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Improving DM Estimates Using Low-Frequency Scattering-Broadening Estimates

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY(2024)

Indian Inst Technol Roorkee | Max Planck Inst Radioastron | IISER Kolkata | Indian Inst Sci Educ & Res | Govt Brennen Coll | IIT Hyderabad | Inst Math Sci | Univ Delhi | Tata Inst Fundamental Res | Kumamoto Univ | Osaka Metropolitan Univ | Indian Inst Sci | Raman Res Inst | Indian Inst Sci Educ & Res Bhopal | Univ Wisconsin Milwaukee

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Abstract
A pulsar's pulse profile gets broadened at low frequencies due to dispersion along the line of sight or due to multipath propagation. The dynamic nature of the interstellar medium makes both of these effects time-dependent and introduces slowly varying time delays in the measured times-of-arrival similar to those introduced by passing gravitational waves. In this article, we present an improved method to correct for such delays by obtaining unbiased dispersion measure (DM) measurements by using low-frequency estimates of the scattering parameters. We evaluate this method by comparing the obtained DM estimates with those, where scatter-broadening is ignored using simulated data. A bias is seen in the estimated DMs for simulated data with pulse-broadening with a larger variability for a data set with a variable frequency scaling index, alpha , as compared to that assuming a Kolmogorov turbulence. Application of the proposed method removes this bias robustly for data with band averaged signal-to-noise ratio larger than 100. We report the measurements of the scatter-broadening time and alpha from analysis of PSR J1643 - 1224, observed with upgraded Giant Metrewave Radio Telescope as part of the Indian Pulsar Timing Array experiment. These scattering parameters were found to vary with epoch and alpha was different from that expected for Kolmogorov turbulence. Finally, we present the DM time-series after application of this technique to PSR J1643 - 1224.
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pulsars: general,pulsars: individual (PSR J1643-1224),ISM: general
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