Late X-ray flares from the interaction of a reverse shock with a stratified ejecta in GRB afterglows: simulations on a moving mesh
arXiv:2004.04179 · doi:10.1093/mnras/staa1397
Abstract
Late activity of the central engine is often invoked in order to explain the flares observed in the early X-ray afterglow of gamma-ray bursts, either in the form of an active neutron star remnant or (fall-back) accretion onto a black hole. However, these scenarios are not always plausible, in particular when flares are delayed to very late times after the burst. Recently, a new scenario was proposed that suggests X-ray flares can be the result of the passing of a long-lived reverse shock through a stratified ejecta, with the advantage that it does not require late-time engine activity. In this work, we numerically demonstrate this scenario to be physically plausible, by performing onedimensional simulations of ejecta dynamics and emission using our novel moving-mesh relativistic hydrodynamics code. Improved efficiency and precision over previous work enables the exploration of a broader range of setups. We can introduce a more physically realistic description of the circumburst medium mass density. We can also locally trace the cooling of electrons when computing the broadband emission from these setups. We show that the synchrotron cooling timescale can dominate the flare decay time if the stratification in the ejecta is constrained to a localised angular region inside the jet, with size corresponding to the relativistic causal connection angle, and that it corresponds to values reported in observations. We demonstrate that this scenario can produce a large range of observed flare times, suggesting a connection between flares and initial ejection dynamics rather than with late-time remnant activity.
17 pages, 22 figures, accepted by MNRAS (18 May 2020)
References in corpus (22)
- Multi-messenger Observations of a Binary Neutron Star Merger
- An Ordinary Short Gamma-Ray Burst with Extraordinary Implications: Fermi-GBM Detection of GRB 170817A
- INTEGRAL Detection of the First Prompt Gamma-Ray Signal Coincident with the Gravitational Wave Event GW170817
- The X-ray counterpart to the gravitational wave event GW 170817
- Illuminating Gravitational Waves: A Concordant Picture of Photons from a Neutron Star Merger
- A Radio Counterpart to a Neutron Star Merger
- The First Survey of X-ray Flares from Gamma Ray Bursts Observed by Swift: Temporal Properties and Morphology
- The First Survey of X-ray Flares from Gamma Ray Bursts Observed by Swift: Spectral Properties and Energetics
- An HLLC Solver for Relativistic Flows -- II. Magnetohydrodynamics
- On the Mechanism of Gamma-Ray Burst Afterglows
- Off-axis short GRBs from structured jets as counterparts to GW events
- Can the early X-ray afterglow of GRBs be explained by a contribution from the reverse shock?
- Phase transitions and He-synthesis driven winds in neutrino cooled accretion disks: prospects for late flares in short gamma-ray bursts
- Gamma Ray Bursts Are Observed Off-Axis
- Deceleration of arbitrarily magnetized GRB ejecta: the complete evolution
- Smooth Light Curves from a Bumpy Ride: Relativistic Blast Wave Encounters a Density Jump
- Electrons' energy in GRB afterglows implied by radio peaks
- EM counterparts of recoiling black holes: general relativistic simulations of non-Keplerian discs
- On the existence of a reverse shock in magnetized GRB ejecta
- Gamma-ray burst afterglow plateau break time - luminosity correlations favour thick shell models over thin shell models
- No visible optical variability from a relativistic blast wave encountering a wind-termination shock
- Episodic jet power extracted from a spinning black hole surrounded by a neutrino-dominated accretion flow in gamma-ray bursts