Search for a correlation between very-high-energy gamma rays and giant radio pulses in the Crab pulsar

TL;DR

This study conducted simultaneous radio and gamma-ray observations of the Crab pulsar to investigate potential correlations between very-high-energy gamma rays and giant radio pulses, but found no significant association within the sensitivity limits.

Contribution

First simultaneous multi-wavelength search for correlations between VHE gamma rays and giant radio pulses in the Crab pulsar, setting upper limits on possible emission enhancements.

Findings

No significant gamma-ray enhancement detected during GRPs.

Upper limits set at 5-10 times the average VHE flux for certain time scales.

Results are consistent with models predicting low or no correlation.

Abstract

We present the results of a joint observational campaign between the Green Bank radio telescope and the VERITAS gamma-ray telescope, which searched for a correlation between the emission of very-high-energy (VHE) gamma rays ($E_{\gamma} >$ 150 GeV) and Giant Radio Pulses (GRPs) from the Crab pulsar at 8.9 GHz. A total of 15366 GRPs were recorded during 11.6 hours of simultaneous observations, which were made across four nights in December 2008 and in November and December 2009. We searched for an enhancement of the pulsed gamma-ray emission within time windows placed around the arrival time of the GRP events. In total, 8 different time windows with durations ranging from 0.033 ms to 72 s were positioned at three different locations relative to the GRP to search for enhanced gamma-ray emission which lagged, led, or was concurrent with, the GRP event. Further, we performed separate searches on main pulse GRPs and interpulse GRPs and on the most energetic GRPs in our data sample. No significant enhancement of pulsed VHE emission was found in any of the preformed searches. We set upper limits of 5-10 times the average VHE flux of the Crab pulsar on the flux simultaneous with interpulse GRPs on single-rotation-period time scales. On $\sim$8-second time scales around interpulse GRPs, we set an upper limit of 2-3 times the average VHE flux. Within the framework of recent models for pulsed VHE emission from the Crab pulsar, the expected VHE-GRP emission correlations are below the derived limits.