The Earliest Optical Observations of GRB 030329

Abstract

We present the earliest optical imaging observations of GRB 030329 related to SN 2003dh. The burst was detected by the HETE-2 satellite at 2003 March 29, 11:37:14.67 UT. Our wide-field monitoring started 97 minutes before the trigger and the burst position was continuously observed. We found no precursor or contemporaneous flare brighter than $V=5.1$ ($V=5.5$) in 32 s (64 s) timescale between 10:00 and 13:00 UT. Follow-up time series photometries started at 12:51:39 UT (75 s after position notice through the GCN) and continued for more than 5 hours. The afterglow was $Rc=12.35\pm 0.07$ at $t=74$ min after burst. Its fading between 1.2 and 6.3 hours is well characterized by a single power-law of the form $f(\mathrm{mJy})=(1.99\pm 0.02(\mathrm{statistic})\pm 0.14(\mathrm{systematic}))\times (t/1\mathrm{day}{)}^{-0.890\pm 0.006(\mathrm{statistic})\pm 0.010(\mathrm{systematic})}$ in $Rc$-band. No significant flux variation was detected and upper limits are derived as $(\Delta f/f{)}_{\mathrm{RMS}}=3-5$% in minutes to hours timescales and $(\Delta f/f{)}_{\mathrm{RMS}}=35-5$% in seconds to minutes timescales. Such a featureless lightcurve is explained by the smooth distribution of circumburst medium. Another explanation is that the optical band was above the synchrotron cooling frequency where emergent flux is insensitive to the ambient density contrasts. Extrapolation of the afterglow lightcurve to the burst epoch excludes the presence of an additional flare component at $t<10$ minutes as seen in GRB 990123 and GRB 021211.

arXiv commentApJL, in press

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• A Large Catalogue of Multi-wavelength GRB Afterglows I: Color Evolution And Its Physical Implication
• Revealing the Jet Structure of GRB 030329 with High Resolution Multicolor Photometry
• GRB 030227: the first multiwavelength afterglow of an INTEGRAL GRB
• Early ($<$0.3 day) R-band light curve of the optical afterglow of GRB030329
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• Out of the darkness: the infrared afterglow of the INTEGRAL burst GRB 040422 observed with the VLT
• The weak INTEGRAL bursts GRB040223 and GRB040624: an emerging population of dark afterglows
• SCUBA sub-millimeter observations of gamma-ray bursters III. GRB 030329: The brightest sub-millimeter afterglow to date
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