Checking the empirical relations with the current localized fast radio bursts

Comparative analysis of machine learning techniques for feature selection and classification of Fast Radio Bursts

Abstract More than 800 fast radio bursts (FRBs) have been observed, including some FRBs with unusual properties. Notably, in 2022, the CHIME/FRB Collaboration reported three FRBs exhibiting subsecond periodic/quasiperiodic structures, although FRB 20191221A has recently been reclassified to originate from a galactic pulsar rather than a genuine FRB. In this paper, we propose a novel scenario to account for this class of FRBs with very short subsecond quasiperiodicity. When a neutron star (NS) follows an elliptical orbit around a stellar-mass black hole or another NS near coalescence, its crust may fracture due to direct tidal force from its companion and magnetic stress from the nonuniform magnetic field within, triggering starquake-induced FRBs. The subsecond period in the FRB is explained by the orbital period. We apply our model to current observations and explain the periodic property in FRB 20210206A and FRB 20210213A from CHIME using the appropriate model parameters. The strong magnetic field required by the fitting results of these two FRBs suggests that their central engine is a magnetar.

Abstract We develop a new statistical framework for studying the host galaxies of astrophysical sources that accounts for both redshift evolution and the multivariate nature of the properties of host galaxies. These aspects are critical when dealing with sources that span a wide range of redshifts, and/or with unknown redshift-dependent selection effects. We apply our method to a sample of fast radio burst (FRB) host galaxies as a means of probing the uncertain progenitor(s) of these events. Using our method, we are able to rule out that FRBs track star formation rate (SFR), as would be expected if FRBs are associated exclusively with young neutron stars born via core-collapse supernovae (SNe). Furthermore, we rule out a recently proposed metallicity-dependent model whereby FRBs track SFR only above an oxygen abundance of 12 + log ( O / H ) ∼ 8 . Motivated by the fact that at least one FRB has been localized to a globular cluster (GC), we also investigate the hypothesis that FRB sources track GC mass and explicitly rule out this scenario. Alternatively, we find that a “mixed” model, whereby FRBs track a linear combination of SFR and stellar mass, best explains the data. The preferred parameters of such a mixed model are similar to those inferred for Type Ia SNe and imply a possible connection between the progenitors of these different transients.

Abstract The periodicity of repeating fast radio bursts (FRBs) is crucial for understanding their origins and usually requires appropriate methods to identify. In a recent paper, we developed the Phase-folding probability Binomial Analysis (PBA) periodogram and found a candidate period of 4.605 days for FRB 20121102A. As a follow-up, thorough tests of the PBA method are first performed using numerically generated data in this paper. The tests are done for observations of 20 hr with different observation windows. PBA shows its different effects in identifying the periodicity of bursts compared with the Lomb–Scargle periodogram and χ 2 test. The PBA method is particularly sensitive for bursty sources with high burst rates ( R ≥ 2 hr −1 ), narrow active phase widths (Δ P ≤ 0.2), and a high percentage of bursts that show periodicity ( p b ≥ 0.8). We then apply PBA to analyze the periodicity of bursts from FRB 20190520B, aiming toward periods ranging from 1 day to 1024 days. For bursts with fluences higher than 0.5 Jy ms, a period of 381.1 4 − 0.29 + 1.25 days with an active phase width of 0.1 is identified. For bursts with fluences lower than 0.5 Jy ms, no periodicity is detected.

Probing cosmic curvature with fast radio bursts and DESI DR2 data

Abstract Follow-up studies of persistent emission from fast radio burst (FRB) sources are critical for understanding their elusive emission mechanisms and the nature of their progenitors. This work presents new observations of the persistent radio source (PRS) associated with FRB 20190520B. We observe a gradual decay in the PRS brightness, which is punctuated by periods of brightening and dimming at both 1.5 and 3 GHz. Furthermore, our low-frequency (<1 GHz) observations—the first for this source—reveal evidence of a spectral break, which can be attributed to absorption processes. Interpreted within the framework of the magnetar wind nebula model, our data constrain the age of the magnetar progenitor to 5 2 − 10 + 16 yr, broadly consistent with previous work. Assuming the observed 1.5 GHz variability is driven by scintillation, we discuss the constraints on the size of the persistent source. The observations presented here challenge the predictions of the previously published best-fit hypernebula model for this source.

Abstract The physical origin of fast radio bursts (FRBs) remains uncertain. Although multiwavelength observations have been widely conducted, only Galactic FRB 20200428D is associated with an X-ray burst from the magnetar SGR J1935+2154. Here we present multiwavelength follow-up observations of the nearby bright FRB 20250316A, including the Five-hundred-meter Aperture Spherical radio Telescope (FAST), Einstein Probe (EP) X-ray mission, Chandra X-ray Observatory, Wide Field Survey Telescope (WFST), and Space Variable Objects Monitor/Visible Telescope (SVOM/VT). The 13.08 hr FAST follow-up campaign without pulse detection requires an energy distribution flatter than those of well-known repeating FRBs, suggesting that this burst is likely a one-off event. A prompt EP follow-up and multiepoch observational campaign totaling >100 ks led to the detection of an X-ray source within the angular resolution of its Follow-up X-ray Telescope (FXT; 10″). A subsequent Chandra observation revealed this source to be offset by 7″ from the FRB position and established a 0.5–10 keV flux upper limit of 7.6 × 10 −15 erg cm −2 s −1 at the FRB position, corresponding to ∼10 39 erg s −1 at the 40 Mpc distance of the host galaxy NGC 4141. These results set one of the most stringent limits on X-ray emission from a nonrepeating FRB, disfavoring ultraluminous X-ray sources as counterparts of apparently one-off FRBs and offering critical insights into afterglow models. Our study suggests that an arcsecond localization of both the FRB and its potential X-ray counterpart is essential for exploring the X-ray counterpart of an FRB.

Abstract Fast radio bursts (FRBs) have emerged as a powerful tool for cosmological studies, particularly through the dispersion measure–redshift (DM– z ) relation. This work proposes a novel calibration method for FRBs using the Yang–Li–Zhang (YLZ) empirical relation, which links the rotation measure of FRBs to the luminosity of their associated persistent radio sources (PRS). We demonstrate that this approach provides independent constraints on cosmological parameters, bypassing limitations inherent to the traditional DM– z method. Utilizing the current sample of four YLZ-calibrated FRBs, we derive a Hubble constant measurement of H 0 = 86.1 8 − 14.99 + 18.03 km s − 1 Mpc − 1 (68% CL). Monte Carlo simulations indicate that a future catalog of 400 FRB-PSR systems could reduce the relative uncertainty of H 0 to 4.5%. Combining YLZ-calibrated FRBs with the DM– z sample reveals critical synergies: joint analysis of equalized samples ( N = 100 for both methods) reduces the relative uncertainty of H 0 to 2.9%, mainly because the incorporation of PRS observations substantially mitigates the degeneracy between the parameters such as intergalactic medium baryon mass fraction ( f IGM ) and other cosmological parameters inherent to the DM− z relation.

Context. The origin(s) of fast radio bursts (FRBs), mysterious radio bursts coming from extragalactic distances, remains unknown. Multiwavelength observations are arguably the only way to answer this question unambiguously. Aims. We attempt to detect hard X-ray/soft γ -ray counterparts to one of the most active FRB sources, FRB 20121102A, as well as improve our understanding of burst properties in radio through a long-term monitoring campaign using the Nançay Radio Telescope (NRT). Methods. Multiwavelength campaigns involving the International Gamma-ray Astrophysics Laboratory (INTEGRAL) satellite, the Nançay Radio Observatory, the optical telescopes at the Observatoire de Haute-Provence, as well as Arecibo were conducted between 2017 and 2019. In 2017, the telescopes were scheduled to observe simultaneously between September 24–29. We specifically used the Fast Response Enhanced CCDs for the optical observations to ensure a high time resolution. In 2019, we changed the strategy to instead conduct ToO observations on INTEGRAL and other available facilities upon positive detection triggers from the NRT. Results. In the 2017 campaign, FRB 20121102A was not in its burst active phase periodic window. We obtain a 5 σ optical flux limit of 12 mJy ms using the GASP and a 3 σ limit from OHP T120cm R -band image of R = 22.2 mag of any potential persistent emission not associated with radio bursts. In the 2019 campaign, we have simultaneous INTEGRAL data with at least 11 radio bursts from the NRT and Arecibo. We obtain a 5 σ upper limit of 2.7 × 10 −7 erg cm −2 in the 25–400 keV energy range for contemporary radio and high energy bursts, and a 5 σ upper limit of 3.8 × 10 −11 erg cm −2 for permanent emission in the 25–100 keV energy range. In addition, we report on the regular observations from NRT between 2016–2020, which account for 120 additional radio bursts from FRB 20121102A. We observe temporal dispersion measure (DM) variations at a level of ΔDM ∼ +2.04(4) pc cm −3 /yr, in broad agreement with the literature. We also present an updated fit of the periodic active window, the emission bandwidth and the burst width distribution.

The Galactic magnetar SGR 1935$+$2154 has exhibited prolific high-energy (HE) bursting activity in recent years. Investigating its potential tera-electronvolt counterpart could provide insights into the underlying mechanisms of magnetar emission and very high-energy (VHE) processes in extreme astrophysical environments. We aim to search for a possible tera-electronvolt counterpart to both its persistent and sub-second-scale burst emission. We analysed over SI hour of observations from the Large-Sized Telescope prototype (LST-1) of the Cherenkov Telescope Array Observatory (CTAO) during periods of HE activity from SGR 1935$+$2154 in 2021 and 2022 to search for persistent emission. For bursting emission, we selected and analysed nine SI second time windows centred around known short X-ray bursts, targeting potential sub-second-scale tera-electronvolt counterparts in a low-photon-statistics regime. While no persistent or bursting emission was detected in our search, we establish upper limits for the tera-electronvolt emission of a short magnetar burst simultaneous to its soft gamma-ray flux. Specifically, for the brightest burst in our sample, the ratio between tera-electronvolt and X-ray flux is łesssim e-3 The non-detection of either persistent or bursting tera-electronvolt emission from SGR 1935$+$2154 suggests that if such components exist, they may occur under specific conditions not covered by our observations. This aligns with theoretical predictions of VHE components in magnetar-powered fast radio bursts and the detection of si electronvolt electronvolt emission in giant magnetar flares. These findings underscore the potential of magnetars, fast radio bursts, and other fast transients as promising candidates for future observations in the low-photon-statistics regime with Imaging Atmospheric Cherenkov Telescopes, particularly with the CTAO.

Abstract The origin of fast radio bursts (FRBs) has remained a mystery up to now. There are two kinds of process invoking neutron stars as an origin of FRBs, namely inner-driven starquakes and outer-driven collisions with interstellar objects (ISOs). The former origin should exhibit an earthquake-like statistical behavior while the latter should show a stochastic process. In this paper, we introduce a new statistical method by making use of the energy structure function of active repeating FRBs and earthquakes. We find that the energy structure function of FRBs exhibits a very different statistical behavior compared to that of earthquakes. On small time-interval scales, the energy of an earthquake show a tendency to decay with time-interval and the energy difference of a pair of events increases with time-interval. Such a behavior is not found in FRBs, whose energy function is very similar to those of a stochastic process. Our result shows that repeating FRBs may have an origin process differing from that of earthquakes, i.e., FRBs arise from a series of unrelated events such as collisions of a neutron star with ISOs.

Abstract The association between FRB 20200428D and the Galactic magnetar SGR J1935+2154 makes magnetars the leading engine of cosmological fast radio bursts (FRBs). However, there is a list of puzzles for this magnetar-for-all-FRBs scenario: known Galactic magnetars are all isolated, and none of them are active repeaters; some cosmological repeaters have extremely high repetition rates but without any measurable spin-related periodicity; some show long-term periodic active windows; and some show diverse rotation measure (RM) evolution patterns, such as quasiperiodic fluctuations, sign reversals, and abrupt RM flares. Here we propose a unified theoretical paradigm for FRBs within the framework of the magnetar engine: most active repeating FRBs originate from magnetars in binary systems with nearly aligned rotation and magnetic axes, some of which have a triple-aligned geometry, i.e., an alignment with the orbital axis as well, whereas apparent nonrepeaters and inactive repeaters originate from magnetars in isolated systems or in binaries with a misaligned geometry. By studying various magnetar formation channels using population synthesis, we show that a few percent of magnetars in the Universe can be in binary systems, most with a massive star companion and some with aligned geometry. We suggest that such binary systems can account for the rich phenomenology of active repeaters. We suggest that the existence of a companion helps to maintain the aligned geometry and that the companion may play an active role in triggering FRBs in an active repeater source.

Abstract This paper is devoted to the study of the viability of DESI and the fast radio burst to constrain the free parameters of modified theories of gravity. Thus, we present a model supported in f ( R ) gravity involving a function of the Ricci scalar named Starobinsky-type with the peculiarity that the non-commutative essence is intrinsic to the coefficients. Additionally, to understand the dynamics within a flat Friedmann–Lemaitre–Robertson–Walker universe, we explore the possibility of deriving a Friedman equation (in measure) that results from an adequate mathematical treatment. As we mentioned previously, to test the outlined model, a Monte Carlo Markov chain analysis is implemented, using cosmic chronometers, type Ia supernovae, Hydrogen II galaxies, Intermediate-luminosity quasars, Baryon Acoustic oscillations and Fast Radio Bursts data, to constraint the free parameters of the model and presenting H ( z ), q ( z ) and $$\omega _{eff}(z)$$ ω eff ( z ) . The final results are compared with the $$\Lambda $$ Λ CDM model and a robust discussion is presented about the viability of DESI and fast radio burst to constraint free parameters in specific to a modified theory of gravity.

Abstract Fast radio bursts (FRBs) are luminous, dispersed pulses of extragalactic origin. The physics of the emission mechanism, the progenitor environment, and their origin are unclear. Some repeating FRBs exhibit a frequency-dependent decrease in linear polarisation fraction. This has been attributed to multipath propagation in a surrounding complex magneto-ionic environment. In this framework, the depolarisation magnitude can be quantified using the parameter $\sigma ^{\prime }_{\rm RM}$, which can be used to model the magneto-ionic complexity of the medium. In addition to depolarisation, some repeating sources (specifically, those with complex magneto-ionic environments) have been identified to have co-located persistent radio sources (PRS). Searches for depolarisation of non-repeating sources are challenging due to the limited bandwidth of most FRB detection systems. However, even with a limited bandwidth, such depolarisation can be identified if it lies within the $\sigma ^{\prime }_{\rm RM}$ sensitivity window of the telescope. In this paper, we present a search for depolarisation in 12 one-off FRBs detected by the Australian SKA Pathfinder. We report on a strongly depolarised (apparently) non-repeating FRB detected by ASKAP (FRB 20230526A). The source shows a decrease in linear polarisation fraction from ∼60 % at 1440 MHz to ∼20 % at 1110 MHz. We also report constraints on the presence of a PRS coincident with FRB 20230526A using observations obtained with the Australia Telescope Compact Array. We use this to study the relationship between $\sigma ^{\prime }_{\rm RM}$ and PRS luminosity. Our investigation supports a scenario in which repeaters and non-repeaters share a common origin and where non-repeaters represent an older population relative to repeating FRB sources.

Abstract Impulsive radio signals such as fast radio bursts (FRBs) are imprinted with the signatures of multi-path propagation through ionised media in the form of frequency-dependent temporal broadening of the pulse profile, commonly referred to as scattering. The dominant source of scattering for most FRBs is expected to be within their host galaxies, an assumption which can be tested by examining potential correlations between the scattering properties of the FRBs and global properties of their hosts. Using results from the Commensal Real-time ASKAP Fast Transient (CRAFT) survey, we investigate correlations across a range of host galaxy properties against attributes of the FRB that encode propagation effects: scattering timescale τ, polarisation fractions, and absolute Faraday rotation measure. From 21 host galaxy properties considered, we find three that are correlated with τ, including the stellar surface density (or compactness; Pearson p-value p = 0.002 and Spearman p = 0.010), the mass-weighted age (Spearman p-value p = 0.009), and a weaker correlation with the gas-phase metallicity (Spearman p = 0.017). Weakly significant correlations are also found with H α equivalent widths and stellar gravitational potential. From 10,000 trials of reshuffled datasets, we expect 2 strong Spearman correlations only 2% of the time, and three weaker correlations in 6.6% of cases. Compact host galaxies may have more ionised content which scatters the FRB further. Compact galaxies were also found to correlate with gas-phase metallicity in our sample, while HII regions along the line-of-sight are also a potential contributing factor. No correlation is seen with host galaxy inclination, which weakens the case for an inclination bias, as previously suggested for samples of localised FRBs. A strong ( p = 0.002) correlation is found for absolute rotation measure with optical disc axis ratio b/a; greater rotation measures are seen for edge-on host galaxies. Further high-time resolution FRB detections, coupled with localisation and detailed follow-up on their host galaxies, are necessary to corroborate these initial findings and shed further light into the FRB mechanism.

Abstract The discovery of persistent radio sources (PRSs) associated with three repeating fast radio bursts (FRBs) has provided insight into the local environments of these FRBs. Here, we present deep radio observations of the fields surrounding three highly active repeating FRBs, namely, FRB 20220912A, FRB 20240114A, and FRB 20240619D, using the upgraded Giant Metrewave Radio Telescope at low radio frequencies. Toward FRB 20240114A, we report the detection of compact source at 650 MHz with a flux density of 65.6 ± 8.1 μ Jy beam −1 . Our measurements of the spectral index, star formation rate of the host galaxy, and recently reported constraints on the physical size strongly argue for our detected source to be a PRS associated with the FRB 20240114A. We investigate possible origins of the PRS associated with FRB 20240114A. Based on its brightness and age, we rule out central engines formed via accretion-induced collapse of a white dwarf, while superluminous supernovae, long gamma-ray bursts, and neutron star merger channels remain viable. An off-axis GRB afterglow could also explain the observed emission. For FRB 20220912A, we detect radio emission that is most likely due to star formation in the host galaxy. For FRB 20240619D, we provide upper limits on the radio emission from an associated PRS or the host galaxy. The detection of the PRS associated with FRB 20240114A is a useful addition to the PRSs known to be associated with only three other FRBs so far, and further supports the origin of the PRS in the form of magnetoionic medium surrounding the FRB sources.

Abstract The behaviour of fast radio bursts (FRBs) at radio frequencies <400 MHz is poorly understood, with only two sources detected below 300 MHz. We robustly characterise the 150-MHz activity of CHIME-detected FRB sources relative to their 600-MHz activity — using their non-detection in 473 hours of archival observations from the LOFAR Tied-Array All-Sky Survey (LOTAAS), and in 252 hours of LOFAR observations of 14 repeating FRB sources – the largest sub-300 MHz targeted FRB campaign to date. We search the LOTAAS data for repeat bursts from 33 CHIME/FRB repeaters, 10 candidate repeaters and 430 apparent non-repeaters. Their non-detection yields a population-level statistical spectral index constraint of $\alpha _{s, 135\, \rm {MHz}/600\, \rm {MHz}}>-0.9$, indicating that FRB spectral indices are, on average, flatter than those of pulsars. From the targeted campaign, the prolific repeater FRB 20201124A shows αs > 0.55, implying reduced low-frequency activity, unlike the typically negative αs seen from FRBs at higher frequency bands. We explore free-free absorption in its circumburst environment as a cause of the non-detection at 150 MHz, and find that it is consistent with either a very young ∼10 yr old supernova remnant; or a typical H ii region. Our simulations indicate that LOFAR2.0 can detect 0.3–9 FRBs per week, with up to 4 FRBs originating from redshifts 1 < z < 3. Such detections will provide robust constraints on cosmological parameters due to their clean environments. Our results thus inform future low-frequency FRB searches through the limits we place on repetition rates, and show how even non-detections can place meaningful constraints on FRB circumburst environments.

Abstract Fast radio bursts (FRBs) are millisecond-duration radio transients that serve as unique probes of ionizedextragalactic matter. We report the discovery and localization of two FRBs piercing the Andromeda galaxy (M31) with the realfast transient-detection system at the Very Large Array. These unique sightlines enable constraints on M31’s electron density distribution. We localized FRB 20230930A to a host galaxy at redshift z = 0.0925 and FRB 20230506C to a host galaxy at redshift z = 0.3896. After accounting for the dispersion contributions from the Milky Way, the host galaxies, and the intergalactic medium, we estimate M31’s contribution to be 26–239 pc cm −3 toward FRB 20230930A and 51–366 pc cm −3 toward FRB 20230506C, within the 90% credible interval (CI). By modeling the M31 disk’s contribution, we isolate the halo component and find that M31’s halo contributes 7–169 pc cm −3 along FRB 20230930A (90% CI). The inferred values of DM M31,halo from the FRBs are consistent with predictions from a modified Navarro–Frenk–White profile at the corresponding impact parameter. The cool and warm phase gas is unlikely to account for the DM M31,halo unless the ionization fraction is as high as 90%. While limited to two sightlines, these results offer tentative evidence for the existence of a hot halo surrounding M31. We also discuss the potential contribution of other foreground structures, particularly in explaining the DM excess observed in FRB 20230506C. This work demonstrates how FRBs can be used to probe the circumgalactic medium of intervening galaxies.

Abstract Fast radio bursts (FRBs) are unique probes of extragalactic ionized baryonic structure as each signal, through its burst properties, holds information about the ionized matter it encounters along its sightline. FRB 20200723B is a burst with a scattering timescale of τ 400 MHz > 1 s at 400 MHz and a dispersion measure of DM ∼244 pc cm −3 . Observed across the entire Canadian Hydrogen Intensity Mapping Experiment (CHIME)/FRB frequency band, it is the single-component burst with the largest scattering timescale yet observed by CHIME/FRB. The combination of its high scattering timescale and relatively low dispersion measure present an uncommon opportunity to use FRB 20200723B to explore the properties of the cosmic web it traversed. With an ∼arcminute-scale localization region, we find the most likely host galaxy is NGC 4602 (with PATH probability P ( O ∣ x ) = 0.985), which resides ∼30 Mpc away within a cosmic sheet structure on the outskirts of the Virgo Cluster. We place an upper limit on the average free electron density of this cosmic structure of 〈 n e 〉 < 4 . 6 − 2.0 + 9.6 × 1 0 − 5 cm −3 , broadly consistent with expectations from cosmological simulations. We investigate whether the source of scattering lies within the same galaxy as the FRB, or at a farther distance from an intervening structure along the line of sight. Comparing with Milky Way pulsar observations, we suggest the scattering may originate from within the host galaxy of FRB 20200723B.