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 ~ 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 H.E.S.S. instrument. The analysis of
the H.E.S.S. data shows no indication of emission and yields an integral flux upper limit above ~380 GeV of 4:2X10-12 cm-2 s-1 (95% confidence
level), assuming a simple...
DOI
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