GRB 130427A: A Nearby Ordinary Monster

Abstract

2Long-duration Gamma-Ray Bursts (GRBs) are an extremely rare outcome of the collapse of massive stars, and are typically found in the distant Universe.Because of its intrinsic luminosity (L ∼ 3 × 10 53 erg s −1 ) and its relative proximity (z = 0.34), GRB 130427A was a unique event that reached the highest fluence observed in the γ-ray band. Here we present a comprehensive multiwavelength view of GRB 130427A with Swift, the 2-m Liverpool and Faulkes telescopes and by other ground-based facilities, highlighting the evolution of the burst emission from the prompt to the afterglow phase. The properties of GRB 130427A are similar to those of the most luminous, high-redshift GRBs,suggesting that a common central engine is responsible for producing GRBs in both the contemporary and the early Universe and over the full range of GRB isotropic energies.GRB 130427A was the brightest burst detected by Swift (1) as well as by several γ-ray detectors onboard other space missions. It was also the brightest and longest burst detected above 100 MeV, with the most energetic photon detected at 95 GeV (2). It was detected by Fermi-GBM (3) at T 0,GBM = 07:47:06.42 UT on April 27 2013. Hereafter this time will be our reference time T 0 . The Burst Alert Telescope (BAT, (4)) onboard Swift triggered on GRB 130427Aat t = 51.1 s, when Swift completed a pre-planned slew. The Swift slew to the source started at t = 148 s and ended at t = 192 s. The Swift UltraViolet Optical Telescope (UVOT, (5)) began observations at t = 181 s while observations by the Swift X-ray Telescope (XRT, (6)) started at t = 195 s (see (7) for more details). The structure of the γ-ray light curve revealed by the Swift-BAT in the 15-350 keV band ( Fig. 1) can be divided in three main episodes: an initial peak, beginning at t = 0.1 s and peaking at t = 0.5 s; a second large peak showing a complex 3 structure with a duration of ∼ 20 s and a third, much weaker episode, starting at t ∼120 s showing a fast rise/exponential decay behavior. The overall duration of the prompt emission was T 90(15−150 keV) = 276 ± 5 s (i.e. the time containing 90% of the fluence) calculated over the first 1830 s of BAT observation from T 0,GBM . During the early phases of the γ-ray emission strong spectral variability is observed (Fig. 1). A marked spectral hardening is observed during is (2.68 ± 0.01) × 10 −3 erg cm −2 , with a spectrum peaking at E peak = 1028 ± 8 keV, while the fluence of the emission episode at (120 -250 s) is ∼ 9 × 10 −5 erg cm −2 , with a spectrum peaking at ∼240 keV (9).This event was extremely bright also in the optical and it was immediately detected by various robotic telescopes: in particular, the Raptor robotic telescope detected a bright optical counterpart already at t = 0.5 s (10). Optical spectroscopy of the afterglow determined the redshift to be z = 0.34 (11); an UVOT UV grism spectrum (7) was also acquired. At this distance the rest frame 1 keV-10 MeV isotropic energy is E iso = 8.1 × 10 53 erg and the peak luminosity is L iso = 2.7 × 10 53 erg s −1 . Acc...

Temporal Evolution of the Gamma-ray Burst Afterglow Spectrum for an Observer: GeV–TeV Synchrotron Self-Compton Light Curve

“…The soft spectrum results in brighter optical flux than observed. Maselli et al (2014) claimed that the optical extinction is negligible from the SED analysis. The relatively dim optical fluxes and the steep X-ray decay seem difficult to explain simultaneously by a single source model with constant microscopic parameters.…”

“…GRB 130427A (Ackermann et al 2014;Maselli et al 2014) is a very nearby GRB (z = 0.34) with a very large isotropic energy release (8.5 × 10 53 erg; Perley et al 2014) in gamma-ray. Surprisingly, the X-ray afterglow flux is well fitted by a simple power-law of t −1.309 (hereafter we omit the subscript "obs") as far as 8 × 10 7 s without a signature of the jet break (De Pasquale et al 2016).…”

“…Especially for the early stage of the afterglow, complicated models including a reverse shock component with a stellar-wind profile (Laskar et al 2013;Perley et al 2014;Vestrand et al 2014), spine-sheathlike two-component jets (van der Horst et al 2014), temporally evolving microscopic parameters (η, ǫ e and ǫ B ; Maselli et al 2014), or a non-standard radial density profile (Kouveliotou et al 2013;van der Horst et al 2014) have been attempted. Nevertheless, we adopt our single-component model focusing on the GeV-TeV emission in the early phase; our numerical method is ideal to calculate the GeV-TeV light curve with SSC emission consistently as explained in the previous section.…”

“…The results of the two-dimensional hydrodynamical simulations by van Eerten et al (2012) with the analytical broken-power-law formula have been widely used to fit the observed light curves (see, e.g. Guidorzi et al 2014;Maselli et al 2014;Zhang et al 2015). Such multidimensional hydrodynamical simulations provide precise evolution of the shock propagation and angular structure of the collimated jet and are a powerful tool to constrain jet parameters, especially in the off-axis cases.…”

Challenging the Forward Shock Model with the 80 Ms Follow up of the X-ray Afterglow of Gamma-Ray Burst 130427A

“…A large corpus of literature has already been written on this GRB; some works deal with the prompt emission (e.g., [4,5]), others present a modeling of the X-ray, optical, and radio afterglow emission (e.g., [1,[6][7][8] K13, P14, L13, V14 and M14 henceforth). The studies on the afterglow, however, rely on data taken up to 100 days after the GRB trigger.…”