Coordinated millimeter-wave observations of bright, variable gamma-ray blazars with the Haystack radio telescope

We present results of an ongoing program to monitor at millimeter wavelengths a select sample of bright, variable gamma-ray blazars with the 37-m Haystack radio telescope. Our primary objective during the 1996–1997 observing season was to follow the blazars 3C 279 and PKS 0528+134, each the subject of intense multiwavelength observing campaigns in parallel with observations carried out with the Compton Gamma Ray Observatory (CGRO). Our secondary objective was to monitor those active galactic nuclei (AGN) identified as particularly strong candidates for gamma-ray flares based on their CGRO detection history. Quasi-weekly monitoring sessions were carried at frequencies of 43 and 86 GHz with the Haystack telescope using new beam-switching instrumentation. In particular, we have applied a promising new technique (termed “multiple drift scanning”) that has been demonstrated to reliably and repeatedly measure continuum source fluxes to levels of a few hundred milliJanskys at 43 GHz, and to ∼1–1.3 Jy at 86 GHz. ...