Cut-off characterisation of energy spectra of bright fermi sources: Current instrument limits and future possibilities

Abstract

In this paper some of the brightest GeV sources observed by the Fermi -LAT were analysed, focusing on their spectral cut-off region. The sources chosen for this investigation were the brightest blazar flares of 3C 454.3 and 3C 279 and the Vela pulsar with a reanalysis with the latest Fermi -LAT software. For the study of the spectral cut-off we first explored the Vela pulsar spectrum, whose statistics in the time interval of the 3FGL catalog allowed strong constraints to be obtained on the parameters. We subsequently performed a new analysis of the flaring blazar SEDs. For these sources we obtained constraints on the cut-off parameters under the assumption that their underlying spectral distribution is described by a power-law with a stretched exponential cut-off. We then highlighted the significant potential improvements on such constraints by observations with next generation ground based Cherenkov telescopes, represented in our study by the Cherenkov Telescope Array (CTA). Adopting currently available simulations for this future observatory, we demonstrate the considerable improvement in cut-off constraints achievable by observations with this new instrument when compared with that achievable by satellite observations.

On the origin of gamma-rays in Fermi blazars: beyondthe broad-line region

“…The mild, smooth cut-off often seen between few GeV to few tens GeV is most likely due to the end of the accelerated particle distribution. This opens up the possibility of powerful diagnostics on the accelerated particle spectrum, studying the shape of the cut-off and in comparison with the synchrotron spectrum (Lefa et al 2012;Romoli et al 2017).…”

“…4 shows that 3C 454.3 can be easily detected at VHE in less than an hour with the present generation of air-Cherenkov telescopes, and up to 300-400 GeV despite the large redshift and EBL attenuation. This makes 3C 454.3 an excellent and important target for VHE observations during such flares, which can reveal the spectral evolution of the freshly accelerated particles near the cut-off region (Lefa et al 2012;Romoli et al 2017).…”

Scenarios for Ultrafast Gamma-Ray Variability in AGN

“…Obviously, the study of individual peaks in a statistically meaningful way requires a detailed lightcurve that can be obtained withfuture observations, in particular with CTA (see, e.g., Romoli et al 2017). …”

Prospects for the characterization of the VHE emission from the Crab nebula and pulsar with the Cherenkov Telescope Array

“…Different values of k can reflect either the energy-dependence of the particle propagation mechanisms with k=1/3, 3/11, 1/4, and 1/5 being the Bohm, Kraichnan, Kolmogorov, and hard-sphere turbulence spectral models (in Thomson regime), respectively (Romoli et al 2017) or the transition from the Thomson to the KN region of the IC mechanism. In the specific case of IC scattering of synchrotron photons in the KN regime, which is the dominant regime in the Crab nebula, Lefa et al 2012 computed the following possibilities: k= 3/2, 5/3, 2, 3 (corresponding, in this regime, to the same electron cutoff shape; k = βe, see Table 1 of the cited paper).…”