The analysis of the largest sample of multifrequency pulsar scatter time estimates

Abstract

We present our results of pulse broadening time estimates and the study of the frequency scaling of this quantity for 60 pulsars based on actual multi-frequency scattering estimates. This research was based on our own measurements, performed on the observational data and the profiles from various pulsar profile databases, as well as the scatter time measurements that were found in the literature. We were able to construct a database of over 60 pulsars with true multi-frequency α measurements, which allowed us to revise the previously proposed relations between the scatter time spectral slope and the dispersion measure (DM). We found that the deviations from theoretical predictions of the value of α appear for pulsars regardless of their DM, however the DM-averaged value of the scaling index is almost constant except for pulsars with very high DMs. Based on the obtained slopes we were also able to estimate the amount of scattering at the standard frequency of 1 GHz. We found that while the estimated standardized pulse broadening time increases with DM the relation seems to be much flatter than it was previously proposed, which suggests higher values of the scatter time for mid-DM pulsars, and lower values of expected pulse broadening for highly dispersed sources.

Scatter Broadening of Pulsars and Implications on the Interstellar Medium Turbulence

“…(28). Departures from the Kolmogorov prediction and a flattening of the τ sc spectrum with the slope ≤ 4 for low-latitude and high-DM pulsars have been clearly shown by observations (Löhmer et al 2001(Löhmer et al , 2004Bhat et al 2004;Lewandowski et al 2013Lewandowski et al , 2015. By adopting the scaling τ sc ∝ ν −4 and using the β value from Eq.…”

“…With regards to the frequency scaling of τ sc , in Fig. 3(c) and 3(d), we also display the multifrequency scattering measurements taken from Lewandowski et al (2015), where they provided the largest sample of pulsars with multifrequency estimates of pulse broadening to date. With some doubtful results excluded (see their table 1), each data point represents a measurement at one of the observing frequencies.…”

“…That is, there are multiple data points with the same DM value but different frequencies corresponding to an individual pulsar. Since the τ sc measurements suffer from various sources of error, e.g., the error estimates listed in table 1 in Lewandowski et al 2015 range from 0.02 to 0.86 (see more discussions on other possible sources of errors in Bhat et al 2004;Lewandowski et al 2013), when comparing the ν scaling index derived from our analysis with the observationally measured value, we consider our result as "consistency" if their difference is within the range [−1, 1], an "overestimation" if the difference is larger than 1, and an "underestimation" if the difference is smaller than −1. Obviously, by adopting a ν-dependent f , we see a good agreement between the model predictions and observational measurements (Fig.…”

“…The Kolmogorov scaling is commonly employed for this as- (51)). The same symbols are used in (c) and (d), but with the observational data from Lewandowski et al (2015) superposed on the predicted scattering regimes. Circles, upward-pointing triangles, and downward-pointing triangles indicate our results are comparable to, overestimate, or underestimate the actual ν scaling index according to the observational measurements.…”

“…Indeed, the observed scalings of pulse broadening time with both DM (Ramachandran et al 1997;Löhmer et al 2004;Krishnakumar et al 2015) and frequency (Cordes et al 1985;Johnston et al 1998a;Löhmer et al 2001Löhmer et al , 2004Lewandowski et al 2013) for low-DM pulsars (DM< 100 pc cm −3 ) are in agreement with the Kolmogorov's theory predictions, irrespective of Galactic latitudes. On the other hand, significant deviations from the Kolmogorov scaling are commonly seen in scatter broadening measurements of high-DM pulsars (Löhmer et al 2001(Löhmer et al , 2004Bhat et al 2004;Lewandowski et al 2013Lewandowski et al , 2015Krishnakumar et al 2015;Cordes et al 2016). These discrepant observations eliminate a single power law for a global description of density spectra within the ISM.…”