Gamma-ray flare and absorption in the Crab nebula: Lovely TeV-PeV astrophysics

Abstract

We spectrally fit the GeV gamma-ray flares that have recently been observed in the Crab nebula by considering a small blob Lorentz-boosted towards us. We point out that the corresponding inverse Compton flare at the TeV-PeV region is more enhanced than synchrotron emission by a Lorentz factor squared (~Γ2). This already excludes Γ≳200 and it will be detected by future TeV-PeV observatories, such as the Cherenkov Telescope Array (CTA), the Tibet Air Shower plus Muon Detector (Tibet AS+MD) array and the Large High Altitude Air Shower Observatory (LHAASO), for Γ≳30. We also show that PeV photons emitted from the Crab nebula are absorbed by cosmic microwave background radiation through electron-positron pair creation. © 2012 The Authors. Monthly Notices of the Royal Astronomical Society © 2012 RAS.