About the search for pulsed radiation from the magnetar SGR1935+2154 at the LPA LPI

Abstract

J1935+2154 is known as a source of soft gamma radiation. Hyperflares from magnetar were detected at a frequency of 1.25 GHz on the FAST telescope in May 2020. The magnetar enters the survey conducted on LPA radio telescope at 111 MHz. A check of the previously published (Fedorova et al. 2021) pulse from the magnetar SGR1935+2154 was carried out. The data received on the LPA is recorded in parallel in two modes having low and high frequency-time resolution: 6 channels with a channel width of 415 kHz and a time resolution of Δt = 100 ms; 32 channels with a channel width of 78 kHz and a time resolution of Δt = 12.5 ms. The original search was carried out using data with low time-frequency resolution. The search for dispersed signals in the meter wavelength range is difficult, compared with the search in the decimeter range, due to scattering proportional to the fourth power of frequency and dispersion smearing of the pulse in frequency channels proportional to the second power of frequency. In order to collect a broadened pulse signal and obtain the best value of S/N, the search was carried out using an algorithm based on the convolution of multichannel data with a scattered pulse pattern. The shape of the template corresponds to the shape of a scattered pulse with a dispersion measure (DM) of 375 pc/cm3. For repeated verification, the same data was used in which the pulse from the magnetar was detected. An additional check of the published pulse was also carried out using data with a higher frequency-time resolution. Since the dispersion smearing in the frequency channel in the 32-channel data is 5 times less than in the 6-channel data, an increase approximately 2 times in the S/N pulse could be expected. Pulse radiation with S/N>4 having a pulse peak shift depending on DM from SGR1935+2154 was not detected in either 32-channel or 6-channel data.