Multi-frequency Scatter Broadening Evolution of Pulsars. I

Abstract

We present multi-wavelength scatter broadening observations of 47 pulsars, made with the Giant Metre-wave Radio Telescope (GMRT), Ooty Radio Telescope (ORT) and Long Wavelength Array (LWA). The GMRT observations have been made in the phased array mode at 148, 234, and 610 MHz and the ORT observations at 327 MHz. The LWA data sets have been obtained from the LWA pulsar data archive. The broadening of each pulsar as a function of observing frequency provides the frequency scaling index, α. The estimations of α have been obtained for 39 pulsars, which include entirely new estimates for 31 pulsars. This study increases the total sample of pulsars available with α estimates by ∼50%. The overall distribution of α with the dispersion measure (DM) of pulsar shows interesting variations, which are consistent with the earlier studies. However, for a given value of DM a range of α values are observed, indicating the characteristic turbulence along each line of sight. For each pulsar, the estimated level of turbulence, C 2 ne , has also been compared with α and DM. Additionally, we compare the distribution of α with the theoretically predicated model to infer the general characteristics of the ionized interstellar medium (ISM). Nearly 65% of the pulsars show a flatter index (i.e., α < 4.4) than that is expected from the Kolmogorov turbulence model. Moreover, the group of pulsars having flatter index is typically associated with an enhanced value of C 2 ne than those with steeper index.

Evidence for magnetospheric effects on the radiation of radio pulsars

“…This suggests the RM(φ) curve is potentially time variable. Krishnakumar et al (2017) observed scatter broadening at lower frequencies for this pulsar and estimated a timescale of 0.06 ms at 1 GHz, which is relatively low. The largest ∆(V/I)(φ) variations occur at longitude ∼ 173 • , which is not where V changes most rapidly, suggesting a magnetospheric origin for the RM(φ) variations.…”

“…There are two wiggles in the PA swing towards the trailing edge of the profile, and this region is where significant RM(φ) variations (∼ 5 rad m −2 ) occur. Krishnakumar et al (2017) estimated a scattering timescale of 0.13 ms at 1GHz, which is low. If the observed RM variations were caused by scattering, ∆(V/I)(φ) variations would be expected at most longitudes, as Stokes V is steeply changing across the entire profile.…”

“…The only significant deviations can be seen around longitude 186 • , where Stokes V is changing the most, indicating that scattering is the likely cause for the apparent RM variations. Krishnakumar et al (2017) estimated a scattering timescale of 0.3 ms at 1 GHz.…”

Observed glitches in 8 young pulsars

“…P (pulse period) was taken from the ATNF pulsar catalog 3 , whereas W (width of the pulse) was corrected for pulse scatter-broadening from W 50 4 as explained below. The effect of scatter broadening was taken into account by convolving a top hat pulse of width W 50 with the exponential scatter-broadening function using characteristic time-scales obtained from Krishnakumar et al (2017a) and NE2001 model (Cordes & Lazio 2002). The final width W is taken as 50% of the peak height of the convolved pulse profile.…”

Discovery of recombining plasma inside the extended gamma-ray supernova remnant HB9

“…The closest compact source to HB9 is the pulsar PSR B0458+46/PSR J0502+4654 that is located within the radio continuum shell of the SNR (Krishnakumar et al 2017). This pulsar is at a distance of 1.79 kpc and so far no gammaray emission has been detected from it.…”