Dark Bursts in the Swift Era: The Palomar 60 Inch-Swift Early Optical Afterglow Catalog
Abstract
We present multicolor optical observations of long-duration γ-ray bursts (GRBs) made over a three-year period with the robotic Palomar 60 inch telescope (P60). Our sample consists of all 29 events discovered by Swift for which P60 began observations less than 1 hr after the burst trigger. We were able to recover 80% of the optical afterglows from this prompt sample, and we attribute this high efficiency to our red coverage. Like Melandri et al. (2008), we find that a significant fraction (≈50%) of Swift events show a suppression of the optical flux with regard to the X-ray emission (the so-called "dark" bursts). Our multicolor photometry demonstrates this is likely due in large part to extinction in the host galaxy. We argue that previous studies, by selecting only the brightest and best-sampled optical afterglows, have significantly underestimated the amount of dust present in typical GRB environments.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 2009
- DOI:
- arXiv:
- arXiv:0808.3983
- Bibcode:
- 2009ApJ...693.1484C
- Keywords:
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- gamma rays: bursts;
- Astrophysics
- E-Print:
- 49 pages, including 6 figures and 3 tables (one of which is quite long). Re-submitted to ApJ following referee report. Comments welcome. v2: Corrected minor typos