Related papers: Intergalactic Extinction of High Energy Gamma-Rays
We have used the Giant Meterwave Radio Telescope (GMRT) to measure the Galactic HI 21-cm line absorption towards 102 extragalactic radio continuum sources, located at high (|b| >15deg.) Galactic latitudes. The Declination coverage of the…
In this paper, we compile the very-high-energy and high-energy spectral indices of 43 BL Lac objects from the literature. Based on a simple math model, $\Delta\Gamma_{obs}=\alpha {\rm{z}}+\beta $, we present evidence for the origin of an…
We present results on the X-ray spectrum of the quasar PG 1114+445 from an ASCA observation performed in 1996 June, and a ROSAT observation performed 3 years earlier. We show good agreement between all the datasets can be obtained if the…
We consider the neutron star (NS) of the magnetar type inside the massive binary system. We determine the conditions under which the matter from the stellar wind can penetrate the inner magnetosphere of the magnetar. At some distance from…
We have found a strong absorption feature at 2598\AA~ in the spectra of two distant radio galaxies, which we interpret as due to interstellar FeII. We discuss this interpretation and the possibility of obtaining important information on the…
Absorption due to HeII Ly-alpha has been detected at low resolution in the spectra of four quasars between redshifts z = 2.74-3.29. We assess these observations, giving particular attention to the radiative transfer of the ionizing…
We aim to understand the multi-wavelength properties of 2XMM J123204+215255, the source with the most extreme X-ray-to-optical flux ratio amongst a sample of bright X-ray selected EXOs drawn from a cross-correlation of the 2XMMp catalogue…
In this paper, we study the photon-photon pair production optical depth for 10 GeV--1 TeV gamma rays from 3C 279 due to the diffuse radiation of broad-line region (BLR). Assuming a power-law spectrum of $E_{\gamma}^{-a_2}$ for the photon…
Inverse-Compton cascades initiated by energetic gamma rays (E>100 GeV) enhance the GeV emission from bright, extragalactic TeV sources. The absence of this emission from bright TeV blazars has been used to constrain the intergalactic…
The propagation of very high energy gamma-rays ($E>100$~GeV) over cosmological distances is suppressed by pair-production processes with the ubiquitous extra-galactic soft photon background, mainly in the optical to near infra-red. The…
We measure the effective opacity ($\tau_{eff}$) of the Intergalactic Medium (IGM) from the composite spectra of 281 Lyman-Break Galaxies (LBGs) in the redshift range $2 \lesssim z \lesssim 3$. Our spectra are taken from the COSMOS…
Observations of the multi-TeV spectra of the nearby BL Lac objects Mkn 421 and Mkn 501 exhibit the high energy cutoffs predicted to be the result of intergalactic annihilation interactions, primarily with IR photons having a flux level as…
The problem of missing baryons in the local universe remains an open question. One propose alternative is that at low redshift missing baryons are in the form of the Warm Hot Intergalactic Medium (WHIM). In order to test this idea, we…
LHAASO, a ground-based observatory, is unveiling new frontiers in our understanding of high-energy $\gamma-$rays and cosmic rays. It has recently observed high energy diffuse $\gamma-$rays from the Galactic plane in the TeV-PeV range. For…
The extragalactic background light (EBL) is the aggregate of all optical and infrared emissions from thermal processes since the cosmic dark ages. While the integrated light of galaxies is expected to be the main contribution to the EBL,…
We present new high-precision measurements of the opacity of the intergalactic and circumgalactic medium (IGM, CGM) at <z>=2.4. Using Voigt profile fits to the full Lyman alpha and Lyman beta forests in 15 high-resolution high-S/N spectra…
I report detections of four new HI 21-cm absorbers associated with sources at intermediate redshifts, 0.7 < z < 1.0. The sources are part of a sample of 11 radio-loud galaxies, all at 0.7 < z < 1.0, that were searched for associated HI…
We study the four BL Lac objects (RGB J0152+017, 1ES 0229+200, 1ES 0347-121 and PKS 0548-322) detected in the TeV band but not present in the 1FGL catalogue of the Fermi/Large Area Telescope. We analize the 24 months of LAT data deriving…
The discovery of distant sources of very high energy (VHE) gamma-rays with hard energy spectra enabled to derive strong upper limits on the density of the extragalactic background light (EBL). These limits are close to the lower limits…
High-energy photons emitted from gamma-ray bursts (GRBs) are subject to pair-production interactions with lower energy photons, leading to an effective optical depth. In this Letter, we estimate the opacity resulting from photon fields…