GMRT discovery of PSR J1544+4937, an eclipsing black-widow pulsar identified with a Fermi LAT source

Using the Giant Metrewave Radio Telescope (GMRT) we performed deep observations to search for radio pulsations in the directions of unidentified Fermi Large Area Telescope (LAT) gamma-ray sources. We report the discovery of an eclipsing black-widow millisecond pulsar, PSR J1544+4937, identified with the un-cataloged gamma-ray source Fermi J1544.2+4941. This 2.16 ms pulsar is in a 2.9 hours compact circular orbit with a very low-mass companion (Mc > 0.017 Msun). At 322 MHz this pulsar is found to be eclipsing for 13% of its orbit, whereas at 607 MHz the pulsar is detected throughout the low-frequency eclipse phase. Variations in the eclipse ingress phase are observed, indicating a clumpy and variable eclipsing medium. Moreover, additional short-duration absorption events are observed around the eclipse boundaries. Using the radio timing ephemeris we were able to detect gamma-ray pulsations from this pulsar, confirming it as the source powering the gamma-ray emission.

Wide profile drifting pulsars : an elegant way to probe pulsar magnetospheres

We present the results from a study of wide profile pulsars using high sensitivity multifrequency observations with the GMRT. Since the line of sight samples a large region of the polar cap in case of the wide profile pulsars, presence of simultaneous multiple drift regions is quite probable (as seen in PSR B0826-34 and PSR B0818-41). We solve the aliasing problem of PSR B0818-41 using the observed phase relationship of the drift regions, and determine its pattern rotation period P4 to be ~ 10s, which makes it the fastest known carousel. We find that, for all the pulsars showing drifting in multiple rings of emission, the drift pattern from the rings are phase locked. This can constraint the theoretical models of pulsar emission as it favors a pan magnetospeheric radiation mechanism.