Rapid Gamma-ray flux variability during the 2013 March Crab Nebula flare

TL;DR

The paper reports a rapid, intense gamma-ray flare from the Crab Nebula in March 2013, with flux variability on 5-hour timescales, revealing a highly dynamic synchrotron component while the pulsar emission stays steady.

Contribution

It presents the first detailed analysis of a short-timescale gamma-ray flare from the Crab Nebula, highlighting rapid flux variability and spectral changes in the synchrotron emission.

Findings

Flux increased nearly sixfold during the flare.

Flux variability occurred on approximately 5-hour timescales.

The pulsar emission remained constant during the flare.

Abstract

We report on a bright flare in the Crab Nebula detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. The period of significantly increased luminosity occurred in 2013 March and lasted for approximately 2 weeks. During this period, we observed flux variability on timescales of approximately 5\,hours. The combined photon flux above 100 MeV from the pulsar and its nebula reached a peak value of $(12.5\pm 0.8)\cdot 10^{-6}$\,cm$^{-2}$\,s$^{-1}$ on 2013 March 6. This value exceeds the average flux by almost a factor of 6 and implies a $\sim20$ times higher flux for the synchrotron component of the nebula alone. This is the second brightest flare observed from this source. Spectral and temporal analysis of the LAT data collected during the outburst reveal a rapidly varying synchrotron component of the Crab Nebula while the pulsar emission remains constant in time.