VLA/realfast localization and deep imaging of FRB 20201124A

ATel #14526; Casey Law (Caltech), Shriharsh Tendulkar (TIFR/NCRA), Tracy Clarke (NRL), Kshitij Aggarwal (WVU), Suryarao Bethapudy (UT-RGV), realfast collaboration, CHIME/FRB collaboration, VLITE collaboration
on 7 Apr 2021; 18:56 UT
Credential Certification: Casey Law (claw@astro.caltech.edu)

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We report results of new observations of FRB 20201124A (ATels #14497, #14508) with the Karl G. Jansky Very Large Array (VLA). On 2021-04-06, at 23h55m UT, we started a 50 minute observation in a frequency band from 1 to 2 GHz. Visibility data with a sampling time of 10 milliseconds was commensally run through the realfast FRB search system in real time (Law et al 2018).

The realfast system detected one burst with an MJD of 59311.0129359 (topocentric at 2.0 GHz) with SNR=26 and a dispersion measure of 420+-10 pc/cm3. This significance is measured in a single 10-ms image using a band from 1.3 to 1.5 GHz that includes all of the burst emission. We applied gain and flux calibration to the 10 ms image to measure a burst fluence of 2.4+-0.1 Jy ms. The burst position (J2000 epoch) is (RA, Dec) = (5:08:03.50, 26:03:37.8) with an uncertainty of 2" (dominated by estimated systematic error). The VLA and ASKAP localizations are formally inconsistent, and the VLA position is consistent with the optical center of the proposed host galaxy SDSS J050803.48+260338.0 (ATel #14515, #14516).

We have analyzed 5-s visibilities recorded from the same observation to generate a deep image of the FRB field. The VLA antennas are in the compact D configuration (1 km baselines), which has a resolution of 48" at 1.4 GHz and a confusion limit of 170 microJy. The full 1--2 GHz band image shows no source brighter than 500 microJy (3 sigma limit) at the FRB location. This field was also observed in the VLA Sky Survey epoch 1.2 in the 2--4 GHz band. No source is seen at the FRB location brighter than 500 microJy (3 sigma limit).

VLITE-Fast running on the VLA Low-band Ionosphere and Transient Experiment (VLITE, http://vlite.nrao.edu ) commensally searched for the bursts using the incoherently summed (13 antenna) total intensity filterbank data in a 320-361 MHz frequency window. No bursts were found using the standard triggering of S/N>8 for machine learning based follow-up baseband dumps, placing a limit of ~ 40 Jy ms.

Visualizations of realfast detection and host