There are several unexplored regions of the short-duration radio transient phase space. One such unexplored region is the luminosity gap between giant pulses (from pulsars) and cosmologically located fast radio bursts (FRBs). The Survey for Transient Astronomical Radio Emission 2 (STARE2) is a search for such transients out to 7 Mpc. STARE2 has a field of view of 3.6 steradians and is sensitive to one-millisecond transients above $\sim300$ kJy. With a two-station system we have detected and localized a solar burst, demonstrating that the pilot system is capable of detecting short duration radio transients. We found no convincing transients with duration between 65 $μ$s and 34 ms in 200 days of observing, limiting with 95% confidence the all-sky rate of transients above $\sim300$ kJy to $< 40$ ${\rm sky^{-1} year^{-1}}$. If the luminosity function of FRBs could be extrapolated down to 300 kJy for a distance of 10 kpc, then one would expect the rate to be $\sim2$ ${\rm sky^{-1} year^{-1}}$.
Fast Radio Bursts (FRBs) are highly energetic transient events with duration of order of microseconds to milliseconds and of unknown origin. They are known to lie at cosmological distances, through localisation to host galaxies. Recently, an FRB-like event was seen from the Milky Way magnetar SGR 1935+2154 by the CHIME and STARE2 telescopes. This is the only magnetar that has produced FRB events in our galaxy. Finding similar events in the Milky Way is of great interest to understanding FRB progenitors. Such events will be strongly affected by the turbulent interstellar medium in the Milky Way…
Fast radio bursts (FRBs) are intense bursts of radio emission with durations of milliseconds. Although researchers have found them happening frequently all over the sky, they are still in the dark to understand what causes the phenomena because the existing radio observatories have encountered certain challenges during the discovery of FRB progenitors. The construction of Bustling Universe Radio Survey Telescope in Taiwan (BURSTT) is being proposed to solve these challenges. We simulate mock Galactic FRB-like events by applying a range of spatial distributions, pulse widths and luminosity func…
Recently, there have been reports of six bright, dispersed bursts of coherent radio emission found in pulsar surveys with the Parkes Multi-beam Receiver. Not much is known about the progenitors of these bursts, but they are highly-energetic, and probably of extragalactic origin. Their properties suggest extreme environments and interesting physics, but in order to understand and study these events, more examples need to be found. Fortunately, the recent boom in radio astronomy means many 'next-generation' radio telescopes are set to begin observing in the near future. In this paper we discuss …
Observations of millisecond-long radio bursts from beyond the Milky Way have revealed a repeat pattern with a roughly 16-day period -- a finding that adds to the enigma of the origin of these bursts.
Fast Radio Bursts (FRBs) are short duration highly energetic dispersed radio pulses. We developed a generic formalism (Bera {\em et al.}, 2016) to estimate the FRB detection rate for any radio telescope with given parameters. By using this model, we estimated the FRB detection rate for two Indian radio telescope; the Ooty Wide Field Array (OWFA) (Bhattacharyya {\em et al.}, 2017) and the upgraded Giant Metrewave Radio Telescope (uGMRT) (Bhattacharyya {\em et al.}, 2018) with three beam forming modes. In this review article, I summarize these two works. We considered the energy spectrum of FRBs…
Gamma-ray bursts are flashes of light from distant exploding stars. Cube satellites that monitor photons across different energy bands are used to detect these bursts. There is a need for computationally efficient algorithms, able to run using the limited computational resource onboard a cube satellite, that can detect when gamma-ray bursts occur. Current algorithms are based on monitoring photon counts across a grid of different sizes of time window. We propose a new algorithm, which extends the recently developed FOCuS algorithm for online change detection to Poisson data. Our algorithm is m…
A key tool astronomers have to investigate the nature of extragalactic transients is their position on their host galaxies. Galactocentric offsets, enclosed fluxes and the fraction of light statistic are widely used at different wavelengths to help infer the nature of transient progenitors. Motivated by the proposed link between magnetars and fast radio bursts (FRBs), we create a face-on image of the Milky Way using best estimates of its size, structure and colour. We place Galactic magnetars, pulsars, low mass and high mass X-ray binaries on this image, using the available distance informatio…
We present the Deep Synoptic Array (DSA-110) discovery and interferometric localization of the so far non-repeating FRB 20220319D. The FRB originates in a young, rapidly star-forming barred spiral galaxy, IRAS 02044$+$7048, at just 50 Mpc. Although the NE2001 and YMW16 models for the Galactic interstellar-medium (ISM) contribution to the DM of FRB 20220319D exceed its total observed DM, we show that uncertainties in these models accommodate an extragalactic origin for the burst. We derive a conservative upper limit on the DM contributed by the circumgalactic medium (CGM) of the Milky Way: the …
We calculate the distance-dependent performance of a few representative terrestrial neutrino detectors in detecting and measuring the properties of the $ν_e$ breakout burst light curve in a Galactic core-collapse supernova. The breakout burst is a signature phenomenon of core collapse and offers a probe into the stellar core through collapse and bounce. We examine cases of no neutrino oscillations and oscillations due to normal and inverted neutrino-mass hierarchies. For the normal hierarchy, other neutrino flavors emitted by the supernova overwhelm the $ν_e$ signal, making a detection of the …
Intense, millisecond-duration bursts of radio waves have been detected from beyond the Milky Way [1]. Their extragalactic origins are evidenced by their large dispersion measures, which are greater than expected for propagation through the Milky Way interstellar medium alone, and imply contributions from the intergalactic medium and potentially host galaxies [2]. Although several theories exist for the sources of these fast radio bursts, their intensities, durations and temporal structures suggest coherent emission from highly magnetised plasma [3,4]. Two sources have been observed to repeat […
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…
A planet having protective ozone within the collimated beam of a Gamma Ray Burst (GRB) may suffer ozone depletion, potentially causing a mass extinction event to existing life on a planet's surface and oceans. We model the dangers of long GRBs to planets in the Milky Way and utilize a static statistical model of the Galaxy that matches major observable properties, such as the inside-out star formation history, metallicity evolution, and 3-dimensional stellar number density distribution. The GRB formation rate is a function of both the star formation history and metallicity; however, the extent…
Detection of gravitational waves (GW) from highly eccentric binary black hole (BBH) systems can provide insight into their dynamics and formation. To date, all of the LIGO-Virgo BBH detections have been made using quasi-circular templates in their initial discovery. However, recent studies have found some of these systems to be compatible with high eccentricity in the LIGO band, $e_{10 \textrm{Hz}} > 0.1$, possibly pointing to a population of sources that are challenging to detect. Current low-latency search methods used with ground-based GW detector data are not well equipped to detect highly…
Gamma ray bursts (GBRs) are a class of highly energetic explosions emitting radiation in a very short timescale of a few seconds and with a very narrow opening angle. Although, all GRBs observed so far are extragalactic in origin, there is a high probability of a GRB of galactic origin beaming towards the Earth in the past ~ 0.5 Gyr. Such an intense burst of gamma rays would ionize the atmosphere and deplete the ozone layer. With depleted ozone, there will be an increased flux of solar UVB on the Earth's surface with harmful biological effects. In addition to the atmospheric damage, secondary …
Predictions of the thermodynamic conditions for phase transitions at high baryon densities and large chemical potentials are currently uncertain and largely phenomenological. Neutrino observations of core-collapse supernovae can be used to constrain the situation. Recent simulations of stellar core collapse that include a description of quark matter predict a sharp burst of anti ν_e several hundred milliseconds after the prompt ν_e neutronization burst. We study the observational signatures of that anti ν_e burst at current neutrino detectors - IceCube and Super-Kamiokande. For a Galactic core…
The recent detection of a repeating fast radio burst (FRB) in an old globular cluster in M81 challenges traditional FRB formation mechanisms based on magnetic activity in young neutron stars formed recently in core-collapse supernovae. Furthermore, the detection of this repeater in such a nearby galaxy implies a high local universe rate of similar events in globular clusters. Building off the properties inferred from the M81 FRB, we predict the number of FRB sources in nearby ($d \lesssim 20\,$Mpc) galaxies with large globular cluster systems known. Incorporating the uncertain burst energy dis…
Fast radio bursts (FRBs) are bright, millisecond-duration radio pulses whose origins are unknown. To date, only one (FRB 121102) out of several dozen has been seen to repeat, though the extent to which it is exceptional remains unclear. We discuss detecting repetition from FRBs, which will be very important for understanding their physical origin, and which also allows for host galaxy localisation. We show how the combination of instrument sensitivity, beamshapes, and individual FRB luminosity functions affect the detection of sources whose repetition is not necessarily described by a homogene…
The recently observed chirping signature in the light curves of Seyfert 1 galaxy SDSSJ1430$+$2303 could be explained by a late-inspiralling supermassive binary black hole (SMBBH) system in the galactic center, which will merge in the near future (or could have merged already). For the merging SMBBH scenario, SDSSJ1430$+$2303 can be a source of nonlinear gravitational wave (GW) burst with memory (BWM), which may provide a promising target for future pulsar timing array (PTA) observations. In this work, we investigate the prospects for detecting the BWM signal from SDSSJ1430$+$2303 by the Intern…
Presently only 30% of short gamma ray bursts (SGRBs) have accurate redshifts, and this sample is highly biased by the limited sensitivity of {\it Swift} to detect SGRBs. We account for the dominant biases to calculate a realistic SGRB rate density out to $z = 0.5$ using the {\it Swift} sample of peak fluxes, redshifts, and those SGRBs with a beaming angle constraint from X-ray/optical observations. Assuming a significant fraction of binary neutron star mergers produce SGRBs, we calculate lower and upper detection rate limits of (1-180) per Yr by an advanced LIGO and Virgo coincidence search. O…
We investigate the possibility of measuring intergalactic magnetic fields using the dispersion measures and rotation measures of fast radio bursts. With Bayesian methods, we produce probability density functions for values of these measures. We distinguish between contributions from the intergalactic medium, the host galaxy and the local environment of the progenitor. To this end, we use constrained, magnetohydrodynamic simulations of the local Universe to compute lines-of-sight integrals from the position of the Milky Way. In particular, we differentiate between predominantly astrophysical an…
The detection of two NS--BH mergers by LIGO-Virgo provided the first direct confirmation of the existence of this type of system in the Universe. These detections also imply the existence of pulsar--black hole (PSR--BH) systems. In this analysis, we use the non-detection of any PSR--BH systems in current radio surveys to estimate a 95\% upper limit of $\sim$150 PSR--BH binary systems that are beaming towards the Earth in the Milky Way. This corresponds to a 95\% upper limit of $\mathcal{R}_{\rm LIGO} = 7.6$~yr$^{-1}$ on the merger detection rate for the LIGO-Virgo network scaled to a range dis…
In the era of second generation ground-based gravitational wave detectors, short gamma-ray bursts (GRBs) will be among the most promising astrophysical events for joint electromagnetic and gravitational wave observation. A targeted search for gravitational wave compact binary merger signals in coincidence with short GRBs was developed and used to analyze data from the first generation LIGO and Virgo instruments. In this paper, we present improvements to this search that enhance our ability to detect gravitational wave counterparts to short GRBs. Specifically, we introduce an improved method fo…
Long-duration gamma-ray bursts are associated with the explosions of massive stars and are accordingly expected to reside in star-forming regions with molecular gas (the fuel for star formation). Previous searches for carbon monoxide (CO), a tracer of molecular gas, in burst host galaxies did not detect any emission. Molecules have been detected as absorption in the spectra of gamma-ray burst afterglows, and the molecular gas is similar to the translucent or diffuse molecular clouds of the Milky Way. Absorption lines probe the interstellar medium only along the line of sight, so it is not clea…
Fast radio bursts (FRB) probe the electron density of the universe along the path of propagation, making high redshift FRB sensitive to the helium reionization epoch. We analyze the signal to noise with which a detection of the amplitude of reionization can be made, and its redshift, for various cases of future FRB survey samples, assessing survey characteristics including total number, redshift distribution, peak redshift, redshift depth, and number above the reionization redshift, as well as dependence on reionization redshift. We take into account scatter in the dispersion measure due to an…
Using the generic hydrodynamic model of Gamma-Ray Burst (GRB) afterglows, we calculate the radio afterglow light curves of low luminosity, high luminosity, failed and standard GRBs in different observational bands of FAST's energy window. The GRBs are assumed to be located at different distances from us. Our results rank the detectability of GRBs in descending order as high luminosity, standard, failed and low luminosity GRBs. We predict that almost all types of radio afterglows except that of low luminosity GRBs could be observed by the large radio telescope as long as the domains of time and…
We present the Galactic Radio Explorer (GReX), an all-sky monitor to probe the brightest bursts in the radio sky. Building on the success of STARE2, we will search for fast radio bursts (FRBs) emitted from Galactic magnetars as well as bursts from nearby galaxies. GReX will search down to ten microseconds time resolution, allowing us to find new super giant radio pulses from Milky Way pulsars and study their broadband emission. The proposed instrument will employ ultra-wide band (0.7-2 GHz) feeds coupled to a high performance (receiver temperature 10 K) low noise amplifier (LNA) originally dev…
We discuss the prospects for the detection of gamma-ray bursts (GRBs) by the Cherenkov Telescope Array (CTA), the next generation, ground-based facility of imaging atmospheric Cherenkov telescopes (IACTs) operating above a few tens of GeV. By virtue of its fast slewing capabilities, the lower energy threshold compared to current IACTs, and the much larger effective area compared to satellite instruments, CTA can measure the spectra and variability of GRBs with excellent photon statistics at multi-GeV energies. Employing a model of the GRB population whose properties are broadly consistent with…
Core-collapse supernovae (SNe) of Types Ib and Ic arise from hydrogen-stripped stars, while the latter are also stripped of their helium. Both SN types have a similar temporal evolution, suggesting broadly similar progenitors. However, while some Ic SNe are associated with relativistic jets of gamma-ray bursts (GRBs), no GRB has yet been found in association with Type Ib SNe. Here we find that, even if GRB-like central engines operate in both SNe Ib and Ic, different properties of their envelopes may accommodate this potential tension. In particular, we focus on the case of a low-mass, extende…
Fast radio bursts (FRBs) can be scattered by ionized gas in their local environments, host galaxies, intervening galaxies along their lines-of-sight, the intergalactic medium, and the Milky Way. The relative contributions of these different media depend on their geometric configuration and the internal properties of the gas. When these relative contributions are well understood, FRB scattering is a powerful probe of density fluctuations along the line-of-sight. The precise scattering measurements for FRB 121102 and FRB 180916 allow us to place an upper limit on the amount of scattering contrib…
To assess the potential of a small telescopes for a high temporal resolution astrophysics, we observed the field of FRB~121102 repeating source of fast radio bursts on a 50-cm D50 telescope of Ondřejov observatory, equipped with a fast frame rate EMCCD detector. In a three nights of observations we did not detect any optical flares from the source, which allows us to place an upper limit of 10 mJy for a brightness of possible fast optical events on a time scale of 10 ms. We also characterize the apparent brightness stability of a field stars on the same time scale in order to investigate the p…
Fast radio bursts (FRBs) are highly dispersed, sporadic radio pulses that are likely extragalactic in nature. Here we investigate the constraints on the source population from surveys carried out at frequencies $<1$~GHz. All but one FRB has so far been discovered in the 1--2~GHz band, but new and emerging instruments look set to become valuable probes of the FRB population at sub-GHz frequencies in the near future. In this paper, we consider the impacts of free-free absorption and multi-path scattering in our analysis via a number of different assumptions about the intervening medium. We consi…
The origin of fast radio bursts (FRBs) is still unknown. Multi-wavelength observations during or shortly after the FRB phase would be essential to identify the counterpart of an FRB and to constrain its progenitor and environment. In this work, we investigate the brightness of the "fast optical bursts" (FOBs) associated with FRBs and the prospects of detecting them. We investigate several inverse Compton (IC) scattering processes that might produce an FOB, including both the one-zone and two-zone models. We also investigate the extension of the same mechanism of FRB emission to the optical ban…
We explore a novel search strategy for dark matter in the form of massive compact halo objects (MACHOs) such as primordial black holes or dense mini-halos in the mass range from $10^{-4}$ to 0.1 solar masses. These objects can gravitationally lens the signal of fast radio bursts (FRBs), producing a characteristic interference pattern in the frequency spectrum, similar to the previously studied femtolensing signal in gamma ray burst spectra. Unlike traditional searches using microlensing, FRB lensing will probe the abundance of MACHOs at cosmological distance scales (~Gpc) rather than just thei…
Probing the origin of r-process elements in the universe represents a multi-disciplinary challenge. We review the observational evidence that probe the properties of r-process sites, and address them using galactic chemical evolution simulations, binary population synthesis models, and nucleosynthesis calculations. Our motivation is to define which astrophysical sites have significantly contributed to the total mass of r-process elements present in our Galaxy. We found discrepancies with the neutron star (NS-NS) merger scenario. Assuming they are the only site, the decreasing trend of [Eu/Fe] …
Short gamma-ray bursts result from mergers of two neutron stars or from collapsars, but probably at a smaller rate. In the first case, a kilonova occurs while in the second case a Type Ic supernova is expected. } {Even if future observations of kilonovae in association with gravitational wave events provide better data, detecting a kilonova during an afterglow follow-up would remain useful for exploring the diversity of the kilonova phenomenon. As supernovae produce a weaker gravitational signal, afterglow follow-up will be the only possible method to find one. In this work, we identify the co…
Correlated red noise recently reported from pulsar timing observations may be an indication of stochastic gravitational waves emitted by cosmic strings that formed during a primordial phase transition near the Grand Unification energy scale. Unfortunately, known probes of cosmic strings, namely the Cosmic Microwave Background anisotropies and string lensing of extragalactic galaxies, are not sensitive enough for low string tensions of $Gμ= 10^{-10}-10^{-7}$ that are needed to explain this putative signal. We show that strong gravitational lensing of Fast Radio Bursts (FRBs) by cosmic strings i…
We present constraints on the origins of fast radio bursts (FRBs) using large cosmological simulations. We calculate contributions to FRB dispersion measures (DMs) from the Milky Way, from the local Universe, from cosmological large-scale structure, and from potential FRB host galaxies, and then compare these simulations to the DMs of observed FRBs. We find that the Milky Way contribution has previously been underestimated by a factor of ~2, and that the foreground-subtracted DMs are consistent with a cosmological origin, corresponding to a source population observable to a maximum redshift z~…
With the localization of fast radio bursts (FRBs) to galaxies similar to the Milky Way and the detection of a bright radio burst from SGR J1935+2154 with energy comparable to extragalactic radio bursts, a magnetar origin for FRBs is evident. By studying the environments of FRBs, evidence for magnetar formation mechanisms not observed in the Milky Way may become apparent. In this paper, we use a sample of FRB host galaxies and a complete sample of core-collapse supernova (CCSN) hosts to determine whether FRB progenitors are consistent with a population of magnetars born in CCSNe. We also compar…
We investigate the detectability of a proposed population of Gamma-Ray Bursts (GRBs) from the collapse of Population III (Pop III) stars. The James Webb Space Telescope (JWST) and Space Infrared telescope for Cosmology and Astrophysics (SPICA) will be able to observe the late time infrared afterglows. We have developed a new method to calculate their detectability, which takes into account the fundamental initial mass function (IMF) and formation rates of Pop III stars, from which we find the temporal variability of the afterglows and ultimately the length of time JWST and SPICA can detect the…
The distances of Fast Radio Burst (FRB) sources are currently unknown. We show that the 21-cm absorption line of hydrogen can be used to infer the redshifts of FRB sources, and determine whether they are Galactic or extragalactic. We calculate a probability of $\sim 10\%$ for the host galaxy of an FRB to exhibit a 21-cm absorption feature of equivalent width $\gtrsim 10 ~\mathrm{km}~\mathrm{s}^{-1}$. Arecibo, along with several future radio observatories, should be capable of detecting such associated 21-cm absorption signals for strong bursts of $\gtrsim {\rm several}~\mathrm{Jy}$ peak flux d…
We report on the discovery of FRB 20200120E, a repeating fast radio burst (FRB) with low dispersion measure (DM), detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME)/FRB project. The source DM of 87.82 pc cm$^{-3}$ is the lowest recorded from an FRB to date, yet is significantly higher than the maximum expected from the Milky Way interstellar medium in this direction (~ 50 pc cm$^{-3}$). We have detected three bursts and one candidate burst from the source over the period 2020 January-November. The baseband voltage data for the event on 2020 January 20 enabled a sky localiza…
We synthesize the known information about Fast Radio Bursts and radio magnetars, and describe an allowed origin near nuclei of external, but non-cosmological, galaxies. This places them at $z\ll1$, within a few hundred megaparsecs. In this scenario, the high DM is dominated by the environment of the FRB, modelled on the known properties of the Milky Way Center, whose innermost 100pc provides 1000 pc/cm$^3$. A radio loud magnetar is known to exist in our galactic center, within $\sim$2 arc seconds of Sgr A*. Based on the polarization, DM, and scattering properties of this known magnetar, we ext…
Fast radio bursts (FRBs) are millisecond-duration events thought to originate beyond the Milky Way galaxy. Uncertainty surrounding the burst sources, and their propagation through intervening plasma, has limited their use as cosmological probes. We report on a mildly dispersed (dispersion measure 266.5+-0.1 pc cm^-3), exceptionally intense (120+-30 Jy), linearly polarized, scintillating burst (FRB 150807) that we directly localize to 9 arcmin^2. Based on a low Faraday rotation (12.0+-0.7 rad m^-2), we infer negligible magnetization in the circum-burst plasma and constrain the net magnetization…
We have conducted an Arecibo 327 MHz search of two dwarf irregular galaxies in the Local Group, Leo A and T, for radio pulsars and single pulses from fast radio bursts and other giant pulse emitters. We detected no astrophysical signals in this search, and we estimate flux density limits on both periodic and burst emission. Our derived luminosity limits indicate that only the most luminous radio pulsars known in our Galaxy and in the Magellanic Clouds (MCs) would have been detectable in our search if they were at the distances of Leo A and T. Given the much smaller stellar mass content and sta…
