Fast radio burst (FRBs) are an exciting class of bright, extragalactic, millisecond radio transients. The recent development of large field-of-view (FOV) radio telescopes has caused a rapid rise in the number of identified single burst and repeating FRBs. This has allowed for the extensive multi-wavelength follow-up to search for the potential counterparts predicted by theoretical models. New observations of similar radio transients in Galactic magnetars like SGR 1935+2154 have continued to motivate the search for rapid optical and very-high-energy (VHE, >100 GeV) counterparts. Since 2016 VERITAS has engaged in an FRB observing campaign to search for the prompt optical, and VHE emission from multiple repeating FRBs. We present these new results from VERITAS observations of five repeating sources including data taken simultaneously with bursts observed by the CHIME radio telescope.
During its first cycle of observations, VERITAS observed several GRBs in response to broadcast alerts from the Gamma-ray bursts Coordinates Network (GCN). The GRBs were followed up and observed thereafter with typical delays of 2 to 4 minutes from the beginning of the burst and of 92 s in the best case, searching for a very high energy (VHE) component above 100 GeV. The aim of the search for VHE emission from GRBs is to understand the behavior, composition and dynamics of the most accelerated particles in the bursts, as well as to get a better overall understanding of the model of GRBs. We rep…
Ultraluminous X-ray bursts (hereafter ULXBs) are ultraluminous X-ray flares with a fast rise ($\sim$ one minute) and a slow decay ($\sim$ an hour), which are commonly observed in extragalactic globular clusters. Most ULXBs are observational one-off bursts, whereas five flares from the same source in NGC 5128 were discovered by Irwin et al. (2016). In this Letter, we propose a neutron star (NS)-white dwarf (WD) binary model with super-Eddington accretion rates to explain the repeating behavior of the ULXB source in NGC 5128. With an eccentric orbit, the mass transfer occurs at the periastron wh…
Repeating Fast Radio Bursts show temporal symmetry breaking on millisecond time scales (the "sad trombone"). On a time scale of days the repetitions of FRB 180916B occur at frequency-dependent phases of its 16.3 d period. Some models predict that all such periodic repeating FRB have the same sign of temporal asymmetry, while others predict that sources with both signs are equally abundant. Future observations of other periodically modulated repeating FRB may distinguish among models on this basis.
It is proposed that sources of repeating fast radio bursts with detected periodicity are magnetars with extremely short initial spin periods at the protoneutron star stage, formed in binaries after tidal synchronization of their progenitor cores on late stages of thermonuclear burning in very close systems with orbital periods about a few days. This formation channel is in several respects different from evolution of progenitors of normal magnetars, and thus, it explains some differences between repeating and non-repeating sources of FRBs.
The nature of fast radio bursts (FRBs) is currently unknown. Repeating FRBs offer better opportunity than non-repeating FRBs since their simultaneous multi-wavelength counterparts might be identified. The magnetar flare model of FRBs is one of the most promising models which predicts high energy emission in addition to radio burst emission. To investigate such a possibility, we have searched for simultaneous and quasi-simultaneous short-term hard X-ray bursts in all the Swift/BAT event mode data which covered the periods when fast radio bursts were reported detections in the repeating FRB 1211…
According to the number of detected bursts, fast radio bursts (FRBs) can be classified into two categories, i.e., one-off FRBs and repeating ones. We make a statistical comparison of these two categories based on the first FRB catalog of the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst Project. Using the Anderson-Darling, Kolmogrov-Smirnov, and Energy statistic tests, we find significant statistical differences ($p$-value $<$ 0.001) of the burst properties between the one-off FRBs and the repeating ones. More specifically, after controlling for distance, we find that the pea…
We study the statistical properties of the soft gamma repeater SGR 1935+2154. We find that the cumulative distributions of duration, waiting time, fluence and flux can be well fitted by bent power law. In addition, the probability density functions of fluctuations of duration, waiting time, fluence and flux well follow the Tsallis $q$-Gaussian distribution. The $q$ values keep steady for different temporal scale intervals, indicating a scale-invariant structure of the bursts. Those features are very similar to the property of the repeating fast radio burst FRB 121102, indicating the underlying…
In this paper, we present a sample of 21 repeating fast radio bursts (FRBs) detected by different radio instruments before September 2021. Using the Anderson--Darling test, we compared the distributions of extra-Galactic dispersion measure ($DM_{\rm E}$) of non-repeating FRBs, repeating FRBs and all FRBs. It was found that the $ DM_{\rm E}$ values of three sub-samples are log-normally distributed. The $DM_{\rm E}$ of repeaters and non-repeaters were drawn from a different distribution on basis of the Mann--Whitney--Wilcoxon test. In addition, assuming that the non-repeating FRBs identified cur…
A method is presented to limit the volumetric density of repeating fast radio bursts based on the number (or lack) of repeating bursts identified in a survey. The method incorporates the instantaneous sensitivity of the instrument, its beam pattern, and the dwell time per pointing, as well as the energy and timing distribution of repeat bursts. Applied to the Australian Square Kilometre Array Pathfinder's (ASKAP's) Commensal Real-time ASKAP Fast Transients (CRAFT) `lat50' survey, the presence of an FRB similar to FRB 121102 is excluded within a volume of $1.9 \cdot 10^6$ Mpc$^3$ at 95% confide…
Observationally, the mysterious fast radio bursts (FRBs) are classified as repeating ones and apparently non-repeating ones. While repeating FRBs cannot be classified into the non-repeating group, it is unknown whether the apparently non-repeating FRBs are actually repeating FRBs whose repetitions are yet to be discovered, or whether they belong to another physically distinct type from the repeating ones. In a series of two papers, we attempt to disentangle this mystery with machine learning methods. In this first paper, we focus on an array of supervised machine learning methods. We train the…
Primordial black holes are black holes that may have formed from density fluctuations in the early universe. It has been theorized that black holes slowly evaporate. If primordial black holes of initial mass of $10^{14}$g were formed, their evaporation would end in this epoch, in a bright burst of very-high-energy gamma rays. A Cherenkov telescope experiment like VERITAS can look for these primordial black hole bursts in its archival data, constraining the rate-density of their final evaporation. New analysis techniques and search methodologies were used and will be presented here, leading to …
Fast radio bursts (FRBs) are bright, unresolved, millisecond-duration flashes of radio emission originating from outside of the Milky Way. The source of these mysterious outbursts is unknown, but their high luminosity, high dispersion measure and short duration requires an extreme, high-energy, astrophysical process. The majority of FRBs have been discovered as single events which would require a chance coincidence for contemporaneous multiwavelength observations. However, two have been observed to repeat: FRB 121102 and the recently detected FRB 180814.J0422+73. These repeating FRBs have allo…
The phenomenon of giant radio pulses (GRP) from the Crab Pulsar can be studied at gamma-ray energies using atmospheric-Cherenkov telescopes such as VERITAS and the SGARFACE experiment attached to the Whipple 10 m telescope. Although these instruments are generally used for very-high-energy gamma-ray astronomy above 100 GeV, they also provide substantial sensitivity to short bursts of photons above 100 MeV lasting up to 15 $μ$s. Motivated by the theoretical predictions for short microsecond-scale GeV bursts as counterparts to GRPs \cite{Lyutikov2007}, we report on a search for gamma-ray emissio…
Fast radio bursts (FRBs) are bright millisecond radio bursts at cosmological distances. Only a small fraction of FRBs apparently repeat. Polarization, a fundamental property of electromagnetic signals, often carries critical information about the radiation processes, the environment, and the intervening medium of FRBs. Here we report circular polarization detections of two active repeating FRBs, namely FRBs 20121102A and 20190520B, with the Five-hundred-meter Aperture Spherical radio Telescope. We detect circular polarization in both active repeating FRBs, which increases the number of repeati…
The statistical properties of the repeating fast radio burst FRB 121102 are investigated. We find that the cumulative distributions of fluence, flux density, total energy and waiting time can be well fitted by the bent power law. In addition, the probability density functions of fluctuations of fluence, flux density and total energy well follow the Tsallis $q$-Gaussian distribution. The $q$ values keep steady around $q\sim 2$ for different scale intervals, indicating a scale-invariant structure of the bursts. The statistical properties of FRB 121102 are very similar to that of the soft gamma r…
Fast radio bursts (FRBs) are extragalactic, bright pulses of emission at radio frequency with milliseconds duration. Observationally, FRBs can be divided into two classes, repeating FRBs and non-repeating FRBs. At present, twenty repeating FRBs have been discovered with unknown physical origins. Localization of the first repeating FRB 121102 and discovery of an associated persistent radio source support that FRBs are powered by young millisecond magnetars, which could be formed by core-collapses of massive stars or binary neutron stars mergers. These two formation channels can be distinguished…
The mechanism that produces fast radio burst (FRB) emission is poorly understood. Targeted monitoring of repeating FRB sources provides the opportunity to fully characterize the emission properties in a manner impossible with one-off bursts. Here, we report observations of the source of FRB 20201124A, with the Australian Square Kilometre Array Pathfinder (ASKAP) and the ultra-wideband low (UWL) receiver at the Parkes 64-m radio telescope (Murriyang). The source entered a period of emitting bright bursts during early 2021 April. We have detected 16 bursts from this source. One of the bursts det…
There are some similarities between bursts of repeating fast radio bursts (FRBs) and giant pulses (GPs) of pulsars. To explore possible relations between them, we study the cumulative energy distributions of these two phenomena using the observations of repeating FRB 121102 and the GPs of Crab pulsar. We find that the power-law slope of GPs (with fluence $\geq$130 Jy ms) is $2.85\pm0.10$. The energy distribution of FRB 121102 can be well fitted by a smooth broken power-law function. For the bursts of FRB 121102 above the break energy (1.22 $\times 10^{37}$ erg), the best-fitting slope is $2.90…
Very recently Spitler et al. (2016) and Scholz et al. (2016) reported their detections of sixteen additional bright bursts from the direction of the fast radio burst (FRB) 121102. This repeating FRB is inconsistent with all the catastrophic event models put forward previously for hypothetically non-repeating FRBs. Here we propose a different model, in which highly magnetized pulsars travel through asteroid belts of other stars. We show that a repeating FRB could originate from such a pulsar encountering lots of asteroids in the belt. During each pulsar-asteroid impact, an electric field induce…
We present the results of sixteen Swift-triggered GRB follow-up observations taken with the VERITAS telescope array from January, 2007 to June, 2009. The median energy threshold and response time of these observations was 260 GeV and 320 s, respectively. Observations had an average duration of 90 minutes. Each burst is analyzed independently in two modes: over the whole duration of the observations and again over a shorter time scale determined by the maximum VERITAS sensitivity to a burst with a t^-1.5 time profile. This temporal model is characteristic of GRB afterglows with high-energy, lon…
The nature of fast radio bursts (FRBs), which occurs on millisecond time scales in the radio band, has not been well-understood. Among their unknown observational properties are their broadband spectra and persistent and transient multi-wavelength counterparts. Well-localized FRBs provide us the opportunity to address these issues in archival observations. We have performed searches for 15-150 keV hard X-ray bursts on time scales as short as millisecond in the direction of the repeating FRB 121102 (with a spacial resolution of a few arcminutes) in the archival Swift/BAT data during the period …
The first repeating fast radio burst (FRB), FRB 121102, was found to be associated with a spatially coincident, persistent nonthermal radio source, but the origin of the persistent emission remains unknown. In this paper, we propose that the persistent emission is produced via synchrotron-heating process by multiple bursts of FRB 121102 in a self-absorbed synchrotron nebula. As a population of bursts of the repeating FRB absorbed by the synchrotron nebula, the energy distribution of electrons in the nebula will change significantly. As a result, the spectrum of the nebula will show a hump stea…
We collect 133 Fast Radio Bursts (FRBs), including 110 non-repeating and 23 repeating ones, and systematically investigate their observational properties. To check the frequency dependence of FRB classifications, we define our samples with a central frequency below/above 1GHz as subsample I/II. We find that there is a clear bimodal distribution of pulse width for the subsample I. And If we classify FRBs into short FRBs (\emph{s}FRBs) ($<$100 ms) and long FRBs (\emph{l}FRBs) ($>$100 ms) as done for short and long Gamma-Ray Bursts (GRBs), the \emph{s}FRBs at higher central frequency are commonly…
Superluminous supernovae (SLSNe) and long gamma ray bursts (LGRBs) have been proposed as progenitors of repeating Fast Radio Bursts (FRBs). In this scenario, bursts originate from the interaction between a young magnetar and its surrounding supernova remnant (SNR). Such a model could explain the repeating, apparently non-Poissonian nature of FRB121102, which appears to display quiescent and active phases. This bursting behaviour is better explained with a Weibull distribution, which includes parametrisation for clustering. We observed 10 SLSNe/LGRBs for 63 hours, looking for repeating FRBs wit…
Assuming: fast radio bursts (FRBs) are produced by neutron stars at cosmological distances; FRB rate tracks core-collapse supernova rate; and all FRBs repeat with a universal energy distribution function (EDF) dN/dE ~ E^(-beta) with a high-end cutoff at burst energy E_max. We find that observations so far are consistent with a universal EDF with a power-law index 1.5 < beta < 2.2, high-end cutoff E_max/E_0 > 30 and normalization N_0 < 2 per day; where N_0 is the integrated rate above the reference burst energy E_0 = 1.2e39 f_r^(-1) erg (f_r is the radio emission efficiency). Implications of su…
We report on the discovery and analysis of bursts from nine new repeating fast radio burst (FRB) sources found using the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope. These sources span a dispersion measure (DM) range of 195 to 1380 pc cm$^{-3}$. We detect two bursts from three of the new sources, three bursts from four of the new sources, four bursts from one new source, and five bursts from one new source. We determine sky coordinates of all sources with uncertainties of $\sim$10$^\prime$. We detect Faraday rotation measures for two sources, with values $-20(1)$ and $-499…
We have conducted a search for bright repeating Fast Radio Bursts in our nearby Universe with the Australian Square Kilometer Array Pathfinder (ASKAP) in single-dish mode. We used eight ASKAP 12-m dishes, each equipped with a Chequerboard Phased Array Feed forming 36 beams on the sky, to survey $\sim$30,000 deg$^{2}$ of the southern sky ($-90^{\circ} < δ< +30^{\circ}$) in 158 antenna days. The fluence limit of the survey is 22 Jyms. We report the detection of FRB 180515 in our survey. We found no repeating FRBs in a total mean observation of 3hrs per pointing divided into one-hour intervals, w…
Fast Radio Bursts are millisecond-duration astronomical radio pulses of unknown physical origin that appear to come from extragalactic distances. Previous follow-up observations have failed to find additional bursts at the same dispersion measures (i.e. integrated column density of free electrons between source and telescope) and sky position as the original detections. The apparent non-repeating nature of the fast radio bursts has led several authors to hypothesise that they originate in cataclysmic astrophysical events. Here we report the detection of ten additional bursts from the direction…
We present a detection of a bright burst from FRB 20201124A, which is one of the most active repeating FRBs, based on S-band observations with the 64-m radio telescope at the Usuda Deep Space Center/JAXA. This is the first FRB observed by using a Japanese facility. Our detection at 2 GHz in February 2022 is the highest frequency for this FRB and the fluence of $>$ 189 Jy ms is one of the brightest bursts from this FRB source. We place an upper limit on the spectral index $α$ = -2.14 from the detection of the S band and non-detection of the X band at the same time. We compare an event rate of t…
Discovery of 30 Repeating Fast Radio Burst Sources and Uniform Population Statistics of 80 Repeating Sources from CHIME/FRB
McGill University（麦吉尔大学）；University of Amsterdam（阿姆斯特丹大学）；California Institute of Technology（加州理工学院）；Netherlands Institute for Radio Astronomy（荷兰射电天文研究所）
The polarization of fast radio bursts (FRBs), bright astronomical transients, contains crucial information about their environments. We report polarization measurements of five repeating FRBs, the abundant signals of which enable wide-band observations with two telescopes. A clear trend of lower polarization at lower frequencies was found, which can be well characterized by a single parameter rotation-measure-scatter (σRM) and modeled by multi-path scatter. Sources with higher σRM have higher RM magnitude and scattering timescales. The two sources with the most substantial σRM, FRB 20121102A a…
Popular Fast Radio Burst models involve rotating magnetized neutron stars, yet no rotational periodicities have been found. Small datasets exclude exact periodicity in FRB 121102. Recent observations of over 1500 bursts from each of FRB 121102 and FRB 20201124A also have not found periodicity. Periodograms of events with cosine-distributed random offsets as large as $\pm 0.6 P$ from a strict period $P$ would still reveal the underlying periodicity. The sensitivity of periodograms of long data series, such as bursts observed on multiple days, to slow frequency drifts is mitigated by considering…
We present Monte-Carlo simulations of a cosmological population of repeating fast radio burst (FRB) sources whose comoving density follows the cosmic star formation rate history. We assume a power-law model for the intrinsic energy distribution for each repeating FRB source located at a randomly chosen position in the sky and simulate their dispersion measures (DMs) and propagation effects along the chosen lines-of-sight to various telescopes. In one scenario, an exponential distribution for the intrinsic wait times between pulses is chosen, and in a second scenario we model the observed pulse…
Fast radio bursts (FRBs) are a new kind of extragalactic radio transients. Some of them show repeating behaviors. Recent observations indicate that a few repeating FRBs (e.g., FRB 121102) present time--frequency downward drifting patterns and nearly 100$\%$ linear polarization. Following the model of \citet{dai 2016} who proposed that repeating FRBs may originate from a slowly-rotating, old-aged pulsar colliding with an asteroid belt around a stellar-mass object, we focus on the prediction of time--frequency drifting and polarization. In this scenario, the frequency drifting is mainly caused b…
Random Polarization Position Angle Behaviors across Bursts of Repeating Fast Radio Bursts
State Key Laboratory of Radio Astronomy and Technology, National Astronomical Observatories, CAS（中国科学院国家天文台射电天文与技术重点实验室）；School of Astronomy and Space Science, University of Chinese Academy of Sciences（中国科学院大学天文与空间科学学院）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；Department of Astronomy, Beijing Normal University（北京师范大学天文学系）；The Nevada Center for Astrophysics, University of Nevada, Las Vegas（内华达大学拉斯维加斯分校天体物理中心）；Department of Physics and Astronomy, University of Nevada, Las Vegas（内华达大学拉斯维加斯分校物理与天文系）
Fast radio busts (FRBs) can exhibit a wide variety of polarisation properties, not only between sources but also from burst to burst for a same one. In this work, we revisit the polarisation characters of coherent curvature radiation from a bulk of charged bunches in the magnetosphere of a highly magnetized neutron star. FRBs have been observed to have a variety of polarisation features, such as high levels of circular polarisation or a sign change of circular polarisation. High linear polarisation would appear when the line of sight is inside the emission beam (the on-beam geometry), whereas …
We propose a compact binary model for the fast radio burst (FRB) repeaters, where the system consists of a magnetic white dwarf (WD) and a neutron star (NS) with strong bipolar magnetic fields. When the WD fills its Roche lobe, mass transfer will occur from the WD to the NS through the inner Lagrange point. The accreted magnetized materials may trigger magnetic reconnection when they approach the NS surface, and therefore the electrons can be accelerated to an ultra-relativistic speed. In this scenario, the curvature radiation of the electrons moving along the NS magnetic field lines can accou…
Fast radio bursts (FRBs) at cosmological distances still hold concealed physical origins. Previously Liu (2018) proposes a scenario that the collision between a neutron star (NS) and a white dwarf (WD) can be one of the progenitors of non-repeating FRBs and notices that the repeating FRBs can also be explained if a magnetar formed after such NS-WD merger. In this paper, we investigate this channel of magnetar formation in more detail. We propose that the NS-WD post-merger, after cooling and angular momentum redistribution, may collapse to either a black hole or a new NS or even remains as a hy…
The repeating fast radio burst (FRB) 121102 was recently localized in a dwarf galaxy at a cosmological distance. The dispersion measure (DM) derived for each burst from FRB 121102 so far has not shown significant evolution, even though an apparent increase was recently seen with newly detected VLA bursts. It is expected that more repeating FRB sources may be detected in the future. In this work, we investigate a list of possible astrophysical processes that might cause DM variation of a particular FRB source. The processes include (1) the cosmological scale effects such as Hubble expansion and…
Strange stars (SSs) are compact objects made of deconfined quarks. It is hard to distinguish SSs from neutron stars as a thin crust composed of normal hadronic matter may exist and obscure the whole surface of the SS. Here we suggest that the intriguing repeating fast radio bursts (FRBs) are produced by the intermittent fractional collapses of the crust of an SS induced by refilling of accretion materials from its low-mass companion. The periodic/sporadic/clustered temporal behaviors of FRBs could be well understood in our scenario. Especially, the periodicity is attributed to the modulation o…
Fast radio bursts (FRBs) are mysterious transient phenomena. The study of repeating FRBs may provide useful information about their nature due to their redetectability. The two most famous repeating sources are FRBs 121102 and 180916, with a period of 157 days and 16.35 days, respectively. Previous studies suggest that the periodicity of FRBs is likely associated with neutron star (NS) binary systems. Here we introduce a new model which proposes that periodic repeating FRBs are due to the interaction of a NS with its planet in a highly elliptical orbit. The periastron of the planet is very clo…
The newly discovered second repeating fast radio burst (FRB) source, FRB 180814.J0422+73, was reported to exhibit a time-frequency downward drifting pattern, which is also seen in the first repeater FRB 121102. We propose a generic geometrical model to account for the observed downward drifting of sub-pulse frequency, within the framework of coherent curvature radiation by bunches of electrons or positrons in the magnetosphere of a neutron star. A sudden trigger event excites these coherent bunches of charged particles, which stream outwards along open field lines. As the field lines sweep acr…
A Search for Rotation Measure Flare Candidates in Repeating Fast Radio Bursts
Purple Mountain Observatory, Chinese Academy of Sciences（中国科学院紫金山天文台）；State Key Laboratory of Radio Astronomy and Technology, Purple Mountain Observatory, Chinese Academy of Sciences（中国科学院紫金山天文台射电天文与技术重点实验室）
Repeating fast radio bursts (FRBs) present excellent opportunities to identify FRB progenitors and host environments, as well as decipher the underlying emission mechanism. Detailed studies of repeating FRBs might also hold clues to the origin of FRBs as a population. We aim to detect the first two repeating FRBs: FRB 121102 (R1) and FRB 180814.J0422+73 (R2), and characterise their repeat statistics. We also want to significantly improve the sky localisation of R2. We use the Westerbork Synthesis Radio Telescope to conduct extensive follow-up of these two repeating FRBs. The new phased-array f…
The model that fast radio bursts are caused by plunges of asteroids onto neutron stars can explain both repetitive and non-repetitive bursts. If a neutron star passes through an asteroid belt around another star, there would be a series of bursts caused by series of asteroid impacts. Moreover, the neutron star would cross the same belt repetitively if it is in a binary with the star hosting the asteroid belt, leading to a repeated series of bursts. I explore the properties of neutron star binaries which could lead to the only known repetitive fast radio burst so far (FRB121102). In this model,…
The event rate, energy distribution, and time-domain behaviour of repeating fast radio bursts (FRBs) contains essential information regarding their physical nature and central engine, which are as yet unknown. As the first precisely-localized source, FRB 121102 has been extensively observed and shows non-Poisson clustering of bursts over time and a power-law energy distribution. However, the extent of the energy distribution towards the fainter end was not known. Here we report the detection of 1652 independent bursts with a peak burst rate of 122~hr^{-1}, in 59.5 hours spanning 47 days. A pea…
