Search for burst and periodic radio emission from SGR1935+2154 using GBT observations at 800 MHz and S-band

ATel #14151; Samayra Straal (NYU Abu Dhabi, UAE), Yogesh Maan (ASTRON, NL), Joseph Gelfand (NYU Abu Dhabi, UAE), Joeri van Leeuwen (ASTRON, NL), and Chryssa Kouveliotou (George Washington University, USA)
on 5 Nov 2020; 15:31 UT
Credential Certification: Yogesh Maan (maan@astron.nl)

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On October 8 the CHIME/FRB collaboration reported three more radio bursts from SGR 1935+2154 (ATel #13681, #13684), known to produce bright FRB-like radio bursts (ATel #14074, #14080). On October 10, FAST reported the detection of radio bursts and pulsed periodic emission at L-band (ATel #14084), speculating a possible transition to a rotation powered pulsar phase.

To search for bright radio bursts and periodic emission, we observed SGR1935+2154 on October 16, 2020 using the Green Bank Telescope (GBT) at 820 MHz (720 - 920 MHz) and S-band (1.6 - 2.4 GHz) to complement the detection by FAST at L-band (1.4 GHz). We observed the source for 1h11m at 820 MHz with 512 channels across a BW of 200 MHz, and for 1h45m at S-band centred at 2.00 GHz with 2048 channels across a BW of 800 MHz. Both the observations were conducted in coherent dedispersion mode using a DM of 332.66 pc cm-3, as reported by CHIME/FRB ATel#14080, and the data were recorded at a sampling time of 40.96 us. The nearby pulsar PSR B1919+21 was observed as a test pulsar.

The data were searched for periodic emission, both completely blind and by folding the data around the known period, and for bright single pulses, in the DM range of 320 - 345 pc cm-3. We do not detect any significant periodic or single-pulse emission. For periodic emission we place an 8-sigma upper limit on the average flux density of 29.6 microJy and 6.3 microJy at 820 MHz and S band respectively; assuming a 10% duty cycle.

For single-pulse emission, we place 8-sigma upper limits on the pulse-integrated flux density of 136 mJy and 35 mJy at 820 MHz and S-band respectively, assuming a pulse-width of 2 ms. The 2 ms wide radio burst detected at 1.4 GHz by FAST from SGR 1935+2154 in April (ATel #13699) had an estimated flux density of 30 mJy, and hence a fluence of 60 mJy ms, which is brighter than the single pulses reported in their latest ATel (#14084, fluence upto 40 mJy ms). For any potential 30 mJy broadband burst at 1.4 GHz concurrent with our observations, our upper limits at 820 MHz and S-band will imply the spectral index to be > -2.8 and < 0.43, respectively.

We thank the Green Bank Observatory and staff for the prompt allocation and scheduling of our requested observations and their support.