Detection of extended γ-ray emission around the Geminga pulsar with H.E.S.S.
Astronomy & Astrophysics EDP Sciences 673 (2023) a148
Constraints on axionlike particles from a combined analysis of three flaring Fermi flat-spectrum radio quasars
Physical Review D American Physical Society 107:8 (2023) 83027
Abstract:
Many theories beyond the Standard Model of particle physics predict the existence of axionlike particles (ALPs) that mix with photons in the presence of a magnetic field. Searching for the effects of ALP-photon mixing in gamma-ray observations of blazars has provided some of the strongest constraints on ALP parameter space so far. Previously, only individual sources have been analyzed. We perform a combined analysis on Fermi Large Area Telescope data of three bright flaring flat-spectrum radio quasars, with the blazar jets themselves as the dominant mixing region. For the first time, we include a full treatment of photon-photon dispersion within the jet and account for the uncertainty in our B-field model by leaving the field strength free in the fitting. Overall, we find no evidence for ALPs but are able to exclude the ALP parameters 5 neV≲ma≲200 neV and gaγ≳5×10-12 GeV-1 with 95% confidence.Search for the evaporation of primordial black holes with H.E.S.S.
Journal of Cosmology and Astroparticle Physics IOP Publishing 2023:04 (2023) 040
H.E.S.S. follow-up observations of GRB 221009A
Astrophysical Journal Letters American Astronomical Society 946 (2023) L27
Abstract:
GRB 221009A is the brightest gamma-ray burst (GRB) ever detected. To probe the very-high-energy (VHE; >100 GeV) emission, the High Energy Stereoscopic System (H.E.S.S.) began observations 53 hr after the triggering event, when the brightness of the moonlight no longer precluded observations. We derive differential and integral upper limits using H.E.S.S. data from the third, fourth, and ninth nights after the initial GRB detection, after applying atmospheric corrections. The combined observations yield an integral energy flux upper limit of Φ UL 95 % = 9.7 × 10 − 12 erg cm − 2 s − 1 above E thr = 650 GeV. The constraints derived from the H.E.S.S. observations complement the available multiwavelength data. The radio to X-ray data are consistent with synchrotron emission from a single electron population, with the peak in the spectral energy distribution occurring above the X-ray band. Compared to the VHE-bright GRB 190829A, the upper limits for GRB 221009A imply a smaller gamma-ray to X-ray flux ratio in the afterglow. Even in the absence of a detection, the H.E.S.S. upper limits thus contribute to the multiwavelength picture of GRB 221009A, effectively ruling out an IC-dominated scenario.Optical spectroscopy of blazars for the Cherenkov Telescope Array – II
Monthly Notices of the Royal Astronomical Society Oxford University Press 518:2 (2022) 2675-2692