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THE ASTRONOMER Electronic Circular No 2220      2006 Apr 18 06.43UT
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      Backup: gmh@wdcc1.bnsc.rl.ac.uk
WORLD WIDE WEB                         http://www.theastronomer.org
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GRB 060418: BRIGHT AFTERGLOW
A. D. Falcone (PSU) et. al., report on GCN 4966 behalf of the Swift 
Team: At 03:06:08 UT on 2006 April 18, the Swift Burst Alert Telescope 
(BAT) triggered and located GRB 060418 (trigger=205851). Swift slewed 
immediately to the burst. The BAT on-board calculated location is RA,Dec 
236.420, -3.643 {15h 45m 41s, -03d 38' 35"} (J2000) with an uncertainty 
of 3 arcmin.

The BAT light curve shows a broad smooth peak starting at T-8 sec. It 
decays almost to background, and then a bright peak at T+27 sec (FWHM ~3 
sec). There is possibly emission at T+130 sec. The peak count rate was 
~6000 counts/sec (15-350 keV), at ~27 sec after the trigger.

The XRT began observing the field at 03:07:26 UT, 78 seconds after the 
BAT trigger. XRT found a bright, variable, uncatalogued X-ray source 
located at:
RA(J2000) = 15h 45m 42.8s, Dec(J2000) = -03d 38' 26.1"., with
an estimated uncertainty of 5.8 arcseconds (90% confidence radius). This 
location is 32 arcseconds from the BAT on-board position, within the BAT 
error circle.

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 88 seconds after the BAT trigger. There is 
a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at:
RA 15h 45m 42.60s DEC -03 38'20.0" (2000)
This position is 7.2 arc sec. from the centre of the XRT error circle. 
The estimated V magnitude is 14.5 with a 1-sigma error of about 0.5 mag. 
No correction has been made for the expected extinction corresponding to 
E(B-V) of 0.22.

S. Covino et. al., report on GCN 4967 on behalf of the  REM/ROSS Team:

We imaged the field of GRB 060418 (Falcone et al. GCN 4966) with the 
robotic 60-cm REM telescope located at La Silla (Chile). Observations 
were performed automatically in the near infrared (J, H, K, z bands) 
soon after the GRB alert.

We find a single bright source in the XRT error circle, not visible in 
the 2MASS survey. Its H magnitude is about 11.25.

Andrea Melandri et. al.,, A. Gomboc, C.G. Mundell, C. Guidorzi, A. 
Monfardini, C.J. Mottram, R.J. Smith, I.A. Steele, D. Carter, M. 
Burgdorf, S. Kobayashi, D. Bersier, M.F. Bode (Liverpool JMU) report on 
GCN 4968:

"The 2-m Liverpool Telescope immediately observed the field of GRB060418 
and started observing its position about 5.0
minutes after the GRB. The automatic "detection mode" procedure clearly 
detected the optical afterglow candidate at the XRT position reported by 
Falcone et al. (GCN 4966). This source has a R magnitude of ~14.0 after 
~6 minutes from 3x10-s images and clearly show a rapid early optical 
decay.

Guy M Hurst