Gamma-ray observations of MAXI J1820+070 during the 2018 outburst

MAXI J1820+070 is a low-mass X-ray binary with a black hole (BH) as a compact object. This binary underwent an exceptionally bright X-ray outburst from 2018 March to October, showing evidence of a non-thermal particle population through its radio emission during this whole period. The combined results of 59.5 h of observations of the MAXI J1820+070 outburst with the H.E.S.S., MAGIC and VERITAS experiments at energies above 200 GeV are presented, together with Fermi-LAT data between 0.1 and 500 GeV, and multiwavelength observations from radio to X-rays. Gamma-ray emission is not detected from MAXI J1820+070, but the obtained upper limits and the multiwavelength data allow us to put meaningful constraints on the source properties under reasonable assumptions regarding the non-thermal particle population and the jet synchrotron spectrum. In particular, it is possible to show that, if a high-energy (HE) gamma-ray emitting region is present during the hard state of the source, its predicted flux should be at most a factor of 20 below the obtained Fermi-LAT upper limits, and closer to them for magnetic fields significantly below equipartition. During the state transitions, under the plausible assumption that electrons are accelerated up to ∼500 GeV, the multiwavelength data and the gamma-ray upper limits lead consistently to the conclusion that a potential HE and very-HE gamma-ray emitting region should be located at a distance from the BH ranging between 10¹¹ and 10¹³ cm. Similar outbursts from low-mass X-ray binaries might be detectable in the near future with upcoming instruments such as CTA.H. Abe ... G. Rowell ... et al. (The VERITAS Collaboration), V. Bosch-Ramon, C. Celma, M. Linares, D. M. Russell, and G. Sal

MAGIC very large zenith angle observations of the Crab Nebula up to 100 TeV

Aims. We measure the Crab Nebula γ-ray spectral energy distribution in the ~100 TeV energy domain and test the validity of existing leptonic emission models at these high energies. Methods. We used the novel very large zenith angle observations with the MAGIC telescope system to increase the collection area above 10 TeV. We also developed an auxiliary procedure of monitoring atmospheric transmission in order to assure proper calibration of the accumulated data. This employs recording optical images of the stellar field next to the source position, which provides a better than 10% accuracy for the transmission measurements. Results. We demonstrate that MAGIC very large zenith angle observations yield a collection area larger than a square kilometer. In only ~ 56 h of observations, we detect the γ-ray emission from the Crab Nebula up to 100 TeV, thus providing the highest energy measurement of this source to date with Imaging Atmospheric Cherenkov Telescopes. Comparing accumulated and archival MAGIC and Fermi/LAT data with some of the existing emission models, we find that none of them provides an accurate description of the 1 GeV to 100 TeV γ-ray signal

Discovery of Gamma-Ray Emission From the Shell-Type Supernova Remnant RCW 86 With Hess

6 pages, 5 figuresThe shell-type supernova remnant (SNR) RCW 86, possibly associated with the historical supernova SN 185, with its relatively large size (about 40' in diameter) and the presence of non-thermal X-rays is a promising target for gamma-ray observations. The high sensitivity, good angular resolution of a few arc minutes and the large field of view of the High Energy Stereoscopic System (H.E.S.S.) make it ideally suited for the study of the gamma-ray morphology of such extended sources. H.E.S.S. observations have indeed led to the discovery of the SNR RCW 86 in very high energy (VHE; E > 100 GeV) gamma-rays. With 31 hours of observation time, the source is detected with a statistical significance of 8.5 sigma and is significantly more extended than the H.E.S.S. point spread function. Morphological studies have been performed and show that the gamma-ray flux does not correlate perfectly with the X-ray emission. The flux from the remnant is ~10% of the flux from the Crab nebula, with a similar photon index of about 2.5. Possible origins of the very high energy gamma-ray emission, via either Inverse Compton scattering by electrons or the decay of neutral pions produced by proton interactions, are discussed on the basis of spectral features obtained both in the X-ray and gamma-ray regimes

Search for gamma rays from dark matter annihilations around intermediate mass black holes with the HESS experiment

12 pages, 7 figures, accepted for publication in Phys. Rev. D on June 16, 2008The H.E.S.S. array of Cherenkov telescopes has performed, from 2004 to 2007, a survey of the inner Galactic plane at photon energies above 100 GeV. About 400 hours of data have been accumulated in the region between -30 and +60 degrees in Galactic longitude, and between -3 and +3 degrees in Galactic latitude. Assuming that dark matter is composed of Weakly Interacting Massive Particles, we calculate here the H.E.S.S. sensitivity map for dark matter annihilations, and derive the first experimental constraints on the ''mini-spikes'' scenario, in which a gamma-ray signal arises from dark matter annihilation around Intermediate Mass Black Holes. The data exclude the proposed scenario at a 90% confidence level for dark matter particles with velocity-weighted annihilation cross section sigma v above 10^28 cm3s^-1 and mass between 800 GeV and 10 TeV

Design concepts for the Cherenkov Telescope Array CTA: An advanced facility for ground-based high-energy gamma-ray astronomy

Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA. © 2011 The Author(s)