OBSERVATION OF GAMMA-RAY EMISSION FROM THE GALAXY M87 ABOVE 250 GeV WITH VERITAS1

摘要

The multiwavelength observation of the nearby radio galaxy M87 provides a unique opportunity to study in detail processes occurring in active galactic nuclei from radio waves to TeV 7-rays. Here we report the detection of 7-ray emission above 250 GeV from M87 in spring 2007 with the VERITAS atmospheric Cerenkov telescope array and discuss its correlation with the X-ray emission. The γ-ray emission is measured to be pointlike with an intrinsic source radius less than 4.5'. The differential energy spectrum is fitted well by a power-law function: dΦ/dE = (7.4 ± 1.3_(sta) ± 1.5_(sys))(E/TeV)~(-2.31±0.17_(stat)±0.2_(sys))10~(-9) m~(-2) s~(-1) TeV~(-1). We show strong evidence for a year-scale correlation between the γ-ray flux reported by TeV experiments and the X-ray emission measured by the ASM RXTE observatory, and discuss the possible short-timescale variability. These results imply that the γ-ray emission from M87 is more likely associated with the core of the galaxy than with other bright X-ray features in the jet.