A Search for Radio Bursts and Periodic Radio Emission from SGR 1830-0645 using the Deep Space Network
ATel #14102; Aaron B. Pearlman (Caltech), Walid A. Majid (JPL, Caltech), Thomas A. Prince (Caltech, JPL), Karishma Bansal (JPL), Shinji Horiuchi (CSIRO), Richard Stephenson (CSIRO), Charles J. Naudet (JPL), Jonathon Kocz (Caltech, UC Berkeley)
on 17 Oct 2020; 06:54 UT
Credential Certification: Aaron B. Pearlman (aaron.b.pearlman@caltech.edu)
Subjects: Radio, X-ray, Neutron Star, Soft Gamma-ray Repeater, Star, Transient, Pulsar, Magnetar
SGR 1830-0645 was discovered using the Swift Burst Alert Telescope (BAT) after a bright, short X-ray burst was detected from the source on 2020 October 10 (GCN #
28594, ATel #
14083). Following this report, an additional X-ray burst from SGR 1830-0645 was found in a sub-threshold search of Swift BAT data, acquired five days earlier, on 2020 October 5 (ATel #
14088). Follow-up observations of the source with Swift's X-ray Telescope (XRT) (ATel #
14085), NICER (ATel #
14086), NuSTAR (ATel #
14092), Chandra (ATel #
14097), and XMM-Newton (ATel #
14099) have all found evidence of coherent X-ray pulsations at a period of 10.42 s, which has been associated with the neutron star's spin period. SGR 1830-0645 is believed to be a newly discovered magnetar based on the nature of its short X-ray bursts and the detection of a rotational period that is comparable to other Galactic magnetars.
Radio observations of SGR 1830-0645 were subsequently performed between 550-750 MHz using the upgraded Giant Metrewave Radio Telescope (uGMRT) on 2020 October 11, which were used to place upper limits on the source's continuum, periodic, and single pulse emission (ATel #
14091). Upper limits on SGR 1830-0645's periodic and single pulse emission at L-band (1.1-1.9 GHz) and S-band (1.6-2.4 GHz) were also reported based on additional radio observations using the Green Bank Telescope (GBT) (ATel #
14098).
Here, we present the results of a radio observation of SGR 1830-0645 using the Deep Space Network (DSN) 34-m diameter radio telescope (DSS-34), located in Canberra, Australia. We observed SGR 1830-0645 continuously for 5.15 hr, starting at 2020 October 12 07:00:01 UTC, and used the pulsar backend to simultaneously record data at S-band (center frequency: 2.2 GHz, bandwidth: ~118 MHz) and X-band (center frequency: 8.3 GHz, bandwidth: ~441 MHz). Power spectral density measurements at both frequency bands were channelized and saved in digital polyphase filterbanks with a frequency and time resolution of 1 MHz and 512 us, respectively.
We dedispersed the S-band and X-band data with trial DMs between 0 and 10,000 pc cm^-3 and independently searched the data in each frequency band for periodic radio emission. We used a GPU-accelerated Fast Folding Algorithm (FFA) algorithm to search for pulsed radio emission with periods between 9 and 12 s. We also used a GPU-accelerated Fourier Domain Acceleration Search (FDAS) pipeline, which employs a matched filtering algorithm to correct for Doppler smearing, to search for periodicity. No statistically significant periods, with a signal-to-noise (S/N) ratio above 7.0, were found after folding the data modulo each of the period candidates identified by the two algorithms. We also folded the data using trial periods around the 10.42 s rotational period, but found no evidence of radio pulsations at or near the previously reported period. For an assumed duty cycle of 10%, we place the following (7-sigma) upper limits on SGR 1830-0645's radio flux density during our radio observation: < 0.14 mJy at S-band and < 0.08 mJy at X-band.
We also searched the dedispersed S-band and X-band data for radio bursts using a Fourier domain matched filtering algorithm, where each dedispersed time-series was convolved with boxcar functions with logarithmically spaced widths between 512 us and 153.6 ms. Candidates with detection signal-to-noise ratios above 7.0 were saved and classified using a GPU-accelerated machine learning pipeline based on the FETCH (Fast Extragalactic Transient Candidate Hunter) software package (Agarwal et al. 2020). The dynamic spectra of the candidates were also visually inspected for verification. No radio bursts were detected above a 7-sigma fluence detection threshold of 1.8 Jy ms for a 1-ms burst at S-band and 1.0 Jy ms for a 1-ms burst at X-band.
We thank the CDSCC staff for their rapid response in scheduling and carrying out these observations.