ORCID Profile
0000-0001-5801-3945
Current Organisation
Universität Heidelberg Landessternwarte Königstuhl
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Publisher: EDP Sciences
Date: 04-2018
DOI: 10.1051/0004-6361/201629377
Abstract: The nine-year H.E.S.S. Galactic Plane Survey (HGPS) has yielded the most uniform observation scan of the inner Milky Way in the TeV gamma-ray band to date. The sky maps and source catalogue of the HGPS allow for a systematic study of the population of TeV pulsar wind nebulae found throughout the last decade. To investigate the nature and evolution of pulsar wind nebulae, for the first time we also present several upper limits for regions around pulsars without a detected TeV wind nebula. Our data exhibit a correlation of TeV surface brightness with pulsar spin-down power Ė . This seems to be caused both by an increase of extension with decreasing Ė , and hence with time, compatible with a power law R PWN ( Ė ) ~ Ė −0.65±0.20 , and by a mild decrease of TeV gamma-ray luminosity with decreasing Ė , compatible with L 1−10 TeV ~ Ė 0.59±0.21 . We also find that the offsets of pulsars with respect to the wind nebula centre with ages around 10 kyr are frequently larger than can be plausibly explained by pulsar proper motion and could be due to an asymmetric environment. In the present data, it seems that a large pulsar offset is correlated with a high apparent TeV efficiency L 1−10 TeV ∕ Ė . In addition to 14 HGPS sources considered firmly identified pulsar wind nebulae and 5 additional pulsar wind nebulae taken from literature, we find 10 HGPS sources that are likely TeV pulsar wind nebula candidates. Using a model that subsumes the present common understanding of the very high-energy radiative evolution of pulsar wind nebulae, we find that the trends and variations of the TeV observables and limits can be reproduced to a good level, drawing a consistent picture of present-day TeV data and theory.
Publisher: EDP Sciences
Date: 02-2012
Publisher: EDP Sciences
Date: 27-01-2017
DOI: 10.1051/0004-6361/201629419
Abstract: Studying the temporal variability of BL Lac objects at the highest energies provides unique insights into the extreme physical processes occurring in relativistic jets and in the vicinity of super-massive black holes. To this end, the long-term variability of the BL Lac object PKS 2155−304 is analyzed in the high (HE, 100 MeV E 300 GeV) and very high energy (VHE, E 200 GeV) γ -ray domain. Over the course of ~9 yr of H.E.S.S. observations the VHE light curve in the quiescent state is consistent with a log-normal behavior. The VHE variability in this state is well described by flicker noise (power-spectral-density index β VHE = 1.10 +0.10 -0.13 ) on timescales larger than one day. An analysis of ~5.5 yr of HE Fermi -LAT data gives consistent results (β HE = 1.20 +0.21 -0.23 , on timescales larger than 10 days) compatible with the VHE findings. The HE and VHE power spectral densities show a scale invariance across the probed time ranges. A direct linear correlation between the VHE and HE fluxes could neither be excluded nor firmly established. These long-term-variability properties are discussed and compared to the red noise behavior ( β ~ 2) seen on shorter timescales during VHE-flaring states. The difference in power spectral noise behavior at VHE energies during quiescent and flaring states provides evidence that these states are influenced by different physical processes, while the compatibility of the HE and VHE long-term results is suggestive of a common physical link as it might be introduced by an underlying jet-disk connection.
Publisher: American Astronomical Society
Date: 13-02-2014
Publisher: American Physical Society (APS)
Date: 30-12-2014
Publisher: EDP Sciences
Date: 02-2014
Publisher: EDP Sciences
Date: 12-2020
DOI: 10.1051/0004-6361/202038851
Abstract: The unidentified very-high-energy (VHE E 0.1 TeV) γ -ray source, HESS J1826−130, was discovered with the High Energy Stereoscopic System (HESS) in the Galactic plane. The analysis of 215 h of HESS data has revealed a steady γ -ray flux from HESS J1826−130, which appears extended with a half-width of 0.21° ± 0.02 stat ° ± 0.05 sys °. The source spectrum is best fit with either a power-law function with a spectral index Γ = 1.78 ± 0.10 stat ± 0.20 sys and an exponential cut-off at 15.2 −3.2 +5.5 TeV, or a broken power-law with Γ 1 = 1.96 ± 0.06 stat ± 0.20 sys , Γ 2 = 3.59 ± 0.69 stat ± 0.20 sys for energies below and above E br = 11.2 ± 2.7 TeV, respectively. The VHE flux from HESS J1826−130 is contaminated by the extended emission of the bright, nearby pulsar wind nebula, HESS J1825−137, particularly at the low end of the energy spectrum. Leptonic scenarios for the origin of HESS J1826−130 VHE emission related to PSR J1826−1256 are confronted by our spectral and morphological analysis. In a hadronic framework, taking into account the properties of dense gas regions surrounding HESS J1826−130, the source spectrum would imply an astrophysical object capable of accelerating the parent particle population up to ≳200 TeV. Our results are also discussed in a multiwavelength context, accounting for both the presence of nearby supernova remnants, molecular clouds, and counterparts detected in radio, X-rays, and TeV energies.
Publisher: American Physical Society (APS)
Date: 22-01-2013
Publisher: American Astronomical Society
Date: 24-04-2012
Publisher: EDP Sciences
Date: 04-2013
Publisher: EDP Sciences
Date: 02-2014
Publisher: EDP Sciences
Date: 02-2018
DOI: 10.1051/0004-6361/201732426
Abstract: Context. Recently, the high-energy (HE, 0.1–100 GeV) γ -ray emission from the object LMC P3 in the Large Magellanic Cloud (LMC) has been discovered to be modulated with a 10.3-day period, making it the first extra-galactic γ -ray binary. Aim. This work aims at the detection of very-high-energy (VHE, GeV) γ -ray emission and the search for modulation of the VHE signal with the orbital period of the binary system. Methods. LMC P3 has been observed with the High Energy Stereoscopic System (H.E.S.S.) the acceptance-corrected exposure time is 100 h. The data set has been folded with the known orbital period of the system in order to test for variability of the emission. Results. VHE γ -ray emission is detected with a statistical significance of 6.4 σ . The data clearly show variability which is phase-locked to the orbital period of the system. Periodicity cannot be deduced from the H.E.S.S. data set alone. The orbit-averaged luminosity in the 1–10 TeV energy range is (1.4 ± 0.2) × 1035 erg s −1 . A luminosity of (5 ± 1) × 1035 erg s −1 is reached during 20% of the orbit. HE and VHE γ -ray emissions are anti-correlated. LMC P3 is the most luminous γ -ray binary known so far.
Publisher: EDP Sciences
Date: 19-11-2012
Publisher: EDP Sciences
Date: 06-2019
DOI: 10.1051/0004-6361/201935242
Abstract: Young core-collapse supernovae with dense-wind progenitors may be able to accelerate cosmic-ray hadrons beyond the knee of the cosmic-ray spectrum, and this may result in measurable gamma-ray emission. We searched for gamma-ray emission from ten supernovae observed with the High Energy Stereoscopic System (H.E.S.S.) within a year of the supernova event. Nine supernovae were observed serendipitously in the H.E.S.S. data collected between December 2003 and December 2014, with exposure times ranging from 1.4 to 53 h. In addition we observed SN 2016adj as a target of opportunity in February 2016 for 13 h. No significant gamma-ray emission has been detected for any of the objects, and upper limits on the TeV gamma-ray flux of the order of ~10 −13 cm −2 s −1 are established, corresponding to upper limits on the luminosities in the range ~2 × 10 39 to ~1 × 10 42 erg s −1 . These values are used to place model-dependent constraints on the mass-loss rates of the progenitor stars, implying upper limits between ~2 × 10 −5 and ~2 × 10 −3 M ⊙ yr −1 under reasonable assumptions on the particle acceleration parameters.
Publisher: American Astronomical Society
Date: 22-09-2014
Publisher: EDP Sciences
Date: 03-2012
Publisher: Oxford University Press (OUP)
Date: 02-05-2014
DOI: 10.1093/MNRAS/STU459
Publisher: EDP Sciences
Date: 02-2014
Publisher: EDP Sciences
Date: 04-2018
DOI: 10.1051/0004-6361/201526545
Abstract: Aim. We aim for an understanding of the morphological and spectral properties of the supernova remnant RCW 86 and for insights into the production mechanism leading to the RCW 86 very high-energy γ -ray emission. Methods. We analyzed High Energy Spectroscopic System (H.E.S.S.) data that had increased sensitivity compared to the observations presented in the RCW 86 H.E.S.S. discovery publication. Studies of the morphological correlation between the 0.5–1 keV X-ray band, the 2–5 keV X-ray band, radio, and γ -ray emissions have been performed as well as broadband modeling of the spectral energy distribution with two different emission models. Results. We present the first conclusive evidence that the TeV γ -ray emission region is shell-like based on our morphological studies. The comparison with 2–5 keV X-ray data reveals a correlation with the 0.4–50 TeV γ -ray emission. The spectrum of RCW 86 is best described by a power law with an exponential cutoff at E cut = (3.5 ± 1.2 stat ) TeV and a spectral index of Γ ≈ 1.6 ± 0.2. A static leptonic one-zone model adequately describes the measured spectral energy distribution of RCW 86, with the resultant total kinetic energy of the electrons above 1 GeV being equivalent to ~0.1% of the initial kinetic energy of a Type Ia supernova explosion (10 51 erg). When using a hadronic model, a magnetic field of B ≈ 100 μ G is needed to represent the measured data. Although this is comparable to formerly published estimates, a standard E −2 spectrum for the proton distribution cannot describe the γ -ray data. Instead, a spectral index of Γ p ≈ 1.7 would be required, which implies that ∼7 × 10 49 / n cm −3 has been transferred into high-energy protons with the effective density n cm −3 = n /1 cm −3 . This is about 10% of the kinetic energy of a typical Type Ia supernova under the assumption of a density of 1 cm −3 .
Publisher: Oxford University Press (OUP)
Date: 11-02-2014
DOI: 10.1093/MNRAS/STU139
Publisher: EDP Sciences
Date: 05-2015
Publisher: EDP Sciences
Date: 04-2018
DOI: 10.1051/0004-6361/201628695
Abstract: Using the High Energy Spectroscopic System (H.E.S.S.) telescopes we have discovered a steady and extended very high-energy (VHE) γ -ray source towards the luminous blue variable candidate LBV 1806−20, massive stellar cluster Cl* 1806−20, and magnetar SGR 1806−20. The new VHE source, HESS J1808−204, was detected at a statistical significance of σ (post-trial) with a photon flux normalisation (2.9 ± 0.4 stat ± 0.5 sys ) × 10 −13 ph cm −2 s −1 TeV −1 at 1 TeV and a power-law photon index of 2.3 ± 0.2 stat ± 0.3 sys . The luminosity of this source (0.2 to 10 TeV scaled to distance d = 8.7 kpc) is L VHE ~ 1.6 × 10 34 ( d /8.7 kpc) 2 erg s −1 . The VHE γ -ray emission is extended and is well fit by a single Gaussian with statistical standard deviation of 0.095° ± 0.015°. This extension is similar to that of the synchrotron radio nebula G10.0−0.3, which is thought to be powered by LBV 1806−20. The VHE γ -ray luminosity could be provided by the stellar wind luminosity of LBV 1806−20 by itself and/or the massive star members of Cl* 1806−20. Alternatively, magnetic dissipation (e.g. via reconnection) from SGR 1806−20 can potentially account for the VHE luminosity. The origin and hadronic and/or leptonic nature of the accelerated particles responsible for HESS J1808−204 is not yet clear. If associated with SGR 1806−20, the potentially young age of the magnetar (650 yr) can be used to infer the transport limits of these particles to match the VHE source size. This discovery provides new interest in the potential for high-energy particle acceleration from magnetars, massive stars, and/or stellar clusters.
Publisher: WORLD SCIENTIFIC
Date: 26-02-2018
DOI: 10.1142/10986
Publisher: EDP Sciences
Date: 04-2018
DOI: 10.1051/0004-6361/201732125
Abstract: Shell-type supernova remnants (SNRs) are considered prime candidates for the acceleration of Galactic cosmic rays (CRs) up to the knee of the CR spectrum at E ≈ 3 × 10 15 eV. Our Milky Way galaxy hosts more than 350 SNRs discovered at radio wavelengths and at high energies, of which 220 fall into the H.E.S.S. Galactic Plane Survey (HGPS) region. Of those, only 50 SNRs are coincident with a H.E.S.S source and in 8 cases the very high-energy (VHE) emission is firmly identified as an SNR. The H.E.S.S. GPS provides us with a legacy for SNR population study in VHE γ -rays and we use this rich data set to extract VHE flux upper limits from all undetected SNRs. Overall, the derived flux upper limits are not in contradiction with the canonical CR paradigm. Assuming this paradigm holds true, we can constrain typical ambient density values around shell-type SNRs to n ≤ 7 cm −3 and electron-to-proton energy fractions above 10 TeV to ϵ ep ≤ 5 × 10 −3 . Furthermore, comparisons of VHE with radio luminosities in non-interacting SNRs reveal a behaviour that is in agreement with the theory of magnetic field lification at shell-type SNRs.
Publisher: EDP Sciences
Date: 16-06-2011
Publisher: EDP Sciences
Date: 09-2012
Publisher: EDP Sciences
Date: 04-2017
DOI: 10.1051/0004-6361/201629427
Abstract: Context. The addition of a 28 m Cherenkov telescope (CT5) to the H.E.S.S. array extended the experiment’s sensitivityto lower energies. The lowest energy threshold is obtained using monoscopic analysis of data taken with CT5, providing access to gamma-ray energies below 100 GeV for small zenith angle observations. Such an extension of the instrument’s energy range is particularly beneficial for studies of active galactic nuclei with soft spectra, as expected for those at a redshift ≥0.5. The high-frequency peaked BL Lac objects PKS 2155−304 ( z = 0.116) and PG 1553+113 (0.43 z 0.58) are among the brightest objects in the gamma-ray sky, both showing clear signatures of gamma-ray absorption at E 100 GeV interpreted as being due to interactions with the extragalactic background light (EBL). Aims. The aims of this work are twofold: to demonstrate the monoscopic analysis of CT5 data with a low energy threshold, and to obtain accurate measurements of the spectral energy distributions (SED) of PKS 2155−304 and PG 1553+113 near their SED peaks at energies ≈100 GeV. Methods. Multiple observational c aigns of PKS 2155−304 and PG 1553+113 were conducted during 2013 and 2014 using the full H.E.S.S. II instrument (CT1–5). A monoscopic analysis of the data taken with the new CT5 telescope was developed along with an investigation into the systematic uncertainties on the spectral parameters which are derived from this analysis. Results. Using the data from CT5, the energy spectra of PKS 2155−304 and PG 1553+113 were reconstructed down to conservative threshold energies of 80 GeV for PKS 2155−304 , which transits near zenith, and 110 GeV for the more northern PG 1553+113 . The measured spectra, well fitted in both cases by a log-parabola spectral model (with a 5.0 σ statistical preference for non-zero curvature for PKS 2155−304 and 4.5 σ for PG 1553+113 ), were found consistent with spectra derived from contemporaneous Fermi -LAT data, indicating a sharp break in the observed spectra of both sources at E ≈ 100 GeV. When corrected for EBL absorption, the intrinsic H.E.S.S. II mono and Fermi -LAT spectrum of PKS 2155−304 was found to show significant curvature. For PG 1553+113 , however, no significant detection of curvature in the intrinsic spectrum could be found within statistical and systematic uncertainties.
Publisher: EDP Sciences
Date: 18-04-2012
Publisher: Oxford University Press (OUP)
Date: 08-2013
Publisher: Oxford University Press (OUP)
Date: 03-06-2014
DOI: 10.1093/MNRAS/STU826
Publisher: EDP Sciences
Date: 13-02-2013
Publisher: EDP Sciences
Date: 04-2018
DOI: 10.1051/0004-6361/201730737
Abstract: A search for new supernova remnants (SNRs) has been conducted using TeV γ -ray data from the H.E.S.S. Galactic plane survey. As an identification criterion, shell morphologies that are characteristic for known resolved TeV SNRs have been used. Three new SNR candidates were identified in the H.E.S.S. data set with this method. Extensive multiwavelength searches for counterparts were conducted. A radio SNR candidate has been identified to be a counterpart to HESS J1534−571. The TeV source is therefore classified as a SNR. For the other two sources, HESS J1614−518 and HESS J1912+101, no identifying counterparts have been found, thus they remain SNR candidates for the time being. TeV-emitting SNRs are key objects in the context of identifying the accelerators of Galactic cosmic rays. The TeV emission of the relativistic particles in the new sources is examined in view of possible leptonic and hadronic emission scenarios, taking the current multiwavelength knowledge into account.
Publisher: EDP Sciences
Date: 11-2014
Publisher: EDP Sciences
Date: 06-2013
Publisher: American Astronomical Society
Date: 22-11-2017
Publisher: EDP Sciences
Date: 23-04-2014
Publisher: EDP Sciences
Date: 06-2013
Publisher: EDP Sciences
Date: 30-01-2015
Publisher: EDP Sciences
Date: 15-01-2013
Publisher: EDP Sciences
Date: 07-2019
DOI: 10.1051/0004-6361/201935458
Abstract: Context. Pulsar wind nebulae (PWNe) represent the most prominent population of Galactic very-high-energy gamma-ray sources and are thought to be an efficient source of leptonic cosmic rays. Vela X is a nearby middle-aged PWN, which shows bright X-ray and TeV gamma-ray emission towards an elongated structure called the cocoon. Aims. Since TeV emission is likely inverse-Compton emission of electrons, predominantly from interactions with the cosmic microwave background, while X-ray emission is synchrotron radiation of the same electrons, we aim to derive the properties of the relativistic particles and of magnetic fields with minimal modelling. Methods. We used data from the Suzaku XIS to derive the spectra from three compact regions in Vela X covering distances from 0.3 to 4 pc from the pulsar along the cocoon. We obtained gamma-ray spectra of the same regions from H.E.S.S. observations and fitted a radiative model to the multi-wavelength spectra. Results. The TeV electron spectra and magnetic field strengths are consistent within the uncertainties for the three regions, with energy densities of the order 10 −12 erg cm −3 . The data indicate the presence of a cutoff in the electron spectrum at energies of ~ 100 TeV and a magnetic field strength of ~6 μ G. Constraints on the presence of turbulent magnetic fields are weak. Conclusions. The pressure of TeV electrons and magnetic fields in the cocoon is dynamically negligible, requiring the presence of another dominant pressure component to balance the pulsar wind at the termination shock. Sub-TeV electrons cannot completely account for the missing pressure, which may be provided either by relativistic ions or from mixing of the ejecta with the pulsar wind. The electron spectra are consistent with expectations from transport scenarios dominated either by advection via the reverse shock or by diffusion, but for the latter the role of radiative losses near the termination shock needs to be further investigated in the light of the measured cutoff energies. Constraints on turbulent magnetic fields and the shape of the electron cutoff can be improved by spectral measurements in the energy range ≳ 10 keV.
Publisher: EDP Sciences
Date: 04-2018
DOI: 10.1051/0004-6361/201630002
Abstract: Aims. We study γ -ray emission from the shell-type supernova remnant (SNR) RX J0852.0−4622 to better characterize its spectral properties and its distribution over the SNR. Methods. The analysis of an extended High Energy Spectroscopic System (H.E.S.S.) data set at very high energies ( E 100 GeV) permits detailed studies, as well as spatially resolved spectroscopy, of the morphology and spectrum of the whole RX J0852.0−4622 region. The H.E.S.S. data are combined with archival data from other wavebands and interpreted in the framework of leptonic and hadronic models. The joint Fermi -LAT-H.E.S.S. spectrum allows the direct determination of the spectral characteristics of the parent particle population in leptonic and hadronic scenarios using only GeV-TeV data. Results. An updated analysis of the H.E.S.S. data shows that the spectrum of the entire SNR connects smoothly to the high-energy spectrum measured by Fermi -LAT. The increased data set makes it possible to demonstrate that the H.E.S.S. spectrum deviates significantly from a power law and is well described by both a curved power law and a power law with an exponential cutoff at an energy of E cut = (6.7 ± 1.2 stat ± 1.2 syst ) TeV. The joint Fermi -LAT-H.E.S.S. spectrum allows the unambiguous identification of the spectral shape as a power law with an exponential cutoff. No significant evidence is found for a variation of the spectral parameters across the SNR, suggesting similar conditions of particle acceleration across the remnant. A simple modeling using one particle population to model the SNR emission demonstrates that both leptonic and hadronic emission scenarios remain plausible. It is also shown that at least a part of the shell emission is likely due to the presence of a pulsar wind nebula around PSR J0855−4644.
Publisher: Oxford University Press (OUP)
Date: 18-11-2014
Publisher: American Physical Society (APS)
Date: 15-05-2018
Publisher: American Physical Society (APS)
Date: 24-02-2015
Publisher: Springer Science and Business Media LLC
Date: 20-11-2019
DOI: 10.1038/S41586-019-1743-9
Abstract: Gamma-ray bursts (GRBs) are brief flashes of γ-rays and are considered to be the most energetic explosive phenomena in the Universe
Publisher: EDP Sciences
Date: 04-2018
DOI: 10.1051/0004-6361/201629790
Abstract: Supernova remnants exhibit shock fronts (shells) that can accelerate charged particles up to very high energies. In the past decade, measurements of a handful of shell-type supernova remnants in very high-energy gamma rays have provided unique insights into the acceleration process. Among those objects, RX J1713.7−3946 (also known as G347.3−0.5) has the largest surface brightness, allowing us in the past to perform the most comprehensive study of morphology and spatially resolved spectra of any such very high-energy gamma-ray source. Here we present extensive new H.E.S.S. measurements of RX J1713.7−3946, almost doubling the observation time compared to our previous publication. Combined with new improved analysis tools, the previous sensitivity is more than doubled. The H.E.S.S. angular resolution of 0.048° (0.036° above 2 TeV) is unprecedented in gamma-ray astronomy and probes physical scales of 0.8 (0.6) parsec at the remnant’s location. The new H.E.S.S. image of RX J1713.7−3946 allows us to reveal clear morphological differences between X-rays and gamma rays. In particular, for the outer edge of the brightest shell region, we find the first ever indication for particles in the process of leaving the acceleration shock region. By studying the broadband energy spectrum, we furthermore extract properties of the parent particle populations, providing new input to the discussion of the leptonic or hadronic nature of the gamma-ray emission mechanism.
Publisher: EDP Sciences
Date: 06-2012
Publisher: EDP Sciences
Date: 10-2017
DOI: 10.1051/0004-6361/201731200
Abstract: Very high-energy γ rays (VHE, E ≳ 100 GeV) propagating over cosmological distances can interact with the low-energy photons of the extragalactic background light (EBL) and produce electron-positron pairs. The transparency of the Universe to VHE γ rays is then directly related to the spectral energy distribution (SED) of the EBL. The observation of features in the VHE energy spectra of extragalactic sources allows the EBL to be measured, which otherwise is very difficult. An EBL model-independent measurement of the EBL SED with the H.E.S.S. array of Cherenkov telescopes is presented. It was obtained by extracting the EBL absorption signal from the reanalysis of high-quality spectra of blazars. From H.E.S.S. data alone the EBL signature is detected at a significance of 9.5 σ , and the intensity of the EBL obtained in different spectral bands is presented together with the associated γ -ray horizon.
Publisher: EDP Sciences
Date: 07-2011
Publisher: EDP Sciences
Date: 2017
Publisher: EDP Sciences
Date: 27-07-2015
Publisher: Oxford University Press (OUP)
Date: 12-06-2012
Publisher: EDP Sciences
Date: 27-02-2015
Publisher: EDP Sciences
Date: 04-2018
DOI: 10.1051/0004-6361/201732098
Abstract: We present the results of the most comprehensive survey of the Galactic plane in very high-energy (VHE) γ -rays, including a public release of Galactic sky maps, a catalog of VHE sources, and the discovery of 16 new sources of VHE γ -rays. The High Energy Spectroscopic System (H.E.S.S.) Galactic plane survey (HGPS) was a decade-long observation program carried out by the H.E.S.S. I array of Cherenkov telescopes in Namibia from 2004 to 2013. The observations amount to nearly 2700 h of quality-selected data, covering the Galactic plane at longitudes from ℓ = 250° to 65° and latitudes | b |≤ 3°. In addition to the unprecedented spatial coverage, the HGPS also features a relatively high angular resolution (0.08° ≈ 5 arcmin mean point spread function 68% containment radius), sensitivity (≲1.5% Crab flux for point-like sources), and energy range (0.2–100 TeV). We constructed a catalog of VHE γ -ray sources from the HGPS data set with a systematic procedure for both source detection and characterization of morphology and spectrum. We present this likelihood-based method in detail, including the introduction of a model component to account for unresolved, large-scale emission along the Galactic plane. In total, the resulting HGPS catalog contains 78 VHE sources, of which 14 are not reanalyzed here, for ex le, due to their complex morphology, namely shell-like sources and the Galactic center region. Where possible, we provide a firm identification of the VHE source or plausible associations with sources in other astronomical catalogs. We also studied the characteristics of the VHE sources with source parameter distributions. 16 new sources were previously unknown or unpublished, and we in idually discuss their identifications or possible associations. We firmly identified 31 sources as pulsar wind nebulae (PWNe), supernova remnants (SNRs), composite SNRs, or gamma-ray binaries. Among the 47 sources not yet identified, most of them (36) have possible associations with cataloged objects, notably PWNe and energetic pulsars that could power VHE PWNe.
Publisher: American Astronomical Society
Date: 13-09-2012
Publisher: EDP Sciences
Date: 16-11-2012
Publisher: EDP Sciences
Date: 04-2018
DOI: 10.1051/0004-6361/201730824
Abstract: The diffuse very high-energy (VHE GeV) γ -ray emission observed in the central 200 pc of the Milky Way by H.E.S.S. was found to follow dense matter distribution in the central molecular zone (CMZ) up to a longitudinal distance of about 130 pc to the Galactic centre (GC), where the flux rapidly decreases. This was initially interpreted as the result of a burst-like injection of energetic particles 10 4 yr ago, but a recent more sensitive H.E.S.S. analysis revealed that the cosmic-ray (CR) density profile drops with the distance to the centre, making data compatible with a steady cosmic PeVatron at the GC. In this paper, we extend this analysis to obtain, for the first time, a detailed characterisation of the correlation with matter and to search for additional features and in idual γ -ray sources in the inner 200 pc. Taking advantage of 250 h of H.E.S.S. data and improved analysis techniques, we perform a detailed morphology study of the diffuse VHE emission observed from the GC ridge and reconstruct its total spectrum. To test the various contributions to the total γ -ray emission, we used an iterative 2D maximum-likelihood approach that allows us to build a phenomenological model of the emission by summing a number of different spatial components. We show that the emission correlated with dense matter covers the full CMZ and that its flux is about half the total diffuse emission flux. We also detect some emission at higher latitude that is likely produced by hadronic collisions of CRs in less dense regions of the GC interstellar medium. We detect an additional emission component centred on the GC and extending over about 15 pc that is consistent with the existence of a strong CR density gradient and confirms the presence of a CR accelerator at the very centre of our Galaxy. We show that the spectrum of full ridge diffuse emission is compatible with that previously derived from the central regions, suggesting that a single population of particles fills the entire CMZ. Finally, we report the discovery of a VHE γ -ray source near the GC radio arc and argue that it is produced by the pulsar wind nebula candidate G0.13−0.11.
Publisher: EDP Sciences
Date: 28-03-2014
Publisher: EDP Sciences
Date: 2012
Publisher: Springer Science and Business Media LLC
Date: 17-06-2020
Publisher: EDP Sciences
Date: 04-2018
DOI: 10.1051/0004-6361/201527773
Abstract: Context. Microquasars are potential γ -ray emitters. Indications of transient episodes of γ -ray emission were recently reported in at least two systems: Cyg X-1 and Cyg X-3. The identification of additional γ -ray-emitting microquasars is required to better understand how γ -ray emission can be produced in these systems. Aim. Theoretical models have predicted very high-energy (VHE) γ -ray emission from microquasars during periods of transient outburst. Observations reported herein were undertaken with the objective of observing a broadband flaring event in the γ -ray and X-ray bands. Methods. Contemporaneous observations of three microquasars, GRS 1915+105, Circinus X-1, and V4641 Sgr, were obtained using the High Energy Spectroscopic System (H.E.S.S.) telescope array and the Rossi X-ray Timing Explorer (RXTE) satellite. X-ray analyses for each microquasar were performed and VHE γ -ray upper limits from contemporaneous H.E.S.S. observations were derived. Results. No significant γ -ray signal has been detected in any of the three systems. The integral γ -ray photon flux at the observational epochs is constrained to be I ( GeV) 7.3 × 10 −13 cm −2 s −1 , I ( GeV ) 1.2 × 10 −12 cm −2 s −1 , and I ( GeV) 4.5 × 10 −12 cm −2 s −1 for GRS 1915+105, Circinus X-1, and V4641 Sgr, respectively. Conclusions. The γ -ray upper limits obtained using H.E.S.S. are examined in the context of previous Cherenkov telescope observations of microquasars. The effect of intrinsic absorption is modelled for each target and found to have negligible impact on the flux of escaping γ -rays. When combined with the X-ray behaviour observed using RXTE, the derived results indicate that if detectable VHE γ -ray emission from microquasars is commonplace, then it is likely to be highly transient.
Publisher: EDP Sciences
Date: 04-2018
DOI: 10.1051/0004-6361/201630151
Abstract: Context. Runaway stars form bow shocks by ploughing through the interstellar medium at supersonic speeds and are promising sources of non-thermal emission of photons. One of these objects has been found to emit non-thermal radiation in the radio band. This triggered the development of theoretical models predicting non-thermal photons from radio up to very-high-energy (VHE, E ≥ 0.1 TeV) gamma rays. Subsequently, one bow shock was also detected in X-ray observations. However, the data did not allow discrimination between a hot thermal and a non-thermal origin. Further observations of different candidates at X-ray energies showed no evidence for emission at the position of the bow shocks either. A systematic search in the Fermi -LAT energy regime resulted in flux upper limits for 27 candidates listed in the E-BOSS catalogue. Aim. Here we perform the first systematic search for VHE gamma-ray emission from bow shocks of runaway stars. Methods. Using all available archival H.E.S.S. data we search for very-high-energy gamma-ray emission at the positions of bow shock candidates listed in the second E-BOSS catalogue release. Out of the 73 bow shock candidates in this catalogue, 32 have been observed with H.E.S.S. Results. None of the observed 32 bow shock candidates in this population study show significant emission in the H.E.S.S. energy range. Therefore, flux upper limits are calculated in five energy bins and the fraction of the kinetic wind power that is converted into VHE gamma rays is constrained. Conclusions. Emission from stellar bow shocks is not detected in the energy range between 0.14 and 18 TeV.The resulting upper limits constrain the level of VHE gamma-ray emission from these objects down to 0.1–1% of the kinetic wind energy.
Publisher: American Astronomical Society
Date: 09-05-2017
Publisher: EDP Sciences
Date: 09-2011
Publisher: EDP Sciences
Date: 07-2019
DOI: 10.1051/0004-6361/201935704
Abstract: The flat spectrum radio quasar 3C 279 is known to exhibit pronounced variability in the high-energy (100 MeV E 100 GeV) γ -ray band, which is continuously monitored with Fermi -LAT. During two periods of high activity in April 2014 and June 2015 target-of-opportunity observations were undertaken with the High Energy Stereoscopic System (H.E.S.S.) in the very-high-energy (VHE, E 100 GeV) γ -ray domain. While the observation in 2014 provides an upper limit, the observation in 2015 results in a signal with 8.7 σ significance above an energy threshold of 66 GeV. No VHE variability was detected during the 2015 observations. The VHE photon spectrum is soft and described by a power-law index of 4.2 ± 0.3. The H.E.S.S. data along with a detailed and contemporaneous multiwavelength data set provide constraints on the physical parameters of the emission region. The minimum distance of the emission region from the central black hole was estimated using two plausible geometries of the broad-line region and three potential intrinsic spectra. The emission region is confidently placed at r ≳ 1.7 × 10 17 cm from the black hole, that is beyond the assumed distance of the broad-line region. Time-dependent leptonic and lepto-hadronic one-zone models were used to describe the evolution of the 2015 flare. Neither model can fully reproduce the observations, despite testing various parameter sets. Furthermore, the H.E.S.S. data were used to derive constraints on Lorentz invariance violation given the large redshift of 3C 279 .
Publisher: EDP Sciences
Date: 2020
DOI: 10.1051/0004-6361/201935906
Abstract: Context. Flat-spectrum radio-quasars (FSRQs) are rarely detected at very high energies ( E ≥ 100 GeV) due to their low-frequency-peaked spectral energy distributions. At present, only six FSRQs are known to emit very high-energy (VHE) photons, representing only 7% of the VHE extragalactic catalog, which is largely dominated by high-frequency-peaked BL Lacertae objects. Aims. Following the detection of MeV–GeV γ -ray flaring activity from the FSRQ PKS 0736+017 ( z = 0.189) with Fermi -LAT, the H.E.S.S. array of Cherenkov telescopes triggered target-of-opportunity (ToO) observations on February 18, 2015, with the goal of studying the γ -ray emission in the VHE band. Methods. H.E.S.S. ToO observations were carried out during the nights of February 18, 19, 21, and 24, 2015. Together with Fermi -LAT, the multi-wavelength coverage of the flare includes Swift observations in soft X-ray and optical-UV bands, and optical monitoring (photometry and spectro-polarimetry) by the Steward Observatory, and the ATOM, the KAIT, and the ASAS-SN telescopes. Results. VHE emission from PKS 0736+017 was detected with H.E.S.S. only during the night of February 19, 2015. Fermi -LAT data indicate the presence of a γ -ray flare, peaking at the time of the H.E.S.S. detection, with a flux doubling timescale of around six hours. The γ -ray flare was accompanied by at least a 1 mag brightening of the non-thermal optical continuum. No simultaneous observations at longer wavelengths are available for the night of the H.E.S.S. detection. The γ -ray observations with H.E.S.S. and Fermi -LAT are used to put constraints on the location of the γ -ray emitting region during the flare: it is constrained to be just outside the radius of the broad-line region r B L R with a bulk Lorentz factor Γ ≃ 20, or at the level of the radius of the dusty torus r torus with Γ ≃ 60. Conclusions. PKS 0736+017 is the seventh FSRQ known to emit VHE photons, and at z = 0.189 is the nearest so far. The location of the γ -ray emitting region during the flare can be tightly constrained thanks to opacity, variability, and collimation arguments.
Publisher: American Astronomical Society
Date: 08-06-2011
Publisher: American Physical Society (APS)
Date: 20-11-2013
Publisher: EDP Sciences
Date: 29-08-2012
Publisher: EDP Sciences
Date: 10-12-2014
Publisher: SAGE Publications
Date: 11-2015
DOI: 10.4278/AJHP.140206-QUAN-62
Abstract: To examine associations of intervention dose with weight, physical activity, glycemic control, and diet outcomes in a randomized trial of a telephone counseling intervention. Study design was a secondary analysis of intervention group. Study setting was primary care practices in a disadvantaged community in Australia. Participants were adult patients with type 2 diabetes (n = 151). Up to 27 telephone counseling calls were made during 18 months. Intervention dose was assessed as the number of calls completed (in tertile categories). Primary outcomes were weight and HbA1c, and moderate to vigorous intensity physical activity via accelerometer. Secondary outcomes were dietary energy intake and diet quality via a validated questionnaire. Analyses employed were bivariate associations of call completion with sociodemographics, and confounder-adjusted linear mixed models for associations of call completion with outcomes (multiple imputation of missing data). Only previous diagnosis of depression/anxiety had a statistically significant (p= .008) association with call completion. Call completion was significantly associated with weight loss (p .001) but not the other outcomes (p .05). Relative to low call completion, mean weight loss (as a percentage of baseline weight) was greater in the high–call completion group by −3.3% (95% confidence interval, −5.0% to −1.5%). Increased dose of intervention was associated with greater weight loss. More needs to be done to retain patients for the duration of weight loss and behavior change interventions, particularly those with diabetes and comorbid depression, who were the most difficult to engage.
Publisher: EDP Sciences
Date: 03-2020
DOI: 10.1051/0004-6361/201936761
Abstract: Aims. Colliding wind binary systems have long been suspected to be high-energy (HE 100 MeV E 100 GeV) γ -ray emitters. η Car is the most prominent member of this object class and is confirmed to emit phase-locked HE γ rays from hundreds of MeV to ~100 GeV energies. This work aims to search for and characterise the very-high-energy (VHE E GeV) γ -ray emission from η Car around the last periastron passage in 2014 with the ground-based High Energy Stereoscopic System (H.E.S.S.). Methods. The region around η Car was observed with H.E.S.S. between orbital phase p = 0.78−1.10, with a closer s ling at p ≈ 0.95 and p ≈ 1.10 (assuming a period of 2023 days). Optimised hardware settings as well as adjustments to the data reduction, reconstruction, and signal selection were needed to suppress and take into account the strong, extended, and inhomogeneous night sky background (NSB) in the η Car field of view. Tailored run-wise Monte-Carlo simulations (RWS) were required to accurately treat the additional noise from NSB photons in the instrument response functions. Results. H.E.S.S. detected VHE γ -ray emission from the direction of η Car shortly before and after the minimum in the X-ray light-curve close to periastron. Using the point spread function provided by RWS, the reconstructed signal is point-like and the spectrum is best described by a power law. The overall flux and spectral index in VHE γ rays agree within statistical and systematic errors before and after periastron. The γ -ray spectrum extends up to at least ~400 GeV. This implies a maximum magnetic field in a leptonic scenario in the emission region of 0.5 Gauss. No indication for phase-locked flux variations is detected in the H.E.S.S. data.
Publisher: EDP Sciences
Date: 03-2013
Publisher: American Association for the Advancement of Science (AAAS)
Date: 23-01-2015
Abstract: There's a new lab for studying the origins of cosmic rays: our neighbor galaxy, the Large Magellanic Cloud. Astronomers are now making progress on this topic by examining the gamma rays that are produced when cosmic rays interact with gas or lower-energy photons. The H.E.S.S. Collaboration has detected three sources of gamma rays in a variety of forms in the galactic satellite to the Milky Way. The sources include the pulsar wind nebula of N 157B, the supernova remnant N 132D, and the superbubble 30 Dor C. Oddly, supernova 1987A was not detected. Science , this issue p. 406
Publisher: EDP Sciences
Date: 04-2018
DOI: 10.1051/0004-6361/201527843
Abstract: The supernova remnant (SNR) W49B originated from a core-collapse supernova that occurred between one and four thousand years ago, and subsequently evolved into a mixed-morphology remnant, which is interacting with molecular clouds (MC). Gamma-ray observations of SNR-MC associations are a powerful tool to constrain the origin of Galactic cosmic rays, as they can probe the acceleration of hadrons through their interaction with the surrounding medium and subsequent emission of non-thermal photons. We report the detection of a γ -ray source coincident with W49B at very high energies (VHE E 100 GeV) with the H.E.S.S. Cherenkov telescopes together with a study of the source with five years of Fermi -LAT high-energy γ -ray (0.06–300 GeV) data. The smoothly connected, combined source spectrum, measured from 60 MeV to multi-TeV energies, shows two significant spectral breaks at 304 ± 20 MeV and 8.4 −2.5 +2.2 GeV the latter is constrained by the joint fit from the two instruments. The detected spectral features are similar to those observed in several other SNR-MC associations and are found to be indicative of γ -ray emission produced through neutral-pion decay.
Publisher: American Astronomical Society
Date: 24-03-2015
Publisher: American Physical Society (APS)
Date: 29-12-2014
Publisher: EDP Sciences
Date: 11-2013
Location: Germany
No related grants have been discovered for Michael Zacharias.