Refine
Has Fulltext
- no (26)
Language
- English (26)
Is part of the Bibliography
- yes (26)
Keywords
- radiation mechanisms: non-thermal (10)
- galaxies: active (8)
- gamma rays: galaxies (7)
- gamma rays: general (6)
- ISM: supernova remnants (4)
- galaxies: jets (3)
- ISM: individual objects: G338.3-0.0 (2)
- acceleration of particles (2)
- cosmic rays (2)
- gamma-rays: galaxies (2)
- BL Lacertae objects: general (1)
- BL Lacertae objects: individual (PG 1553+113) (1)
- BL Lacertae objects: individual: 1ES 1312-423 (1)
- BL Lacertae objects: individual: AP Librae (1)
- BL Lacertae objects: individual: PKS 0301-243 (1)
- BL Lacertae objects: individual: PKS 0447-439 (1)
- BL Lacertae objects: individual: PKS 2155-304 (1)
- BL Lacertae objects: individual: SHBL J001355.9-185406 (1)
- ISM: clouds (1)
- ISM: individual objects (SNR G338.3-0.0, SNR G338.5+0.1) (1)
- ISM: individual objects: Crab nebula (1)
- ISM: individual objects: HESS J1832-093 (1)
- ISM: individual objects: SNR G1.9+0.3 (1)
- ISM: individual objects: SNR G22.7-0.2 (1)
- ISM: individual objects: SNR G330.2+1.0 (1)
- ISM: magnetic fields (1)
- X-rays: binaries (1)
- X-rays: general (1)
- X-rays: individuals: G15.4+0.1 (1)
- X-rays: stars (1)
- astroparticle physics (1)
- binaries: general (1)
- black hole physics (1)
- errata, addenda (1)
- galaxies: distances and redshifts (1)
- galaxies: individual (M 87) (1)
- galaxies: nuclei (1)
- gamma rays: ISM (1)
- gamma rays: general(HESS J0632+057, VER J0633+057) (1)
- gamma rays: stars (1)
- gamma-ray burst: individual: GRB 100621A (1)
- gamma-rays: ISM (1)
- gamma-rays: general (1)
- globular clusters: general (1)
- infrared: diffuse background (1)
- methods: observational (1)
- pulsars: general (1)
- pulsars: individual: PSR B1259-63 (1)
- quasars: individual: PKS 1510-089 (1)
- relativistic processes (1)
- stars: individual: LS 2883 (1)
- supernovae: individual: HESS J1818-154 (1)
Institute
Very high energy (VHE, E > 100 GeV)gamma-ray flaring activity of the high-frequency peaked BL Lac object PG 1553 + 113 has been detected by the H.E.S.S. telescopes. The flux of the source increased by a factor of 3 during the nights of 2012 April 26 and 27 with respect to the archival measurements with a hint of intra-night variability. No counterpart of this event has been detected in the Fermi-Large Area Telescope data. This pattern is consistent with VHE gamma(-)ray flaring being caused by the injection of ultrarelativistic particles, emitting.-rays at the highest energies. The dataset offers a unique opportunity to constrain the redshift of this source at z = 0.49 +/- 0.04 using a novel method based on Bayesian statistics. The indication of intra-night variability is used to introduce a novel method to probe for a possible Lorentz invariance violation (LIV), and to set limits on the energy scale at which Quantum Gravity (QG) effects causing LIV may arise. For the subluminal case, the derived limits are E-QG,E- 1 > 4.10 x 10(17) GeV and E-QG,E- 2 > 2.10 x 10(10) GeV for linear and quadratic LIV effects, respectively.
Search for dark matter annihilation signatures in HESS observations of
dwarf spheroidal galaxies
(2014)
Dwarf spheroidal galaxies of the Local Group are close satellites of the Milky Way characterized by a large mass-to-light ratio and are not expected to be the site of nonthermal high-energy gamma-ray emission or intense star formation. Therefore they are among the most promising candidates for indirect dark matter searches. During the last years the High Energy Stereoscopic System (H.E.S.S.) of imaging atmospheric Cherenkov telescopes observed five of these dwarf galaxies for more than 140 hours in total, searching for TeV gamma-ray emission from annihilation of dark matter particles. The new results of the deep exposure of the Sagittarius dwarf spheroidal galaxy, the first observations of the Coma Berenices and Fornax dwarves and the reanalysis of two more dwarf spheroidal galaxies already published by the H.E.S.S. Collaboration, Carina and Sculptor, are presented. In the absence of a significant signal new constraints on the annihilation cross section applicable to weakly interacting massive particles (WIMPs) are derived by combining the observations of the five dwarf galaxies. The combined exclusion limit depends on the WIMP mass and the best constraint is reached at 1-2 TeV masses with a cross-section upper bound of similar to 3.9 x 10(-24) cm(3) s(-1) at a 95% confidence level.
In this paper we report on the analysis of all the available optical and very high-energy gamma-ray (> 200 GeV) data for the BL Lac object PKS 2155-304, collected simultaneously with the ATOM and H.E.S.S. telescopes from 2007 until 2009. This study also includes X-ray (RXTE, Swift) and high-energy gamma-ray (Fermi-LAT) data. During the period analysed, the source was transitioning from its flaring to quiescent optical states, and was characterized by only moderate flux changes at different wavelengths on the timescales of days and months. A flattening of the optical continuum with an increasing optical flux can be noted in the collected dataset, but only occasionally and only at higher flux levels. We did not find any universal relation between the very high-energy gamma-ray and optical flux changes on the timescales from days and weeks up to several years. On the other hand, we noted that at higher flux levels the source can follow two distinct tracks in the optical flux-colour diagrams, which seem to be related to distinct gamma-ray states of the blazar. The obtained results therefore indicate a complex scaling between the optical and gamma-ray emission of PKS 2155 304, with different correlation patterns holding at different epochs, and a gamma-ray flux depending on the combination of an optical flux and colour rather than a flux alone.
This Letter reports the discovery of a remarkably hard spectrum source, HESS J1641-463, by the High Energy Stereoscopic System (H.E.S.S.) in the very high energy (VHE) domain. HESS J1641-463 remained unnoticed by the usual analysis techniques due to confusion with the bright nearby source HESS J1640-465. It emerged at a significance level of 8.5 standard deviations after restricting the analysis to events with energies above 4 TeV. It shows a moderate flux level of phi(E > 1TeV) = (3.64 +/- 0.44(stat)+/- 0.73(sys)) x 10(-13) cm(-2) s(-1), corresponding to 1.8% of the Crab Nebula flux above the same energy, and a hard spectrum with a photon index of Gamma = 2.07 +/- 0.11(stat)+/- 0.20(sys). It is a point-like source, although an extension up to a Gaussian width of sigma = 3 arcmin cannot be discounted due to uncertainties in the H.E.S.S. point-spread function. The VHE gamma-ray flux of HESS J1641-463 is found to be constant over the observed period when checking time binnings from the year-by-year to the 28 minute exposure timescales. HESS J1641-463 is positionally coincident with the radio supernova remnant SNR G338.5+0.1. No X-ray candidate stands out as a clear association; however, Chandra and XMM-Newton data reveal some potential weak counterparts. Various VHE gamma-ray production scenarios are discussed. If the emission from HESS J1641-463 is produced by cosmic ray protons colliding with the ambient gas, then their spectrum must extend close to 1 PeV. This object may represent a source population contributing significantly to the galactic cosmic ray flux around the knee.
Context. On March 4, 2013 the Fermi-EAT and AGILE reported a flare from the direction of the Crab nebula in which the high-energy (HE; E > 100 MeV) flux was six times above its quiescent level. Simultaneous observations in other energy bands give us hints about the emission processes during the flare episode and the physics of pulsar wind nebulae in general.
Aims. We search for variability in the emission of the Crab nebula at very-high energies (VHF,; E > 100 GeV), using contemporaneous data taken with the H.E.S.S. array of Cherenkov telescopes.
Methods. Observational data taken with the H.E.S.S. instrument on five consecutive days during the flare were analysed for the flux and spectral shape of the emission from the Crab nebula. Night-wise light curves are presented with energy thresholds of 1 TeV and 5 TeV.
Results. The observations conducted with H.E.S.S. on March 6 to March 10, 2013 show no significant changes in the flux. They limit the variation in the integral flux above 1 TeV to less than 63% and the integral flux above 5 TeV to less than 78% at a 95% confidence level.