Recent observations have shown that repeating Fast Radio Bursts (FRBs) exhibit band-limited emission, whose frequency-dependent amplitude can be modeled using a Gaussian function. In this analysis, we show that banded emission of FRBs can lead to incompleteness across the observing band. This biases the detected sample of bursts and can explain the various shapes of cumulative energy distributions seen for repeating FRBs. We assume a Gaussian shape of the burst spectra and used simulations to demonstrate the above bias using an FRB 121102-like example. We recovered energy distributions that showed a break in power-law and flattening of power-law at low energies, based on the fluence threshold of the observations. We provide recommendations for single-pulse searches and analysis of repeating FRBs to account for this incompleteness. Primarily, we recommend that burst spectra should be modeled to estimate the intrinsic fluence and bandwidth of the burst robustly. Also, bursts that lie mainly within the observing band should be used for analyses of energy distributions. We show that the bimodality reported in the distribution of energies of FRB 121102 by Li et al. (2021) disappears when burst bandwidth, instead of the center frequency of the observation, is used to estimate energy. Sub-banded searches will also aid in detecting band-limited bursts. All the analysis scripts used in this work are available in a Github repository.
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…
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) ($<$100 ms) and long FRBs (\emph{l}FRBs) ($>$100 ms) as done for short and long Gamma-Ray Bursts (GRBs), the \emph{s}FRBs at higher central frequency are commonly…
Fast radio bursts (FRBs) are extragalactic, bright pulses of emission at radio frequency with milliseconds duration. Observationally, FRBs can be divided into two classes, repeating FRBs and non-repeating FRBs. At present, twenty repeating FRBs have been discovered with unknown physical origins. Localization of the first repeating FRB 121102 and discovery of an associated persistent radio source support that FRBs are powered by young millisecond magnetars, which could be formed by core-collapses of massive stars or binary neutron stars mergers. These two formation channels can be distinguished…
Observationally, the mysterious fast radio bursts (FRBs) are classified as repeating ones and apparently non-repeating ones. While repeating FRBs cannot be classified into the non-repeating group, it is unknown whether the apparently non-repeating FRBs are actually repeating FRBs whose repetitions are yet to be discovered, or whether they belong to another physically distinct type from the repeating ones. In a series of two papers, we attempt to disentangle this mystery with machine learning methods. In this first paper, we focus on an array of supervised machine learning methods. We train the…
According to the number of detected bursts, fast radio bursts (FRBs) can be classified into two categories, i.e., one-off FRBs and repeating ones. We make a statistical comparison of these two categories based on the first FRB catalog of the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst Project. Using the Anderson-Darling, Kolmogrov-Smirnov, and Energy statistic tests, we find significant statistical differences ($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…
Fast radio bursts (FRBs) are mysterious radio bursts with a time scale of approximately milliseconds. Two populations of FRB, namely repeating and non-repeating FRBs, are observationally identified. However, the differences between these two and their origins are still cloaked in mystery. Here we show the time-integrated luminosity-duration ($L_ν$-$w_{\rm int,rest}$) relations and luminosity functions (LFs) of repeating and non-repeating FRBs in the FRB Catalogue project. These two populations are obviously separated in the $L_ν$-$w_{\rm int,rest}$ plane with distinct LFs, i.e., repeating FRBs…
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 fast radio bursts ( FRBs ) are energetic radio bursts with millisecond duration only observed at radio frequencies. The generation mechanism is still mysterious. We have proposed a generation mechanism of both repeating and one-off FRBs. They arise from the axion star collision with neutron star or magnetized accretion disk of galactic black hole. Once we accept the existence of the axions, we find that the mechanism well explain previously observed spectral-temporal features. In this paper we show that it also explains recently observed phenomena such as downward drifting in the repeating…
Fast radio bursts (FRBs) are mysterious astronomical radio transients with extremely short intrinsic duration. Until now, the physical origins of them still remain elusive especially for the non-repeating FRBs. Strongly inspired by recent progress on possible evidence of Earth-mass primordial black holes, we revisit the model of Earth-mass primordial black holes mergers as sources for non-repeating FRBs. Under the null hypothesis that the observed non-repeating FRBs are originated from the mergers of Earth-mass primordial black holes, we analyzed four independent samples of non-repeating FRBs …
The newly discovered 16.35 days period for repeating FRB 180916.J0158+65 provides an essential clue for understanding the sources and emission mechanism of repeating FRBs. Many models propose that the periodically repeating FRBs might be related to binary star systems that contain at least one neutron star (NSC-FRB system). It has been suggested that the NS "combed" by the strong wind from a companion star might provide a solution. Following the "Binary Comb" model, we use the population synthesis method to study in detail the properties of the companion stars and the nature of NSC-FRB systems…
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…
Since their serendipitous discovery, Fast Radio Bursts (FRBs) have garnered a great deal of attention from both observers and theorists. A new class of radio telescopes with wide fields of view have enabled a rapid accumulation of FRB observations, confirming that FRBs originate from cosmological distances. The high occurrence rate of FRBs and the development of new instruments to observe them create opportunities for FRBs to be utilized for a host of astrophysical and cosmological studies. We focus on the rare, and as yet undetected, subset of FRBs that undergo repeated bursts and are strongl…
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…
Observationally, fast radio bursts (FRBs) can be divided into repeating and apparently non-repeating (one-off) ones. It is unclear whether all FRBs repeat and whether there are genuine non-repeating FRBs. We attempt to address these questions using Monte Carlo simulations. We define a parameter $T_c$ at which the accumulated number of non-repeating sources becomes comparable to the total number of the repeating sources, which is a good proxy to denote the intrinsic repeater fraction among FRBs. Assuming that both types of sources exist and that their burst energies follow power law distributio…
We propose a geometrical explanation for periodically and nonperiodically repeating fast radio bursts (FRBs) under neutron star (NS)-companion systems. We suggest a constant critical binary separation, $r_{\rm c}$, within which the interaction between the NS and companion can trigger FRB bursts. For an elliptic orbit with the minimum and maximum binary separations, $r_{\rm min}$ and $r_{\rm max}$, a periodically repeating FRB with an active period could be reproduced if $r_{\rm min}<r_{\rm c}<r_{\rm max}$. However, if $r_{\rm max}<r_{\rm c}$, the modulation of orbital motion will not work due …
Fast Radio Bursts (FRBs) are extremely luminous and brief signals (with duration of milliseconds or even shorter) of extragalactic origin. Despite the fact that hundreds of FRBs have been discovered to date, their nature still remains unclear. Precise localizations of FRBs can unveil their host galaxies and local environments -- and thus shed light on the physical processes that led to the burst production. However, this has only been achieved for a few FRBs to date. The European VLBI Network (EVN) is currently the only instrument capable of localizing FRBs down to the milliarcsecond level. Th…
Although fast radio bursts (FRBs) have been an active field in astronomy and cosmology, their origin is still unknown to date. One of the interesting topics is the classification of FRBs, which is closely related to the origin of FRBs. Different physical mechanisms are required by different classes of FRBs. In the literature, they usually could be classified into non-repeating and repeating FRBs. Well motivated by the observations, here we are interested in the possible subclassification of FRBs. By using the first CHIME/FRB catalog, we propose to subclassify non-repeating (type I) FRBs into t…
We have proposed a generation mechanism of non repeating ( repeating ) fast radio bursts: They arise by axion star collisions with neutron stars ( accretion disks of galactic black holes ). The axion star as coherent state of axions with mass $m_a$ generates homogeneous electric field oscillating with frequency $m_a/2π$ under strong magnetic fields. The field makes electrons coherently oscillate and emit the coherent dipole radiations ( FRBs ). The radiations stop when thermal fluctuations produced by the oscillation disturb the coherent oscillations. Thus, the duration of the FRBs is determin…
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…
Fast radio bursts (FRBs) are millisecond transients of unknown origin(s) occurring at cosmological distances. Here we, for the first time, show time-integrated-luminosity functions and volumetric occurrence rates of non-repeating and repeating FRBs against redshift. The time-integrated-luminosity functions of non-repeating FRBs do not show any significant redshift evolution. The volumetric occurrence rates are almost constant during the past $\sim$10 Gyr. The nearly-constant rate is consistent with a flat trend of cosmic stellar-mass density traced by old stellar populations. Our findings indi…
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 VERI…
Most of fast radio bursts (FRB) do not show evidence for repetition, and such non-repeating FRBs may be produced at the time of a merger of binary neutron stars (BNS), provided that the BNS merger rate is close to the high end of the currently possible range. However, the merger environment is polluted by dynamical ejecta, which may prohibit the radio signal to propagate. We examine this by using a general-relativistic simulation of a BNS merger, and show that the ejecta appears about 1 ms after the rotation speed of the merged star becomes the maximum. Therefore there is a time window in whic…
Fast radio bursts (FRBs) last for $\sim $ few milli-seconds and, hence, are likely to arise from the gravitational collapse of supra-massive, spinning neutron stars after they lose the centrifugal support (Falcke \& Rezzolla 2014). In this paper, we provide arguments to show that the repeating burst, FRB 121102, can also be modeled in the collapse framework provided the supra-massive object implodes either into a Kerr black hole surrounded by highly magnetized plasma or into a strange quark star. Since the estimated rates of FRBs and SN Ib/c are comparable, we put forward a common progenitor s…
Fast radio bursts (FRBs) are millisecond-duration radio signals occurring at cosmological distances. However the physical model of FRBs is mystery, many models have been proposed. Here we study the frequency distributions of peak flux, fluence, duration and waiting time for the repeating FRB 121102. The cumulative distributions of peak flux, fluence and duration show power-law forms. The waiting time distribution also shows power-law distribution, and is consistent with a non-stationary Poisson process. These distributions are similar as those of soft gamma repeaters (SGRs). We also use the st…
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…
We calculate the dispersion measures (DMs) contributed by host galaxies of fast radio bursts (FRBs). Based on a few host galaxy observations, a large sample of galaxy with similar properties to observed ones has been selected from the IllustrisTNG simulation. They are used to compute the distributions of host galaxy DMs for repeating and non-repeating FRBs. For repeating FRBs, we infer the DM$ _{\mathrm{host}} $ for FRBs like FRB 121102 and FRB 180916 by assuming that the burst sites are tracing the star formation rates in host galaxies. The median DM$_{\mathrm{host}}$ are $35 (1+z)^{1.08}$ an…
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…
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 origins of fast radio bursts (FRBs), astronomical transients with millisecond timescales, remain unknown. One of the difficulties stems from the possibility that observed FRBs could be heterogeneous in origin; as some of them have been observed to repeat, and others have not. Due to limited observing periods and telescope sensitivities, some bursts may be misclassified as non-repeaters. Therefore, it is important to clearly distinguish FRBs into repeaters and non-repeaters, to better understand their origins. In this work, we classify repeaters and non-repeaters using unsupervised machine …
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）
Fast radio bursts (FRBs) are brief, bright, extragalactic radio flashes. Their physical origin remains unknown, but dozens of possible models have been postulated. Some FRB sources exhibit repeat bursts. Though over a hundred FRB sources have been discovered to date, only four have been localised and associated with a host galaxy, with just one of the four known to repeat. The properties of the host galaxies, and the local environments of FRBs, provide important clues about their physical origins. However, the first known repeating FRB has been localised to a low-metallicity, irregular dwarf g…
A correlation between the intrinsic energy and the burst duration of non-repeating fast radio bursts (FRBs) has been reported. If it exists, the correlation can be used to estimate intrinsic energy from the duration, and thus can provide us with a new distance measure for cosmology. However, the correlation suffered from small number statistics (68 FRBs) and was not free from contamination by latent repeating populations, which might not have such a correlation. How to separate/exclude the repeating bursts from the mixture of all different types of FRBs is essential to see this property. Using…
The observed Fast Radio Burst (FRB) population can be divided into one-off and repeating FRB sources. Either this division is a true dichotomy of the underlying sources, or selection effects and low activity prohibit us from observing repeat pulses from all constituents making up the FRB source population. We attempt to break this degeneracy through FRB population synthesis. With that aim we extend frbpoppy, which earlier only handled one-off FRBs, to also simulate repeaters. We next model the Canadian Hydrogen Intensity Mapping Experiment FRB survey (CHIME/FRB). Using this implementation, we …
The discovery that at least some Fast Radio Bursts (FRBs) repeat has ruled out cataclysmic events as the progenitors of these particular bursts. FRB~121102 is the most well-studied repeating FRB but despite extensive monitoring of the source, no underlying pattern in the repetition has previously been identified. Here, we present the results from a radio monitoring campaign of FRB~121102 using the 76-m Lovell telescope. Using the pulses detected in the Lovell data along with pulses from the literature, we report a detection of periodic behaviour of the source over the span of five years of dat…
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 …
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…
Coherent curvature radiation as the radiation mechanism for fast radio bursts (FRBs) has been discussed since FRBs were discovered. We study the spectral and polarization properties of repeating FRBs within the framework of coherent curvature radiation by charged bunches in the magnetosphere of a highly magnetized neutron star. The spectra can be generally characterized by multisegment broken power laws, and evolve as bunches move and the line of sight sweeps. Emitted waves are highly linear polarized if the line of sight is confined to the beam within an angle of $1/γ$, while circular polariz…
A unified model of active repeating fast radio bursts associated with persistent radio sources
School of Astronomy and Space Science, Nanjing University（南京大学天文与空间科学学院）；Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education（教育部现代天文学和天体物理重点实验室（南京大学））；Research Center for Astronomical Computing, Zhejiang Laboratory（浙江实验室天体计算研究中心）；Institute for Astronomy, School of Physics, Zhejiang University（浙江大学物理学院天体物理研究所）；School of Physics and Physical Engineering, Qufu Normal University（曲阜师范大学物理与光电工程学院）；Department of Astronomy, University of Science and Technology of China（中国科学技术大学天文学系）；Department of Physics, The University of Hong Kong（香港大学物理系）
Fast spinning (e.g., sub-second) neutron star with ultra-strong magnetic fields (or so-called magnetar) is one of the promising origins of repeating fast radio bursts (FRBs). Here we discuss circularly polarised emissions produced by propagation effects in the magnetosphere of fast spinning magnetars. We argue that the polarisation-limiting region is well beyond the light cylinder, suggesting that wave mode coupling effects are unlikely to produce strong circular polarisation for fast spinning magnetars. Cyclotron absorption could be significant if the secondary plasma density is high. However…
Fast radio bursts, or FRBs, are transient sources of unknown origin. Recent radio and optical observations have provided strong evidence for an extragalactic origin of the phenomenon and the precise localization of the repeating FRB 121102. Observations using the Karl G. Jansky Very Large Array (VLA) and very-long-baseline interferometry (VLBI) have revealed the existence of a continuum non-thermal radio source consistent with the location of the bursts in a dwarf galaxy. All these new data rule out several models that were previously proposed, and impose stringent constraints to new models. W…
