Discovery of Low DM Fast Radio Transients: Geminga Pulsar Caught in the Act

TL;DR

This paper reports the discovery of low DM fast radio transients from the Geminga pulsar at 34 MHz, revealing intermittent radio emission and DM variations that could explain its previous radio silence.

Contribution

It presents the first detection of radio bursts from Geminga, demonstrating occasional radio emission and DM variability, with implications for pulsar emission mechanisms.

Findings

Bursts exhibit dispersive delays and Faraday rotation.

Bursts originate from Geminga pulsar.

DM varies on short timescales.

Abstract

We report discovery of several energetic radio bursts at 34 MHz, using the Gauribidanur radio telescope. The radio bursts exhibit two important properties associated with the propagation of astronomical signals through the interstellar medium: (i) frequency dependent dispersive delays across the observing bandwidth, and (ii) Faraday rotation of the plane of linear polarization. These bursts sample a range of dispersion measures (DM; 1.4--3.6$~{\rm pc}~{\rm cm}^{-3}$), and show DM-variation at timescales of the order of a minute. Using groups of bursts having a consistent DM, we show that the bursts have originated from the radio-quiet gamma-ray pulsar Geminga. Detection of these bursts supports the existence of occasional radio emission from Geminga. The rare occurrence of these bursts, and the short timescale variation in their DM (if really caused by the intervening medium or the pulsar magnetosphere), might provide clues as to why the pulsar has not been detected in earlier sensitive searches. We present details of the observations and search procedure used to discover these bursts, a detailed analysis of their properties, and evidences of these bursts being associated with Geminga pulsar, and discuss briefly the possible emission mechanism of these bursts.