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1. Search for dark matter signals towards a selection of recently detected DES dwarf galaxy satellites of the Milky Way with HESS

Author

26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, Tej B., 31125417 - Chandra, Sunil, 33379009 - Kreter, Michael, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 34208968 - Zywucka-Hejzner, Natalia, Abdallah, H., Arcara, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Kreter, M., Ndiyavala, H., Schutte, H.M., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., Żywucka, N., H.E.S.S. Collaboration, 26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, Tej B., 31125417 - Chandra, Sunil, 33379009 - Kreter, Michael, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 34208968 - Zywucka-Hejzner, Natalia, Abdallah, H., Arcara, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Kreter, M., Ndiyavala, H., Schutte, H.M., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., Żywucka, N., and H.E.S.S. Collaboration

Abstract

Dwarf spheroidal galaxy satellites of the Milky Way are prime targets for indirect detection of dark matter with gamma rays due to their proximity, high dark matter content, and absence of nonthermal emission processes. Recently, the Dark Energy Survey (DES) revealed the existence of new ultrafaint dwarf spheroidal galaxies in the southern-hemisphere sky, therefore ideally located for ground-based observations with the imaging atmospheric Cherenkov telescope array H.E.S.S. We present a search for very-high-energy ( E ≳ 100 GeV ) gamma-ray emission using H.E.S.S. observations carried out recently towards Reticulum II, Tucana II, Tucana III, Tucana IV, and Grus II satellites. No significant very-high-energy gamma-ray excess is found from the observations on any individual object nor in the combined analysis of all the datasets. Using the most recent modeling of the dark matter distribution in the dwarf galaxy halo, we compute for the first time on DES satellites individual and combined constraints from Cherenkov telescope observations on the annihilation cross section of dark matter particles in the form of Weakly Interacting Massive Particles. The combined 95% C.L. observed upper limits reach ⟨ σ v ⟩ ≃ 1 × 10 − 23 cm 3 s − 1 in the W + W − channel and 4 × 10 − 26 cm 3 s − 1 in the γ γ channels for a dark matter mass of 1.5 TeV. The H.E.S.S. constraints well complement the results from Fermi-LAT, HAWC, MAGIC, and VERITAS and are currently the most stringent in the γ γ channels in the multi-GeV/multi-TeV mass range.

Published
2020

2. Very high energy γ-ray emission from two blazars of unknown redshift and upper limits on their distance

Author

26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, Tej B., 31125417 - Chandra, Sunil, 33379009 - Kreter, Michael, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 34208968 - Zywucka-Hejzner, Natalia, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Kreter, M., Ndiyavala, H., Schutte, H.M., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., Żywucka, N., H.E.S.S. Collaboration, 26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, Tej B., 31125417 - Chandra, Sunil, 33379009 - Kreter, Michael, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 34208968 - Zywucka-Hejzner, Natalia, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Kreter, M., Ndiyavala, H., Schutte, H.M., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., Żywucka, N., and H.E.S.S. Collaboration

Abstract

We report on the detection of very high energy (VHE; E > 100 GeV) γ-ray emission from the BL Lac objects KUV 00311−1938 and PKS 1440−389 with the High Energy Stereoscopic System (H.E.S.S.). H.E.S.S. observations were accompanied or preceded by multiwavelength observations with Fermi/LAT, XRT and UVOT onboard the Swift satellite, and ATOM. Based on an extrapolation of the Fermi/LAT spectrum towards the VHE γ-ray regime, we deduce a 95 per cent confidence level upper limit on the unknown redshift of KUV 00311−1938 of z < 0.98 and of PKS 1440−389 of z < 0.53. When combined with previous spectroscopy results, the redshift of KUV 00311−1938 is constrained to 0.51 ≤ z < 0.98 and of PKS 1440−389 to 0.14 ⪅ z < 0.53

Published
2020

3. Exploiting morphological data from Pulsar Wind Nebulae via a spatiotemporal leptonic transport code

Author

21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 20126999 - Seyffert, Albertus Stefanus, Van Rensburg, C., Venter, C., Seyffert, A.S., Harding, Alice K., 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 20126999 - Seyffert, Albertus Stefanus, Van Rensburg, C., Venter, C., Seyffert, A.S., and Harding, Alice K.

Abstract

The next era of ground-based Cherenkov telescope development will see a great increase in both quantity and quality of γ-ray morphological data. This initiated the development of a spatiotemporal leptonic transport code to model pulsar wind nebulae. We present results from this code that predicts the evolution of the leptonic particle spectrum and radiation at different radii in a spherically symmetric source. We simultaneously fit the overall broad-band spectral energy distribution, the surface brightness profile, and the X-ray photon index versus radius for PWN 3C 58, PWN G21.5 − 0.9, and PWN G0.9 + 0.1. Such concurrent fitting of disparate data sets is non-trivial and we thus investigate the utility of different goodness-of-fit statistics, specifically the traditional χ2 test statistic and a newly developed scaled-flux-normalized test statistic to obtain best-fitting parameters. We find reasonable fits to the spatial and spectral data of all three sources, but note some remaining degeneracies that will have to be broken by future observations

Published
2020

4. H.E.S.S. detection of very high-energy γ-ray emission from the quasar PKS 0736+017

Author

26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, Tej B., 31125417 - Chandra, Sunil, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 34208968 - Zywucka-Hejzner, Natalia, 21106266 - Van Rensburg, Carlo, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Ndiyavala, H., Schutte, H., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiazingh, Z., Zacharias, M., Zywucka, N., H.E.S.S. Collaboration, 26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, Tej B., 31125417 - Chandra, Sunil, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 34208968 - Zywucka-Hejzner, Natalia, 21106266 - Van Rensburg, Carlo, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Ndiyavala, H., Schutte, H., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiazingh, Z., Zacharias, M., Zywucka, N., and H.E.S.S. Collaboration

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 rBLR with a bulk Lorentz factor Γ ' 20, or at the level of the radius of the dusty torus rtorus 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

Published
2020

5. Probing the magnetic field in the GW170817 outflow using HESS observations

Author

26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, Tej B., 31125417 - Chandra, Sunil, 33379009 - Kreter, Michael, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 34208968 - Zywucka-Hejzner, Natalia, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Kreter, M., Ndiyavala, H., Schutte, H.M., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., Żywucka, N., H.E.S.S. Collaboration, 26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, Tej B., 31125417 - Chandra, Sunil, 33379009 - Kreter, Michael, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 34208968 - Zywucka-Hejzner, Natalia, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Kreter, M., Ndiyavala, H., Schutte, H.M., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., Żywucka, N., and H.E.S.S. Collaboration

Abstract

The detection of the first electromagnetic counterpart to the binary neutron star (BNS) merger remnant GW170817 established the connection between short γ-ray bursts and BNS mergers. It also confirmed the forging of heavy elements in the ejecta (a so-called kilonova) via the r-process nucleosynthesis. The appearance of nonthermal radio and X-ray emission, as well as the brightening, which lasted more than 100 days, were somewhat unexpected. Current theoretical models attempt to explain this temporal behavior as either originating from a relativistic off-axis jet or a kilonova-like outflow. In either scenario, there is some ambiguity regarding how much energy is transported in the nonthermal electrons versus the magnetic field of the emission region. Combining the Very Large Array (radio) and Chandra (X-ray) measurements with observations in the GeV–TeV domain can help break this ambiguity, almost independently of the assumed origin of the emission. Here we report for the first time on deep H.E.S.S. observations of GW170817/GRB 170817A between 124 and 272 days after the BNS merger with the full H.E.S.S. array of telescopes, as well as on an updated analysis of the prompt (<5 days) observations with the upgraded H.E.S.S. phase-I telescopes. We discuss implications of the H.E.S.S. measurement for the magnetic field in the context of different source scenarios

Published
2020

6. Resolving the Crab pulsar wind nebula at teraelectronvolt energies

Author

26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, Tej B., 31125417 - Chandra, Sunil, 26403366 - Ndiyavala, Hambeleleni, 10060499 - Van der Walt, Diederick Johannes, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 29092086 - Zacharias, Michael, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Ndiyavala, H., Schutte, H., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., H.E.S.S. Collaboration, 26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, Tej B., 31125417 - Chandra, Sunil, 26403366 - Ndiyavala, Hambeleleni, 10060499 - Van der Walt, Diederick Johannes, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 29092086 - Zacharias, Michael, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Ndiyavala, H., Schutte, H., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., and H.E.S.S. Collaboration

Abstract

The Crab nebula is one of the most-studied cosmic particle accelerators, shining brightly across the entire electromagnetic spectrum up to very-high-energy gamma rays1,2. It is known from observations in the radio to gamma-ray part of the spectrum that the nebula is powered by a pulsar, which converts most of its rotational energy losses into a highly relativistic outflow. This outflow powers a pulsar wind nebula, a region of up to ten light-years across, filled with relativistic electrons and positrons. These particles emit synchrotron photons in the ambient magnetic field and produce very-high-energy gamma rays by Compton up-scattering of ambient low-energy photons. Although the synchrotron morphology of the nebula is well established, it has not been known from which region the very-high-energy gamma rays are emitted3,4,5,6,7,8. Here we report that the Crab nebula has an angular extension at gamma-ray energies of 52 arcseconds (assuming a Gaussian source width), much larger than at X-ray energies. This result closes a gap in the multi-wavelength coverage of the nebula, revealing the emission region of the highest-energy gamma rays. These gamma rays enable us to probe a previously inaccessible electron and positron energy range. We find that simulations of the electromagnetic emission reproduce our measurement, providing a non-trivial test of our understanding of particle acceleration in the Crab nebula

Published
2020

7. Resolving the Crab pulsar wind nebula at teraelectronvolt energies

Author

26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, Tej B., 31125417 - Chandra, Sunil, 26403366 - Ndiyavala, Hambeleleni, 10060499 - Van der Walt, Diederick Johannes, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 29092086 - Zacharias, Michael, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Ndiyavala, H., Schutte, H., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., H.E.S.S. Collaboration, 26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, Tej B., 31125417 - Chandra, Sunil, 26403366 - Ndiyavala, Hambeleleni, 10060499 - Van der Walt, Diederick Johannes, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 29092086 - Zacharias, Michael, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Ndiyavala, H., Schutte, H., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., and H.E.S.S. Collaboration

Abstract

The Crab nebula is one of the most-studied cosmic particle accelerators, shining brightly across the entire electromagnetic spectrum up to very-high-energy gamma rays1,2. It is known from observations in the radio to gamma-ray part of the spectrum that the nebula is powered by a pulsar, which converts most of its rotational energy losses into a highly relativistic outflow. This outflow powers a pulsar wind nebula, a region of up to ten light-years across, filled with relativistic electrons and positrons. These particles emit synchrotron photons in the ambient magnetic field and produce very-high-energy gamma rays by Compton up-scattering of ambient low-energy photons. Although the synchrotron morphology of the nebula is well established, it has not been known from which region the very-high-energy gamma rays are emitted3,4,5,6,7,8. Here we report that the Crab nebula has an angular extension at gamma-ray energies of 52 arcseconds (assuming a Gaussian source width), much larger than at X-ray energies. This result closes a gap in the multi-wavelength coverage of the nebula, revealing the emission region of the highest-energy gamma rays. These gamma rays enable us to probe a previously inaccessible electron and positron energy range. We find that simulations of the electromagnetic emission reproduce our measurement, providing a non-trivial test of our understanding of particle acceleration in the Crab nebula

Published
2020

8. Simultaneous observations of the blazar PKS 2155-304 from ultra-violet to TeV energies

Author

26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, Tej B., 31125417 - Chandra, Sunil, 33379009 - Kreter, Michael, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 34208968 - Zywucka-Hejzner, Natalia, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Kreter, M., Ndiyavala, H., Schutte, H.M., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., Zywucka, N., H.E.S.S. Collaboration, Fermi LAT, 26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, Tej B., 31125417 - Chandra, Sunil, 33379009 - Kreter, Michael, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 34208968 - Zywucka-Hejzner, Natalia, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Kreter, M., Ndiyavala, H., Schutte, H.M., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., Zywucka, N., H.E.S.S. Collaboration, and Fermi LAT

Abstract

Here we report the results of the first ever contemporaneous multi-wavelength observation campaign on the BL Lac object PKS 2155−304 involving Swift, NuSTAR, Fermi-LAT, and H.E.S.S. The use of these instruments allows us to cover a broad energy range, which is important for disentangling the different radiative mechanisms. The source, observed from June 2013 to October 2013, was found in a low flux state with respect to previous observations but exhibited highly significant flux variability in the X-rays. The high-energy end of the synchrotron spectrum can be traced up to 40 keV without significant contamination by high-energy emission. A one-zone synchrotron self-Compton model was used to reproduce the broadband flux of the source for all the observations presented here but failed for previous observations made in April 2013. A lepto-hadronic solution was then explored to explain these earlier observational results

Published
2020

9. Simultaneous observations of the blazar PKS 2155-304 from ultra-violet to TeV energies

Author

26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, Tej B., 31125417 - Chandra, Sunil, 33379009 - Kreter, Michael, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 34208968 - Zywucka-Hejzner, Natalia, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Kreter, M., Ndiyavala, H., Schutte, H.M., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., Zywucka, N., H.E.S.S. Collaboration, Fermi LAT, 26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, Tej B., 31125417 - Chandra, Sunil, 33379009 - Kreter, Michael, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 34208968 - Zywucka-Hejzner, Natalia, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Kreter, M., Ndiyavala, H., Schutte, H.M., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., Zywucka, N., H.E.S.S. Collaboration, and Fermi LAT

Abstract

Here we report the results of the first ever contemporaneous multi-wavelength observation campaign on the BL Lac object PKS 2155−304 involving Swift, NuSTAR, Fermi-LAT, and H.E.S.S. The use of these instruments allows us to cover a broad energy range, which is important for disentangling the different radiative mechanisms. The source, observed from June 2013 to October 2013, was found in a low flux state with respect to previous observations but exhibited highly significant flux variability in the X-rays. The high-energy end of the synchrotron spectrum can be traced up to 40 keV without significant contamination by high-energy emission. A one-zone synchrotron self-Compton model was used to reproduce the broadband flux of the source for all the observations presented here but failed for previous observations made in April 2013. A lepto-hadronic solution was then explored to explain these earlier observational results

Published
2020

10. A very-high-energy component deep in the γ-ray burst afterglow

Author

26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, Tej B., 31125417 - Chandra, Sunil, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 34208968 - Zywucka-Hejzner, Natalia, 33379009 - Kreter, Michael, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Kreter, M., Ndiyavala, H., Schutte, H.M., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., Zywucka, N., 26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, Tej B., 31125417 - Chandra, Sunil, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 34208968 - Zywucka-Hejzner, Natalia, 33379009 - Kreter, Michael, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Kreter, M., Ndiyavala, H., Schutte, H.M., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., and Zywucka, N.

Abstract

Gamma-ray bursts (GRBs) are brief flashes of γ-rays and are considered to be the most energetic explosive phenomena in the Universe1. The emission from GRBs comprises a short (typically tens of seconds) and bright prompt emission, followed by a much longer afterglow phase. During the afterglow phase, the shocked outflow—produced by the interaction between the ejected matter and the circumburst medium—slows down, and a gradual decrease in brightness is observed2. GRBs typically emit most of their energy via γ-rays with energies in the kiloelectronvolt-to-megaelectronvolt range, but a few photons with energies of tens of gigaelectronvolts have been detected by space-based instruments3. However, the origins of such high-energy (above one gigaelectronvolt) photons and the presence of very-high-energy (more than 100 gigaelectronvolts) emission have remained elusive4. Here we report observations of very-high-energy emission in the bright GRB 180720B deep in the GRB afterglow—ten hours after the end of the prompt emission phase, when the X-ray flux had already decayed by four orders of magnitude. Two possible explanations exist for the observed radiation: inverse Compton emission and synchrotron emission of ultrarelativistic electrons. Our observations show that the energy fluxes in the X-ray and γ-ray range and their photon indices remain comparable to each other throughout the afterglow. This discovery places distinct constraints on the GRB environment for both emission mechanisms, with the inverse Compton explanation alleviating the particle energy requirements for the emission observed at late times. The late timing of this detection has consequences for the future observations of GRBs at the highest energies

Published
2019

11. HESS and Suzaku observations of the Vela X pulsar wind nebula

Author

26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, Tej B., 31125417 - Chandra, Sunil, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 12006653 - Venter, Christo, 21106266 - Van Rensburg, Carlo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 34208968 - Zywucka-Hejzner, Natalia, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Ndiyavala, H., Schutte, H., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., Zywucka, N., H.E.S.S. Collaboration, 26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, Tej B., 31125417 - Chandra, Sunil, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 12006653 - Venter, Christo, 21106266 - Van Rensburg, Carlo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 34208968 - Zywucka-Hejzner, Natalia, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Ndiyavala, H., Schutte, H., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., Zywucka, N., and H.E.S.S. Collaboration

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 μG. 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 t

Published
2019

12. Constraints on the emission region of 3C 279 during strong flares in 2014 and 2015 through VHE γ-ray observations with H.E.S.S.

Author

26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, Tej B., 31125417 - Chandra, Sunil, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 34208968 - Zywucka-Hejzner, Natalia, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Ndiyavala, H., Schutte, H., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., Żywucka, N., H.E.S.S. Collaboration, 26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, Tej B., 31125417 - Chandra, Sunil, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 34208968 - Zywucka-Hejzner, Natalia, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Ndiyavala, H., Schutte, H., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., Żywucka, N., and H.E.S.S. Collaboration

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 8.7σ 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 × 1017 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

Published
2019

13. Particle transport within the pulsar wind nebula HESS J1825–137

Author

26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 31125417 - Chandra, Sunil, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 30366755 - Chand, Tej B., Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Ndiyavala, H., Schutte, H., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., H.E.S.S. Collaboration, 26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 31125417 - Chandra, Sunil, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 30366755 - Chand, Tej B., Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Ndiyavala, H., Schutte, H., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., and H.E.S.S. Collaboration

Abstract

Context. We present a detailed view of the pulsar wind nebula (PWN) HESS J1825–137. We aim to constrain the mechanisms dominating the particle transport within the nebula, accounting for its anomalously large size and spectral characteristics. Aims. The nebula was studied using a deep exposure from over 12 years of H.E.S.S. I operation, together with data from H.E.S.S. II that improve the low-energy sensitivity. Enhanced energy-dependent morphological and spatially resolved spectral analyses probe the very high energy (VHE, E > 0.1 TeV) γ-ray properties of the nebula. Methods. The nebula emission is revealed to extend out to 1.5° from the pulsar, ~1.5 times farther than previously seen, making HESS J1825–137, with an intrinsic diameter of ~100 pc, potentially the largest γ-ray PWN currently known. Characterising the strongly energy-dependent morphology of the nebula enables us to constrain the particle transport mechanisms. A dependence of the nebula extent with energy of R ∝ Eα with α = −0.29 ± 0.04stat ± 0.05sys disfavours a pure diffusion scenario for particle transport within the nebula. The total γ-ray flux of the nebula above 1 TeV is found to be (1.12 ± 0.03stat ± 0.25sys) × 10−11 cm−2 s−1, corresponding to ~64% of the flux of the Crab nebula. Results. HESS J1825–137 is a PWN with clearly energy-dependent morphology at VHE γ-ray energies. This source is used as a laboratory to investigate particle transport within intermediate-age PWNe. Based on deep observations of this highly spatially extended PWN, we produce a spectral map of the region that provides insights into the spectral variation within the nebula

Published
2019

14. H.E.S.S. and Suzaku observations of the Vela X pulsar wind nebula

Author

26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 31125417 - Chandra, Sunil, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 30366755 - Chand, Tej B., 34208968 - Zywucka-Hejzner, Natalia, 10060499 - Van der Walt, Diederick Johannes, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Ndiyavala, H., Schutte, H., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., Zywucka, N., H.E.S.S. Collaboration, 26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 31125417 - Chandra, Sunil, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 30366755 - Chand, Tej B., 34208968 - Zywucka-Hejzner, Natalia, 10060499 - Van der Walt, Diederick Johannes, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Ndiyavala, H., Schutte, H., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., Zywucka, N., and H.E.S.S. Collaboration

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 μG. 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 t

Published
2019

15. H.E.S.S. observations of the flaring gravitationally lensed galaxy PKS 1830-211

Author

26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, T.B., 31125417 - Chandra, Sunil, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Ndiyavala, H., Schutte, H., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., H.E.S.S. Collaboration, 26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, T.B., 31125417 - Chandra, Sunil, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Ndiyavala, H., Schutte, H., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., and H.E.S.S. Collaboration

Abstract

PKS 1830–211 is a known macrolensed quasar located at a redshift of z = 2.5. Its high-energy gamma-ray emission has been detected with the Fermi-Large Area Telescope (LAT) instrument and evidence for lensing was obtained by several authors from its high-energy data. Observations of PKS 1830–211 were taken with the High Energy Stereoscopic System (H.E.S.S.) array of Imaging Atmospheric Cherenkov Telescopes in 2014 August, following a flare alert by the Fermi-LAT Collaboration. The H.E.S.S observations were aimed at detecting a gamma-ray flare delayed by 20–27 d from the alert flare, as expected from observations at other wavelengths. More than 12 h of good-quality data were taken with an analysis threshold of ∼67 GeV. The significance of a potential signal is computed as a function of the date and the average significance over the whole period. Data are compared to simultaneous observations by Fermi-LAT. No photon excess or significant signal is detected. An upper limit on PKS 1830–211 flux above 67 GeV is computed and compared to the extrapolation of the Fermi-LAT flare spectrum

Published
2019

16. Upper limits on very-high-energy gamma-ray emission from core-collapse supernovae observed with H.E.S.S.

Author

34208968 - Zywucka-Hejzner, Natalia, 29092086 - Zacharias, Michael, 26594080 - Wadiasingh, Zorawar, 12006653 - Venter, Christo, 21106266 - Van Rensburg, Carlo, 10060499 - Van der Walt, Diederick Johannes, 20126999 - Seyffert, Albertus Stefanus, 22799133 - Schutte, Hester M., 26403366 - Ndiyavala, Hambeleleni, 31125417 - Chandra, Sunil, 30366755 - Chand, Tej B., 24420530 - Böttcher, Markus, 20574266 - Barnard, Monica, 28644743 - Backes, Michael, 30588766 - Arcaro, Cornelia, 26598973 - Abdalla, Hassan, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Ndiyavala, H., Schutte, H., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., Zywucka, N., H.E.S.S. Collaboration, 34208968 - Zywucka-Hejzner, Natalia, 29092086 - Zacharias, Michael, 26594080 - Wadiasingh, Zorawar, 12006653 - Venter, Christo, 21106266 - Van Rensburg, Carlo, 10060499 - Van der Walt, Diederick Johannes, 20126999 - Seyffert, Albertus Stefanus, 22799133 - Schutte, Hester M., 26403366 - Ndiyavala, Hambeleleni, 31125417 - Chandra, Sunil, 30366755 - Chand, Tej B., 24420530 - Böttcher, Markus, 20574266 - Barnard, Monica, 28644743 - Backes, Michael, 30588766 - Arcaro, Cornelia, 26598973 - Abdalla, Hassan, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Ndiyavala, H., Schutte, H., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., Zywucka, N., and H.E.S.S. Collaboration

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 >1 TeV gamma-ray flux of the order of ~10−13 cm−2s−1 are established, corresponding to upper limits on the luminosities in the range ~2 × 1039 to ~1 × 1042 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

Published
2019

17. Upper limits on very-high-energy gamma-ray emission from core-collapse supernovae observed with H.E.S.S.

Author

34208968 - Zywucka-Hejzner, Natalia, 29092086 - Zacharias, Michael, 26594080 - Wadiasingh, Zorawar, 12006653 - Venter, Christo, 21106266 - Van Rensburg, Carlo, 10060499 - Van der Walt, Diederick Johannes, 20126999 - Seyffert, Albertus Stefanus, 22799133 - Schutte, Hester M., 26403366 - Ndiyavala, Hambeleleni, 31125417 - Chandra, Sunil, 30366755 - Chand, Tej B., 24420530 - Böttcher, Markus, 20574266 - Barnard, Monica, 28644743 - Backes, Michael, 30588766 - Arcaro, Cornelia, 26598973 - Abdalla, Hassan, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Ndiyavala, H., Schutte, H., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., Zywucka, N., H.E.S.S. Collaboration, 34208968 - Zywucka-Hejzner, Natalia, 29092086 - Zacharias, Michael, 26594080 - Wadiasingh, Zorawar, 12006653 - Venter, Christo, 21106266 - Van Rensburg, Carlo, 10060499 - Van der Walt, Diederick Johannes, 20126999 - Seyffert, Albertus Stefanus, 22799133 - Schutte, Hester M., 26403366 - Ndiyavala, Hambeleleni, 31125417 - Chandra, Sunil, 30366755 - Chand, Tej B., 24420530 - Böttcher, Markus, 20574266 - Barnard, Monica, 28644743 - Backes, Michael, 30588766 - Arcaro, Cornelia, 26598973 - Abdalla, Hassan, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Ndiyavala, H., Schutte, H., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., Zywucka, N., and H.E.S.S. Collaboration

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 >1 TeV gamma-ray flux of the order of ~10−13 cm−2s−1 are established, corresponding to upper limits on the luminosities in the range ~2 × 1039 to ~1 × 1042 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

Published
2019

18. H.E.S.S. observations of the flaring gravitationally lensed galaxy PKS 1830-211

Author

26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, Tej B., 31125417 - Chandra, Sunil, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Ndiyavala, H., Schutte, H., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., H.E.S.S. Collaboration, 26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, Tej B., 31125417 - Chandra, Sunil, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Ndiyavala, H., Schutte, H., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., and H.E.S.S. Collaboration

Abstract

PKS 1830–211 is a known macrolensed quasar located at a redshift of z = 2.5. Its high-energy gamma-ray emission has been detected with the Fermi-Large Area Telescope (LAT) instrument and evidence for lensing was obtained by several authors from its high-energy data. Observations of PKS 1830–211 were taken with the High Energy Stereoscopic System (H.E.S.S.) array of Imaging Atmospheric Cherenkov Telescopes in 2014 August, following a flare alert by the Fermi-LAT Collaboration. The H.E.S.S observations were aimed at detecting a gamma-ray flare delayed by 20–27 d from the alert flare, as expected from observations at other wavelengths. More than 12 h of good-quality data were taken with an analysis threshold of ∼67 GeV. The significance of a potential signal is computed as a function of the date and the average significance over the whole period. Data are compared to simultaneous observations by Fermi-LAT. No photon excess or significant signal is detected. An upper limit on PKS 1830–211 flux above 67 GeV is computed and compared to the extrapolation of the Fermi-LAT flare spectrum

Published
2019

19. H.E.S.S. observations of the flaring gravitationally lensed galaxy PKS 1830-211

Author

26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, T.B., 31125417 - Chandra, Sunil, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Ndiyavala, H., Schutte, H., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., H.E.S.S. Collaboration, 26598973 - Abdalla, Hassan, 30588766 - Arcaro, Cornelia, 28644743 - Backes, Michael, 20574266 - Barnard, Monica, 24420530 - Böttcher, Markus, 30366755 - Chand, T.B., 31125417 - Chandra, Sunil, 26403366 - Ndiyavala, Hambeleleni, 22799133 - Schutte, Hester M., 20126999 - Seyffert, Albertus Stefanus, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, Abdalla, H., Arcaro, C., Backes, M., Barnard, M., Böttcher, M., Chand, T., Chandra, S., Ndiyavala, H., Schutte, H., Seyffert, A.S., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., and H.E.S.S. Collaboration

Abstract

PKS 1830–211 is a known macrolensed quasar located at a redshift of z = 2.5. Its high-energy gamma-ray emission has been detected with the Fermi-Large Area Telescope (LAT) instrument and evidence for lensing was obtained by several authors from its high-energy data. Observations of PKS 1830–211 were taken with the High Energy Stereoscopic System (H.E.S.S.) array of Imaging Atmospheric Cherenkov Telescopes in 2014 August, following a flare alert by the Fermi-LAT Collaboration. The H.E.S.S observations were aimed at detecting a gamma-ray flare delayed by 20–27 d from the alert flare, as expected from observations at other wavelengths. More than 12 h of good-quality data were taken with an analysis threshold of ∼67 GeV. The significance of a potential signal is computed as a function of the date and the average significance over the whole period. Data are compared to simultaneous observations by Fermi-LAT. No photon excess or significant signal is detected. An upper limit on PKS 1830–211 flux above 67 GeV is computed and compared to the extrapolation of the Fermi-LAT flare spectrum

Published
2019

20. Detection of variable VHE γ-ray emission from the extra-galactic γ-ray binary LMC P3

Author

24420530 - Böttcher, Markus, 26909995 - Garrigoux, Tania, 24790052 - Ivascenko, Alex, 11749903 - Krüger, Petrus Paulus, 26403366 - Ndiyavala, Hambeleleni, 22050574 - Pekeur, Nicolette Whilna, 20126999 - Seyffert, Albertus Stefanus, 25161814 - Spanier, Felix Alexander, 24922986 - Sushch, Iurii, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 20574266 - Barnard, Monica, 26598973 - Abdalla, Hassan, Abdalla, H., Barnard, M., Böttcher, M., Garrigoux, T., Ivascenko, A., Krüger, P.P., Ndiyavala, H., Pekeur, N.W., Seyffert, A.S., Spanier, F., Sushch, I., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., H.E.S.S. Collaboration, 24420530 - Böttcher, Markus, 26909995 - Garrigoux, Tania, 24790052 - Ivascenko, Alex, 11749903 - Krüger, Petrus Paulus, 26403366 - Ndiyavala, Hambeleleni, 22050574 - Pekeur, Nicolette Whilna, 20126999 - Seyffert, Albertus Stefanus, 25161814 - Spanier, Felix Alexander, 24922986 - Sushch, Iurii, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 20574266 - Barnard, Monica, 26598973 - Abdalla, Hassan, Abdalla, H., Barnard, M., Böttcher, M., Garrigoux, T., Ivascenko, A., Krüger, P.P., Ndiyavala, H., Pekeur, N.W., Seyffert, A.S., Spanier, F., Sushch, I., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., and H.E.S.S. Collaboration

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, >100 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

Published
2018

21. TeV gamma-ray observations of the binary neutron star merger GW170817 with H.E.S.S.

Author

24420530 - Böttcher, Markus, 26909995 - Garrigoux, Tania, 24790052 - Ivascenko, Alex, 11749903 - Krüger, Petrus Paulus, 22050574 - Pekeur, Nicolette Whilna, 20126999 - Seyffert, Albertus Stefanus, 25161814 - Spanier, Felix Alexander, 24922986 - Sushch, Iurii, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 26403366 - Ndiyavala, Hambeleleni, 26598973 - Abdalla, Hassan, 20574266 - Barnard, Monica, Abdalla, H., Barnard, M., Böttcher, M., Garrigoux, T., Ivascenko, A., Krüger, P.P., Ndiyavala, H., Pekeur, N.W., Seyffert, A.S., Spanier, F., Sushch, I., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., H.E.S.S. Collaboration, 24420530 - Böttcher, Markus, 26909995 - Garrigoux, Tania, 24790052 - Ivascenko, Alex, 11749903 - Krüger, Petrus Paulus, 22050574 - Pekeur, Nicolette Whilna, 20126999 - Seyffert, Albertus Stefanus, 25161814 - Spanier, Felix Alexander, 24922986 - Sushch, Iurii, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 26403366 - Ndiyavala, Hambeleleni, 26598973 - Abdalla, Hassan, 20574266 - Barnard, Monica, Abdalla, H., Barnard, M., Böttcher, M., Garrigoux, T., Ivascenko, A., Krüger, P.P., Ndiyavala, H., Pekeur, N.W., Seyffert, A.S., Spanier, F., Sushch, I., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., and H.E.S.S. Collaboration

Abstract

We search for high-energy gamma-ray emission from the binary neutron star merger GW170817 with the H.E.S.S. Imaging Air Cherenkov Telescopes. The observations presented here have been obtained starting only 5.3 hr after GW170817. The H.E.S.S. target selection identified regions of high probability to find a counterpart of the gravitational-wave event. The first of these regions contained the counterpart SSS17a that has been identified in the optical range several hours after our observations. We can therefore present the first data obtained by a groundbased pointing instrument on this object. A subsequent monitoring campaign with the H.E.S.S. telescopes extended over several days, covering timescales from 0.22 to 5.2 days and energy ranges between 270 GeV to 8.55 TeV. No significant gamma-ray emission has been found. The derived upper limits on the very-high-energy gamma-ray flux for the first time constrain non-thermal, high-energy emission following the merger of a confirmed binary neutron star system

Published
2017

22. TeV gamma-ray observations of the binary neutron star merger GW170817 with H.E.S.S.

Author

24420530 - Böttcher, Markus, 26909995 - Garrigoux, Tania, 24790052 - Ivascenko, Alex, 11749903 - Krüger, Petrus Paulus, 22050574 - Pekeur, Nicolette Whilna, 20126999 - Seyffert, Albertus Stefanus, 25161814 - Spanier, Felix Alexander, 24922986 - Sushch, Iurii, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 26403366 - Ndiyavala, Hambeleleni, 26598973 - Abdalla, Hassan, 20574266 - Barnard, Monica, Abdalla, H., Barnard, M., Böttcher, M., Garrigoux, T., Ivascenko, A., Krüger, P.P., Ndiyavala, H., Pekeur, N.W., Seyffert, A.S., Spanier, F., Sushch, I., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., H.E.S.S. Collaboration, 24420530 - Böttcher, Markus, 26909995 - Garrigoux, Tania, 24790052 - Ivascenko, Alex, 11749903 - Krüger, Petrus Paulus, 22050574 - Pekeur, Nicolette Whilna, 20126999 - Seyffert, Albertus Stefanus, 25161814 - Spanier, Felix Alexander, 24922986 - Sushch, Iurii, 10060499 - Van der Walt, Diederick Johannes, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, 26594080 - Wadiasingh, Zorawar, 29092086 - Zacharias, Michael, 26403366 - Ndiyavala, Hambeleleni, 26598973 - Abdalla, Hassan, 20574266 - Barnard, Monica, Abdalla, H., Barnard, M., Böttcher, M., Garrigoux, T., Ivascenko, A., Krüger, P.P., Ndiyavala, H., Pekeur, N.W., Seyffert, A.S., Spanier, F., Sushch, I., Van der Walt, D.J., Van Rensburg, C., Venter, C., Wadiasingh, Z., Zacharias, M., and H.E.S.S. Collaboration

Abstract

We search for high-energy gamma-ray emission from the binary neutron star merger GW170817 with the H.E.S.S. Imaging Air Cherenkov Telescopes. The observations presented here have been obtained starting only 5.3 hr after GW170817. The H.E.S.S. target selection identified regions of high probability to find a counterpart of the gravitational-wave event. The first of these regions contained the counterpart SSS17a that has been identified in the optical range several hours after our observations. We can therefore present the first data obtained by a groundbased pointing instrument on this object. A subsequent monitoring campaign with the H.E.S.S. telescopes extended over several days, covering timescales from 0.22 to 5.2 days and energy ranges between 270 GeV to 8.55 TeV. No significant gamma-ray emission has been found. The derived upper limits on the very-high-energy gamma-ray flux for the first time constrain non-thermal, high-energy emission following the merger of a confirmed binary neutron star system

Published
2017

23. Search for dark matter annihilations towards the inner Galactic halo from 10 years of observations with H.E.S.S.

Author

24420530 - Böttcher, Markus, 13146629 - Davids, Isak Delberth, 24790052 - Ivascenko, Alex, 11749903 - Krüger, Petrus Paulus, 22050574 - Pekeur, Nicolette Whilna, 20126999 - Seyffert, Albertus Stefanus, 25161814 - Spanier, Felix Alexander, 10060499 - Van der Walt, Diederick Johannes, 12006653 - Venter, Christo, 26909995 - Garrigoux, Tania, 20574266 - Barnard, Monica, 26598973 - Abdalla, Hassan, Abdallah, H., Barnard, M., Böttcher, M., Davids, I.D., Garrigoux, T., Ivascenko, A., Krüger, P.P., Pekeur, N.W., Seyffert, A.S., Spanier, F., Van der Walt, D.J., Venter, C., H.E.S.S. Collaboration, 24420530 - Böttcher, Markus, 13146629 - Davids, Isak Delberth, 24790052 - Ivascenko, Alex, 11749903 - Krüger, Petrus Paulus, 22050574 - Pekeur, Nicolette Whilna, 20126999 - Seyffert, Albertus Stefanus, 25161814 - Spanier, Felix Alexander, 10060499 - Van der Walt, Diederick Johannes, 12006653 - Venter, Christo, 26909995 - Garrigoux, Tania, 20574266 - Barnard, Monica, 26598973 - Abdalla, Hassan, Abdallah, H., Barnard, M., Böttcher, M., Davids, I.D., Garrigoux, T., Ivascenko, A., Krüger, P.P., Pekeur, N.W., Seyffert, A.S., Spanier, F., Van der Walt, D.J., Venter, C., and H.E.S.S. Collaboration

Abstract

The inner region of the Milky Way halo harbors a large amount of dark matter (DM). Given its proximity, it is one of the most promising targets to look for DM. We report on a search for the annihilations of DM particles using γ-ray observations towards the inner 300 parsecs of the Milky Way, with the H.E.S.S. array of ground-based Cherenkov telescopes. The analysis is based on a 2D maximum likelihood method using Galactic center (GC) data accumulated by H.E.S.S. over the last 10 years (2004-2014), and does not show any significant γ-ray signal above background. Assuming Einasto and Navarro-Frenk-White DM density profiles at the GC, we derive upper limits on the annihilation cross section ⟨σv⟩. These constraints are the strongest obtained so far in the TeV DM mass range and improve upon previous limits by a factor 5. For the Einasto profile, the constraints reach ⟨σv⟩ values of 6×10−26cm3s−1 in the W+W− channel for a DM particle mass of 1.5 TeV, and 2×10−26cm3s−1 in the τ+τ− channel for 1 TeV mass. For the first time, ground-based γ-ray observations have reached sufficient sensitivity to probe ⟨σv⟩ values expected from the thermal relic density for TeV DM particles

Published
2016

24. Discovery of variable VHE γ-ray emission from the binary system 1FGL J1018.6-5856

Author

24420530 - Böttcher, Markus, 13146629 - Davids, Isak Delberth, 24790052 - Ivascenko, Alex, 11749903 - Krüger, Petrus Paulus, 22050574 - Pekeur, Nicolette Whilna, 25161814 - Spanier, Felix Alexander, 24922986 - Sushch, Iurii, 10060499 - Van der Walt, Diederick Johannes, 12006653 - Venter, Christo, 20126999 - Seyffert, Albertus Stefanus, Abramowski, A., Böttcher, M., Davids, I.D., Ivascenko, A., Krüger, P.P., Pekeur, N.W., Seyffert, A.S., Spanier, F., Sushch, I., Van der Walt, D.J., Venter, C., H.E.S.S. Collaboration, 24420530 - Böttcher, Markus, 13146629 - Davids, Isak Delberth, 24790052 - Ivascenko, Alex, 11749903 - Krüger, Petrus Paulus, 22050574 - Pekeur, Nicolette Whilna, 25161814 - Spanier, Felix Alexander, 24922986 - Sushch, Iurii, 10060499 - Van der Walt, Diederick Johannes, 12006653 - Venter, Christo, 20126999 - Seyffert, Albertus Stefanus, Abramowski, A., Böttcher, M., Davids, I.D., Ivascenko, A., Krüger, P.P., Pekeur, N.W., Seyffert, A.S., Spanier, F., Sushch, I., Van der Walt, D.J., Venter, C., and H.E.S.S. Collaboration

Abstract

Re-observations with the HESS telescope array of the very high-energy (VHE) source HESS J1018–589 A that is coincident with the Fermi-LAT γ-ray binary 1FGL J1018.6–5856 have resulted in a source detection significance of more than 9σ and the detection of variability (χ2/ν of 238.3/155) in the emitted γ-ray flux. This variability confirms the association of HESS J1018–589 A with the high-energy γ-ray binary detected by Fermi-LAT and also confirms the point-like source as a new VHE binary system. The spectrum of HESS J1018–589 A is best fit with a power-law function with photon index Γ = 2.20 ± 0.14stat ± 0.2sys. Emission is detected up to ~20 TeV. The mean differential flux level is (2.9 ± 0.4) × 10-13 TeV-1 cm-2 s-1 at 1 TeV, equivalent to ~1% of the flux from the Crab Nebula at the same energy. Variability is clearly detected in the night-by-night light curve. When folded on the orbital period of 16.58 days, the rebinned light curve peaks in phase with the observed X-ray and high-energy phaseograms. The fit of the HESS phaseogram to a constant flux provides evidence of periodicity at the level of Nσ> 3σ. The shape of the VHE phaseogram and measured spectrum suggest a low-inclination, low-eccentricity system with amodest impact from VHE γ-ray absorption due to pair production (τ ≲ 1 at 300 GeV)

Published
2015

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