MAXI J1820+070 is a low-mass X-ray binary with a black hole as a compact object. This binary underwent an exceptionally bright X-ray outburst from March to October 2018, showing evidence of a non-thermal particle population through its radio emission during this whole period. The combined results of 59.5 hours 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 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 high-energy and very-high-energy gamma-ray emitting region should be located at a distance from the black hole ranging between 10^11 and 10^13 cm. Similar outbursts from low-mass X-ray binaries might be detectable in the near future with upcoming instruments such as CTA.

10.48550/arxiv.2209.09785

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H.E.S.S. Follow-up Observations of Binary Black Hole Coalescence Events during the Second and Third Gravitational-wave Observing Runs of Advanced LIGO and Advanced Virgo

The Astrophysical Journal (2021)

H. Abdalla F. Aharonian F. Ait Benkhali E. O. Angüner Halim Ashkar

Abstract We report on the observations of four well-localized binary black hole (BBH) mergers by the High Energy Stereoscopic System (H.E.S.S.) during the second and third observing runs of Advanced LIGO and Advanced Virgo, O2 and O3. H.E.S.S. can observe 20 deg 2 of the sky at a time and follows up gravitational-wave (GW) events by “tiling” localization regions to maximize the covered localization probability. During O2 and O3, H.E.S.S. observed large portions of the localization regions, between 35% and 75%, for four BBH mergers (GW170814, GW190512_180714, GW190728_064510, and S200224ca). For these four GW events, we find no significant signal from a pointlike source in any of the observations, and we set upper limits on the very high energy (>100 GeV) γ -ray emission. The 1–10 TeV isotropic luminosity of these GW events is below 10 45 erg s −1 at the times of the H.E.S.S. observations, around the level of the low-luminosity GRB 190829A. Assuming no changes are made to how follow-up observations are conducted, H.E.S.S. can expect to observe over 60 GW events per year in the fourth GW observing run, O4, of which eight would be observable with minimal latency.

Black hole (networking)

10.3847/1538-4357/ac2e04

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Acceleration and transport of relativistic electrons in the jets of the microquasar SS 433

Science (2024)

F. Aharonian F. Ait Benkhali J. Aschersleben Halim Ashkar Michael Backes

SS 433 is a microquasar, a stellar binary system that launches collimated relativistic jets. We observed SS 433 in gamma rays using the High Energy Stereoscopic System (H.E.S.S.) and found an energy-dependent shift in the apparent position of the gamma-ray emission from the parsec-scale jets. These observations trace the energetic electron population and indicate that inverse Compton scattering is the emission mechanism of the gamma rays. Our modeling of the energy-dependent gamma-ray morphology constrains the location of particle acceleration and requires an abrupt deceleration of the jet flow. We infer the presence of shocks on either side of the binary system, at distances of 25 to 30 parsecs, and that self-collimation of the precessing jets forms the shocks, which then efficiently accelerate electrons.

Collimated light

Astrophysical jet

10.1126/science.adi2048

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HESS J1809−193: A halo of escaped electrons around a pulsar wind nebula?

Astronomy and Astrophysics (2023)

F. Aharonian F. Ait Benkhali J. Aschersleben Halim Ashkar Michael Backes

Context. HESS J1809$-$193 is an unassociated very-high-energy $\gamma$-ray source located on the Galactic plane. While it has been connected to the nebula of the energetic pulsar PSR J1809$-$1917, supernova remnants and molecular clouds present in the vicinity also constitute possible associations. Recently, the detection of $\gamma$-ray emission up to energies of $\sim$100 TeV with the HAWC observatory has led to renewed interest in HESS J1809$-$193. Aims. We aim to understand the origin of the $\gamma$-ray emission of HESS J1809$-$193. Methods. We analysed 93.2 h of data taken on HESS J1809$-$193 above 0.27 TeV with the High Energy Stereoscopic System (H.E.S.S.), using a multi-component, three-dimensional likelihood analysis. In addition, we provide a new analysis of 12.5 yr of Fermi-LAT data above 1 GeV within the region of HESS J1809$-$193. The obtained results are interpreted in a time-dependent modelling framework. Results. For the first time, we were able to resolve the emission detected with H.E.S.S. into two components: an extended component that exhibits a spectral cut-off at $\sim$13 TeV, and a compact component that is located close to PSR J1809$-$1917 and shows no clear spectral cut-off. The Fermi-LAT analysis also revealed extended $\gamma$-ray emission, on scales similar to that of the extended H.E.S.S. component. Conclusions. Our modelling indicates that based on its spectrum and spatial extent, the extended H.E.S.S. component is likely caused by inverse Compton emission from old electrons that form a halo around the pulsar wind nebula. The compact component could be connected to either the pulsar wind nebula or the supernova remnant and molecular clouds. Due to its comparatively steep spectrum, modelling the Fermi-LAT emission together with the H.E.S.S. components is not straightforward. (abridged)

Galactic plane

Pulsar wind nebula

10.1051/0004-6361/202245459

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

Monthly Notices of the Royal Astronomical Society (2022)

Hidetarô Abe S. Abe V. A. Acciari T. Aniello Stefano Ansoldi

Equipartition theorem

Black hole (networking)

10.1093/mnras/stac2686

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HESS J1640-465 - an exceptionally luminous TeV gamma-ray supernova remnant (vol 439, pg 2828, 2014)

A. Abramowski F. Aharonian F. Ait Benkhali A. G. Akhperjanian E. O. Anguener

Source

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VizieR Online Data Catalog: RX J1713.7-3946 HESS spectrum (HESS+, 2018)

yCat (2017)

Hassan Abdalla A. Abramowski F. Aharonian F. Ait Benkhali A. G. Akhperjanian

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HESS J1640-465 - an exceptionally luminous TeV gamma-ray SNR

arXiv (Cornell University) (2014)

A. Abramowski F. Aharonian F. Ait Benkhali A. G. Akhperjanian E. O. Angüner

The results of follow-up observations of the TeV gamma-ray source HESSJ 1640-465 from 2004 to 2011 with the High Energy Stereoscopic System (H.E.S.S.) are reported in this work. The spectrum is well described by an exponential cut-off power law with photon index Gamma=2.11 +/- 0.09_stat +/- 0.10_sys, and a cut-off energy of E_c = (6.0 +2.0 -1.2) TeV. The TeV emission is significantly extended and overlaps with the north-western part of the shell of the SNR G338.3-0.0. The new H.E.S.S. results, a re-analysis of archival XMM-Newton data, and multi-wavelength observations suggest that a significant part of the gamma-ray emission from HESS J1640-465 originates in the SNR shell. In a hadronic scenario, as suggested by the smooth connection of the GeV and TeV spectra, the product of total proton energy and mean target density could be as high as W_p n_H ~ 4 x 10^52 (d/10kpc)^2 erg cm^-3.

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Contributions of the High Energy Stereoscopic System (H.E.S.S.) to the 35th International Cosmic Ray Conference (ICRC), Busan, Korea

arXiv (Cornell University) (2017)

H. E. S. S. Collaboration NULL AUTHOR_ID H. Abdalla A. Abramowski F. Aharonian

Index of H.E.S.S. conference proceedings to the 35th ICRC, Busan, Korea

10.48550/arxiv.1709.06442

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Citations (12)