Related papers: An infrared background--TeV gamma-ray crisis?
Motivated by the discovery of the ultra-strong emission line starburst galaxies (EELGs) known as "green pea galaxies", we consider here their contribution to the intergalactic flux of ionizing UV at high redshifts. Most galaxies that have…
The detection of the hyper-bright gamma-ray burst (GRB) 221009A enables us to explore the nature of GRB emission and the origin of very-high-energy (VHE) gamma-rays. We analyze the ${\it Fermi}$-LAT data and investigate GeV-TeV emission in…
Galactic diffuse continuum gamma-ray emission is intricately related to cosmic-ray physics and radio astronomy. We describe recent results from an approach which endeavours to take advantage of this. Information from cosmic-ray composition…
A number of signals involving charged cosmic rays and high-energy photons have been interpreted as being due to annihilating dark matter. This article provides an overview of the experimental evidence and discusses in particular detections…
Exceptionally strong and long lasting flaring activity of the blazar Markarian 421 (Mrk 421) occurred between January and March 2001. Based on the excellent signal-to-noise ratio of the data we derive the energy spectrum between 260 GeV -…
Relativistic jets from blazars are known to be sources of very-high-energy gamma rays (VHEGRs). During their propagation in the intergalactic space, VHEGRs interact with pervasive cosmological photon fields such as the extragalactic…
Motivated by the recent finding of hierarchical X-ray flaring phenomenon in Mrk 421, we conducted a systematic search for X-ray flares from Mrk 501, another well-known TeV blazar, by making use of the rich {\em RXTE} archival database. We…
A detection of TeV $\gamma$-rays from Mkn 501 is reported, based on observations made between March and August 1996 with the first HEGRA Cherenkov telescope (CT1). From the image analysis, 351 excess candidate $\gamma$-ray events are…
The Galactic diffuse gamma-ray emission is conventionally modeled as the product of cosmic-ray interactions with the interstellar medium. However, the cumulative contribution of stellar atmospheres acting as hadronic interaction targets…
The observed spectra of blazars, their intrinsic emission, and the underlying populations of radiating particles are intimately related. The use of these sources as probes of the extragalactic infrared background, a prospect propelled by…
We present exactly simultaneous X-ray and TeV monitoring with {\it RXTE} and HEGRA of the TeV blazar Mrk 501 during 15 days in 1998 June. After an initial period of very low flux at both wavelengths, the source underwent a remarkable flare…
Gamma-ray bursts (GRBs) have been considered as potential very high-energy photon emitters due to the large amount of energy released as well as the strong magnetic fields involved in their jets. However, the detection of TeV photons is not…
Recently, the MILAGRO collaboration reported on the detection of a diffuse multi-TeV emission from a region of the Galactic disk close to the inner Galaxy. The emission is in excess of what is predicted by conventional models for cosmic ray…
The all-sky surveys in gamma-rays by the imaging Compton telescope (COMPTEL) and the Energetic Gamma Ray Experiment Telescope (EGRET) on board the Compton Gamma Ray Observatory for the first time allows detailed studies of the extragalactic…
For the first time an excess of photons above an energy threshold of 730 GeV from the giant radio galaxy M87 has been measured at a significance level above 4 sigma. The data have been taken during the years 1998 and 1999 with the HEGRA…
Gamma rays of ~TeV energies from distant sources suffer attenuation due to pair production off of ~1 micron EBL photons. We may exploit this process in order to indirectly measure the EBL and constrain models of galaxy formation. Here,…
More than 90% of the Galactic gas-related gamma-ray emissivity above 1 GeV is attributed to the decay of neutral pions formed in collisions between cosmic rays and interstellar matter, with lepton-induced processes becoming increasingly…
The Tibet ASgamma experiment just reported their measurement of sub-PeV diffuse gamma ray emission from the Galactic disk, with the highest energy up to 957 TeV. These gamma-rays are most likely the hadronic origin by cosmic ray interaction…
We calculate the intergalactic photon density as a function of both energy and redshift for 0 < z < 6 for photon energies from .003 eV to the Lyman limit cutoff at 13.6 eV in a Lambda-CDM universe with $\Omega_{\Lambda} = 0.7$ and…
The recently discovered correlation between black hole mass and stellar velocity dispersion provides a new method to determine the masses of black holes in active galaxies. We have obtained optical spectra of Markarian 501, a nearby…