Properties Of Bursts Research Articles

A Thorough Search for Short-timescale Periodicity in Four Active Repeating Fast Radio Bursts

Fast radio bursts (FRBs) are bright radio transients with millisecond durations, which typically occur at extragalactic distances. The association of FRB 20200428 with the Galactic magnetar SGR J1935+2154 strongly indicates that they could originate from neutron stars, which naturally leads to the expectation that periodicity connected with the spinning of magnetars should exist in the activities of repeating FRBs. However, previous studies have failed to find any signatures supporting such a conjecture. Here we perform a thorough search for short-timescale periodicity in the four most active repeating sources, i.e., FRBs 20121102A, 20200120E, 20201124A, and 20220912A. Three different methods are employed, including a phase folding algorithm, the H-test, and Lomb–Scargle periodograms. For the three most active repeaters from which more than 1000 bursts have been detected, i.e., FRBs 20121102A, 20201124A, and 20220912A, more in-depth period searches are conducted by considering various burst properties such as the pulse width, peak flux, fluence, and the brightness temperature. No clear periodicity is found in a period range of 0.001–1000 s in all efforts. Implications of such a null result on the theoretical models of FRBs are discussed.

Gene therapy for targeting a prenatally enriched potassium channel associated with severe childhood epilepsy and premature death.

Dysfunction of the sodium-activated potassium channel KNa1.1 (encoded by KCNT1) is associated with a severe condition characterized by frequent seizures (up to hundreds per day) and is often fatal by age three years. We defined the early developmental onset of KNa1.1 channels in prenatal and neonatal brain tissue, establishing a timeline for pathophysiology and a window for therapeutic intervention. Using patch-clamp electrophysiology, we observed age-dependent increases in KNa1.1 K+ conductance. In neurons derived from a child with a gain-of-function KCNT1 pathogenic variant (p.R474H), we detected abnormal excitability and action potential afterhyperpolarization kinetics. In a clinical trial, two individuals with the p.R474H variant showed dramatic reductions in seizure occurrence and severity with a first-in-human antisense oligonucleotide (ASO) RNA therapy. ASO-treated p.R474H neurons in vitro exhibited normalized spiking and burst properties. Finally, we demonstrated the feasibility of ASO knockdown of KNa1.1 in mid-gestation human neurons, suggesting potential for early therapeutic intervention before the onset of epileptic encephalopathy.

Modelling of long gamma-ray burst host galaxies at cosmic noon from damped Lyman-α absorption statistics

ABSTRACT We study the properties of long gamma-ray burst (GRB) host galaxies using a statistical modelling framework derived to model damped Lyman-$\alpha$ absorbers (DLAs) in quasar spectra at high redshift. The distribution of $N_{\rm H\, {\small I}}$ for GRB-DLAs is $\sim$10 times higher than what is found for quasar-DLAs at similar impact parameters. We interpret this as a temporal selection effect due to the short-lived GRB progenitor probing its host at the onset of a starburst where the interstellar medium may exhibit multiple overdense regions. Owing to the larger $N_{\rm H\, {\small I}}$, the dust extinction is larger with 29 per cent of GRB-DLAs exhibiting $A(V)\gt 1$ mag in agreement with the fraction of ‘dark bursts’. Despite the differences in $N_{\rm H\, {\small I}}$ distributions, we find that high-redshift $2 \lt z \lt 3$ quasar- and GRB-DLAs trace the luminosity function of star-forming host galaxies in the same way. We propose that their differences may arise from the fact that the galaxies are sampled at different times in their star formation histories, and that the absorption sightlines probe the galaxy haloes differently. Quasar-DLAs sample the full H i cross-section, whereas GRB-DLAs sample only regions hosting cold neutral medium. Previous studies have found that GRBs avoid high-metallicity galaxies ($\sim$0.5 $Z_{\odot }$). Since at these redshifts galaxies on average have lower metallicities, our sample is only weakly sensitive to such a threshold. Lastly, we find that the modest detection rate of cold gas (H$_2$ or C i) in GRB spectra can be explained mainly by a low volume filling factor of cold gas clouds and to a lesser degree by destruction from the GRB explosion itself.

Host Galaxy Properties of Gamma-Ray Bursts Involving Neutron Star Binary Mergers and Their Impact on Kilonovae Rates

In the upcoming gravitational-wave (GW) observing runs, identifying host galaxies is crucial as it provides essential redshift information and enables the use of GW events as standard sirens. However, pinpointing host galaxies remains challenging due to the large localization uncertainties and the rapidly fading nature of their optical counterparts. Analyzing the host galaxies of short gamma-ray bursts (sGRBs) offers an alternative approach to deepen our understanding of the environments where binary neutron stars (BNS) primarily merge. This study compiles archival photometric data for the host galaxies of 76 sGRBs and four hybrid GRBs that are long GRBs accompanied by kilonova-like signals. We use this data to evaluate their physical properties through spectral energy distribution fitting. To assess the characteristics of the host galaxies, we utilized a volume-limited sample (z < 0.5) from the COSMOS field as a control group. Contrary to expectations that the BNS merger rate is proportional to host stellar mass, the short and hybrid GRB population appears less massive than the mass-weighted distribution of the control sample. Instead, we propose a formulation for the expected BNS merger rate from a galaxy as log(nBNSGyr-1)=0.86×log(M*/M⊙) + 0.44×log(sSFRyr-1)+0.857 , which optimally explains the deviation between the stellar mass distributions of the GRB host galaxies and the control sample. These insights provide a strategic framework for targeted GW follow-ups and enhance our ability to identify potential host galaxies for future GW events.

A Localization Method of High Energy Transients for All-sky Gamma-ray Monitor

Fast and reliable localization of high-energy transients is crucial for characterizing the burst properties and guiding the follow-up observations. Localization based on the relative counts of different detectors has been widely used for all-sky gamma-ray monitors. There are two major methods for this count distribution localization: χ 2 minimization method and the Bayesian method. Here we propose a modified Bayesian method that could take advantage of both the accuracy of the Bayesian method and the simplicity of the χ 2 method. With comprehensive simulations, we find that our Bayesian method with Poisson likelihood is generally more applicable for various bursts than the χ 2 method, especially for weak bursts. We further proposed a location-spectrum iteration approach based on the Bayesian inference, which could alleviate the problems caused by the spectral difference between the burst and location templates. Our method is very suitable for scenarios with limited computation resources or time-sensitive applications, such as in-flight localization software, and low-latency localization for rapidly follow-up observations.

Rotation of Polarization Angle in Gamma-Ray Burst Prompt Phase. II. The Influence of the Parameters

In addition to the light curve and energy spectrum, polarization is also important for inferring the physical properties of the gamma-ray burst (GRB). Rotation of the polarization angle (PA) with time will cause depolarization of the time-integrated polarization degree. However, it has rarely been studied before. Here, we use a magnetic reconnection model with a large-scale ordered aligned magnetic field in the emitting region to study the influence of the parameters on the PA rotations in the GRB prompt phase. We find that the half-opening angle of the jet θ j , the observational angle θ V , and the bulk Lorentz factor Γ all have significant impacts on the PA rotations. The PA rotations are affected by the product value of θ j Γ0 (Γ0 is the normalization factor of Γ with Γ(r)=Γ0(r/r0)s ), but are roughly independent of the concrete values of both θ j and Γ0. For the typical parameters, the changes of the PA within T 90 (△PA) would be within (12°, 66°) for slight off-axis observations, where T 90 is the duration of the burst with the accumulated flux density ranging from 5% to 95%. The q range for △PA > 10° becomes smaller with the increase of the product value of θ j Γ0. The most significant PA rotation with △PA ∼ 90° will happen when θ j Γ0 > 50 and 1.0 < q ≤ 1.2.

Coherent Inverse Compton Scattering in Fast Radio Bursts Revisited

Growing observations of temporal, spectral, and polarization properties of fast radio bursts (FRBs) indicate that the radio emission of the majority of bursts is likely produced inside the magnetosphere of its central engine, likely a magnetar. We revisit the idea that FRBs are generated via coherent inverse Compton scattering (ICS) off low-frequency X-mode electromagnetic waves (fast magnetosonic waves) by bunches at a distance of a few hundred times the magnetar radius. The following findings are revealed: (1) Crustal oscillations during a flaring event would excite kHz Alfvén waves. Fast magnetosonic waves with essentially the same frequency can be generated directly or be converted from Alfvén waves at a large radius, with an amplitude large enough to power FRBs via the ICS process. (2) The cross section increases rapidly with radius and significant ICS can occur at r ≳ 100R ⋆ with emission power much greater than the curvature radiation power but still in the linear scattering regime. (3) The low-frequency fast magnetosonic waves naturally redistribute a fluctuating relativistic plasma in the charge-depleted region to form bunches with the right size to power FRBs. (4) The required bunch net charge density can be sub-Goldreich–Julian, which allows a strong parallel electric field to accelerate the charges, maintain the bunches, and continuously power FRB emission. (5) This model can account for a wide range of observed properties of repeating FRB bursts, including high degrees of linear and circular polarization and narrow spectra as observed in many bursts from repeating FRB sources.

Burst-recurrence properties revealed with Insight-HXMT and NICER for the newly discovered accreting millisecond pulsar MAXI J1816--195

We report the results of our analysis of 83 type-I bursts during the 2022 outburst of the newly discovered accreting millisecond pulsar MAXI J1816--195 based on Insight-HXMT and NICER observations. We focus on the burst-recurrence time and its correlation with persistent flux and outburst evolution. The extensive observations of Insight-HXMT and NICER confirm the presence of quasi-periodic thermonuclear bursts during this outburst, with a recurrence time in the range of 1.15 to 2 hours, which varies with the source persistent flux. The burst recurrence times are, in general, longer at comparable flux levels in the outburst rising phase than those in the fading phase, forming an apparent hysteresis phenomenon. These burst properties make MAXI J1816--195 a unique target for investigating the underlying burst-accretion mechanisms. We discuss the plausible explanations for the hysteresis phenomenon, which appears to be related to changes in the ignition condition or accretion geometry during the outburst.

A Study of the Spectral Properties of Gamma-Ray Bursts with the Precursors and Main Bursts

There is no consensus yet on whether the precursor and the main burst of gamma-ray bursts (GRBs) have the same origin, and their jet composition is still unclear. In order to further investigate this issue, we systematically search 21 Fermi GRBs with both a precursor and main burst for spectral analysis. We first perform Bayesian time-resolved spectral analysis and find that almost all the precursors and the main bursts (94.4%) exhibit thermal components and that the vast majority of them have a low-energy spectral index (α; 72.2%) that exceeds the limit of synchrotron radiation. We then analyze the evolution and correlation of the spectral parameters and find that approximately half of the α (50%) of the precursors and the main bursts evolve in a similar pattern, while peak energy (E p ; 55.6%) behaves similarly, and their evolution is mainly characterized by flux tracking; for the α−F (the flux) relation, more than half of the precursors and the main bursts (61.1%) exhibit roughly similar patterns; the E p −F relation in both the precursor and main burst (100%) exhibits a positive correlation of at least moderate strength. Next, we constrain the outflow properties of the precursors and the main bursts and find that most of them exhibit typical properties of photosphere radiation. Finally, we compare the time-integrated spectra of the precursors and the main bursts and find that nearly all of them are located in similar regions of the Amati relation and follow the Yonetoku relation. Therefore, we conclude that main bursts are continuations of precursors and may share a common physical origin.

Fermi GBM Observations of the Galactic Magnetar SGR 1935+2154 during Its 2022 January Activity

The X-ray and radio burst-emitting soft gamma-ray repeater SGR 1935+2154 has been the most active magnetar during the past decade, with at least one active episode each year since 2019. We report on the 2022 January activity as observed by the Fermi Gamma-Ray Burst Monitor and present the temporal and time-integrated spectral properties of the observed 112 X-ray bursts. No radio bursts were reported during the activity. The mean burst duration is comparable to most of the previous activities but is shorter than that of 2020, during which the magnetar emitted radio bursts. The mean burst spectrum is softer than the earlier activities and a long-term softening trend since 2016 is evident and is accompanied by a rise in the mean burst fluence and blackbody emission radii. The power-law indices of the RBB2−kTBB correlation also show an evolution during 2019–2022, where the soft component started becoming steeper, whereas the hard component shows a less steep trend. The burst properties show no significant evolution within the activity, which lasted for ∼ 45 days, and none of the observed bursts showed properties reminiscent of those of the hard, long X-ray counterpart to the 2020 fast radio burst FRB 200428 from the source. We discuss the results comparatively with the 8 yr history of the source since its discovery in 2014.

A Comparative Analysis of Two Peculiar Gamma-Ray Bursts: GRB 230307A and GRB 211211A

GRB 211211A is a peculiar long gamma-ray burst (GRB) with very high brightness and short burst properties. Its full light curve consists of three emission episodes, i.e., a precursor, a main burst, and an extended emission. We find that a recently detected long-duration GRB 230307A also includes the three consistent emission episodes. Furthermore, the two bursts have similar redshifts, 0.076 and 0.065, respectively. We perform a detailed temporal and spectral analysis of the two GRBs to compare their temporal and spectral properties. Our analysis shows that the two bursts share great similarities for both the whole emission and the three corresponding emission phases, which are listed as follows: (1) they have near zero spectral lag; (2) they have very short minimum variability timescale (MVT); (3) they lie in the same region of in the MVT–T 90, Amati relation and hardness–T 90 planes; (4) the three phases are quasi-thermal spectra; (5) both the peak energy and the low-energy index track the flux; (6) the time-resolved spectra are much wider than those of the blackbody predicted by the model; (7) there are strong correlations between thermal flux and total flux and the correlation coefficients, and the slopes for the corresponding stages are very consistent; and (8) the photosphere emission properties are very consistent. Other investigations and observations suggest that the two GRBs indeed belong to a short burst with a compact star merger origin. Therefore, we think that GRB 230307A and GRB 211211A are rare and similar GRBs, and the photospheric radiation can interpret their radiation mechanisms.

A Comparative Analysis of Scale-invariant Phenomena in Repeating Fast Radio Bursts and Glitching Pulsars

The recent discoveries of a remarkable glitch/antiglitch accompanied by fast radio burst (FRB)-like bursts from the Galactic magnetar SGR J1935+2154 have revealed the physical connection between the two. In this work, we study the statistical properties of radio bursts from the hyperactive repeating source FRB 20201124A and of glitches from the pulsar PSR B1737–30. For FRB 20201124A, we confirm that the probability density functions of fluctuations of energy, peak flux, duration, and waiting time well follow the Tsallis q-Gaussian distribution. The derived q values from q-Gaussian distribution keep approximately steady for different temporal interval scales, which indicates that there is a common scale-invariant structure in repeating FRBs. Similar scale-invariant properties can be found in PSR B1737–30's glitches, implying an underlying association between the origins of repeating FRBs and pulsar glitches. These statistical features can be well understood within the same physical framework of self-organized criticality systems.

Plasma Motions and Compressive Wave Energetics in the Solar Corona and Solar Wind from Radio Wave Scattering Observations

Radio signals propagating via the solar corona and solar wind are significantly affected by compressive waves, impacting the properties of solar bursts as well as sources viewed through the turbulent solar atmosphere. While static fluctuations scatter radio waves elastically, moving, turbulent, or oscillating density irregularities act to broaden the frequency of the scattered waves. Using a new anisotropic density fluctuation model from the kinetic scattering theory for solar radio bursts, we deduce the plasma velocities required to explain observations of spacecraft signal frequency broadening. The inferred velocities are consistent with motions that are dominated by the solar wind at distances ≳10 R ⊙, but the levels of frequency broadening for ≲10 R ⊙ require additional radial speeds ∼(100–300) km s−1 and/or transverse speeds ∼(20–70) km s−1. The inferred radial velocities also appear consistent with the sound or proton thermal speeds, while the speeds perpendicular to the radial direction are consistent with nonthermal motions measured via coronal Doppler-line broadening, interpreted as Alfvénic fluctuations. Landau damping of parallel propagating ion-sound (slow MHD) waves allows an estimate of the proton heating rate. The energy deposition rates due to ion-sound wave damping peak at a heliocentric distance of ∼(1–3) R ⊙ are comparable to the rates available from a turbulent cascade of Alfvénic waves at large scales, suggesting a coherent picture of energy transfer, via the cascade or/and parametric decay of Alfvén waves to the small scales where heating takes place.

Properties of Type-II Radio Bursts in Relation to Magnetic Complexity of the Solar Active Regions

Properties of Type-II Radio Bursts in Relation to Magnetic Complexity of the Solar Active Regions

198 Human Focal Seizures Induce Wavelike States in Bursts of Neuronal Activity

INTRODUCTION: Recent advances in high-density microelectrode arrays (MEAs) have allowed clinicians to record from individual neurons (single-unit activity) or from ensembles of neurons (multi-unit activity, MUA) in the human brain. These recordings have yielded fundamental advances both in epilepsy and in normal brain function. However, the properties of bursts of neuronal activity during seizures have not been characterized. METHODS: Five patients at our institution were implanted with microelectrode arrays and met inclusion criteria. Bursts were captured using custom code (MATLAB). We used statistical techniques to compute the rate similarity or sequence similarity between any two sequences. RESULTS: We found strong internal consistency within groups of pathological discharges -- that is, IED and seizure related bursts -- for both rate and sequence similarity. We found that baseline, IED, and seizure-related bursts all reside in particular subspaces, after dimensionality reduction using UMAP. During seizures, the LFP exhibits strong wavelike properties. Interestingly, the MUA direction echoes that of the LFP in this patient. However, MUA discharges are only partially wavelike. In IEDs, while the LFP is quite wavelike, the MUA does not exhibit wavelike properties. We found that LFP wave directions, for both seizures and IEDs, tend to arise from the seizure source, as determined using the ECoG. The relationship between the ECoG source and the MUA wave direction is less consistent. Seizure sequences start near the baseline subspace. Over time, seizure bursts are recruited to a distinct subspace, at which time they develop wavelike properties. CONCLUSIONS: Seizure events induce wavelike states in neuronal bursts. These findings may help explain why seizures alter cognition.

Concise Spectrotemporal Studies of Magnetar SGR J1935+2154 Bursts

SGR J1935+2154 has truly been the most prolific magnetar over the last decade: it has been entering into burst active episodes once every 1–2 yr since its discovery in 2014, it emitted the first Galactic fast radio burst associated with an X-ray burst in 2020, and it has emitted hundreds of energetic short bursts. Here, we present the time-resolved spectral analysis of 51 bright bursts from SGR J1935+2154. Unlike conventional time-resolved X-ray spectroscopic studies in the literature, we follow a two-step approach to probe true spectral evolution. For each burst, we first extract spectral information from overlapping time segments, fit them with three continuum models, and employ a machine-learning-based clustering algorithm to identify time segments that provide the largest spectral variations during each burst. We then extract spectra from those nonoverlapping (clustered) time segments and fit them again with the three models: the cutoff power-law model, the sum of two blackbody functions, and the model considering the emission of a modified blackbody undergoing resonant cyclotron scattering, which is applied systematically at this scale for the first time. Our novel technique allowed us to establish the genuine spectral evolution of magnetar bursts. We discuss the implications of our results and compare their collective behavior with the average burst properties of other magnetars.

Time-resolved Spectral Properties of Fermi-GBM Bright Long Gamma-Ray Bursts

The prompt emission mechanism of gamma-ray bursts (GRBs) is still unclear, and the time-resolved spectral analysis of GRBs is a powerful tool for studying their underlying physical processes. We performed a detailed time-resolved spectral analysis of 78 bright long GRB samples detected by Fermi/Gamma-ray Burst Monitor. A total of 1490 spectra were obtained and their properties were studied using a typical Band-shape model. First, the parameter distributions of the time-resolved spectrum are given as follows: the low-energy spectral index α ∼ − 0.72, high-energy spectral index β ∼ − 2.42, the peak energy E p ∼ 221.69 keV, and the energy flux F ∼ 7.49 × 10−6 erg cm−2 s−1. More than 80% of the bursts exhibit the hardest low-energy spectral index αmax exceeding the synchrotron limit (−2/3). Second, the evolution patterns of α and E p were statistically analyzed. The results show that for multi-pulse GRBs the intensity-tracking pattern is more common than the hard-to-soft pattern in the evolution of both E p and α. The hard-to-soft pattern is generally shown in single-pulse GRBs or in the initial pulse of multi-pulse GRBs. Finally, we found a significant positive correlation between F and E p, with half of the samples exhibiting a positive correlation between F and α. We discussed the spectral evolution of different radiation models. The diversity of spectral evolution patterns indicates that there may be more than one radiation mechanism occurring in the GRB radiation process, including photospheric radiation and synchrotron radiation. However, it may also involve only one radiation mechanism, but more complicated physical details need to be considered.

Comparative Analysis of Type III Radio Bursts and Solar Flares: Spatial Localization and Correlation with Solar Flare Intensity

We present a comprehensive study of type III radio bursts and their association with solar flares of magnitude M1.0 and larger, as observed by four widely separated spacecraft (Parker Solar Probe, Solar Orbiter, STEREO-A, and Wind). Our main focus is the introduction and validation of two methods for localizing radio bursts using the available multispacecraft data. The first method utilizes intensity fitting with a circular Gaussian distribution, while the second method is based on the time arrival of radio bursts. We demonstrate the effectiveness of these methods through the analysis of a single type III burst event and compare their results with the traditional radio triangulation technique. Furthermore, we conduct a statistical study of 17 type III bursts associated with M- and X-class solar flares in years 2020–2022. Our findings suggest a possible correlation between solar flare intensities and longitudes, with east limb flares tending to be weaker than west limb flares. We also observe a systematic drift of radio burst longitudes toward the east, potentially explained by a poleward component of the local density gradient. Our results suggest a strong correlation between solar flare intensities and radio burst properties, enhancing our understanding of the relationship between solar flares and type III radio bursts.

Statistical Properties of X-Ray Bursts from SGR J1935+2154 Detected by Insight-HXMT

As one class of the most important objects in the universe, magnetars can produce a lot of different frequency bursts including X-ray bursts. In Cai et al., 75 X-ray bursts produced by magnetar SGR J1935+2154 during an active period in 2020 are published, including the duration and net photon counts of each burst, and waiting time based on the trigger time difference. In this paper, we utilize the power-law model, , to fit the cumulative distributions of these parameters. It can be found that all the cumulative distributions can be well fitted, which can be interpreted by a self-organizing criticality theory. Furthermore, we check whether this phenomenon still exists in different energy bands and find that there is no obvious evolution. These findings further confirm that the X-ray bursts from magnetars are likely to be generated by some self-organizing critical process, which can be explained by a possible magnetic reconnection scenario in magnetars.

Contributions of M- and Persistent Sodium Currents in Regulating Locomotor Rhythms: A Computational Modeling Study

Physiological experiments have demonstrated that M-current ([Formula: see text]) and persistent sodium current ([Formula: see text]) expressed in rhythm-generating neurons play a key role in the generation and regulation of locomotor rhythms. However, the intrinsic mechanisms by which these two ionic currents control the locomotor rhythms are poorly understood. Here, a computational model is constructed to investigate the roles of [Formula: see text] and [Formula: see text] in regulating locomotor rhythms and explain the underlying ionic mechanisms. The simulation results show that decreasing [Formula: see text] or increasing [Formula: see text] facilitates the generation of the bursting activity; during the bursting activity, the burst frequency of the model has a positive dependence on [Formula: see text], and the flexion-extension as well as left-right coordination are not affected by varying [Formula: see text]. These results accurately reproduce the experimental results. In addition, the results also show that the dependence of burst frequency-[Formula: see text] is similar to that of burst frequency-[Formula: see text], but with distinct regulation mechanisms, i.e. [Formula: see text] regulates the burst frequency by affecting the burst and interburst durations, whereas [Formula: see text] regulates the burst frequency via manipulating the interburst duration. Finally, a dynamical analysis is given to reveal the intrinsic neural mechanisms of [Formula: see text] and [Formula: see text] in regulating the burst properties. Our study provides new insights into how outward and inward currents work in tandem to set the speed of locomotion, and provides testable predictions for biological experimental studies.