Dipanjan Mitra

Vacuum gaps in pulsars and PSR J2144-3933

In this paper we revisit the radio pulsar death line problem within the framework of curvature radiation and/or the inverse Compton scattering-induced vacuum gap model above neutron star polar caps. Our special interest is in the recently detected pulsar PSR J2144-3933 with extremal period 8.5 s, which lies far beyond conventional death lines. We argue that the formation of vacuum gaps requires a complicated multipolar surface magnetic field, with a strength Bs typically much higher than the surface dipolar component Bd and a radii of curvature much smaller than the neutron star radius R = 106 cm. Such a multipolar surface field is also consistent with death lines including the extremal pulsar PSR J2144-3933. Since vacuum gap models produce sparks, our paper naturally supports the spark related models of subpulse drift phenomenon as well as the spark-associated models of coherent pulsar radio emission.

Anomalous Scattering of Highly Dispersed Pulsars

We report multifrequency measurements of scatter-broadening times for nine highly dispersed pulsars over a wide frequency range (0.6-4.9 GHz). We find the scatter-broadening times to be larger than expected and to scale with frequency with an average power-law index of 3.44 ± 0.13, i.e., significantly less than that expected from standard theories. Such possible discrepancies have been predicted very recently by Cordes and Lazio.

UNRAVELING THE NATURE OF COHERENT PULSAR RADIO EMISSION

Forty years have passed since the discovery of pulsars, yet the physical mechanism of their coherent radio emission is a mystery. Recent observational and theoretical studies strongly suggest that the radiation coming out from the pulsar magnetosphere mainly consists of extraordinary waves polarized perpendicular to the planes of pulsar dipolar magnetic field. However, the fundamental question of whether these waves are excited by maser or coherent curvature radiation, remains open. High-quality single-pulse polarimetry is required to distinguish between these two possible mechanisms. Here we showcase such decisive, strong single pulses from 10 pulsars observed with the Giant Meterwave Radio Telescope, showing extremely high linear polarization with the position angle following locally the mean position angle traverse. These pulses, which are relatively free from depolarization, must consist exclusively of a single polarization mode. We associate this mode with the extraordinary wave excited by the coherent curvature radiation. This crucial observational signature enables us to argue, for the first time, in favor of the coherent curvature emission mechanism, excluding the maser mechanism.

SCATTER BROADENING MEASUREMENTS OF 124 PULSARS AT 327 MHZ

We present the measurements of scatter broadening time-scales (

Vacuum gap model for PSR B0943+10

\tau_{sc}

Evolution of the multipolar magnetic field in isolated neutron stars

) for 124 pulsars at 327 MHz, using the upgraded Ooty Radio Telescope (ORT). These pulsars lie in the dispersion measure range of 37

On the aberration–retardation effects in pulsars

-

The effect of HII regions on rotation measure of pulsars

503 pc cm

Frequency dependence of the drifting subpulses of PSR B0031-07

^{-3}

The parallax, mass and age of the PSR J2145 0750 binary system

and declination (