The Unique Diagnostic Infrared Colors of Blazars The WISE Blazar Strip

We have discovered that the mid-infrared colors of blazars are a powerful tool for their identification. We have used this diagnostic to identify probable new blazars, including some gamma-ray sources, and to begin to address the physical mechanism(s) responsible. From a sample of 1365 previously known blazars (from the ROMA BZCAT) observed in the first release of the WISE Preliminary Source catalog we prepared a color-color analysis; additional objects will be incorporated after the full WISE data release. We find that blazars lie on a narrow strip in [3.4]-[4.6] vs [4.6]-[12] colors. The strip is distinctly redder on average at the short bands than either average stars, starbursts, LIRGS, ULIRGS or LINERS, and is of intermediate redness in the longer wavelength bands. Similar narrow strips can be defined with other combinations of WISE colors, and in color-magnitude plots. The defining width of the "WISE blazar strip" is quite restrictive - only about 0.6 mag. We will present results, analyses, and a discussion of the implications of this property of blazars. This work was supported in part by NASA grants NNX10AD50G and NNX10AD68G