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17 Jun 2002
An excess of TeV-energy gamma rays from galaxy Markarian 421 may oblige astronomers to revise their models of active galactic nuclei (AGN). Many suspect that AGNs, quasars, and indeed all the most violent celestial objects in the universe share a common energy-production architecture-- a black hole, supplied by a surrounding accretion disk, broadcasting powerful jets of matter in two polar directions.
Mrk421 (400 million light years away) is the closest such object whose jet axis is aimed directly at us. Last year Mrk421 rewarded patient observers with the most explosive gamma display ever, with a flux ten times higher than that of the much closer Crab Nebula, the strongest known steady gamma source in the sky.
At last week's APS/AAPT meeting in Washington, DC, Trevor Weekes of the Whipple Observatory presented a detailed spectrum for Mrk421. The flux of gammas falls off at the highest energies (up past 6 TeV), but not nearly as fast as one would have expected. Weekes suggested that the anticipated effect of two sources of attenuation, dust near the AGN and the amorphous population of infrared photons in intergalactic space, may have been overestimated.
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