GMRT detection of high activity from FRB 20240619D at 650 MHz

ATel #16745; Ajay Kumar (NCRA--TIFR), Ujjwal Panda (NCRA--TIFR), Yash Bhusare (NCRA--TIFR), Yogesh Maan (NCRA--TIFR), Jayanta Roy (NCRA--TIFR), Siddhartha Bhattacharyya (NCRA--TIFR), Chahat Dudeja (NCRA--TIFR), Banshi Lal (NCRA--TIFR)
on 31 Jul 2024; 07:46 UT
Credential Certification: Yogesh Maan (maan@astron.nl)

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We report the detection of 60 bursts from the recently discovered repeating FRB, FRB 20240916D (ATel #16690), using the uGMRT. Observations were conducted at band 4 (550 - 750 MHz) with a time resolution of 0.33 ms in phased-array mode on July 25, 2024, and July 29, 2024, with on-source times of 40 and 134 minutes, respectively.

We searched for bursts above a S/N threshold of 7 in a dispersion measure (DM) range of 460 to 480 pc cm^-3 for the 25th July session, and at the structure optimized DM of 464.87 pc cm^-3 (as reported in ATel #16732) for the 29th July session. Widths of the detected bursts range from 2 ms to 21 ms, based on the FWHM of a Gaussian fit to the SNR-optimized temporal profiles of bursts in the 25th July session. Using the radiometer equation, we measure the fluence of the brightest burst detected on 29th July to be 2.8 Jy ms, with a typical uncertainty of 10%. We estimate the burst rate from the 29th July session (using only the scans where the phased-array beam was not affected by scintillation) to be approximately 28 bursts per hour above a fluence threshold of 0.23 Jy ms (corresponding to a 8-sigma detection for a 2 ms wide burst). The bursts show band-limited emission and frequency drifting, which are typical characteristics of repeating FRBs. We also obtained preliminary estimates of the structure-optimized DM for two bursts to be 465.48 +/- 0.06 pc cm^-3 and 465.11 +/- 0.05 pc cm^-3 using DM-phase (Seymour 2019).

The above burst rate at 650 MHz suggests that the source is still highly active at lower frequencies, and further follow-up observations at multiple wavelengths, particularly at lower radio frequencies, are encouraged.

We would like to thank the Director and the operations group of the observatory for the prompt time-allocation and scheduling of our observations. GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research.