Low-radio-frequency eclipses of the redback pulsar J2215+5135 observed in the image plane with LOFAR

Abstract

We have observed and analysed the eclipses of the black widow pulsar J1810+1744 at low radio frequencies. Using LOw-Frequency ARray (LOFAR) and Westerbork Synthesis Radio Telescope observations between 2011-2015 we have measured variations in flux density, dispersion measure and scattering around eclipses. High-time-resolution, simultaneous beamformed and interferometric imaging LOFAR observations show concurrent disappearance of pulsations and total flux from the source during the eclipses, with a 3σ upper limit of 36 mJy (< 10% of the pulsar's averaged out-of-eclipse flux density). The dispersion measure variations are highly asymmetric, suggesting a tail of material swept back due to orbital motion. The egress deviations are variable on timescales shorter than the 3.6 hr orbital period and are indicative of a clumpy medium. Additional pulse broadening detected during egress is typically < 20% of the pulsar's spin period, showing no evidence of scattering the pulses beyond detectability in the beamformed data. The eclipses, lasting ∼ 13% of the orbit at 149 MHz, are shown to be frequency-dependent with total duration scaling as ∝ ν −0.41±0.03. The results are discussed in the context of the physical parameters of the system, and an examination of eclipse mechanisms reveals cyclotron-synchrotron absorption as the most likely primary cause, although non-linear scattering mechanisms cannot be quantitatively ruled out. The inferred mass loss rate is a similar order-of-magnitude to the mean rate required to fully evaporate the companion in a Hubble time.

Study of spider pulsar binary eclipses and discovery of an eclipse mechanism transition

“…Colours are consistent between panels, and error bars represent 1σ uncertainties from the simultaneous DM and scattering fits, as explained in Section 3.1. et al 2015;Broderick et al 2016). Taking the definition of an eclipse to be a persistent region of measured flux density less than or equal to the average flux density away from the nominal eclipse phases, we find that the duration of the eclipses show significant frequency dependence (see also Section 5.1).…”

“…Measuring the eclipse durations observed at different frequencies can give information on the dependence of the eclipses on the radiation frequency, and thus potentially give insight into the eclipse mechanism or properties of the eclipse medium. To achieve such measurements a method similar to those in P18 and Broderick et al (2016) was applied here. The eclipse ingress (egress) flux densities, f , as a function of orbital phase, φ, were fit to a Fermi-Dirac type function, f = e φ−p 1…”

“…Unless otherwise stated -see Section 5.5 for PSR J2215+5135 -these formal uncertainties were assumed throughout further analyses, meaning that each individual measurement made no attempt to account for temporal variability in the eclipses. As in previous analyses (P18; Nice et al 1990;Fruchter et al 1990;Ryba & Taylor 1991;Broderick et al 2016) we attempted to glean insight from these results by fitting power law curves to the measured durations of the form ∆φ = A(ν/150) −α , where ν is the observing frequency and A and α are free parameters to be fit, representing the effective location and steepness of the curve, respectively. Similarly to the Fermi-Dirac fits explained above, we utilised the curve fit function to perform least squares fits.…”

“…However, the last few years have marked a revival of the field with detailed and novel studies beginning to give important insight into the nature of eclipsing pulsar systems (e.g. Broderick et al 2016;Main et al 2018;Li et al 2019). Observing spider pulsars at low-radio frequencies offers a particularly good opportunity to further our understanding of the eclipses.…”

Searching for pulsars associated with the Fermi GeV excess

“…This image-based approach has been used in the past to find pulsars with some success (e.g. Navarro et al 1995;Broderick et al 2016;Frail et al 2016a). In this paper we carry out a pilot study, using the recently published GMRT 150 MHz all-sky survey (TGSS ADR; Intema et al 2016) and existing images at higher frequencies to search for compact, steep spectrum radio sources within the central 2.5 • radius of the gamma-ray excess.…”