Constraints on the Low-frequency Radio Emission of the Galactic Fast Radio Burst Source SGR 1935+2154
Abstract
We present a search for radio pulses from the Galactic magnetar SGR 1935+2154, a well-known source of fast radio bursts (FRBs), at ∼110 MHz using the Large Phased Array (LPA) of the Pushchino Radio Astronomy Observatory. Data from two active periods in 2020 (March–May and September–November, with ∼3.5 minutes of daily coverage) were analyzed with new methods tailored to both FRB-like single pulses and pulsar-like periodic signals. No significant FRB-like pulses were found. Using Monte Carlo simulations, 3σ upper limits were derived for the burst rate: for a lognormal energy distribution the limit is ∼101.5 day−1 for a mean of average monochromatic isotropic luminosity Lν,mean ∼ 1.3 × 1029 erg s−1 Hz−1 and a natural log-space scatter of σ ∼ 0.85; while for a power-law distribution it is ∼101.8 day−1 for an index β ≲ 3.0 and a minimum average monochromatic isotropic luminosity Lν,min≲0.7×1025ergs−1Hz−1 . When folded at the known 3.24781628 s period of SGR 1935+2154, a weak pulse was noted (S/N < 3.16), but the significance is insufficient for a secure detection of the pulsar-like emission signal. A conservative upper limit on the average monochromatic isotropic luminosity of any possible periodic emission is 2.08 × 1019 erg s−1 Hz−1. Our results offer meaningful low-frequency upper limits on the burst rate of SGR 1935+2154, and hint at very faint pulsar-like radiation at meter wavelengths.