Detection of Small Flares from the Crab Nebula with Fermi-LAT

Abstract

Gamma radiation from the Crab pulsar wind nebula (PWN) shows significant variability at $\sim 100$ MeV energies, recently revealed with spaceborne gamma-ray telescopes. Here we report the results of a systematic search for gamma-ray flares using a 7.4-year data set acquired with the Fermi Large Area Telescope. Analyzing the off-pulse phases of the Crab pulsar, we found seven previously unreported low-intensity flares ("small flares"). The "small flares'' originate from the variable synchrotron component of the Crab PWN and show clearly different features from the steady component of the Crab PWN emission. They are characterized by larger fluxes and harder photon indices, similar to previously reported flares. These flares show day-scale time variability and imply a strong magnetic field of $B_{\min }\approx 1\mathrm{mG}$ at the site of the gamma-ray production. This result seems to be inconsistent with the typical values revealed with modeling of the non-thermal emission from the nebula. The detection of the "small flares'' gives a hint of production of gamma rays above $100$ MeV in a part of the nebula with properties which are different from the main emitters, e.g., due to bulk relativistic motion.

18 pages, 9 figures, accepted for publication in ApJ

References in corpus (14)

• TEMPO2, a new pulsar timing package. I: Overview
• Gamma-ray flares from the Crab Nebula
• Discovery of Powerful Gamma-Ray Flares from the Crab Nebula
• Rapid Variability of Blazar 3C 279 during Flaring States in 2013-2014 with Joint Fermi-LAT, NuSTAR, Swift, and Ground-Based Multi-wavelength Observations
• Pulsar Wind Nebulae as Cosmic Pevatrons: A Current Sheet's Tale
• Simulated synchrotron emission from Pulsar Wind Nebulae
• Non-thermal emission from relativistic MHD simulations of PWNe: from synchrotron to inverse Compton
• Broadband X-ray Imaging and Spectroscopy of the Crab Nebula and Pulsar with NuSTAR
• Variable gamma-ray emission from the Crab Nebula: short flares and long "waves"
• Constraints on particle acceleration sites in the Crab Nebula from relativistic MHD simulations
• Multi-D magnetohydrodynamic modelling of pulsar wind nebulae: recent progress and open questions
• H.E.S.S. and Suzaku observations of the Vela X pulsar wind nebula
• Detection of UHE gamma rays from the Crab Nebula: Physical Implications
• Off-axis emission from relativistic plasma flows

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