On 29 March, 2003, at 11:37:14, the HETE-II satellite detected a very bright, long, gamma-ray burst. Its gamma-ray light curve is depiced below (from the HETE page):
Both active ROTSE-III telescopes have now observed the optical counterpart to GRB 030329. ROTSE-IIIa began taking images about 1.5 h after the burst, and despite bad weather managed to take a series of useful images before the source set. When night next fell in Texas, ROTSE-IIIb began imaging the field, and the source was still well above background. However, as you can see from the image below, the decay curve has clearly steepened. The points on the left are from ROTSE-IIIa (diamonds), while all the points from 10 h to 30 h after the burst are from ROTSE-IIIb (triangles).
The magnitudes are all ROTSE-III unfiltered magnitudes, calibrated against the USNO 2.0 catalog in R band. The lines are best-fit power-law flux decays, fit using a simple chi-squared minimization to each instrument's dataset. The best fit slope for the early decay is 1.0. The later slope initially showed a best-fit value of 1.9, implying that the break occured around 12.1 h after the burst. However, the subsequent evolution of the afterglow is clearly inconsistent with a single power law decay, and is steepening as time goes on. The above figure shows a best fit power-law slope of 2.1, but the fit is very bad. Below is a zoom-in view of the Texas observations.
The raw data is also available from our ApJ Letter Smith et al. (2003). The format is seven columns: a flag to identify the line as containing observations, a number 0/1 to identify the telescope as ROTSE-III A/B, the start and end times of the image, a flag 1/0 for dection/upper limit, the calibrated magnitude, and the estimated error. We also provide an IDL script that will read in this file and format it into a structure for plotting. For details, please see the paper.
We also have some interesting postscript files available. This afterglow, observed over an hour after the burst, was much, much brighter than the afterglow from GRB 990123 at the equivalent time. See this postscript plot. Here is a PostScript finding chart that shows the field.
Here are some images of the burst counterpart. The first is an early image taken with ROTSE-IIIa in Australia, then a picture with ROTSE-IIIb in Texas (about 12 hours later). Then back to IIIa about 6 h after that, and finally returning to IIIb about 6 h after that.