Journal
ASTRONOMY & ASTROPHYSICS
Volume 565, Issue -, Pages -Publisher
EDP SCIENCES S A
DOI: 10.1051/0004-6361/201322984
Keywords
gamma rays: general; gamma-ray burst: individual: GRB 100621A; gamma rays: stars; X-rays: stars
Categories
Funding
- German Ministry for Education and Research (BMBF)
- Max Planck Society
- German Research Foundation (DFG)
- French Ministry for Research
- CNRS-IN2P3
- Astroparticle Interdisciplinary Programme of the CNRS
- UK Science and Technology Facilities Council (STEC)
- IPNP of the Charles University
- Czech Science Foundation
- Polish Ministry of Science and Higher Education
- South African Department of Science and Technology
- National Research Foundation
- University of Namibia
- Science and Technology Facilities Council [ST/I001573/1, ST/L00075X/1, PP/E001041/1, ST/H001972/1, PP/E001319/1] Funding Source: researchfish
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The long gamma-ray burst (GRB) 100621A, at the time the brightest X-ray transient ever detected by Swift-XRT in the 0.3-10 keV range, has been observed with the H.E.S.S. imaging air Cherenkov telescope array, sensitive to gamma radiation in the very-high-energy (VHE, >100 GeV) regime. Due to its relatively small redshift of z similar to 0.5, the favourable position in the southern sky and the relatively short follow-up time (<700 s after the satellite trigger) of the H.E.S.S. observations, this GRB could be within the sensitivity reach of the HESS. instrument. The analysis of the HESS. data shows no indication of emission and yields an integral flux upper limit above similar to 380 GeV of 4.2 x 10(-12) cm(-2) s(-1) s (95% confidence level), assuming a simple Band function extension model. A comparison to a spectral-temporal model, normalised to the prompt flux at sub-MeV energies, constraints the existence of a temporally extended and strong additional hard power law, as has been observed in the other bright X-ray GRB 130427A. A comparison between the HESS. upper limit and the contemporaneous energy output in X-rays constrains the ratio between the X-ray and VHE gamma-ray fluxes to be greater than 0.4. This value is an important quantity for modelling the afterglow and can constrain leptonic emission scenarios, where leptons are responsible for the X-ray emission and might produce VHE gamma rays.
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