparison to the DSS (second epoch) reveals no new sources within the 
SXC/WFC error box reported in GCN 3402
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 ; however, we are limited as the 
field is somewhat crowded. Individual images have limiting magnitudes 
ranging from 15.8-17.1. In particular, we set a limit of magnitude 15.9 
in a single 5 s exposure, starting 25.7 s after the burst. Coadding the 
images into sets of 10 reveals no new sources down to limits of 17.0 
(136 s effective length (t_end-t_start), beginning 25.7 s post-burst), 
17.5 (295.4 s effective length, beginning 170.7 s post-burst), and 17.7 
(695 s effective length, beginning 466.1 s post-burst).

L.A. Antonelli on behalf of the REM/ROSS Team report:

Please, note that GCN 3400
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  (D'Avanzo et al.)  having subject  
"GRB050509: REM NIR and Optical observations" is referring to GRB 
050509c.
Thanks to Alberto Castro-Tirado and Nicola Masetti to point out the 
misleading subject.

GRB050509c (=H3751): An X-Ray Flash Localized By HETE

G. Prigozhin, G. Ricker, J-L. Atteia, N. Kawai, D. Lamb,
and S. Woosley, on behalf of the HETE Science Team;
 
M. Arimoto, T. Donaghy, E. Fenimore, M. Galassi, C. Graziani,
J. Kotoku, M. Maetou, M. Matsuoka, Y. Nakagawa, T. Sakamoto, R. Sato,
Y. Shirasaki, M. Suzuki, T. Tamagawa, K. Tanaka, Y. Yamamoto,
and A. Yoshida, on behalf of the HETE WXM Team;
 
N. Butler, G. Crew, J. Doty, R. Vanderspek, J. Villasenor,
J. G. Jernigan, A. Levine, G. Azzibrouck, J. Braga, R. Manchanda,
and G. Pizzichini, on behalf of the HETE Operations and HETE
Optical-SXC Teams;
 
M. Boer, J-F Olive, J-P Dezalay, and K. Hurley, on behalf of the HETE
FREGATE Team;
 
report:

The HETE FREGATE, WXM, and SXC instruments detected GRB 050509c at 
22:45:54 UT (81953.95 SOD) on 9 May 2005.  This was a weak burst
consisting of a single pulse ~25 s long, with almost no emission above
18 keV in the WXM.

The WXM flight localization can be expressed as a circle of radius 14
arcminutes (90% confidence) that is centered at 

WXM-Flight:  RA = 12h 52m 39s, Dec =-44d 17' 50" (J2000).  

The first flight localization was distributed in a GCN Notice issued
at 22:46:13 UT, 19 s after the burst trigger.

Ground analysis of the WXM data produced a refined WXM localization
that was in a GCN Notice issued 10 May 05 at 00:43:29 UT.  This ground
WXM localization can be expressed as a rectangle with corners:

 R.A. = 12 52 15.4 ; Dec. = -44 23 06
 R.A. = 12 54 05.0 ; Dec. = -44 23 46
 R.A. = 12 54 01.7 ; Dec. = -45 10 01
 R.A. = 12 52 11.3 ; Dec. = -45 09 18 (J2000).

The burst was also detected by the SXC Y camera.  Ground analysis of
the SXC data produced a long thin rectangle.  Truncating the rectangle 
by the WXM ground localization results in a rectangle with corners:

 R.A. = 12 54 02.9 ; Dec. = -44 52 23
 R.A. = 12 52 12.7 ; Dec. = -44 51 43
 R.A. = 12 52 13.2 ; Dec. = -44 48 43
 R.A. = 12 54 03.1 ; Dec. = -44 49 23 (J2000).

A preliminary spectral analysis indicates that Epk < 19 keV.  The
preliminary fluences are: S(2-30 keV) = 6E-07 erg cm^-2,
S(30-400) = 3E-07 erg cm^-2.  Therefore GRB 050509c is an X-ray flash.

A light curve, skymap, and spectral information for GRB 050509c are
provided at the following URL:

http://space.mit.edu/HETE/Bursts/GRB050509C/

P. D'Avanzo, S. Piranomonte, L.A. Antonelli, S. Covino, F.M. Zerbi, G. 
Chincarini, M. Rodono', G. Tosti,  P. Conconi, G. Cutispoto, E. 
Molinari, L. Nicastro, E. Palazzi, V. Testa, F. Vitali, E. Meurs, P. 
Goldoni, on behalf of the REM/ROSS Team report:

"We imaged the central part of the field of GRB050509 with the robotic 
60-cm REM telescope located at La Silla, Chile. REM is equipped with 
the REMIR near infrared camera (10x10 sq arcmin FoV, JHK filters) and 
the ROSS optical spectrograph/imager (10x10 sq arcmin FoV, VRI filters 
and AMICI prism).

Observations of GRB 050509 were performed in fully automated mode 
simultaneously in the near infrared and in the optical starting 
approximately 56 seconds after the burst (32 seconds after the 
reception of the burst alert). Then, 2 hrs after the burst, REM 
performed automatically a further observation of  the refined position 
of GRB 050509 few seconds after the new trigger delivered by the HETE 
Team.

A preliminary analysis of both the H and R band images does not reveal 
any new object down to the 2MASS and DSS limits respectively."

This message may be cited.