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Low-frequency detection of FRB180916 with the uGMRT

ATel #13781; Ketan R Sand (University of Delhi), Vishal Gajjar (UC Berkeley), Maura Pilia (INAF-OACagliari), Sanjay Kudale (NCRA-TIFR), Bhal Chandra Joshi (NCRA-TIFR), Vandana S Jagtap (Maharashtra Institute of Technology, Pune), Alak Ray (HBSCE-TIFR), Avinash Deshpande (IUCAA), Biplab Bijay (NCRA-TIFR), Biprateep Dey (University of Pittsburgh), Boris Kalita ( CEA, Paris-Saclay), Debades Bandyopadhyay (SINP, Kolkata), Debashish Jena (deceased), Dipankar Bhattacharya (IUCAA), Gaurav Waratkar (IIT Mumbai), Gururaj Wagle (HBSCE-TIFR), Jaikhomba Singha (IIT Roorkie), Manjari Bagchi (IMSc , Chennai), Mayuresh P. Surnis (JBCA, Manchester), Sajad Bhat (SINP, Kolkata), Satyam Mishra (NISER, Bhubhaneswar), Sushan Konar (NCRA-TIFR), Yogesh Maan (ASTRON-NIRA)
on 4 Jun 2020; 19:56 UT
Credential Certification: Vishal Gajjar (vishalg@berkeley.edu)

Subjects: Radio, Transient, Fast Radio Burst

The FRB 180916.J0158+65 is one of the only known periodically active Fast Radio Bursts (FRBs) with a 16.35 days period [Amiri et al. (2020), arXiv:2001.10275]. Green Bank Telescope [Chawla et al. (2020), arXiv:2004.02862] and Sardinia Radio Telescope [Pilia et al (2020), arXiv:2003.12748] recently reported lower-frequency detection of FRB 180916 across 300 - 400 MHz and 296 - 360 MHz, respectively. We observed FRB 180916 during one of its predicted active windows for a total of 9 hours across 300 - 500 MHz (Band 3) with the upgraded Giant Metrewave Radio Telescope (uGMRT) using the Director's Discretionary Time. The observations were split into two windows; 2020 March 23 06:31:19 UTC for 5 hours and 2020 March 24 06:17:57 UTC for 4 hours. We used 20 antenna phased array beam and coherently dedispersed baseband voltages in realtime around a fiducial DM of 349 pc-cm^-3 for each of 2048 sub-bands. After flagging radio frequency interferences, an incoherent search across these sub-bands was performed using a GPU accelerated pipeline named SPANDAK (Gajjar et al. 2018 ApJ, 863, 2) across DM range of 0 to 500 pc-cm^-3. This pipeline is primarily setup and actively being used to search for FRBs and RRATs with the ongoing uGMRT pulsar survey at similar frequencies.

Here, we report the detection of 4 bursts from the FRB 180916.J0158+65 across 300 to 500 MHz with the uGMRT.

These are the first widest instantaneous bandwidth detections of these bursts (or any FRB) at lowest radio frequencies. Attached preliminary detection plots show a wide variety of spectral structures which will be investigated further due to the excellent wide-bandwidth capabilities of uGMRT. Some of the properties of these bursts, obtained from standard radiometer equation and preliminary analysis based on the detection properties, are shown in a table below. We found that the peak flux density of these bursts varies between 0.1 to 1.7 Jy (upper limits) with widths ranging from 5 to 11 milliseconds (upper limits). Further analysis and detailed spectro-temporal properties will be reported in future publication (K Sand et al. 2020 in prep).

With these observations, we confirm periodic activity and the low-frequency emission of FRB 180916 across a wider instantaneous bandwidth. We encourage more observations across different wavebands during active windows in upcoming months to further investigate spectral coverage of FRB emission mechanism. We thank the observatory Director to grant us time and all of the GMRT staff for their help with these observations. GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research.

 
| Burst |   Time of arrival(UTC) | Fluence (Jy ms) | SNR   | Width (ms) | 
|-----------------------------------------------------------------------| 
| B1	| 23 March, 10:07:02.778 |        	8.89 |95.51  |  5.24  	| 
| B2	| 23 March, 10:53:34.901 |      	15.11 |114.75 | 10.49  	| 
| B3	| 24 March, 08:28:40.842 |        	1.53 |11.6   | 10.49  	| 
| B4	| 24 March, 09:31:23.901 |        	3.51 |26.65  | 10.49  	| 

Detection Plots