Issue |
A&A
Volume 408, Number 3, September IV 2003
|
|
---|---|---|
Page(s) | L21 - L24 | |
Section | Letters | |
DOI | https://doi.org/10.1051/0004-6361:20031153 | |
Published online | 17 November 2003 |
Letter to the Editor
The optical afterglow of the not so dark GRB 021211
1
State Observatory, Manora peak, Naini Tal 263129, Uttaranchal, India
2
Indian Institute of Astrophysics, Bangalore 560 034, India
3
Raman Research Institute, Bangalore 560 080, India
4
Instituto de Astrofísica de Andalucía, PO Box 03004, 18080 Granada, Spain
5
Center for Research & Education in Science & Technology, Hosakote, Bangalore 562 114, India
Corresponding author: S. B. Pandey, shashi@upso.ernet.in
Received:
28
April
2003
Accepted:
29
July
2003
We determine Johnson and Cousins
photometric CCD magnitudes for
the afterglow of GRB 021211 during the first night after the GRB trigger.
The afterglow was very faint and would have been probably missed if no prompt
observations had been conducted. A fraction of the so-called “dark” GRBs
may thus be just “optically dim” and require very deep imaging to be
detected. The early-time optical light curve reported by other observers
shows a prompt emission with properties similar to that of GRB 990123. Following
this, the afterglow emission from ~11 min to ~35 days after the burst
is characterized by an overall power-law decay with a slope
in the R
passband. We derive the value of spectral index in the optical to near-IR
region to be
during 0.13 to 0.8 day after the burst.
The flux decay constant and the spectral slope indicate that during the
first day after the burst, the optical band lies between the cooling
frequency and the synchrotron maximum frequency of the afterglow.
Key words: gamma rays: bursts / techniques: photometric / cosmology: observations
© ESO, 2003
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