Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userIntergalactic electromagnetic cascade component of observable blazar emission
103
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Secondary {gamma}-rays from intergalactic cascades may contribute to observable spectra of blazars, also modifying observable angular and temporal distributions. In this paper we briefly review basic features of intergalactic electromagnetic cascade physics, suggest a new approximation for {gamma}-ray mean free path, consider angular patterns of magnetically broadened cascade emission, and present an example of a fit to the observable blazar spectrum.
rate research
Read More
Recent progress in very high energy (VHE, E >100 GeV) $gamma$-ray observations, together with advances in the extragalactic background light (EBL) modelling, allows to search for new phenomena such as $gamma$-axion-like particle ($gamma rightarrow$ ALP) oscillation and to explore the extragalactic magnetic field (EGMF) strength and structure. These studies are usually performed by searching for some deviation from the so-called absorption-only model, that accounts for only primary photon absorption on the EBL and adiabatic losses. In fact, there exist several indications that the absorption-only model is incomplete. We present and discuss the intergalactic electromagnetic cascade model (IECM) --- the simplest model that allows to coherently explain all known anomalies. This model has a number of robust signatures that could be searched for with present and future instruments. The IECM model may serve as a new background template, allowing to make future searches for $gamma rightarrow$ ALP oscillation more robust. A detailed account of our calculations is available in astro-ph/1609.01013v2 (A&A,in print).
Context. Most of the studies on extragalactic {gamma}-ray propagation performed up to now only accounted for primary gamma-ray absorption and adiabatic losses (absorption-only model). However, there is growing evidence that this model is oversimplified and must be modified in some way. In particular, it was found that the intensity extrapolated from the optically-thin energy range of some blazar spectra is insufficient to explain the optically-thick part of these spectra. This effect was interpreted as an indication for {gamma}-axion-like particle (ALP) oscillation. On the other hand, there are many hints that a secondary component from electromagnetic cascades initiated by primary {gamma}-rays or nuclei may be observed in the spectra of some blazars. Aims. We study the impact of electromagnetic cascades from primary {gamma}-rays or protons on the physical interpretation of blazar spectra obtained with imaging Cherenkov telescopes. Methods. We use the publicly-available code ELMAG to compute observable spectra of electromagnetic cascades from primary {gamma}-rays. For the case of primary proton, we develop a simple, fast and reasonably accurate hybrid method to calculate the observable spectrum. We perform the fitting of the observed spectral energy distributions (SEDs) with various physical models: the absorption-only model, the electromagnetic cascade model (for the case of primary {gamma}-rays), and sever
We estimate the rate of tidal disruption events (TDEs) that will be detectable with future space-based gravitational wave detectors as well as the most probable properties of these events. We find that the Laser Interferometer Space Antenna (LISA) will be able to detect up to few 10 events, but this number will strongly depend on our ability to disentangle the signal from the noise. The future number of (non-)observation will add additional constraints on the typical age of stars surrounding central black holes (BHs), however it will not constrain the unknown regimes of the BH mass function. Most probable events will involve 10 M$_odot$ stars around few $10^6$ M$_odot$ BHs and will be detectable in the X-ray and optical part of the electromagnetic spectrum, which may open the multi-messenger era for TDEs. The generation of detectors following LISA will routinely detect gravitational waves from TDEs at cosmological distances.
Recent claims that the strength B_IGMF of the intergalactic magnetic field (IGMF) is >~ 1e-15 G are based on upper limits to the expected cascade flux in the GeV band produced by blazar TeV photons absorbed by the extragalactic background light. This limit depends on an assumption that the mean blazar TeV flux remains constant on timescales >~2 (B_ IGMF/1e-18 G)^2 / (E/{10 GeV})^2 yr for an IGMF coherence length ~ 1 Mpc, where E is the measured photon energy. Restricting TeV activity of 1ES 0229+200 to ~3 -- 4 years during which the source has been observed leads to a more robust lower limit of B_IGMF >~ 1e-18 G, which can be larger by an order of magnitude if the intrinsic source flux above ~5 -- 10 TeV from 1ES 0229+200 is strong.
We test the synchrotron emission scenario for the very bright gamma-ray flare of blazar 3C 279 observed in 2015 June using time-dependent numerical simulations. A bulk Lorentz factor as high as 100 can bring the synchrotron maximum energy above the GeV energy range. We find two possible solutions for the X-ray to gamma-ray spectrum. One is a prompt electron injection model with a hard power-law index as magnetic reconnection models suggest. A too strong magnetic field yields a too bright synchrotron X-ray flux due to secondary electron--positron pairs. Even in the prompt electron injection model, the Poynting flux luminosity is at most comparable to the gamma-ray or electron luminosity. Another model is the stochastic acceleration model, which leads to a very unique picture accompanying the electromagnetic cascade and re-acceleration of the secondary electron--positron pairs. In this model, the energy budget of the magnetic field is very low compared to gamma rays and electrons.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
