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Burst properties of the highly active FRB 20201124A using uGMRT

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 Publication date 2021
  fields Physics
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We report the observations of the highly active FRB 20201124A with the upgraded Giant Metrewave Radio Telescope at 550-750~MHz. These observations in the incoherent array mode simultaneously provided an arcsecond localization of bursts from FRB 20201124A, the discovery of persistent radio emission associated with the host galaxy, and the detection of 48 bursts. Using the brightest burst in the sample ($F= 108~{rm Jy~ms}$) we find a structure-maximizing dispersion measure of $410.8 pm 0.5~{rm pc~cm}^{-3}$. We find that our observations are complete down to a fluence level of $10~{rm Jy~ms}$, above which the cumulative burst rate scales as a power-law $R(>!F) = 10~{rm hr}^{-1} left(F/10,mathrm{Jy~ms}right)^{gamma}$ with $gamma = -1.2 pm 0.2$. Below $10~{rm Jy~ms}$, we estimate that we miss $gtrsim$ 80% of the bursts down to $1~{rm Jy~ms}$. However, this fainter burst population will be accessible with future observations using the more sensitive phased array mode. We find that the bursts are on an average wider than those reported for other repeating FRBs. We find that the waiting time between bursts is well approximated by an exponential distribution during our observations. We searched for periodicities using both a standard Fourier domain search as well as a search using the Fast Folding Algorithm, but found no significant candidates. We measure bulk spectro-temporal drift rates between $-0.75$ and $-20~{rm MHz~ms}^{-1}$. Finally, we use the brightest burst to set an upper limit to the scattering time of 13.6~ms at 550~MHz. The localization of FRB 20201124A adds strength to the proof-of-concept method described in our earlier work and serves as a potential model for future localizations and follow-up of repeating FRBs with the uGMRT.

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The repeating FRB source, FRB 20201124A, was found to be highly active in March and April 2021. We observed the source with the Effelsberg 100-m radio telescope at 1.36 GHz on 9 April 2021 and detected 20 bursts. A downward drift in frequency over time is clearly seen from the majority of bursts in our sample. A structure-maximizing dispersion measure (DM) search on the multi-component bursts in our sample yields a DM of 411.6$pm$0.6 pc/cm$^3$. We find that the rotation measure (RM) of the bursts varies around their mean value of -605 rad/m$^2$ with a standard deviation of 11.1 rad/m$^2$. This RM magnitude is 10 times larger than the expected Galactic contribution along this line of sight (LoS). We estimate a LoS magnetic field strength of 4--6 $mu$G, assuming that the entire host galaxy DM contributes to the RM. Further polarization measurements will help determine FRB 20201124As RM stability. The bursts are highly linearly polarized, with some showing signs of circular polarization, the first for a repeating FRB. Their polarization position angles (PAs) are flat across the burst envelopes and vary between bursts. We argue that the varying polarization fractions and PAs of FRB 20201124A are similar to known magnetospheric emission from pulsars, while the observed circular polarization, combined with the RM variability, is hard to explain with Faraday conversion. The high linear polarization fractions, flat PAs, and downward drift from FRB 20201124A bursts are similar to previous repeating sources, while the observed circular polarization is a newly seen behaviour among repeaters.
We present the Australian Square Kilometre Array Pathfinder (ASKAP) localization and follow-up observations of the host galaxy of the repeating FRB 20201124A, the fifth such extragalactic repeating fast radio burst (FRB) with an identified host. From spectroscopy using the 6.5-m MMT Observatory, we derive a redshift of $z=0.0979 pm 0.0001$, SFR(H$alpha$) $approx 2.1 M_{odot}$ yr$^{-1}$, and global metallicity of 12+log(O/H)$approx 9.0$. By jointly modeling the 12-filter optical-MIR photometry and spectroscopy of the host, we infer a median stellar mass of $approx 2 times 10^{10} M_{odot}$, internal dust extinction of $A_Vapprox 1-1.5$ mag, and a mass-weighted stellar population age of $approx 5-6$ Gyr. Connecting these data to the radio and X-ray observations, we cannot reconcile the broad-band behavior with strong AGN activity and instead attribute the dominant source of persistent radio emission to star formation, likely originating from the circumnuclear region of the host. The modeling also indicates a hot dust component contributing to the mid-IR luminosity at a level of $approx 10-30%$. We construct the host galaxys star formation and mass assembly histories, finding that the host assembled $>90%$ of its mass by 1 Gyr ago and exhibited a fairly constant rate of star formation for most of its existence, with no clear evidence of any star-burst activity.
The physical properties of fast radio burst (FRB) host galaxies provide important clues towards the nature of FRB sources. The 16 FRB hosts identified thus far span three orders of magnitude in mass and specific star-formation rate, implicating a ubiquitously occurring progenitor object. FRBs localised with ~arcsecond accuracy also enable effective searches for associated multi-wavelength and multi-timescale counterparts, such as the persistent radio source associated with FRB 20121102A. Here we present a localisation of the repeating source FRB 20201124A, and its association with a host galaxy (SDSS J050803.48+260338.0, z=0.098) and persistent radio source. The galaxy is massive ($sim3times10^{10} M_{odot}$), star-forming (few solar masses per year), and dusty. Very Large Array and Very Long Baseline Array observations of the persistent radio source measure a luminosity of $1.2times10^{29}$ erg s$^{-1}$ Hz$^{-1}$, and show that is extended on scales $gtrsim50$ mas. We associate this radio emission with the ongoing star-formation activity in SDSS J050803.48+260338.0. Deeper, more detailed observations are required to better utilise the milliarcsecond-scale localisation of FRB 20201124A reported from the European VLBI Network, and determine the origin of the large dispersion measure ($150-220$ pc cm$^{-3}$) contributed by the host. SDSS J050803.48+260338.0 is an order of magnitude more massive than any galaxy or stellar system previously associated with a repeating FRB source, but is comparable to the hosts of so far non-repeating FRBs, further building the link between the two apparent populations.
286 - L. Piro , G. Bruni , E. Troja 2021
We present the results of a multiwavelength campaign of FRB20201124A, the second closest repeating fast radio burst recently localized in a nearby (z=0.0978) galaxy. Deep VLA observations led to the detection of a quiescent radio emission, also marginally visible in X-rays with Chandra. Imaging at 22 GHz allowed us to resolve the source on a scale of $gtrsim 1$ arcsec in a direction tangential to the center of the host galaxy and locate it at the position of the FRB, within an error of $0.2$ arcsec. EVN and e-MERLIN observations sampled small angular scales, from 2 to 100 mas, providing tight upper limits on the presence of a compact source and evidence for diffuse radio emission. We argue that this emission is associated with enhanced star formation activity in the proximity of the FRB, corresponding to a star formation rate of $approx 10 {rm M}_odot {rm yr}^{-1}$. The surface star formation rate at the location of FRB20201124A is two orders of magnitude larger than typically observed in other precisely localized FRBs. Such a high SFR is indicative of this FRB source being a new-born magnetar produced from a SN explosion of a massive star progenitor. Upper limits to the X-ray counterparts of 49 radio bursts observed in our simultaneous FAST, SRT and Chandra campaign are consistent with a magnetar scenario.
We report the detection of a single burst from the first-discovered repeating Fast Radio Burst source, FRB 121102, with CHIME/FRB, which operates in the frequency band 400-800 MHz. The detected burst occurred on 2018 November 19 and its emission extends down to at least 600 MHz, the lowest frequency detection of this source yet. The burst, detected with a significance of 23.7$sigma$, has fluence 12$pm$3 Jy ms and shows complex time and frequency morphology. The 34 ms width of the burst is the largest seen for this object at any frequency. We find evidence of sub-burst structure that drifts downward in frequency at a rate of -3.9$pm$0.2 MHz ms$^{-1}$. Our best fit tentatively suggests a dispersion measure of 563.6$pm$0.5 pc cm$^{-3}$, which is ${approx}$1% higher than previously measured values. We set an upper limit on the scattering time at 500 MHz of 9.6 ms, which is consistent with expectations from the extrapolation from higher frequency data. We have exposure to the position of FRB 121102 for a total of 11.3 hrs within the FWHM of the synthesized beams at 600 MHz from 2018 July 25 to 2019 February 25. We estimate on the basis of this single event an average burst rate for FRB 121102 of 0.1-10 per day in the 400-800 MHz band for a median fluence threshold of 7 Jy ms in the stated time interval.
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