Observation of supernova remnant with Fermi satellite
The main LAT detector of the Fermi satellite is called a pair-conversion telescope. By measuring tracks and all energy of the electron-positron pairs that are created from gamma-rays coming from the universe in the LAT, it is possible to measure the gamma-rays with energy of 20 Mega to 300 Giga eV. The new LAT has far superior performance compared to its predecessor, i.e., the EGRET detector onboard the Compton satellite and, accordingly, gamma-ray observation of supernova remnants has advanced greatly.
One important outcome provided by LAT observation is that it allows us to estimate the energy amount to be distributed to high-energy protons in shock waves of supernova remnants. The energy amount transferred to high-energy protons is not determined by the current Fermi acceleration theory because of the entranceEproblem above. When a high-energy proton with energy of more than approx. 300 Mega eV collides with a hydrogen nucleus in the interstellar gas, neutral
Escape from supernova remnant
For particles to be accelerated in the Fermi acceleration process, they must be fully scattered even upstream of the shock wave, i.e., just outside the supernova remnant, and return to the shock wave. Turbulent magnetic fields, which work as scatterers in the shock-wave upstream, are thought to be generated by the accelerated particles themselves. Because of this non-linear nature, a theoretical solution to the above exitEproblem is still difficult. In order to understand this issue, it is important to observe the particles that pass through the acceleration process and escapeEfrom the supernova remnants.
For the first time, we were able to find an observational example of such an event by the Fermi satellite. As shown in Fig. 2, when observing the supernova remnant W44, we identified that high-energy particles having escapedEupstream of the shock wave then collided with the nearby giant molecular cloud to emit gamma-rays. Particle acceleration, especially its maximum attainable energy, is inextricably linked to their escape. Thus, we successfully obtained new information from the gamma-ray observation toward the elucidation of the Fermi acceleration mechanism.