Abstract
The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope (Fermi) shows long-lasting high-energy emission in many gamma-ray bursts (GRBs), similar to X-ray afterglows ...observed by the Neil Gehrels Swift Observatory (Swift). Some LAT light curves (LCs) show a late-time flattening reminiscent of X-ray plateaus. We explore the presence of plateaus in LAT temporally extended emission analyzing GRBs from the second Fermi-LAT GRB Catalog from 2008 to 2016 May with known redshifts, and check whether they follow closure relations corresponding to four distinct astrophysical environments predicted by the external forward shock model. We find that three LCs can be fit by the same phenomenological model used to fit X-ray plateaus and show tentative evidence for the existence of plateaus in their high-energy extended emission. The most favorable scenario is a slow-cooling regime, whereas the preferred density profile for each GRBs varies from a constant-density interstellar medium to an
r
−2
wind environment. We also compare the end time of the plateaus in
γ
-rays and X-rays using a statistical comparison with 222 Swift GRBs with plateaus and known redshifts from 2005 January to 2019 August. Within this comparison, the case of GRB 090510 shows an indication of chromaticity at the end time of the plateau. Finally, we update the 3D fundamental plane relation among the rest-frame end time of the plateau, its correspondent luminosity, and the peak prompt luminosity for 222 GRBs observed by Swift. We find that these three LAT GRBs follow this relation.
We report on simultaneous radio and X-ray observations of the repeating fast radio burst source FRB 180916.J0158+65 using the Canadian Hydrogen Intensity Mapping Experiment (CHIME), Effelsberg, and ...Deep Space Network (DSS-14 and DSS-63) radio telescopes and the Chandra X-ray Observatory. During 33 ks of Chandra observations, we detect no radio bursts in overlapping Effelsberg or Deep Space Network observations and a single burst during CHIME/FRB source transits. We detect no X-ray events in excess of the background during the Chandra observations. These non-detections imply a 5 limit of <5 × 10−10 erg cm−2 for the 0.5-10 keV fluence of prompt emission at the time of the radio burst and 1.3 × 10−9 erg cm−2 at any time during the Chandra observations. Given the host-galaxy redshift of FRB 180916.J0158+65 (z ∼ 0.034), these correspond to energy limits of <1.6 × 1045 erg and <4 × 1045 erg, respectively. We also place a 5 limit of <8 × 10−15 erg s−1 cm−2 on the 0.5-10 keV absorbed flux of a persistent source at the location of FRB 180916.J0158+65. This corresponds to a luminosity limit of <2 × 1040 erg s−1. Using an archival set of radio bursts from FRB 180916.J0158+65, we search for prompt gamma-ray emission in Fermi/GBM data but find no significant gamma-ray bursts, thereby placing a limit of 9 × 10−9 erg cm−2 on the 10-100 keV fluence. We also search Fermi/LAT data for periodic modulation of the gamma-ray brightness at the 16.35 days period of radio burst activity and detect no significant modulation. We compare these deep limits to the predictions of various fast radio burst models, but conclude that similar X-ray constraints on a closer fast radio burst source would be needed to strongly constrain theory.
Coal bursts have emerged as the most critical mining hazard for underground coal mines around the world. Seismic monitoring and seismic clustering analysis are the cornerstones to develop an ...understanding of and to quantify coal burst hazards. The prerequisite to successfully detect seismic clustering behaviours is the accuracy of locating seismic events, which however can be a challenging task in underground coal mines. Therefore, the characteristics of location errors of seismic events and their impact on clustering results should be explicitly investigated and considered in seismic cluster analysis. Based on nine months of seismic data and 24 coal bursts from a longwall panel, this paper considers location errors and proposes a modified seismic clustering method to improve the results available for coal burst hazard assessment. The location errors in the area of interest were firstly assessed using the emulation testing method. Within the determined location errors, the clustering possibility between seismic events was calculated. The characteristics of the possible seismic clustering along with mining, named as “the Number of Possible Clustered Events” (NPCE), were investigated. The results showed that location errors presented large variations and strong anisotropic patterns in the longwall panel, with values ranging from 20 to more than 80 m. The NPCE result presented an improved detection on seismic clustering behaviour, and the high NPCE values also indicated a strong correlation with coal burst damages observed at the mine. Several intensive seismic clustering zones were observed in more than two months prior to the longwall passing these locations, which suggest that the method can be used for the medium to long term seismic hazard assessment.
We consider radio bursts that originate from extragalactic neutron stars (NSs) by addressing three questions about source distances. What are the physical limitations on coherent radiation at GHz ...frequencies? Do they permit detection at cosmological distances? How many bursts per NS are needed to produce the inferred burst rate ∼103–104sky−1 d−1? The burst rate is comparable to the NS formation rate in a Hubble volume, requiring only one per NS if they are bright enough. Radiation physics suggests a closer population, requiring more bursts per NS and increasing the chances for repeats. Bursts comprise sub-ns, coherent shot pulses superposed incoherently to produce ms-duration ∼1 Jy amplitudes; each shot pulse can be much weaker than 1 Jy, placing less restrictive requirements on the emission process. None the less, single shot pulses are similar to the extreme, unresolved (<0.4 ns) MJy shot pulse seen from the Crab pulsar, consistent with coherent curvature radiation emitted near the light cylinder by an almost neutral clump with net charge ∼± 1021
e and total energy ≳ 1023 erg. Bursts from Gpc distances require incoherent superposition of
${\sim } 10^{12}d_{\rm Gpc}^2$
shot pulses or a total energy
${\gtrsim } 10^{35} d_{\rm Gpc}^2$
erg. The energy reservoir near the light cylinder limits the detection distance to ≲ few × 100 Mpc for a fluence ∼1 Jy ms unless conditions are more extreme than for the Crab pulsar, such as in magnetars. We discuss contributions to dispersion measures from galaxy clusters and we propose tests for the overall picture presented.
We present optical and near-infrared photometry of GRB 140606B (z = 0.384), and optical photometry and spectroscopy of its associated supernova (SN). The results of our modelling indicate that the ...bolometric properties of the SN (M
Ni = 0.4 ± 0.2 M⊙, M
ej = 5 ± 2 M⊙, and E
K = 2 ± 1 × 1052 erg) are fully consistent with the statistical averages determined for other γ-ray burst (GRB)-SNe. However, in terms of its γ-ray emission, GRB 140606B is an outlier of the Amati relation, and occupies the same region as low luminosity (ll) and short GRBs. The γ-ray emission in llGRBs is thought to arise in some or all events from a shock breakout (SBO), rather than from a jet. The measured peak photon energy (E
p ≈ 800 keV) is close to that expected for γ-rays created by an SBO (≳ 1 MeV). Moreover, based on its position in the M
V, p-Liso, γ plane and the E
K–Γβ plane, GRB 140606B has properties similar to both SBO-GRBs and jetted-GRBs. Additionally, we searched for correlations between the isotropic γ-ray emission and the bolometric properties of a sample of GRB-SNe, finding that no statistically significant correlation is present. The average kinetic energy of the sample is
$\bar{E}_{\rm K} = 2.1\times 10^{52}$
erg. All of the GRB-SNe in our sample, with the exception of SN 2006aj, are within this range, which has implications for the total energy budget available to power both the relativistic and non-relativistic components in a GRB-SN event.
Fast radio bursts (FRBs) are bright, millisecond-duration radio transients originating from sources at extragalactic distances
, the origin of which is unknown. Some FRB sources emit repeat bursts, ...ruling out cataclysmic origins for those events
. Despite searches for periodicity in repeat burst arrival times on timescales from milliseconds to many days
, these bursts have hitherto been observed to appear sporadically and-although clustered
-without a regular pattern. Here we report observations of a 16.35 ± 0.15 day periodicity (or possibly a higher-frequency alias of that periodicity) from the repeating FRB 180916.J0158+65 detected by the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst Project
. In 38 bursts recorded from 16 September 2018 to 4 February 2020 UTC, we find that all bursts arrive in a five-day phase window, and 50 per cent of the bursts arrive in a 0.6-day phase window. Our results suggest a mechanism for periodic modulation either of the burst emission itself or through external amplification or absorption, and disfavour models invoking purely sporadic processes.
We present coronal density profiles derived from low-frequency (80 – 240 MHz) imaging of three Type III solar radio bursts observed at the limb by the
Murchison Widefield Array
(MWA). Each event is ...associated with a white-light streamer at larger heights and is plausibly associated with thin extreme-ultraviolet rays at lower heights. Assuming harmonic plasma emission, we find average electron densities of 1.8
×
10
8
cm
−3
down to 0.20
×
10
8
cm
−3
at heights of 1.3 to 1.9 R
⊙
. These values represent approximately 2.4 – 5.4× enhancements over canonical background levels and are comparable to the highest streamer densities obtained from data at other wavelengths. Assuming fundamental emission instead would increase the densities by a factor of four. High densities inferred from Type III source heights can be explained by assuming that the exciting electron beams travel along overdense fibers or by radio propagation effects that may cause a source to appear at a larger height than the true emission site. We review the arguments for both scenarios in light of recent results. We compare the extent of the quiescent corona to model predictions to estimate the impact of propagation effects, which we conclude can only partially explain the apparent density enhancements. Finally, we use the time- and frequency-varying source positions to estimate electron beam speeds of between 0.24 and 0.60 c.
We present the results of a multiwavelength campaign targeting FRB 20201124A, the third closest repeating fast radio burst (FRB), which was recently localized in a nearby (
z
= 0.0978) galaxy. Deep ...VLA observations led to the detection of quiescent radio emission, which was also marginally visible in X-rays with
Chandra
. Imaging at 22 GHz allowed us to resolve the source on a scale of ≳1″ and locate it at the position of the FRB, within an error of 0.2″. The 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 (SFR) of ≈10
M
⊙
yr
−1
. The surface SFR at the location of FRB 20201124A is two orders of magnitude larger than what is typically observed in other precisely localized FRBs. Such a high SFR is indicative of this FRB source being a newborn magnetar produced from a supernova 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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