ABSTRACT
Multimessenger astronomy received a great boost following the discovery of kilonova (KN) AT2017gfo, the optical counterpart of the gravitational wave source GW170817 associated with the ...short gamma-ray burst GRB 170817A. AT2017gfo was the first KN that could be extensively monitored in time using both photometry and spectroscopy. Previously, only few candidates have been observed against the glare of short GRB afterglows. In this work, we aim to search the fingerprints of AT2017gfo-like KN emissions in the optical/NIR light curves of 39 short GRBs with known redshift. For the first time, our results allow us to study separately the range of luminosity of the blue and red components of AT2017gfo-like kilonovae in short GRBs. In particular, the red component is similar in luminosity to AT2017gfo, while the blue KN can be more than 10 times brighter. Finally, we exclude a KN as luminous as AT2017gfo in GRBs 050509B and 061201.
The fault-slip burst has the features of high frequency, considerable damage and complex mechanisms, because mining activities break the balance of energy in the system of the fault and rock stratum. ...This disruption of balance causes the sudden activation and slip of the fault with an enormous release of energy and abruptly destroys the excavation space. To identify the mechanical behavior and instability characteristics of the critical stage (meta-instability stage) before fault instability, 5 uniaxial static load experiments are conducted to investigate the count and energy characteristics of acoustic emission (AE), and 15 numerical models are carried out with PFC to analyze the distributional characteristics of the stress, displacement, fracture and force chain fields. The evolutional process of energies is monitored in the models. The results show that the AE signal is the most abundant in the meta-instability stage during the whole loading process, and that the AE count and energy account for 37.27% and 39.18%, respectively, of the whole process. The proportion of cracks matured in the meta-instability stage is negatively correlated with the inclination angle of the preexisting crack and positively correlated with the width of the preexisting crack and the speed of graded loading. The distribution of new cracks changes from the reverse airfoil to the airfoil with an increasing inclination angle of the precrack. During the failure process, energy is primarily released in the form of parallel bond strain energy. In the meta-instability stage, energy accounts for more than 49% of the whole process. The trends for the slip energy and dashpot energy are separated at the beginning of the meta-instability stage, which can be considered as a precursor of failure. The distribution of stress around the precrack is transmitted counterclockwise, forming a deformation pattern in which strain energy is released in the center. The research results provide theoretical support for the identification of the meta-instability stage of fault-slip bursts and are beneficial to research on the risk assessment of coal and rock dynamic disasters.
•The AE signal is released most abundantly in the meta-instability stage, which reflects the deformation synergy.•Precracks affect the stress and failure mode; the proportion of cracks in the meta-instability stage is the highest.•Energy is primarily released in the form of pbstrain energy, and the coal is mainly damaged in a shearing slip manner.•Stress transmits counterclockwise and evolves from low-level uniformity to local concentration.
Abstract
The neonatal brain is characterized by intermittent bursts of oscillatory activity interspersed by relative silence. Although well-characterized for many cortical areas, to what extent these ...propagate and interact with subcortical brain areas is largely unknown. Here, early network activity was recorded from the developing basal ganglia, including motor/somatosensory cortex, dorsal striatum, and intralaminar thalamus, during the first postnatal weeks in mice. An unsupervised detection and classification method revealed two main classes of bursting activity, namely spindle bursts and nested gamma spindle bursts, characterized by oscillatory activity at ~ 10 and ~ 30 Hz frequencies, respectively. These were reliably identified across all three brain regions and exhibited region-specific differences in their structural, spectral, and developmental characteristics. Bursts of the same type often co-occurred in different brain regions and coherence and cross-correlation analyses reveal dynamic developmental changes in their interactions. The strongest interactions were seen for cortex and striatum, from the first postnatal week onwards, and cortex appeared to drive burst events in subcortical regions. Together, these results provide the first detailed description of early network activity within the developing basal ganglia and suggest that cortex is one of the main drivers of activity in downstream nuclei during this postnatal period.
We present the first realistic 3D simulations of flame front instabilities during type I X-ray bursts. The unperturbed front is characterized by the balance between the pressure gradient and the ...Coriolis force of a spinning neutron star ( = 450 Hz in our case). This balance leads to a fast horizontal velocity field parallel to the flame front. This flow is strongly sheared in the vertical direction. When we perturb the front an instability quickly corrugates the front. We identify this instability as the baroclinic instability. Most importantly, the flame is not disrupted by the instability and there are two major consequences: the overall flame propagation speed is ∼10 times faster than in the unperturbed case and distinct flame vortices appear. The speedup is due to the corrugation of the front and the dynamics of the vortices. These vortices may also be linked to the oscillations observed in the light curves of the bursts.
We report on the unambiguous observation of the subcycle ionization bursts in sequential strong-field double ionization of H2 and their disentanglement in molecular frame photoelectron angular ...distributions. This observation was made possible by the use of few-cycle laser pulses with a known carrier-envelope phase, in combination with multiparticle coincidence momentum imaging. The approach demonstrated here will allow sampling of the intramolecular electron dynamics and the investigation of charge-state-specific Coulomb distortions on emitted electrons in polyatomic molecules.
A multi-decade theoretical effort has been devoted to finding an efficient mechanism to use the rotational and electrodynamical extractable energy of a Kerr-Newman black hole (BH), to power the most ...energetic astrophysical sources such as gamma-ray bursts (GRBs) and active galactic nuclei. We show an efficient general relativistic electrodynamical process which occurs in the “inner engine” of a binary driven hypernova. The inner engine is composed of a rotating Kerr BH of mass
M
and dimensionless spin parameter
α
, a magnetic field of strength
B
0
aligned and parallel to the rotation axis, and a very low-density ionized plasma. Here, we show that the gravitomagnetic interaction between the BH and the magnetic field induces an electric field that accelerates electrons and protons from the environment to ultrarelativistic energies emitting synchrotron radiation. We show that in GRB 190114C the BH of mass
M
= 4.4
M
⊙
,
α
= 0.4, and
B
0
≈ 4 × 10
10
G can lead to a high-energy (≳GeV) luminosity of 10
51
erg s
−1
. The inner engine parameters are determined by requiring (1) that the BH extractable energy explains the GeV and ultrahigh-energy emission energetics, (2) that the emitted photons are not subjected to magnetic-pair production, and (3) that the synchrotron radiation timescale agrees with the observed high-energy timescale. We find for GRB 190114C a clear jetted emission of GeV energies with a semi-aperture angle of approximately 60° with respect to the BH rotation axis.
There is no complete description of the emission physics during the prompt phase in gamma-ray bursts. Spectral analyses, however, indicate that many spectra are narrower than what is expected for ...nonthermal emission models. Here, we reanalyze the sample of 37 bursts in Yu et al. by fitting the narrowest time-resolved spectrum in each burst. We perform a model comparison between photospheric and synchrotron emission models based on Bayesian evidence. We compare the shapes of the narrowest expected spectra: emission from the photosphere in a non-dissipative flow and slow cooled synchrotron emission from a narrow electron distribution. We find that the photospheric spectral shape is preferred by 54% 8% of the spectra (20/37), while 38% 8% of the spectra (14/37) prefer the synchrotron spectral shape; three spectra are inconclusive. We hence conclude that GRB spectra are indeed very narrow and that more than half of the bursts have a photospheric emission episode. We also find that a third of all analyzed spectra, not only prefer, but are also compatible with a non-dissipative photosphere, confirming previous similar findings. Furthermore, we notice that the spectra that prefer the photospheric model all have low-energy power-law indices −0.5. This means that is a good estimator for which model is preferred by the data. Finally, we argue that the spectra that statistically prefer the synchrotron model could equally as well be caused by subphotospheric dissipation. If that is the case, photospheric emission during the early, prompt phase would be even more dominant.
Abstract
We show the peak magnitude for orphan afterglows from the jets of gravitational wave (GW) detected black hole/neutron star – neutron star (BH/NS–NS) mergers highly depend on the jet ...half-opening angle θj. Short γ-ray bursts (GRBs) with a homogeneous jet structure and θj > 10°, the orphan afterglow viewed at the typical inclination for a GW detected event, 38°, are brighter at optical frequencies than the comparable macronova emission. Structured jets, where the energetics and Lorentz factor Γ vary with angle from the central axis, may have low-Γ components where the prompt emission is suppressed; GW electromagnetic (EM) counterparts may reveal a population of failed-GRB orphan afterglows. Using a Monte Carlo method assuming an NS–NS detection limit we show the fraction of GW-EM counterparts from homogeneous, two-component, power-law structured and Gaussian jets where the variable structure models include a wide low energy and Γ component: for homogeneous jets, with a θj = 6° and typical short GRB parameters, we find r-band magnitude mr ≤ 21 counterparts for ∼13.6 per cent of GW detected mergers; where jet structure extends to a half-opening angle of 25°, two-component jets produce mr ≤ 21 counterparts in ∼30 per cent of GW detected mergers,
power-law structured-jets result in ∼37 per cent
and Gaussian jets with our parameters ∼13 per cent. We show the features in the light curves from orphan afterglows can be used to indicate the presence of extended structure.
The first binary neutron star merger, GW170817, was accompanied by a radioactivity-powered optical/infrared transient called a kilonova. To date, no compelling kilonova has been found in all-sky ...optical surveys, independently of short gamma-ray burst and gravitational-wave triggers. In this work, we searched the first 23 months of the Zwicky Transient Facility (ZTF) data stream for candidate kilonovae in the form of rapidly evolving transients. We combined ZTF alert queries with forced point-spread-function photometry and nightly flux stacking to increase our sensitivity to faint and fast transients. Automatic queries yielded >11,200 candidates, 24 of which passed quality checks and selection criteria based on a grid of kilonova models tailored for both binary neutron star and neutron star-black hole mergers. None of the candidates in our sample was deemed a possible kilonova after thorough vetting. The sources that passed our selection criteria are dominated by Galactic cataclysmic variables. We identified two fast transients at high Galactic latitude, one of which is the confirmed afterglow of long-duration GRB 190106A, the other is a possible cosmological afterglow. Using a survey simulation code, we constrained the kilonova rate for a range of models including top-hat, linearly decaying light curves, and synthetic light curves obtained with radiative transfer simulations. For prototypical GW170817-like kilonovae, we constrain the rate to be Gpc−3 yr−1 (95% confidence). By assuming a population of kilonovae with the same geometry and composition of GW170817 observed under a uniform viewing angle distribution, we obtained a constraint on the rate of R < 4029 Gpc−3 yr−1.
Long γ-ray bursts are associated with energetic, broad-lined, stripped-envelope supernovae
and as such mark the death of massive stars. The scarcity of such events nearby and the brightness of the ...γ-ray burst afterglow, which dominates the emission in the first few days after the burst, have so far prevented the study of the very early evolution of supernovae associated with γ-ray bursts
. In hydrogen-stripped supernovae that are not associated with γ-ray bursts, an excess of high-velocity (roughly 30,000 kilometres per second) material has been interpreted as a signature of a choked jet, which did not emerge from the progenitor star and instead deposited all of its energy in a thermal cocoon
. Here we report multi-epoch spectroscopic observations of the supernova SN 2017iuk, which is associated with the γ-ray burst GRB 171205A. Our spectra display features at extremely high expansion velocities (around 115,000 kilometres per second) within the first day after the burst
. Using spectral synthesis models developed for SN 2017iuk, we show that these features are characterized by chemical abundances that differ from those observed in the ejecta of SN 2017iuk at later times. We further show that the high-velocity features originate from the mildly relativistic hot cocoon that is generated by an ultra-relativistic jet within the γ-ray burst expanding and decelerating into the medium that surrounds the progenitor star
. This cocoon rapidly becomes transparent
and is outshone by the supernova emission, which starts to dominate the emission three days after the burst.
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