Upper limits on the radio emission from SGR 1830-0645 using GBT observations (L and S bands)

ATel #14098; Yogesh Maan (ASTRON, Dwingeloo, NL), Samayra Straal (NYU Abu Dhabi, Abu Dhabi, UAE) and Joeri van Leeuwen (ASTRON, Dwingeloo, NL)
on 15 Oct 2020; 16:22 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Yogesh Maan (maan@astron.nl)

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On October 10, 2020, Swift/BAT detected a short burst from a new soft gamma-ray repeater, SGR 1830-0645 (Page et al., 2020, GCN circular 28594, ATel#14083). Using a follow-up XRT observation that happened just nearly 1 minute after the burst notification from BAT, Gogus et al. (2020, ATel#14085) uncovered a coherent periodicity with a period of about 10.4 s. In another follow-up observation, Younes et al. (2020, ATel#14086) confirmed and further refined the spin period. This period is well within the range of the magnetar spin periods, supporting the hypothesis that this new source is a magnetar. To search for any pulsed radio emission which might have also onset following the above detected X-ray burst, we observed SGR 1830-0645 using the Green Bank Telescope (GBT) at L (1.1 - 1.9 GHz) and S (1.6 - 2.4 GHz) bands. At lower radio frequencies (650 MHz), a non-detection of the magnetar was already reported (ATel#14091). Our observations were conducted using a sampling time of 327.68 us and 4096 channels across the 800 MHz bandwidth. A nearby pulsar, PSR B1830-08, was observed as a test pulsar. After decimating the data to a time resolution of 1.3 ms, we searched for periodic emission (both in a completely blind fashion, and by folding the data around the known period) as well as for bright single pulses over a DM range of 0 to 4000 cm^-3 pc. We do not detect any significant periodic or single-pulse emission. For periodic emission, we place 8-sigma upper limits on the average flux density of 14.5 microJy and 10.5 microJy at 1.5 and 2 GHz, respectively; assuming a 10% duty cycle. For single-pulse emission, the 8-sigma upper limits on the pulse-integrated flux density are 35 mJy and 27 mJy at 1.5 and 2 GHz, respectively; assuming a single-pulse width of 5 ms. We thank the Green Bank Observatory and staff for the prompt allocation and scheduling of our requested director's discretionary time, and their support.