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THE ASTRONOMER Electronic Circular No 2143      2005 Aug 20 14.15UT
Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise,  Basingstoke,
Hants, RG22 4PP,England.Telephone/FAX(01256)471074Int:+441256471074
INTERNET: GUY@TAHQ.DEMON.CO.UK             GMH at AST.STAR.RL.AC.UK
WORLD WIDE WEB                         http://www.theastronomer.org
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GRB050820
The SWIFT team report on GCN 3830:
At 06:34:53 BAT triggered, located, and immediately slewed to GRB 050820 
(trigger=151207).  The BAT on-board calculated position is RA,Dec 
337.400d, +19.578d {22h 29m 36s, 19d 34' 42"} (J2000). The BAT light 
curve shows a broad double-humped structure about 20 seconds long, with 
peaks around T+1s and T+14 s, with a peak count rate of ~1500 counts 
per second (15-350 keV) at ~1 second after the trigger.
XRT began observing at 06:36:13 UT, 80s after the BAT trigger. A bright 
uncatalogued source was found in the field, which XRT was able to 
centroid on. The on-board calculated coordinates of this source are:
RA(J2000):  22:29:37.8, Dec(J2000): 19:33:32.7, with an uncertainty of 7 
arcseconds radius (90% containment). This position lies 73 arcseconds 
from the center of the BAT error circle, and 6.2 arcseconds from the P60 
position (see below: editor).

Derek Fox (Penn State) and S. Bradley Cenko (Caltech) report on GCN 3829 
their observation of the localised region of the gamma-ray burster 
GRB050820 using the robotic Palomar 60-inch telescope (P60).
They identify a bright, new, variable point source within the XRT (and 
BAT) localization region at coordinates:
RA  22h 29m 38.11s DEC +19 33' 37.1" (J2000)

Photometry of the source relative to the USNO-B1.0 catalog indicates 
that in the R-band it brightens to a peak magnitude of R~14.7 mag at 7 
minutes after the burst and has decayed by 0.4 mag at 12 minutes after 
the burst.
We therefore identify the source as the optical afterglow of GRB050820.
In an image taken ~ 93 minutes after the burst, the afterglow has a
magnitude of R ~ 17.4 (GCN 3834).

J. X. Prochaska (UCO/Lick) et. al. report on NGC 3833:
"Starting at 07h28m59s 20 Aug 2005 UTC, we began spectroscopic
observations of the optical transient with HIRES/Keck I. In a series of 
900 sec exposures the continuum from the afterglow is well detected as 
are many absorption lines.  Based on the identification of a damped Ly 
alpha feature, SiII 1304, OI 1302, and numerous fine structure lines we 
measure the GRB
redshift to be z=2.612 +/- 0.002."

SATELLITES OF (87) SYLVIA
F. Marchis, Department of Astronomy, University of California,
Berkeley, et. al., report the discovery on IAUC 8562 of a new satellite 
of (87) Sylvia. S/2004 (87) 1, of diameter perhaps 7 km, with maximum 
separation 0".44 from the primary, has a prograde near-circular orbit 
with estimated a = 710 km, P = 1.379 days.  Another satellite, S/2001 
(87) 1, of diameter perhaps 18 km, previously reported by M. E. Brown 
and J.-L. Margot is estimated by Marchis et al. to have a = 1360 km, P = 
3.650 days. Bearing in mind that the discoverer named (87) Sylvia for 
Rhea Sylvia, the mother of Romulus, with his twin brother the alleged 
founder of Rome, the IAU Committee on Small-Body Nomenclature has 
approved the permanent designations and names (87) Sylvia I = Romulus 
and (87) Sylvia II = Remus for the outer satellite S/2001 (87) 1 and the 
inner satellite S/2004 (87) 1, respectively.

Guy M Hurst