Correlation of Fermi photons with high-frequency radio giant pulses from the Crab pulsar

TL;DR

This study investigates the correlation between gamma-ray photons and radio giant pulses from the Crab pulsar, finding no significant gamma-ray flux enhancement associated with the radio GPs, thus informing emission mechanism models.

Contribution

The paper provides the first simultaneous gamma-ray and radio observations of the Crab pulsar, setting upper limits on gamma-ray flux enhancement during radio giant pulses.

Findings

No observed increase in gamma-ray flux during GPs within 40-minute windows.

Upper limit of 4 times the average gamma-ray flux for all GPs.

Upper limit of 12 times the average gamma-ray flux for interpulse GPs.

Abstract

To constrain the giant pulse (GP) emission mechanism and test the model of Lyutikov (2007) for GP emission, we have carried out a campaign of simultaneous observations of the Crab pulsar at gamma-ray (Fermi) and radio (Green Bank Telescope) wavelengths. Over 10 hours of simultaneous observations we obtained a sample of 2.1x10^4 giant pulses, observed at a radio frequency of 9 GHz, and 77 Fermi photons, with energies between 100 MeV and 5 GeV. The majority of GPs came from the interpulse (IP) phase window. We found no change in the GP generation rate within 10-120 s windows at lags of up to +-40 min of observed gamma-ray photons. The 95% upper limit for a gamma-ray flux enhancement in pulsed emission phase window around all GPs is 4 times the average pulsed gamma-ray flux from the Crab. For the subset of IP GPs, the enhancement upper limit, within the IP emission window, is 12 times the average pulsed gamma-ray flux. These results suggest that GPs, at least high-frequency IP GPs, are due to changes in coherence of radio emission rather than an overall increase in the magnetospheric particle density.