arXiv subjects

T. Kneiske

Publications and source records attributed to T. Kneiske.

39 records · Page 3Linked to original sources

arXiv2010

First detection of VHE gamma-rays from SN 1006 by H.E.S.S

Recent theoretical predictions of the lowest very high energy (VHE) luminosity of SN 1006 are only a factor 5 below the previously published H.E.S.S. upper limit, thus motivating further in-depth observations of this source. Deep observations at VHE energies (above 100 GeV) were carried out with the High Energy Stereoscopic System (H.E.S.S.) of Cherenkov Telescopes from 2003 to 2008. More than 100 hours of data have been collected and subjected to an improved analysis procedure. Observations resulted in the detection of VHE gamma-rays from SN 1006. The measured gamma-ray spectrum is compatible with a power-law, the flux is of the order of 1% of that detected from the Crab Nebula, and is thus consistent with the previously established H.E.S.S. upper limit. The source exhibits a bipolar morphology, which is strongly correlated with non-thermal X-rays. Because the thickness of the VHE-shell is compatible with emission from a thin rim, particle acceleration in shock waves is likely to be the origin of the gamma-ray signal. The measured flux level can be accounted for by inverse Compton emission, but a mixed scenario that includes leptonic and hadronic components and takes into account the ambient matter density inferred from observations also leads to a satisfactory description of the multi-wavelength spectrum.

astro-ph.HE↗

arXiv2009

Gamma-ray and Cosmic Ray Astrophysics from 10 TeV to 1 EeV with the large-area ($>$10 km$^2$) air-shower Detector SCORE

We propose to explore the so-far poorly measured cosmic ray and gamma-ray sky (accelerator sky) in the energy range from 10 TeV to 1 EeV. New physics questions might be addressed in this last remaining observation window of gamma-ray astronomy. The very high beam-energies provided by Cosmic accelerators and the air-shower detection technique naturally imply an entanglement between fundamental questions of astroparticle physics and particle physics. The new large-area (10 km$^2$) wide-angle (1 sr) air Cherenkov detector SCORE (Study for a Cosmic ORigin Explorer) is based on non-imaging Cherenkov light-front sampling with sensitive large-area detector modules of the order of 1 m$^2$. The lateral photon density and arrival-time distribution will be sampled up to large distances from the shower core. The physics motivations, the detector concept and first simulation results will be presented.

astro-ph.IM↗

arXiv2009

First stars and the extragalactic background light: How recent gamma-ray observations constrain the early universe

The formation of the first stars (Population III; PopIII) marks the end of the dark ages of the universe, a subject of lively scientific debate. Not (yet) accessible to direct observations, this early stage of the universe is mostly studied via theoretical calculations and numerical simulations. An indirect window is provided by integrated present day observables such as the metal abundance or the diffuse extragalactic photon fields. We aim to derive constraints on the properties of the PopIII and low metallicity Population II (LM PopII) stars utilizing limits on the density of the extragalactic background light (EBL), recently derived from very-high-energy (E > 100 GeV; VHE) observations. A model calculation for the evolving EBL density produced by PopIII/LM PopII stars is presented. The model utilizes stellar population spectra (SPS) for zero and low metallicity stars and accounts for the changing emission of an aging stellar population. Emission from the dense HII regions surrounding the stars (nebula) is included. The resulting EBL density for different scenarios (metallicity, star formation rate, initial mass function) is compared to the limit on the EBL density. The potential for detecting a cut-off in HE/VHE spectra is discussed. Assuming a maximum contribution from PopIII/LM PopII stars to the EBL density of 5 nW m^-2 s-1 at 2 micrometer a limit on the star formation rate (SFR) of the first stars of 0.3 to 3 M_solar Mpc^-3 yr^-1 in the redshift range 7 - 14 is derived. The limit depends on the assumed shape of the SFR and metallicity.

astro-ph↗