Spectral analysis of 22 radio pulsars using SKA-Low precursor stations

Abstract

We present the first observational study of pulsars performed with the second-generation precursor stations to the low-frequency component of the Square Kilometre Array (SKA-Low): the Aperture Array Verification System 2 (AAVS2) and the Engineering Development Array 2 (EDA2). Using the SKA-Low stations, we have observed 100 southern-sky pulsars between 70–350 MHz, including follow-up observations at multiple frequencies for a selected sample of bright pulsars. These observations have yielded detections of 22 pulsars, including the lowest-frequency detections ever published for 6 pulsars, despite the modest sensitivity of initial system where the recording bandwidth is limited to ${\sim}{1}\,\mathrm{MHz}$ . By comparing simultaneous flux density measurements obtained with the SKA-Low stations and performing rigorous electromagnetic simulations, we verify the accuracy of the SKA-Low sensitivity simulation code presented in Sokolowski (2022, PASA, 39, e015). Furthermore, we perform model fits to the radio spectra of the detected pulsars using the method developed by Jankowski (2018, MNRAS, 473, 4436), including nine pulsars which were not fitted in the original work. We robustly classify the spectra into five morphological classes and find that all but one pulsar exhibit deviations from simple power-law behaviour. These findings suggest that pulsars with well-determined spectra are more likely to show spectral flattening or turnover than average. Our work demonstrates how SKA-Low stations can be meaningfully used for scientifically useful measurements and analysis of pulsar radio spectra, which are important inputs for informing pulsar surveys and science planned with the SKA-Low.

pulsar_spectra: A pulsar flux density catalogue and spectrum fitting repository

“…is open-source; researchers can upload measurements from new publications into the catalogue, which are then available to all. The software has already been used in Lee et al (2022).…”

A commensal Fast Radio Burst search pipeline for the Murchison Widefield Array

“…As described in Section 4 the pipeline has been verified by observing selected bright pulsars listed in Table 4, where columns 5 and 6 show the expected SNRs of the averaged profile and single pulses, respectively, while columns 7 and 8 show the observed SNRs if a particular pulsar was detected. The selection of these pulsars was based on the early MWA census using an offline incoherent beam pipeline (Xue et al 2017) and observations with SKA-Low stations (Sokolowski et al 2021;Lee et al 2022). This section provides a discussion of pulsar detections and explanations of the non-detections.…”

“…If a pulsar was detected, its mean flux density (m) was measured using its folded profile (procedure described in Appendix A). Otherwise, mean flux density was obtained from PSRCAT or from Lee et al (2022). Pulse widths (w) at low frequencies may be significantly higher than those in PSRCAT due to scattering.…”

“…Finally, we note that as can be seen in Table 1 the most promising low-frequency instrument to realise southern hemisphere 'FRB factory' is an all-sky monitoring system (CHASM) described by Sokolowski et al (2022a) and Sokolowski et al (in preparation), which if implemented on SKA-Low stations can reach a detection threshold between 100-1 000 Jy ms and detect tens if not hundreds of FRBs per year. Lee et al (2022), and peak flux density of 10 Jy was measured using the method described in the Appendix A and data from the Aperture Array Verification System 2 (AAVS2; Macario et al 2022).…”

“…The flux density of a pulsar can be estimated from folded profile created by pulsar processing software such as PRESTO or DSPSR, and SEFD calculated using beam model of an MWA tile or an SKA-Low station (Sokolowski et al 2022b). This approach was successfully applied to SKA-Low prototype stations data to measure flux densities of selected pulsars as described by Lee et al (2022). In this paper, we used the same method to measure mean flux density of Vela pulsar in data from the Aperture Verification System 2 (AAVS2), and we also applied similar procedure using MWA FEE beam model (Sokolowski et al 2017) to the MWA data recorded for the work presented here.…”