Detection of Polarized Quasi-Periodic Microstructure Emission in Millisecond Pulsars

Abstract

Microstructure emission, involving short timescale, often quasi-periodic, intensity fluctuations in subpulse emission, is well known in normal period pulsars. In this Letter, we present the first detections of quasi-periodic microstructure emission from millisecond pulsars (MSPs), from Giant Metrewave Radio Telescope observations of two MSPs at 325 and 610 MHz. Similar to the characteristics of microstructure observed in normal period pulsars, we find that these features are often highly polarized and exhibit quasi-periodic behavior on top of broader subpulse emission, with periods of the order of a few μs. By measuring their widths and periodicities from single pulse intensity profiles and their autocorrelation functions, we extend the microstructure timescale-rotation period relationship by more than an order of magnitude down to rotation periods ∼5 ms, and find it to be consistent with the relationship derived earlier for normal pulsars. The similarity of behavior is remarkable, given the significantly different physical properties of MSPs and normal period pulsars, and rules out several previous speculations about the possible different characteristics of microstructure in MSP radio emission. We discuss the possible reasons for the non-detection of these features in previous high time resolution MSP studies along with the physical implications of our results, both in terms of a geometric beam sweeping model and temporal modulation model for micropulse production.

Dual-frequency single-pulse study of PSR B0950+08

“…observing with sufficient time resolution reveals that individual pulses are often composed of a collection of separate µswide subpulses (micropulses, also dubbed "microstructure", e.g., Hankins 1971). Micropulses have been recorded from a substantial fraction of strong nearby pulsars and are speculated to be a common trait of pulsar radio emission (Lange et al 1998;Popov et al 2002;Kuzmin et al 2003;De et al 2016). Their origin is still as unknown as the GP formation mechanism; although some studies link these phenomena (Petrova 2004a,b).…”

Radio-frequency microstructure and polarization in ion–proton pulsars

“…Many authors have observed that the characteristics of GHz radio emission, including polarization and the large negative spectral indices, are broadly similar over wide intervals of surface magnetic flux density, from 10 8 G in the MSP to more than 10 13 G. This should be in itself sufficient to prompt questions about theories of the emission process that are based on electron-positron pair production. The very recent addition of microstructure to the list by De et al (2016) reinforces this. The ion-proton polar cap is concomitant with the plasma composition that basic nuclear interactions must produce in Ω · Bs < 0 neutron stars.…”

The Journey of a Radio Astronomer: Growth of Radio Astronomy in India

“…Roy & Pal (2013) discovered possibly the youngest supernova remnant at 330 MHz in our Galaxy. De et al (2016) detected polarized quasi-periodic microstructure emission in millisecond pulsars. Recently, Saxena et al (2018) have discovered the most distant radio galaxy identified to date at a redshift of z = 5.72.…”