arXiv subjects

Yash Bhusare

Publications and source records attributed to Yash Bhusare.

8 recordsLinked to original sources

arXiv2026

Unveiling the Local Environment of FRB 20220912A: Sub-arcsecond $4-26$ GHz Radio Continuum Mapping

The local environments of repeating fast radio bursts (FRBs) provide critical clues to their progenitors. While some active repeaters (e.g., FRB~20121102A, FRB~20190520B) are embedded in compact persistent radio sources (PRS), others appear to reside in cleaner environments. We present a high-resolution, multi-frequency (4$-$26 GHz) continuum study of the hyperactive repeater FRB 20220912A using the Karl G. Jansky Very Large Array (VLA). We report the discovery of a previously unknown radio source distinct from the compact PRSs seen in other FRBs, spatially coincident with the FRB position and offset by $\approx 300$~mas ($\approx 450$~pc) from the host galaxy's center. The absence of continuum emission in archival milliarcsecond-resolution VLBI observations indicates that the source is resolved out, ruling out a hyper-compact ($< 1$~pc) central-engine-powered origin. We constrain the physical diameter of the emitting region between 75~pc and 190~pc. We further demonstrate that the source is characterized by a steep non-thermal spectral index ($\alpha \approx -0.73$) and a remarkably high star-formation rate surface density $\Sigma_{\text{SFR}} \gtrsim 13~M_{\odot}~\text{yr}^{-1}~\text{kpc}^{-2}$. We argue that this emission is best explained as a compact star-forming region within the host galaxy. This association with a site of ongoing star formation provides strong observational support for the hypothesis that young magnetars, formed after the deaths of massive stars, are the progenitors of at least some repeating FRBs.

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arXiv2026

Survey of compact sources for pulsars and exotic objects -- I. Overview and initial discoveries

Targeted searches for pulsars based on their counterparts in radio images have resulted in the discovery of interesting pulsars including the first ever discovered millisecond pulsar (MSP). Here, we report the first results from our image-based survey of compact sources for pulsars and exotic objects (SCOPE). SCOPE utilizes interferometric as well as time-domain observations to search for radio pulsations as well as characterize the sources in the image-domain to identify their true nature. In the first stage of the SCOPE survey, we have used the Giant Metrewave Radio Telescope (GMRT) and the Green Bank Telescope (GBT) to follow up a sample of 31 compact and steep-spectrum sources. We provide an overview of the survey, the sample selection, the search procedures, and present discoveries of two MSPs -- PSR J1840+1102 and PSR J1827-0849. PSR J1840+1102 is a 1.6 ms pulsar at the edge of the Scutum-Centaurus arm, while PSR J1827-0849 is the radio counterpart of a gamma-ray pulsar that was earlier thought to be radio-quiet, and both the sources have very steep radio spectra. Using the interferometric data, we also provide a morphological classification of all the sources, model and characterize their spectra and identify the resolved, extragalactic sources in our sample. We discuss these results in the context of future image-based pulsar surveys.

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arXiv2026

CHIME/Slow overview and pilot survey: A new backend to search for second-duration radio transients with the CHIME telescope

We present an overview of CHIME/Slow, a real-time transient search backend under development to search for second-duration radio transients using the CHIME telescope, and results obtained from a pilot survey carried out using the prototype version of the search pipeline. The prototype CHIME/Slow pipeline was tested on archival data obtained in December 2022, January 2023 and February 2023 with a total on-sky time of 17 days with an instantaneous Field of View (FoV) of $\sim$13 deg$^2$ . In this pilot survey, we detected nine bursts, one from a new non-repeating source and eight from the known hyperactive repeating source FRB 20220912A. Out of these nine bursts, two bursts from the repeater were not detected by CHIME/FRB, while the non-repeater was detected in the side-lobe of a beam in the CHIME/FRB exhibiting shorter pulse width and narrower bandwidth compared to the CHIME/Slow detection. Here we report properties of the bursts, discuss the sensitivity and completeness of the current version of the CHIME/Slow pipeline, and outline future development to improve its performance. Finally, based on these results, we report the all-sky rate (95% credible region) of radio transients with pulse widths between 16 ms to 5 s, fluence above 5 Jy ms and observing frequency of 600 MHz to be between 184 and 4556 bursts sky$^{-1}$ day$^{-1}$.

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arXiv2026

The Second CHIME/FRB Catalog of Fast Radio Bursts

We present a catalog of 4539 fast radio bursts (FRBs) observed with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope between 25 July 2018 and 15 September 2023. These bursts originate from 3641 unique sources, including 981 bursts from 83 known repeating sources. For each FRB, the catalog provides a $O(10')$ estimate of sky location along with corresponding measurements of cumulative exposure time and survey sensitivity over the observing period. It includes a total-intensity dynamic spectrum between 400 and 800 MHz at 0.983 ms resolution. From this spectrum, we constrain a model of the burst morphology and measure key parameters such as arrival time, intrinsic temporal width, dispersion measure, scattering time, and flux density. This second catalog includes all FRBs from the first catalog, with every event reprocessed using a uniform and improved analysis framework. We show that previously published inferences remain valid under the updated measurements. We assess consistency of the detection rate across observational parameters, present initial distributions of burst properties, and outline ongoing and future studies that will use this catalog to investigate the nature of FRBs and their utility as astrophysical and cosmological probes.

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arXiv2025

Long-term monitoring of repeating FRB 20220912A with the uGMRT at low radio frequencies

Some repeating FRBs exhibit occasional extreme repetition rates, but very few show a sustained high activity level. One such hyperactive repeater is FRB 20220912A, which was discovered by CHIME/FRB Collaboration on 2022 September 12. Here, we present results from a long-term monitoring campaign of FRB 20220912A using the upgraded Giant Metrewave Radio Telescope (uGMRT) in the frequency range from 300 to 750 MHz. Over the course of nearly two years, we detected a total of 643 bursts in this frequency range. The source exhibited extreme activity for a few months after its discovery and sustained its active phase for more than 1.5 years, with unsystematic modulations in the activity during this phase. The cumulative energy distributions in both bands show a break, consistent with other active repeaters like FRB 20121102A, FRB 202011124A, etc., suggesting common underlying emission mechanisms. Moreover, we show that the energy distribution shape for FRB 20220912A remains broadly same across a large range of frequencies and over time. Overall, the extended high activity, estimated total energy output, persistent power-law tails in the energy distributions, and the lack of detectable short timescale periodicity favor progenitor models invoking young dynamic magnetars, potentially emitting pulses across large rotation phase ranges.

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arXiv2025

FRB 20250316A: A Brilliant and Nearby One-Off Fast Radio Burst Localized to 13 parsec Precision

Precise localizations of a small number of repeating fast radio bursts (FRBs) using very long baseline interferometry (VLBI) have enabled multiwavelength follow-up observations revealing diverse local environments. However, the 2--3\% of FRB sources that are observed to repeat may not be representative of the full population. Here we use the VLBI capabilities of the full CHIME Outriggers array for the first time to localize a nearby (40 Mpc), bright (kJy), and apparently one-off FRB source, FRB 20250316A, to its environment on 13-pc scales. We use optical and radio observations to place deep constraints on associated transient emission and the properties of its local environment. We place a $5\sigma$ upper limit of $L_{\mathrm{9.9~\mathrm{GHz}}} < 2.1\times10^{25}~\mathrm{erg~s^{-1}~Hz^{-1}}$ on spatially coincident radio emission, a factor of 100 lower than any known compact persistent radio source associated with an FRB. Our KCWI observations allow us to characterize the gas density, metallicity, nature of gas ionization, dust extinction and star-formation rate through emission line fluxes. We leverage the exceptional brightness and proximity of this source to place deep constraints on the repetition of FRB 20250316A, and find it is inconsistent with all well-studied repeaters given the non-detection of bursts at lower spectral energies. We explore the implications of a measured offset of 190$\pm20$ pc from the center of the nearest star-formation region, in the context of progenitor channels. FRB 20250316A marks the beginning of an era of routine localizations for one-off FRBs on tens of mas-scales, enabling large-scale studies of their local environments.

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arXiv2024

Low-frequency Probes of the Persistent Radio Sources associated with Repeating FRBs

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 (uGMRT) at low radio frequencies. Towards FRB~20240114A, we report the detection of compact source at 650\,MHz with a flux density of 65.6$\pm$8.1\,$\mu$Jy/beam. 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 persistent radio source (PRS) associated with the FRB 20240114A. 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.

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arXiv2024

Varying activity and the burst properties of FRB 20240114A probed with GMRT down to 300 MHz

Repeating Fast Radio Bursts (FRBs) can exhibit a wide range of burst repetition rates, from none to hundreds of bursts per hour. Here, we report the detection and characteristics of 60 bursts from the recently discovered FRB 20240114A, observed with the upgraded Giant Metrewave Radio Telescope (uGMRT) in the frequency ranges 300-500MHz and 550-750 MHz. The majority of the bursts show narrow emission bandwidth with $\Delta\nu/\nu \sim$ 10\%. All of the bursts we detect are faint ($<$10 Jy ms) and thus probe the lower end of the energy distribution. We determine the rate function for FRB 20240114A at 400 MHz, and downward drift rates at 400 and 650 MHz, and discuss our measurements in the context of the repeating FRB population. We observe sudden variations in the burst activity of FRB 20240114A over time. From our data as well as the publicly available information on other observations of FRB 20240114A so far, there is an indication that FRB 20240114A potentially exhibits chromaticity in its burst activity. While the burst properties of FRB 20240114A are similar to other repeating FRBs, the frequency-dependent activity, if established, could provide crucial clues to the origin of repeating FRBs. We also place the most stringent 5$\sigma$ upper limits of 600 $\mu$Jy and 89 $\mu$Jy on any persistent radio source (PRS) associated with FRB 20240114A at 400 MHz and 650 MHz, respectively, and compare these with the luminosity of the known PRSs associated with FRB121102A and FRB190520B.

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