No abstract

We report the discovery of the first new pulsar with the Murchison Widefield Array (MWA), PSR J0036−1033, a long-period (0.9 s) nonrecycled pulsar with a dispersion measure (DM) of 23.1 pc cm−3. It was found after processing only a small fraction (∼1%) of data from an ongoing all-sky pulsar survey. Follow-up observations have been made with the MWA, the upgraded Giant Metrewave Radio Telescope (uGMRT), and the Parkes 64 m telescopes, spanning a frequency range from ∼150 MHz to 4 GHz. The pulsar is faint, with an estimated flux density (S) of ∼1 mJy at 400 MHz and a spectrum , where ν is frequency. The DM-derived distance implies that it is also a low-luminosity source (∼0.1 mJy kpc2 at 1400 MHz). The analysis of archival MWA observations reveals that the pulsar’s mean flux density varies by up to a factor of ∼5–6 on timescales of several weeks to months. By combining MWA and uGMRT data, the pulsar position was determined to arcsecond precision. We also report on polarization properties detected in the MWA and Parkes bands. The pulsar’s nondetection in previous pulsar and continuum imaging surveys, the observed high variability, and its detection in a small fraction of the survey data searched to date, all hint at a larger population of pulsars that await discovery in the southern hemisphere, with the MWA and the future low-frequency Square Kilometre Array.

Relativistic outflows are believed to be a common feature of black hole X-ray binaries at the lowest accretion rates, when they are in their 'quiescent' spectral state. However, we still lack a detailed understanding of how quiescent jet emission varies with time. Here we present 24 years of archival radio observations (from the Very Large Array and the Very Long Baseline Array) of the black hole X-ray binary V404 Cygni in quiescence (totalling 150 observations from 1.4 -22 GHz). The observed flux densities follow lognormal distributions with means and standard deviations of ( log f ν , σ log fν ) = (−0.53, 0.19) and (−0.53, 0.30) at 4.9 and 8.4 GHz, respectively (where f ν is the flux density in units of mJy). As expected, the average radio spectrum is flat with a mean and standard deviation of ( α r , σ αr ) = (0.02, 0.65) where f ν ∝ ν αr . We find that radio flares that increase the flux density by factors of 2 -4 over timescales as short as <10 min are commonplace, and that long-term variations (over 10-4000 day timescales) are consistent with shot noise impulses that decay to stochastic variations on timescales 10 days (and perhaps as short as tens of minutes to several hours). We briefly compare the variability characteristics of V404 Cygni to jetted active galactic nuclei, and we conclude with recommendations on how to account for variability when placing quiescent black hole X-ray binary candidates with radio luminosities comparable to V404 Cygni (L R ≈ 10 28 erg s −1 ) onto the radio/X-ray luminosity plane.