Browsing by Author "Berger, E."
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Item The Detailed Optical Light Curve of GRB 030329(IOP, 2004-01-19) Lipkin, Y. M.; Ofek, E. O.; Gal-Yam, A.; Leibowitz, E. M.; Poznanski, D.; Kaspi, S.; Polishook, D.; Kulkarni, S. R.; Fox, D. W.; Berger, E.; Mirabal, N.; Halpern, J.; Bureau, M.; Fathi, K.; Price, P. A.; Peterson, B. A.; Frebel, A.; Schmidt, B.; Orosz, J. A.; Fitzgerald, J. B.; Bloom, J. S.; Dokkum, P. G. van; Bailyn, C. D.; Buxton, M. M.; Barsony, M.We present densely sampled BVRI light curves of the optical transient associated with the gamma-ray burst (GRB) 030329, the result of a coordinated observing campaign conducted at five observatories. Augmented with published observations of this GRB, the compiled optical data set contains 2687 photometric measurements, obtained between 78 minutes and 79 days after the burst. This data set allows us to follow the photometric evolution of the transient with unprecedented detail. We use the data to constrain the light curve of the underlying supernova (SN) 2003dh and show that it evolved faster than and was probably somewhat fainter than the Type Ic SN 1998bw, associated with GRB 980425. We find that our data can be described by a broken power-law decay perturbed by a complex variable component. The early- and late-time decay slopes are determined to be α1 ≈ 1.1 and α2 ≈ 2. Assuming this single-break power-law model, we constrain the break to lie between ~3 and ~8 days after the burst. This simple, singly broken power-law model, derived only from the analysis of our optical observations, may also account for available multiband data, provided that the break happened ~8 days after the burst. The more complex double-jet model of Berger et al. provides a comparable fit to the optical, X-ray, millimeter, and radio observations of this event. The unique early coverage available for this event allows us to trace the color evolution of the afterglow during the first hours after the burst. We detect a significant change in optical colors during the first day. Our color analysis is consistent with a cooling-break frequency sweeping through the optical band during the first day. The light curves of GRB 030329 reveal a rich array of variations, superposed over the mean power-law decay. We find that the early variations (lesssim8 days after the burst) are asymmetric, with a steep rise followed by a relatively slower (by a factor of about 2) decline. The variations maintain a similar timescale during the first 4 days and then get significantly longer. The structure of these variations is similar to those previously detected in the afterglows of several GRBs.Item GRB 000418: A Hidden Jet Revealed(IOP, 2001-04-05) Berger, E.; Diercks, A.; Frail, D. A.; Kulkarni, S. R.; Bloom, J. S.; Sari, R.; Halpern, J.; Mirabal, N.; Taylor, G. B.; Hurley, K.; Pooley, G.; Becker, K. M.; Wagner, R. M.; Terndrup, D. M.; Statler, T.; Wik, D. R.; Mazets, E.; Cline, T.We report on optical, near-infrared, and centimeter radio observations of GRB 000418 that allow us to follow the evolution of the afterglow from 2 to 200 days after the γ-ray burst (GRB). In modeling these broadband data, we find that an isotropic explosion in a constant-density medium is unable to simultaneously fit both the radio and optical data. However, a jetlike outflow into either a constant density or wind-stratified medium with an opening angle of 10°-20° provides a good description of the data. The evidence in favor of a jet interpretation is based on the behavior of the radio light curves, since the expected jet break is masked at optical wavelengths by the light of the host galaxy. We also find evidence for extinction, presumably arising from within the host galaxy, with Aimg1.gif = 0.4 mag, as well as host flux densities of FR = 1.1 μJy and FK = 1.7 μJy. These values supersede previous work on this burst as a result of the availability of a broadband data set allowing a global fitting approach. A model in which the GRB explodes isotropically into a wind-stratified circumburst medium cannot be ruled out by these data. However, in examining a sample of other bursts (e.g., GRB 990510, GRB 000301C), we favor the jet interpretation for GRB 000418.Item Multicolor Observations of the GRB 000926 Afterglow(IOP, 2001-02-26) Price, P. A.; Harrison, F. A.; Galama, T. J.; Reichart, D. E.; Axelrod, T. S.; Berger, E.; Bloom, J. S.; Busche, J.; Cline, T.; Diercks, A.; Djorgovski, S. G.; Frail, D. A.; Gal-Yam, A.; Halpern, J.; Holtzman, J. A.; Hunt, M.; Hurley, K.; Jacoby, B.; Kimble, R.; Kulkarni, S. R.; Mirabal, N.; Morrison, G.; Ofek, E.; Pevunova, O.; Sari, R.; Schmidt, B. P.; Turnshek, D.; Yost, S.We present multicolor light curves of the optical afterglow of gamma-ray burst (GRB) 000926. Beginning ~1.5 days after the burst, the light curves of this GRB steepen measurably. The existence of such achromatic breaks is usually taken to be an important observational signature that the ejecta are not expanding isotropically but rather have a collimated jetlike geometry. If we interpret the data in this context, we derive an opening angle of 5°, which reduces the energy release compared with an isotropic model by a factor of ~275, to 1.7 × 10⁵¹ ergs. To fit the data with a simple jet model requires extinction along the line of sight. The derived AV is in the range 0.11-0.82 mag, depending on the adopted extinction law and whether the electrons giving rise to the optical emission are undergoing synchrotron cooling or not. Since this is in excess of the expected extinction from our Galaxy, we attribute this to the GRB host. We note that this extinction is typical of a galactic disk, and therefore the event likely took place in the disk of its host.Item A Redshift Determination for XRF 020903: First Spectroscopic Observations of an X-Ray Flash(IOP, 2004-05-10) Soderberg, A. M.; Kulkarni, S. R.; Berger, E.; Fox, D. B.; Price, P. A.; Yost, S. A.; Hunt, M. P.; Frail, D. A.; Walker, R. C.; Hamuy, M.; Shectman, S. A.; Halpern, J. P.; Mirabal, N.We report the discovery of optical and radio afterglow emission from the extremely soft X-ray flash XRF 020903. Our spectroscopic observations provide the first redshift for an X-ray flash, thereby setting the distance scale for these events. At z = 0.251, XRF 020903 is one of the nearest cosmic explosions ever detected, second only to the recent GRB 030329 and the unusual GRB 980425/SN 1998bw. Moreover, XRF 020903 is the first X-ray flash for which we detect an optical afterglow. The luminosity of the radio afterglow of XRF 020903 is 1000 times greater than that of Ibc supernovae but similar to those of GRB afterglows. From broadband afterglow modeling we show that the explosion energy of XRF 020903 is not dissimilar to values inferred for typical gamma-ray bursts, suggesting that these cosmological explosions may derive from a similar mechanism.