FAST: No detection of fast radio bursts from SGR J1935+2154

ATel #13697; L. Lin (BNU), C. F.Zhang (PKU, NAOC), P. Wang (NAOC),X. Guan (NAOC), J. L. Han (NAOC), H. Xu (PKU, NAOC), J. C. Jiang (PKU, NAOC),P. Jiang (NAOC), K. J. Lee* (PKU, NAOC), D. Li*(NAOC), Y. P. Men (PKU, NAOC),C. C. Miao (NAOC), C. H. Niu (NAOC), C. Sun (NAOC), B. J. Wang (PKU, NAOC),Z. L. Wang (NAOC), J. L. Xu (NAOC), W. Yu (SHAO), B. Zhang*(UNLV), B . B. Zhang (NJU), D. J. Zhou (NAOC), J. R. Niu (NAOC), W. W. Zhu (NAOC).
on 2 May 2020; 05:36 UT
Credential Certification: Wenfei Yu (wenfei@shao.ac.cn)

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Abstract No burst was detected during a 8-hour observational campaign toward SGR J1935+2154 by FAST. Despite 29 SGR bursts detected by Fermi GBM in the time span, stringent upper limits on radio emission associated with these SGR bursts are obtained.

We have been monitoring SGR J1935+2154 using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), an 8-hour radio monitoring campaign to search for FRB- like events in four sessions between UTC 2020-04-15 21:54:00 to 2020-04-15 23:54:00, 2020- 04-26 21:06:55 to 2020-04-26 23:06:55, 2020-04-27 23:55:00 to 2020-04-28 00:50:37; and 2020- 04-28 20:35:00 020-04-28 23:35:00, with the central beam of L-band receiver with a 460 MHz band centered around 1.25 GHz and system temperature is between 20 and 25 K. When the FRB-like event occurred (ATel No. 13681, 13684), FAST was not observing the source. Bursts are searched in terms of both dispersion signature and instrumental saturation, with five types of searching strategy:

Blind searches was done using software BEAR in DM range from 1 to 5000 pc cm-3 with step of 0.3 to 3.0 pc cm-3 and burst width from 0.2 ms to 30 ms. No significant burst with S/N > 8 can be found. Independent searching with a pipeline for 8192 trials between 11.7 to 9904 pc cm-3 incorporating a GPU based PICS AI see no burst with S/N > 7.

Limited DM Search between 200 to 600 pc cm-3 according to ATel No. 13681,13684) (without RFI mitigation) gives no detection above S/N > 8

Windowed search in 1-minute window for the 29-SGR-like bursts detected by the Fermi/GBM daily TTE data on 2020-04-28, from UTC 00:19 to 00:50, was done by manually inspection of dynamic spectra for many DM and DM=0 time series, Neither burst nor saturation compatible with SGR 1935+2145 was detected, with a flux and fluence upper limits for 5 ms pulse are 4.5 mJy and 22 mJy ms, respectively, as given in Figure 2.

Ephemeris folding was done in the third session using the ephemeris of Israel et al., 2016 (MNRAS, 2016, Israel, 457, 3448) and the DM value of 333 pc cm-3 reported in ATel No. 13681,13684, no obvious signal was seen.

Searches for saturation found a short timescale wide-band saturation shown in Figure 2, with a short timescale of 10ms, which is inconsistent with possible 9 kpc distance associated with SGR 1935+2145 and DM of 333 pc cm-3 (ATel No. 13681,13684) which should gives 800 ms across the FAST band. No wide-band saturation (> 300MHz) occurs for timescale of > 500 ms, and no pulse is detected as as high as 1e3 Jy (ATel No. 13681,13684) which can saturate the FAST system.

Different from the reported FRB from SGR J1935+2154 associated with a high-energy event (ATel No. 13685, 13687, 13692), our searches give stringent upper limits in the radio band for FRB-like emission associated with SGR bursts.

Figure 1: Flux and fluence upper limits from FAST observation. The x-axis is the pulse width, upper panel: Flux upper limits, lower panel: Fluence upper limits. https://psr.pku.edu.cn/wp-content/uploads/2020/05/f1.png

Figure 2: Wide-band saturation within 1 minute of a Fermi burst. The timescale is, how- ever, too short to associate it with SGR 1935+2145 that has a large DM of 333 pc cm-3 or a distance of 9kpc. https://psr.pku.edu.cn/wp-content/uploads/2020/05/f2.png