TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3468
SUBJECT: GRB050525: ROTSE-III Refined Analysis 
DATE:    05/05/25 04:09:26 GMT
FROM:    Eli Rykoff at U of Michigan/ROTSE  <erykoff@umich.edu>

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

ROTSE-IIIc, located at the H.E.S.S. site in Namibia, and ROTSE-IIId at 
the Turkish National Observatory in Turkey responded automatically to 
Swift GRB 050525 (GCN 3466, 3467).  Our first 5-s exposure from 
ROTSE-IIIc begain at 00:08:56.7 UT; the response in Turkey was delayed 
approximately 30 minutes due to bad weather.  The images in Namibia were 
affected by clouds passing through the images.

We confirm the fading nature of the afterglow reported in GCN 2465.  The 
afterglow is well detected in images from both ROTSE-IIIc and 
ROTSE-IIId.  The afterglow is 9" (3 pixels) from a 17.2 magnitude USNO 
star, which affected our initial position estimate.  The revised 
position is:

    18:32:32.6   +26:20:23.5 (J2000)

with an uncertainty of ~1".  We note that this is 7.2" from the XRT 
position reported by Band et al (GCN 2465).

We have measured the afterglow flux with our PSF fitting software and 
have found that the early lightcurve is fading with a slow power-law 
decline with index ~-0.5, with a peak of 15.1+/-0.1 at 601s post-burst. 
  The images are unfiltered and calibrated relative to USNO B1.0 R-band 
magnitudes.  This bright afterglow with a slow decline should still be 
bright for follow-up spectroscopy.

An image of the afterglow and burst field from ROTSE-IIId is available at:
http://www.rotse.net/grb_reports/050525_btab.html