NEW UPPER LIMITS ON INTERGALACTIC INFRARED RADIATION FROM HIGH-ENERGY ASTROPHYSICS

Following our previously proposed technique, we have used the recent gamma-ray observations of Mrk 421 obtained by the Whipple Observatory team and the EGRET experiment on Compton Gamma-Ray Observatory as a probe to place significant constraints on the intergalactic infrared energy density. Our 2 sigma upper limits are approximately 10(-8) W m-2 sr-1 for the 1-5 mum range. These constraints are much better than those obtained by direct measurements. They rule out more exotic mechanisms for producing a large intergalactic IR flux and are consistent with radiation produced by stars in normal galaxies.