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Register a new userIs GRB 110715A the progenitor of FRB 171209?
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Xiang-Gao Wang
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The physical origin of fast radio bursts (FRBs) is unknown. Young magnetars born from gamma-ray bursts (GRBs) have been suggested to be a possible central engine of FRBs. We test such a hypothesis by systematically searching for GRB-FRB spatial associations from 110 FRBs and 1440 GRBs. We find that one FRB event, FRB 171209, discovered by the Parkes telescope is spatially coincident with a historical long-duration GRB 110715A at $z=0.82$. The afterglow of GRB 110715A is consistent with being powered by a millisecond magnetar. The extragalactic dispersion measure of FRB 171209 is in excess of that contributed by the intergalactic medium, which can be interpreted as being contributed by a young supernova remnant associated with the GRB. Overall, the significance of the association is $(2.28 - 2.55) sigma$. If the association is indeed physical, our result suggests that the magnetars associated with long GRBs can be the progenitors of at least some FRBs.
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We present the extensive follow-up campaign on the afterglow of GRB 110715A at 17 different wavelengths, from X-ray to radio bands, starting 81 seconds after the burst and extending up to 74 days later. We performed for the first time a GRB afterglow observation with the ALMA observatory. We find that the afterglow of GRB 110715A is very bright at optical and radio wavelengths. We use optical and near infrared spectroscopy to provide further information about the progenitors environment and its host galaxy. The spectrum shows weak absorption features at a redshift z = 0.8225, which reveal a host galaxy environment with low ionization, column density and dynamical activity. Late deep imaging shows a very faint galaxy, consistent with the spectroscopic results. The broadband afterglow emission is modelled with synchrotron radiation using a numerical algorithm and we determine the best fit parameters using Bayesian inference in order to constrain the physical parameters of the jet and the medium in which the relativistic shock propagates. We fitted our data with a variety of models, including different density profiles and energy injections. Although the general behaviour can be roughly described by these models, none of them are able to fully explain all data points simultaneously. GRB 110715A shows the complexity of reproducing extensive multi-wavelength broadband afterglow observations, and the need of good sampling in wavelength and time and more complex models to accurately constrain the physics of GRB afterglows.
We search for host galaxy candidates of nearby fast radio bursts (FRBs), FRB 180729.J1316+55, FRB 171020, FRB 171213, FRB 180810.J1159+83, and FRB 180814.J0422+73 (the second repeating FRB). We compare the absolute magnitudes and the expected host dispersion measure $rm DM_{host}$ of these candidates with that of the first repeating FRB, FRB 121102, as well as those of long gamma ray bursts (LGRBs) and superluminous supernovae (SLSNe), the proposed progenitor systems of FRB 121102. We find that while the FRB 121102 host is consistent with those of LGRBs and SLSNe, the nearby FRB host candidates, at least for FRB 180729.J1316+55, FRB 171020, and FRB180814.J0422+73, either have a smaller $rm DM_{host}$ or are fainter than FRB121102 host, as well as the hosts of LGRBs and SLSNe. In order to avoid the uncertainty in estimating $rm DM_{host}$ due to the line-of-sight effect, we propose a galaxy-group-based method to estimate the electron density in the inter-galactic regions, and hence, $rm DM_{IGM}$. The result strengthens our conclusion. We conclude that the host galaxy of FRB 121102 is atypical, and LGRBs and SLSNe are likely not the progenitor systems of at least most nearby FRB sources. {The recently reported two FRB hosts differ from the host of FRB 121102 and also the host candidates suggested in this paper. This is consistent with the conclusion of our paper and suggests that the FRB hosts are very diverse. }
The curvature of a relativistic blast wave implies that its emission arrives to observers with a spread in time. This effect is believed to wash out fast variability in the lightcurves of GRB afterglows. We note that the spreading effect is reduced if emission is anisotropic in the rest-frame of the blast wave (i.e. if emission is limb-brightened or limb-darkened). In particular, synchrotron emission is almost certainly anisotropic, and may be strongly anisotropic, depending on details of electron acceleration in the blast wave. Anisotropic afterglows can display fast and strong variability at high frequencies (above the fast-cooling frequency). This may explain the existence of bizarre features in the X-ray afterglows of GRBs, such as sudden drops and flares. We also note that a moderate anisotropy can significantly delay the jet break in the lightcurve, which makes it harder to detect.
The jet compositions, central engines, and progenitors of gamma-ray bursts (GRBs) remain open questions in GRB physics. Applying broadband observations, including GRB prompt emission and afterglow properties derived from {em Fermi} and {em Swift} data, as well as from Keck host-galaxy observations, we address these questions for the peculiar, bright GRB 110731A. By using the pair-opacity method, we derive $Gamma_{0}>190$ during the prompt emission phase. Alternatively, we derive $Gamma_{0} approx 580$ and $Gamma_{0} approx 154$ by invoking the early-afterglow phase within the homogeneous density and wind cases, respectively. On the other hand, nondetection of a thermal component in the spectra suggests that the prompt emission is likely powered by dissipation of a Poynting-flux-dominated jet leading to synchrotron radiation in an optically thin region. The nondetection of a jet break in the X-ray and optical bands allows us to place a lower limit on the jet opening angle $theta_{rm j}>5.5^{circ}$. Within a millisecond magnetar central engine scenario, we derive the period $P_{0}$ and polar magnetic field strength $B_{rm p}$, which have extreme (but still allowed) values. The moderately short observed duration (7.3,s) and relatively large redshift ($z=2.83$) places the burst as a rest-frame short GRB, so the progenitor of the burst is subject to debate. Its relatively large $f_{{rm eff}, z}$ parameter (ratio of the 1,s peak flux of a pseudo-GRB and the background flux) and a large physical offset from a potential host galaxy suggest that the progenitor of GRB 110731A may be a compact-star merger.
We present the results of a multiwavelength campaign of FRB20201124A, the second closest repeating fast radio burst recently localized in a nearby (z=0.0978) galaxy. Deep VLA observations led to the detection of a quiescent radio emission, also marginally visible in X-rays with Chandra. Imaging at 22 GHz allowed us to resolve the source on a scale of $gtrsim 1$ arcsec in a direction tangential to the center of the host galaxy and locate it at the position of the FRB, within an error of $0.2$ arcsec. EVN and e-MERLIN observations sampled small angular scales, from 2 to 100 mas, providing tight upper limits on the presence of a compact source and evidence for diffuse radio emission. We argue that this emission is associated with enhanced star formation activity in the proximity of the FRB, corresponding to a star formation rate of $approx 10 {rm M}_odot {rm yr}^{-1}$. The surface star formation rate at the location of FRB20201124A is two orders of magnitude larger than typically observed in other precisely localized FRBs. Such a high SFR is indicative of this FRB source being a new-born magnetar produced from a SN explosion of a massive star progenitor. Upper limits to the X-ray counterparts of 49 radio bursts observed in our simultaneous FAST, SRT and Chandra campaign are consistent with a magnetar scenario.
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