Scattering of Pulsar Radiation and Electron Density Turbulence in the Interstellar Medium

Abstract

We report measurements, using the Culgoora circular array at 80 and 160 MHz and the Parkes 64 m telescope at 410 MHz, of the pulse broadening due to interstellar scattering on 33 pulsars. These results are added to published data on 52 other pulsars in order to investigate the interstellar turbulence levels over 85 paths in the Galaxy. We find a significant relation between the turbulence level C~ and dispersion measure, heliocentric distance, galactocentric distance, galactic latitude and galactic longitude. Our results are consistent with a distribution of turbulence that peaks near the galactic centre and extends out to past the solar circle, with the scale height perpendicular to the plane at least equal to that of the pulsars. The magnitude of the fluctuations in electron density responsible for the scattering is not proportional to the average electron density, but increases much more rapidly than the latter as the galactic centre is approached. The apparent dependence of C~ on heliocentric distance is preferentially interpreted as due to the presence of a highly clumped distribution of turbulence along all lines of sight.

Scattering analysis of LOFAR pulsar observations

“…Two similar τ measurements at 160 MHz were obtained by Alurkar et al (1986) and Slee et al (1980) using the Culgoora circular array, namely 26.5 ± 8.1 and 27 ± 7 ms (Table 2). At 163.5 MHz, we obtain 30.7 ± 1.9 ms, within their estimated error at 160 MHz.…”

“…This value is in good agreement with the values obtained by Löhmer et al (2004), α = 3.4 ± 0.2, and L15b, α = 3.35 +0.36 −0.41 . Both these literature values of α are determined using other published scattering measurements between 110 and 250 MHz (Rickett 1977;Slee et al 1980;Alurkar et al 1986;Löhmer et al 2001;Kuzmin & Losovsky 2007), and therefore serve as an independent check of our measurements. Our AM leads to α = 3.9 ± 0.5, in agreement with theoretical values of 4 or 4.4.…”

“…Published τ measurements from the literature include 50 ± 15 ms at 111 MHz (Kuzmin & Losovsky 2007) and two sets of measurements at 160 MHz of 21.7 ± 1.6 ms (Alurkar et al 1986) and 25 ± 4 ms (Slee et al 1980), as shown in Fig. 11 and Table 2.…”

TMRT Observations of 26 Pulsars at 8.6 GHz

“…At frequencies of a few GHz the pulse profile is dominated by a single component. At frequencies below about 400 MHz, profile broadening due to interstellar scattering is evident (Alurkar et al 1986). Fig.…”

Radio Source Variability as a Tool for Very High Resolution

“…Studies of pulsar scintillation (Arlurkar et al, 1986) and radio sources broadening (Rao and Slee, 1988) have shown that turbulence in the ionized interstellar medium increases towards the galactic plane and towards the galactic centre. Therefore it is reasonable to expect a dependence of source variability on galactic co-ordinates if propagation effects in the interstellar medium take place.…”