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Victoria M. Kaspi

Publications and source records attributed to Victoria M. Kaspi.

At least 55 records · Page 3Linked to original sources
arXiv2024

Statistical association between the candidate repeating FRB 20200320A and a galaxy group

We present results from angular cross-correlations between select samples of CHIME/FRB repeaters and galaxies in three photometric galaxy surveys, which have shown correlations with the first CHIME/FRB catalog containing repeating and nonrepeating sources: WISE$\times$SCOS, DESI-BGS, and DESI-LRG. We find a statistically significant correlation ($p$-value $<0.001$, after accounting for look-elsewhere factors) between a sample of repeaters with extragalactic dispersion measure DM $>395$ pc cm$^{-3}$ and WISE$\times$SCOS galaxies with redshift $z>0.275$. We demonstrate that the correlation arises surprisingly because of a statistical association between FRB 20200320A (extragalactic DM $\approx550$ pc cm$^{-3}$) and a galaxy group in the same dark matter halo at redshift $z\approx0.32$. We estimate that the host halo, along with an intervening halo at redshift $z\approx0.12$, accounts for at least $\sim$$30\%$ of the extragalactic DM. Our results strongly motivate incorporating galaxy group and cluster catalogs into direct host association pipelines for FRBs with $\lesssim$$1'$ localization precision, effectively utilizing the two-point information to constrain FRB properties such as their redshift and DM distributions. In addition, we find marginal evidence for a negative correlation at 99.4% CL between a sample of repeating FRBs with baseband data (median extragalactic DM $=354$ pc cm$^{-3}$) and DESI-LRG galaxies with redshift $0.3\le z<0.45$, suggesting that the repeaters might be more prone than apparent nonrepeaters to propagation effects in FRB-galaxy correlations due to intervening free electrons over angular scales $\sim$$0\mbox{$.\!\!^\circ$}5$.

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arXiv2024

Modeling the Morphology of Fast Radio Bursts and Radio Pulsars with fitburst

We present a framework for modeling astrophysical pulses from radio pulsars and fast radio bursts (FRBs). This framework, called fitburst, generates synthetic representations of dynamic spectra that are functions of several physical and heuristic parameters; the heuristic parameters can nonetheless accommodate a vast range of distributions in spectral energy. fitburst is designed to optimize the modeling of features induced by effects that are intrinsic and extrinsic to the emission mechanism, including the magnitude and frequency dependence of pulse dispersion and scatter-broadening. fitburst removes intra-channel smearing through two-dimensional upsampling, and can account for phase wrapping of "folded" signals that are typically acquired during pulsar-timing observations. We demonstrate the effectiveness of fitburst in modeling data containing pulsars and FRBs observed with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope.

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arXiv2023

Comprehensive Bayesian analysis of FRB-like bursts from SGR 1935+2154 observed by CHIME/FRB

The bright millisecond-duration radio burst from the Galactic magnetar SGR 1935+2154 in 2020 April was a landmark event, demonstrating that at least some fast radio burst (FRB) sources could be magnetars. The two-component burst was temporally coincident with peaks observed within a contemporaneous short X-ray burst envelope, marking the first instance where FRB-like bursts were observed to coincide with X-ray counterparts. In this study, we detail five new radio burst detections from SGR 1935+2154, observed by the CHIME/FRB instrument between October 2020 and December 2022. We develop a fast and efficient Bayesian inference pipeline that incorporates state-of-the-art Markov chain Monte Carlo techniques and use it to model the intensity data of these bursts under a flexible burst model. We revisit the 2020 April burst and corroborate that both the radio sub-components lead the corresponding peaks in their high-energy counterparts. For a burst observed in 2022 October, we find that our estimated radio pulse arrival time is contemporaneous with a short X-ray burst detected by GECAM and HEBS, and Konus-Wind and is consistent with the arrival time of a radio burst detected by GBT. We present flux and fluence estimates for all five bursts, employing an improved estimator for bursts detected in the side-lobes. We also present upper limits on radio emission for X-ray emission sources which were within CHIME/FRB's field-of-view at trigger time. Finally, we present our exposure and sensitivity analysis and estimate the Poisson rate for FRB-like events from SGR 1935+2154 to be $0.005^{+0.082}_{-0.004}$ events/day above a fluence of $10~\mathrm{kJy~ms}$ during the interval from 28 August 2018 to 1 December 2022, although we note this was measured during a time of great X-ray activity from the source.

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arXiv2023

Host Galaxies for Four Nearby CHIME/FRB Sources and the Local Universe FRB Host Galaxy Population

We present the host galaxies of four apparently non-repeating fast radio bursts (FRBs), FRBs 20181223C, 20190418A, 20191220A, and 20190425A, reported in the first Canadian Hydrogen Intensity Mapping Experiment (CHIME/FRB) catalog. Our selection of these FRBs is based on a planned hypothesis testing framework where we search all CHIME/FRB Catalog-1 events that have low extragalactic dispersion measure (< 100 pc cm$^{-3}$), with high Galactic latitude (|b| > 10$°$) and saved baseband data. We associate the selected FRBs to galaxies with moderate to high star-formation rates located at redshifts between 0.027 and 0.071. We also search for possible multi-messenger counterparts, including persistent compact radio and gravitational wave (GW) sources, and find none. Utilizing the four FRB hosts from this study along with the hosts of 14 published local Universe FRBs (z < 0.1) with robust host association, we conduct an FRB host demographics analysis. We find all 18 local Universe FRB hosts in our sample to be spirals (or late-type galaxies), including the host of FRB 20220509G, which was previously reported to be elliptical. Using this observation, we scrutinize proposed FRB source formation channels and argue that core-collapse supernovae are likely the dominant channel to form FRB progenitors. Moreover, we infer no significant difference in the host properties of repeating and apparently non-repeating FRBs in our local Universe FRB host sample. Finally, we find the burst rates of these four apparently non-repeating FRBs to be consistent with those of the sample of localized repeating FRBs observed by CHIME/FRB. Therefore, we encourage further monitoring of these FRBs with more sensitive radio telescopes.

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arXiv2023

Proposed host galaxies of repeating fast radio burst sources detected by CHIME/FRB

We present a search for host galaxy associations for the third set of repeating fast radio burst (FRB) sources discovered by the CHIME/FRB Collaboration. Using the $\sim$ 1 arcmin CHIME/FRB baseband localizations and probabilistic methods, we identify potential host galaxies of two FRBs, 20200223B and 20190110C at redshifts of 0.06024(2) and 0.12244(6), respectively. We also discuss the properties of a third marginal candidate host galaxy association for FRB 20191106C with a host redshift of 0.10775(1). The three putative host galaxies are all relatively massive, fall on the standard mass-metallicity relationship for nearby galaxies, and show evidence of ongoing star formation. They also all show signatures of being in a transitional regime, falling in the ``green valley'' which is between the bulk of star-forming and quiescent galaxies. The plausible host galaxies identified by our analysis are consistent with the overall population of repeating and non-repeating FRB hosts while increasing the fraction of massive and bright galaxies. Coupled with these previous host associations, we identify a possible excess of FRB repeaters whose host galaxies have $M_{\mathrm{u}}-M_{\mathrm{r}}$ colors redder than the bulk of star-forming galaxies. Additional precise localizations are required to confirm this trend.

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arXiv2023

Limits on Fast Radio Burst-like Counterparts to Gamma-ray Bursts using CHIME/FRB

Fast Radio Bursts (FRBs) are a class of highly energetic, mostly extragalactic radio transients lasting for a few milliseconds. While over 600 FRBs have been published so far, their origins are presently unclear, with some theories for extragalactic FRBs predicting accompanying high-energy emission. In this work, we use the Canadian Hydrogen Intensity Mapping Experiment (CHIME) Fast Radio Burst (CHIME/FRB) Project to explore whether any FRB-like radio emission coincides in space and time with 81 gamma-ray bursts (GRBs) detected between 2018 July 17 and 2019 July 8 by Swift/BAT and Fermi/GBM. We do not find any statistically significant, coincident pairs within 3sigma of each other's spatial localization regions and within a time difference of up to one week. In addition to searching for spatial matches between known FRBs and known GRBs, we use CHIME/FRB to constrain FRB-like radio emission before, at the time of, or after the reported high-energy emission at the position of 39 GRBs. Our most constraining radio flux limits in the 400- to 800-MHz band for short gamma-ray bursts (SGRBs) are <50 Jy at 18.6 ks pre-high-energy emission, and <5 Jy at 28.4 ks post-high-energy emission, assuming a 10-ms radio burst width with each limit valid for 60 seconds. We use these limits to constrain models that predict FRB-like prompt radio emission before and after SGRBs. We also place limits as low as 2 Jy for long gamma-ray bursts (LGRBs), but there are no strong theoretical predictions for coincident FRB-like radio emission for LGRBs.

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arXiv2023

A CHIME/FRB study of burst rate and morphological evolution of the periodically repeating FRB 20180916B

FRB 20180916B is a repeating Fast Radio Burst (FRB) with a 16.3-day periodicity in its activity. In this study, we present morphological properties of 60 FRB 20180916B bursts detected by CHIME/FRB between 2018 August and 2021 December. We recorded raw voltage data for 45 of these bursts, enabling microseconds time resolution in some cases. We studied variation of spectro-temporal properties with time and activity phase. We find that the variation in Dispersion Measure (DM) is $\lesssim$1 pc cm$^{-3}$ and that there is burst-to-burst variation in scattering time estimates ranging from $\sim$0.16 to over 2 ms, with no discernible trend with activity phase for either property. Furthermore, we find no DM and scattering variability corresponding to the recent change in rotation measure from the source, which has implications for the immediate environment of the source. We find that FRB 20180916B has thus far shown no epochs of heightened activity as have been seen in other active repeaters by CHIME/FRB, with its burst count consistent with originating from a Poissonian process. We also observe no change in the value of the activity period over the duration of our observations and set a 1$σ$ upper limit of $1.5\times10^{-4}$ day day$^{-1}$ on the absolute period derivative. Finally, we discuss constraints on progenitor models yielded by our results, noting that our upper limits on changes in scattering and dispersion measure as a function of phase do not support models invoking a massive binary companion star as the origin of the 16.3-day periodicity.

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arXiv2023

The Green Bank North Celestial Cap Survey. VIII. 21 New Pulsar Timing Solutions

We present timing solutions for 21 pulsars discovered in 350 MHz surveys using the Green Bank Telescope (GBT). All were discovered in the Green Bank North Celestial Cap pulsar survey, with the exception of PSR J0957-0619, which was found in the GBT 350 MHz Drift-scan pulsar survey. The majority of our timing observations were made with the GBT at 820 MHz. With a spin period of 37 ms and a 528-day orbit, PSR J0032+6946 joins a small group of five other mildly recycled wide binary pulsars, for which the duration of recycling through accretion is limited by the length of the companion's giant phase. PSRs J0141+6303 and J1327+3423 are new disrupted recycled pulsars. We incorporate Arecibo observations from the NANOGrav pulsar timing array into our analysis of the latter. We also observed PSR J1327+3423 with the Long Wavelength Array, and our data suggest a frequency-dependent dispersion measure. PSR J0957-0619 was discovered as a rotating radio transient, but is a nulling pulsar at 820 MHz. PSR J1239+3239 is a new millisecond pulsar (MSP) in a 4-day orbit with a low-mass companion. Four of our pulsars already have published timing solutions, which we update in this work: the recycled wide binary PSR J0214+5222, the non-eclipsing black widow PSR J0636+5128, the disrupted recycled pulsar J1434+7257, and the eclipsing binary MSP J1816+4510, which is in an 8.7 hr orbit with a redback-mass companion.

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arXiv2023

Flux Calibration of CHIME/FRB Intensity Data

Fast radio bursts (FRBs) are bright radio transients of micro-to-millisecond duration and unknown extragalactic origin. Central to the mystery of FRBs are their extremely high characteristic energies, which surpass the typical energies of other radio transients of similar duration, like Galactic pulsar and magnetar bursts, by orders of magnitude. Calibration of FRB-detecting telescopes for burst flux and fluence determination is crucial for FRB science, as these measurements enable studies of the FRB energy and brightness distribution in comparison to progenitor theories. The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a radio interferometer of cylindrical design. This design leads to a high FRB detection rate but also leads to challenges for CHIME/FRB flux calibration. This paper presents a comprehensive review of these challenges, as well as the automated flux calibration software pipeline that was developed to calibrate bursts detected in the first CHIME/FRB catalog, consisting of 536 events detected between July 25th, 2018 and July 1st, 2019. We emphasize that, due to limitations in the localization of CHIME/FRB bursts, flux and fluence measurements produced by this pipeline are best interpreted as lower limits, with uncertainties on the limiting value.

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arXiv2023

TONE: A CHIME/FRB Outrigger Pathfinder for localizations of Fast Radio Bursts using Very Long Baseline Interferometry

The sensitivity and field of view of the Canadian Hydrogen Intensity Mapping Experiment (CHIME) has enabled its fast radio burst (FRB) backend to detect thousands of FRBs. However, the low angular resolution of CHIME prevents it from localizing most FRBs to their host galaxies. Very long baseline interferometry (VLBI) can readily provide the subarcsecond resolution needed to localize many FRBs to their hosts. Thus we developed TONE: an interferometric array of eight $6~\mathrm{m}$ dishes to serve as a pathfinder for the CHIME/FRB Outriggers project, which will use wide field of view cylinders to determine the sky positions for a large sample of FRBs, revealing their positions within their host galaxies to subarcsecond precision. In the meantime, TONE's $\sim3333~\mathrm{km}$ baseline with CHIME proves to be an excellent testbed for the development and characterization of single-pulse VLBI techniques at the time of discovery. This work describes the TONE instrument, its sensitivity, and its astrometric precision in single-pulse VLBI. We believe that our astrometric errors are dominated by uncertainties in the clock measurements which build up between successive Crab pulsar calibrations which happen every $\approx 24~\mathrm{h}$; the wider fields of view and higher sensitivity of the Outriggers will provide opportunities for higher-cadence calibration. At present, CHIME-TONE localizations of the Crab pulsar yield systematic localization errors of ${0.1}-{0.2}~\mathrm{arcsec}$ - comparable to the resolution afforded by state-of-the-art optical instruments ($\sim 0.05 ~\mathrm{arcsec}$).

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arXiv2023

An FRB Sent Me a DM: Constraining the Electron Column of the Milky Way Halo with Fast Radio Burst Dispersion Measures from CHIME/FRB

The CHIME/FRB project has detected hundreds of fast radio bursts (FRBs), providing an unparalleled population to probe statistically the foreground media that they illuminate. One such foreground medium is the ionized halo of the Milky Way (MW). We estimate the total Galactic electron column density from FRB dispersion measures (DMs) as a function of Galactic latitude using four different estimators, including ones that assume spherical symmetry of the ionized MW halo and ones that imply more latitudinal-variation in density. Our observation-based constraints of the total Galactic DM contribution for $|b|\geq 30^\circ$, depending on the Galactic latitude and selected model, span 87.8 - 141 pc cm^-3. This constraint implies upper limits on the MW halo DM contribution that range over 52-111 pc cm^-3. We discuss the viability of various gas density profiles for the MW halo that have been used to estimate the halo's contribution to DMs of extragalactic sources. Several models overestimate the DM contribution, especially when assuming higher halo gas masses (~ 3.5 x 10^12 solar masses). Some halo models predict a higher MW halo DM contribution than can be supported by our observations unless the effect of feedback is increased within them, highlighting the impact of feedback processes in galaxy formation.

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arXiv2023

The First CHIME/FRB Fast Radio Burst Catalog

We present a catalog of 536 fast radio bursts (FRBs) detected by the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst (CHIME/FRB) Project between 400 and 800 MHz from 2018 July 25 to 2019 July 1, including 62 bursts from 18 previously reported repeating sources. The catalog represents the first large sample, including bursts from repeaters and non-repeaters, observed in a single survey with uniform selection effects. This facilitates comparative and absolute studies of the FRB population. We show that repeaters and apparent non-repeaters have sky locations and dispersion measures (DMs) that are consistent with being drawn from the same distribution. However, bursts from repeating sources differ from apparent non-repeaters in intrinsic temporal width and spectral bandwidth. Through injection of simulated events into our detection pipeline, we perform an absolute calibration of selection effects to account for systematic biases. We find evidence for a population of FRBs - comprising a large fraction of the overall population - with a scattering time at 600 MHz in excess of 10 ms, of which only a small fraction are observed by CHIME/FRB. We infer a power-law index for the cumulative fluence distribution of $α=-1.40\pm0.11(\textrm{stat.})^{+0.06}_{-0.09}(\textrm{sys.})$, consistent with the $-3/2$ expectation for a non-evolving population in Euclidean space. We find $α$ is steeper for high-DM events and shallower for low-DM events, which is what would be expected when DM is correlated with distance. We infer a sky rate of $[525\pm30(\textrm{stat.})^{+140}_{-130}({\textrm{sys.}})]/\textrm{sky}/\textrm{day}$ above a fluence of 5 Jy ms at 600 MHz, with scattering time at $600$ MHz under 10 ms, and DM above 100 pc cm$^{-3}$.

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arXiv2023

CHIME Discovery of a Binary Pulsar with a Massive Non-Degenerate Companion

Of the more than $3{,}000$ radio pulsars currently known, only ${\sim}300$ are in binary systems, and only five of these consist of young pulsars with massive non-degenerate companions. We present the discovery and initial timing, accomplished using the Canadian Hydrogen Intensity Mapping Experiment telescope (CHIME), of the sixth such binary pulsar, PSR J2108+4516, a $0.577$-s radio pulsar in a 269-day orbit of eccentricity 0.09 with a companion of minimum mass $11$ M$_{\odot}$. Notably, the pulsar undergoes periods of substantial eclipse, disappearing from the CHIME $400{-}800$ MHz observing band for a large fraction of its orbit, and displays significant dispersion measure and scattering variations throughout its orbit, pointing to the possibility of a circumstellar disk or very dense stellar wind associated with the companion star. Subarcsecond resolution imaging with the Karl G. Jansky Very Large Array unambiguously demonstrates that the companion is a bright, $V \simeq 11$ OBe star, EM* UHA 138, located at a distance of $3.26(14)$ kpc. Archival optical observations of \companion{} approximately suggest a companion mass ranging from $17.5$ M$_{\odot} < M_{\rm c} < 23$ M$_{\odot}$, in turn constraining the orbital inclination angle to $50.3^{\circ} \lesssim i \lesssim 58.3^{\circ}$. With further multi-wavelength followup, PSR J2108+4516 promises to serve as another rare laboratory for the exploration of companion winds, circumstellar disks, and short-term evolution through extended-body orbital dynamics.

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arXiv2022

Sub-arcminute localization of 13 repeating fast radio bursts detected by CHIME/FRB

We report on improved sky localizations of thirteen repeating fast radio bursts (FRBs) discovered by CHIME/FRB via the use of interferometric techniques on channelized voltages from the telescope. These so-called 'baseband localizations' improve the localization uncertainty area presented in past studies by more than three orders of magnitude. The improved localization regions are provided for the full sample of FRBs to enable follow-up studies. The localization uncertainties, together with limits on the source distances from their dispersion measures (DMs), allow us to identify likely host galaxies for two of the FRB sources. FRB 20180814A lives in a massive passive red spiral at z~0.068 with very little indication of star formation, while FRB 20190303A resides in a merging pair of spiral galaxies at z~0.064 undergoing significant star formation. These galaxies show very different characteristics, further confirming the presence of FRB progenitors in a variety of environments even among the repeating sub-class.

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arXiv2022

The Green Bank North Celestial Cap Survey. VII. 12 New Pulsar Timing Solutions

We present timing solutions for 12 pulsars discovered in the Green Bank North Celestial Cap (GBNCC) 350 MHz pulsar survey, including six millisecond pulsars (MSPs), a double neutron star (DNS) system, and a pulsar orbiting a massive white dwarf companion. Timing solutions presented here include 350 and 820 MHz Green Bank Telescope data from initial confirmation and follow-up as well as a dedicated timing campaign spanning one year. PSR J1122$-$3546 is an isolated MSP, PSRs J1221$-$0633 and J1317$-$0157 are MSPs in black widow systems and regularly exhibit eclipses, and PSRs J2022+2534 and J2039$-$3616 are MSPs that can be timed with high precision and have been included in pulsar timing array experiments seeking to detect low-frequency gravitational waves. PSRs J1221$-$0633 and J2039$-$3616 have Fermi Large Area Telescope $γ$-ray counterparts and also exhibit significant $γ$-ray pulsations. We measure proper motion for three of the MSPs in this sample and estimate their space velocities, which are typical compared to those of other MSPs. We have detected the advance of periastron for PSR J1018$-$1523 and therefore measure the total mass of the double neutron star system, $m_{\rm tot}=2.3\pm0.3$ M$_{\odot}$. Long-term pulsar timing with data spanning more than one year is critical for classifying recycled pulsars, carrying out detailed astrometry studies, and shedding light on the wealth of information in these systems post-discovery.

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arXiv2022

Sub-second periodicity in a fast radio burst

Fast radio bursts (FRBs) are millisecond-duration flashes of radio waves that are visible at distances of billions of light-years. The nature of their progenitors and their emission mechanism remain open astrophysical questions. Here we report the detection of the multi-component FRB 20191221A and the identification of a periodic separation of 216.8(1) ms between its components with a significance of 6.5 sigmas. The long (~3 s) duration and nine or more components forming the pulse profile make this source an outlier in the FRB population. Such short periodicity provides strong evidence for a neutron-star origin of the event. Moreover, our detection favours emission arising from the neutron-star magnetosphere, as opposed to emission regions located further away from the star, as predicted by some models.

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arXiv2022

An Injection System for the CHIME/FRB Experiment

Dedicated surveys searching for Fast Radio Bursts (FRBs) are subject to selection effects which bias the observed population of events. Software injection systems are one method of correcting for these biases by injecting a mock population of synthetic FRBs directly into the realtime search pipeline. The injected population may then be used to map intrinsic burst properties onto an expected signal-to-noise ratio (SNR), so long as telescope characteristics such as the beam model and calibration factors are properly accounted for. This paper presents an injection system developed for the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst project (CHIME/FRB). The system was tested to ensure high detection efficiency, and the pulse calibration method was verified. Using an injection population of ~85,000 synthetic FRBs, we found that the correlation between fluence and SNR for injected FRBs was consistent with that of CHIME/FRB detections in the first CHIME/FRB catalog. We also noted that the sensitivity of the telescope varied strongly as a function of the broadened burst width, but not as a function of the dispersion measure. We conclude that some of the machine-learning based Radio Frequency Interference (RFI) mitigation methods used by CHIME/FRB can be re-trained using injection data to increase sensitivity to wide events, and that planned upgrades to the presented injection system will allow for determining a more accurate CHIME/FRB selection function in the near future.

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arXiv2021

A sudden period of high activity from repeating Fast Radio Burst 20201124A

The repeating FRB 20201124A was first discovered by CHIME/FRB in November of 2020, after which it was seen to repeat a few times over several months. It entered a period of high activity in April of 2021, at which time several observatories recorded tens to hundreds more bursts from the source. These follow-up observations enabled precise localization and host galaxy identification. In this paper, we report on the CHIME/FRB-detected bursts from FRB 20201124A, including their best-fit morphologies, fluences, and arrival times. The large exposure time of the CHIME/FRB telescope to the location of this source allows us to constrain its rates of activity. We analyze the repetition rates over different spans of time, constraining the rate prior to discovery to $< 3.4$ day$^{-1}$ (at 3$σ$), and demonstrate significant change in the event rate following initial detection. Lastly, we perform a maximum-likelihood estimation of a power-law luminosity function, finding a best-fit index $α= -4.6 \pm 1.3 \pm 0.6$, with a break at a fluence threshold of $F_{\rm min} \sim 16.6$~Jy~ms, consistent with the fluence completeness limit of the observations. This index is consistent within uncertainties with those of other repeating FRBs for which it has been determined.

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