The high-frequency peaked BL Lac PG 1553+113 was observed in 2005 with the H.E.S.S .
stereoscopic array of imaging atmospheric-Cherenkov telescopes in Namibia .
Using the H.E.S.S .
standard analysis , an excess was measured at the 4.0 \sigma level in these observations ( 7.6 hours live time ) .
Three alternative , lower-threshold analyses yield > 5 \sigma excesses .
The observed integral flux above 200 GeV is ( 4.8 \pm 1.3 _ { stat } \pm 1.0 _ { syst } ) \times 10 ^ { -12 } cm ^ { -2 } s ^ { -1 } , and shows no evidence for variability .
The measured energy spectrum is characterized by a very soft power law ( photon index of \Gamma =4.0 \pm 0.6 ) .
Although the redshift of PG 1553+113 is unknown , there are strong indications that it is greater than z =0.25 and possibly larger than z =0.78 .
The observed spectrum is interpreted in the context of VHE \gamma -ray absorption by the Extragalactic Background Light , and is used to place an upper limit on the redshift of z < 0.74 .