THE AFTERGLOWS OFSWIFT-ERA GAMMA-RAY BURSTS. I. COMPARING PRE-SWIFTANDSWIFT-ERA LONG/SOFT (TYPE II) GRB OPTICAL AFTERGLOWS

Abstract

15131514 KANN ET AL.Vol. 720 ABSTRACT We have gathered optical photometry data from the literature on a large sample of Swift-era gamma-ray burst (GRB) afterglows including GRBs up to 2009 September, for a total of 76 GRBs, and present an additional three pre-Swift GRBs not included in an earlier sample. Furthermore, we publish 840 additional new photometry data points on a total of 42 GRB afterglows, including large data sets for GRBs 050319, 050408, 050802, 050820A, 050922C, 060418, 080413A, and 080810. We analyzed the light curves of all GRBs in the sample and derived spectral energy distributions for the sample with the best data quality, allowing us to estimate the host-galaxy extinction. We transformed the afterglow light curves into an extinction-corrected z = 1 system and compared their luminosities with a sample of pre-Swift afterglows. The results of a former study, which showed that GRB afterglows clustered and exhibited a bimodal distribution in luminosity space, are weakened by the larger sample. We found that the luminosity distribution of the two afterglow samples (Swift-era and pre-Swift) is very similar, and that a subsample for which we were not able to estimate the extinction, which is fainter than the main sample, can be explained by assuming a moderate amount of line-of-sight host extinction. We derived bolometric isotropic energies for all GRBs in our sample, and found only a tentative correlation between the prompt energy release and the optical afterglow luminosity at 1 day after the GRB in the z = 1 system. A comparative study of the optical luminosities of GRB afterglows with echelle spectra (which show a high number of foreground absorbing systems) and those without, reveals no indication that the former are statistically significantly more luminous. Furthermore, we propose the existence of an upper ceiling on afterglow luminosities and study the luminosity distribution at early times, which was not accessible before the advent of the Swift satellite. Most GRBs feature afterglows that are dominated by the forward shock from early times on. Finally, we present the first indications of a class of long GRBs, which form a bridge between the typical highluminosity, high-redshift events and nearby low-luminosity events (which are also associated with spectroscopic supernovae) in terms of energetics and observed redshift distribution, indicating a continuous distribution overall.

Optical and near-infrared flares in GRB afterglows

“…emission component (Roming et al 2006, Kann et al 2010. This fact provides observational support that the strength of the optical emission from the RS may be weaker than previously calculated, or that the RS is not radiated in the optical wavelength regime.…”

Exploring the canonical behaviour of long gamma-ray bursts using an intrinsic multiwavelength afterglow correlation

“…A restframe correlation proved inconclusive due to the small sample size. The cluster of luminosity light curves in Kann et al (2010), showed evidence for narrowing of the distribution with time, also suggesting a relationship between the brightness of the afterglow and the rate of decay. In Oates et al (2012), the UVOT sample was extended to 48 optical/UV GRB light curves.…”

“…Evidence for clustering into two groups, at ∼ 0.5 − 1 day, for the optical/IR GRB afterglows was reported by Boër & Gendre (2000); Gendre & Boër (2005); Nardini et al (2006); Liang & Zhang (2006); Nardini, Ghisellini & Ghirlanda (2008); . However, several more recently published works have suggested that the afterglow distributions are unimodal (Melandri et al 2008;Cenko et al 2009a;Oates et al 2009;Kann et al 2010;Melandri et al 2014). …”

The supernova–gamma-ray burst–jet connection

“…(a) Low-luminosity gamma-ray bursts Low-luminosity gamma-ray bursts (also termed 'sub-energetic' or 'nearby' bursts) seem to be about 100 times as common as the other class discussed below [14], but because of their low The afterglow is assumed to decay as t −1.5 ; the afterglow region reflects the range in afterglow brightness reported by Kann et al [19]. The range in host galaxy magnitudes reflect those detected in the TOUGH survey [20].…”