The red optical afterglow of GRB 030725

Abstract

We present a photometric study of the optical counterpart of the long-duration Gamma Ray Burst (GRB) 030725, which triggered the HETE FREGATE and WXM instruments on July 25th, 2003, and lasted more than 160s. An optical counterpart was identified at the Bronberg Observatory in South Africa about 7 hours after the burst occurred. The optical afterglow (OA) was observed between 4 and 15 days after the burst with the 1.54m Danish telescope at La Silla in the V, Rc, and Ic bands. We fit a broken power law to the data and determine a break time in the light curve between 16 hours and 4.7 days after the first detection of the burst. The decay slope is alpha1 = -0.59 +0.59/-0.44 before and alpha2 = -1.43 +/- 0.06 after the break. A bump may be present in the light curve, only significant at the 2-sigma level, 13.9 days after the main burst. The spectral slope of the OA, measured 12 days after the burst, is -2.9 +/- 0.6 , i.e. it falls in the extreme red end of the distribution of previous OA spectral slopes. Observations of the field 8 months after the burst with the EMMI instrument on the NTT telescope (La Silla) resulted in an upper limit of Rc=24.7 mag for the host galaxy of GRB 030725. The OA of GRB 030725 was discovered at a private, non-professional observatory and we point out that with the current suite of gamma ray satellites, an effort to organize future contributions of amateur observers may provide substantial help in GRB light curve follow up efforts.

arXiv commentAccepted for publication in A&A, 6 pages, 2 figures

References in corpus (24)

• Spectra and Light Curves of Gamma-Ray Burst Afterglows
• Beaming in Gamma-Ray Bursts: Evidence for a Standard Energy Reservoir
• Discovery of the X-Ray Afterglow of the Gamma-Ray Burst of February 28 1997
• Gamma-Ray Bursts: Progress, Problems & Prospects
• The collimation--corrected GRB energies correlate with the peak energy of their $\nu F_{\nu }$ spectrum
• The unusual afterglow of GRB 980326: evidence for the gamma-ray burst/supernova connection
• A Common Origin for Cosmic Explosions Inferred from Fireball Calorimetry
• A Study of the Afterglows of Four GRBs: Constraining the Explosion and Fireball Model
• The host of GRB 030323 at z=3.372: a very high column density DLA system with a low metallicity
• A Systematic Analysis of Supernova Light in Gamma-Ray Burst Afterglows
• Detection of a supernova signature associated with GRB 011121
• The Host Galaxy of GRB 031203: Implications of its low metallicity, low redshift, and starburst nature
• Evidence for Supernova Signatures in the Spectrum of the Late-time Bump of the Optical Afterglow of GRB 021211
• On the Ly-alpha emission from gamma-ray burst host galaxies: evidence for low metallicities
• The Katzman Automatic Imaging Telescope Gamma-Ray Burst Alert System, and Observations of GRB 020813
• The submm properties of GRB host galaxies
• Very high column density and small reddening towards GRB 020124 at z = 3.20
• The Faint Optical Afterglow and Host Galaxy of GRB 020124: Implications for the Nature of Dark Gamma-Ray Bursts
• Discovery of GRB 020405 and its Late Red Bump
• Deep Ly-alpha imaging of two z=2.04 GRB host galaxy fields
• The afterglow and the host galaxy of GRB 011211
• Colors and luminosities of the optical afterglows of the gamma-ray bursts
• On the constraining observations of the dark GRB 001109 and the properties of a z = 0.398 radio selected starburst galaxy contained in its error box
• Optical and near-infrared observations of the GRB 970616 error box

Cited by in corpus (6)

• The Observer's Guide to the Gamma-Ray Burst-Supernova Connection
• A Comprehensive Study of Gamma-Ray Burst Optical Emission: I. Flares and Early Shallow Decay Component
• GRB afterglow light curves in the pre-Swift era - a statistical study
• Properties of X-Ray Rich Gamma Ray Bursts and X-Ray Flashes detected with BeppoSAX and Hete-2
• Spectral Lag Relations in GRB Pulses Detected with HETE-2
• The GRBSN webtool: An open-source repository for gamma-ray burst-supernova associations