A Possible Gamma-Ray Enhancement Event in Tycho's Supernova Remnant

Abstract

We report a possible $\gamma$-ray enhancement event detected from Tycho's supernova remnant (SNR), the outcome of a type Ia supernova explosion that occurred in year 1572. The event lasted for 1.5 years and showed a factor of 3.6 flux increase mainly in the energy range of 4--100 GeV, while notably accompanied with two 478\,GeV photons. Several young SNRs (including Tycho's SNR) were previously found to show peculiar X-ray structures with flux variations in one- or several-year timescales, such an event at $\gamma$-ray energies is for the first time seen. The year-long timescale of the event suggests a synchrotron radiation process, but the hard $\gamma$-ray emission requires extreme conditions of either ultra-high energies for the electrons upto $\sim$10 PeV (well above the cosmic-ray "knee" energy) or high inhomogeneity of the magnetic field in the SNR. This event in Tycho's SNR is likely analogous to the $\gamma$-ray flares observed in the Crab nebula, the comparably short timescales of them both requiring a synchrotron process, and similar magnetohydrodynamic processes such as magnetic reconnection would be at work as well in the SNR to accelerate particles to ultra-relativistic energies. The event, if confirmed, helps reveal the more complicated side of the physical processes that can occur in young SNRs.

12 pages, 6 figures, 2 tables, accepted for publication in ApJ

References in corpus (14)

• Gamma-ray flares from the Crab Nebula
• Discovery of Powerful Gamma-Ray Flares from the Crab Nebula
• Tycho Brahe's 1572 supernova as a standard type Ia explosion revealed from its light echo spectrum
• Fast Variability of Nonthermal X-Ray Emission in Cassiopeia A: Probing Electron Acceleration in Reverse-Shocked Ejecta
• Hadronic gamma-rays from RX J1713.7-3946?
• Chandra Observes the End of an Era SN 1987A
• A 20 Year Radio Light Curve for the Young Supernova Remnant G1.9+0.3
• Analysis of GeV-band gamma-ray emission from SNR RX J1713.7-3946
• Non-thermal emission from the reverse shock of the youngest galactic Supernova remnant G1.9+0.3
• Expected gamma-ray emission of supernova remnant SN 1987A
• Time evolution of broadband non-thermal emission from supernova remnants in different circumstellar environments
• Modeling the broadest spectral band of the Crab nebula and constraining the ions acceleration efficiency
• Time Variability of Nonthermal X-ray Stripes in Tycho's Supernova Remnant with Chandra
• Temporal and Spatial Variation of Synchrotron X-ray Stripes in Tycho's Supernova Remnant