The active galactic nucleus PG 1553+113 was observed by the MAGIC telescope in July 2006 during a multiwavelength campaign , in which telescopes in the optical , X-ray , and very high energies participated . Although the MAGIC data were affected by strong atmospheric absorption ( calima ) , they were analyzed after applying a correction . In 8.5 hours , a signal was detected with a significance of 5.0 \sigma . The integral flux above 150 GeV was ( 2.6 \pm 0.9 ) \cdot 10 ^ { -7 } ~ { } { ph s ^ { -1 } m ^ { -2 } } . By fitting the differential energy spectrum with a power law , a spectral index of -4.1 \pm 0.3 was obtained .