Optical and X-Ray Observations of GRB 060526: A Complex Afterglow with An Achromatic Jet Break

We obtained 98 R-band and 18 B, r, i images of the optical afterglow of GRB 060526 (z = 3.21) with the MDM 1.3m, 2.4m, and the PROMPT telescopes in Cerro Tololo over the 5 nights following the burst trigger. Combining these data with other optical observations reported in GCN and the Swift-XRT observations, we compare the optical and X-ray afterglow light curves of GRB 060526. Both the optical and X-ray afterglow light curves show rich features, such as flares and breaks. The densely sampled optical observations provide very good coverage at T > 10 sec. We observed a break at 2.4× 10 sec in the optical afterglow light curve. Compared with the X-ray afterglow light curve, the break is consistent with an achromatic break supporting the beaming models of GRBs. However, the pre-break and post-break temporal decay slopes are difficult to explain in simple afterglow models. We estimated a jet angle of θj ∼ 7 ◦ and a prompt emission size of Rprompt ∼ 2× 10 14 cm. In addition, we detected several optical flares with amplitudes of ∆m ∼ 0.2, 0.6, and 0.2 mag. The X-ray afterglows detected by Swift have shown complicated decay patterns. Recently, many wellsampled optical afterglows also show decays with flares and multiple breaks. GRB 060526 provides an additional case of such a complex, well observed optical afterglow. The accumulated well-sampled afterglows indicate that most of the optical afterglows are complex. Subject headings: gamma rays: bursts Department of Astronomy, Ohio State University, Columbus, OH 43210. Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027. Department of Physics, University of California, San Diego, CA 92093. Department of Astronomy, University of Michigan, Ann Arbor, MI 48109. Department of Physics and Astronomy, University of North Carolina, Chapel Hill, NC 27599.