A large sample of pulsars was observed as part of the Meterwavelength Single-pulse Polarimetric Emission Survey. We carried out a detailed fluctuation spectral analysis which revealed periodic features in 46% pulsars including 22 pulsars where drifting characteristics were reported for the first time. The pulsar population can be categorized into three distinct groups, pulsars which show systematic drift motion within the pulse window, the pulsars showing no systematic drift but periodic amplitude fluctuation and pulsars with no periodic variations. We discovered the dependence of the drifting phenomenon on the spin down energy loss (Ė), with the three categories occupying distinctly different regions along theĖ axis. The estimation of the drift periodicity (P 3 ) from the peak frequency in the fluctuation spectra is ambiguous due to the aliasing effect. However, using basic physical arguments we were able to determine P 3 in pulsars showing systematic drift motion. The estimated P 3 values in these pulsars were anti-correlated withĖ which favoured the Partially Screened Gap model of Inner Acceleration Region in pulsars.

In this paper we return to the old problem of conal component-pair widths and profile dimensions. Observationally, we consider a set of 10 pulsars with prominent conal component pairs, for which well measured profiles exist over the largest frequency range now possible. Apart from some tendency to narrow at high frequency, the conal components exhibit almost constant widths. We use all three profile measures, the component separation as well as the outside half-power and 10% widths, to determine conal beam radii, which are the focus of our subsequent analysis. These radii at different frequencies are well fitted by a relationship introduced by Thorsett (1991), but the resulting parameters are highly correlated. Three different types of behavior are found: one group of stars exhibits a continuous variation of beam radius which can be extrapolated down to the stellar surface along the "last open field lines"; a second group exhibits beam radii which asymptotically approach a minimum high frequency value that is 3-5 times larger; and a third set shows almost no spectral change in beam radius at all. The first two behaviors are associated with outer-cone component pairs; whereas the constant separation appears to reflect inner-cone emission. The first group, remarkably, can be fitted by a Thorsett relation in which the constant term is constrained to be the field-tangent direction at the edge of the polar cap ρ pc , but the others cannot. The first group can also be fitted well using an index of -1/3, but the second group cannot.We first compute heights from the conal beam radii, assuming dipolar fields and emission along the "last open field lines"-which we find are again well fitted by a suitable Thorsett relation. Here we find that the first group can be fitted using a constant term h pc of 10 km and also that the first two groups are remarkably well fitted by an index of -2/3. We then argue that physical emission heights can be estimated using the component separation along an interior annulus of field lines having their "feet" about halfway out on the polar cap-and such values agree well with most existing height values based on physical criteria. Therefore, we find that "radius-to-frequency" mapping is associated with outer-conal component pairs. The near constant behavior of inner-cones is thus arresting. We explore possible interrelationships between the spectral behavior of the component and profile widths produced both by the field-line flaring and the changing sightline geometry. We also attempt to understand the physical implications of the parameter values resulting from the Thorsett-relation fits.

We present the measurements of scatter broadening time-scales (τ sc ) for 124 pulsars at 327 MHz, using the upgraded Ooty Radio Telescope (ORT). These pulsars lie in the dispersion measure range of 37 -503 pc cm −3 and declination (δ) range of −57 • < δ < 60 • . New τ sc estimates for 58 pulsars are presented, increasing the sample of all such measurements by about 40% at 327 MHz. Using all available τ sc measurements in the literature, we investigate the dependence of τ sc on dispersion measure. Our measurements, together with previously reported values for τ sc , affirm that the ionized interstellar medium upto 3 kpc is consistent with Kolmogorov spectrum, while it deviates significantly beyond this distance.Subject headings: ISM :scattering -pulsars: general IntroductionFree electrons in the interstellar medium (ISM) affect the pulsar signal in three different ways: cold plasma dispersion, free-free absorption and scattering. The broadband pulsar signal gets dispersed in the ISM resulting in delay in pulse arrival time, which is a function of wavelength, λ, and its magnitude is described by the quantity known as dispersion measure DM =