The investigators will carry out an extensive research program to examine, at other wavelengths, blazar sources of gamma rays observed by GLAST (Gamma-ray Large Aperture Space Telescope, scheduled for launch in 2008). The work will consist of radio monitoring, VLBA radio imaging and polarimetry, optical identification, and optical spectral line observations which will provide a multifrequency foundation for the GLAST blazar observations. They will carry out a flux density monitoring campaign on the Owens Valley Radio Observatory 40m and Torun 32m telescopes, and an intensive identification and spectral line observational program at Palomar, Keck, the Hobby-Eberley Telesope, and the SALT and ESO telescopes in the southern hemisphere.
The broader impacts include working with a Chilean graduate student and developing projects and teacher tools that will be used by students in fourteen states of the United States and in several other countries. One third of the time on the Owens Valley Radio Observatory 40m Telescope will be dedicated to K-12 programs involved in GLAST observations.
This was a project to study the nuclei of a particular class of Active Galaxies called "Blazars" in order to answer some questions that have been puzzling scientists since the discovery of quasars in 1964. Quasars are a particular type of Active Galaxy and blazars are a subset of quasars. We now know that most galaxies harbor massive black holes in their centers, or nuclei. Our own galaxy has a black hole in its nucleus that is three million times more massive than our sun. Some galaxies harbor supermassive black holes in their nuclei - with masses as large as a hundred million to three billion times as massive as our sun. These galaxies exhibit a wide variety of observable properties that are all related to the supermassive black hole and the "accretion disk" that rotates around the black hole and funnels material into the black hole, thereby increasing its mass. These are, for obvious reasons, called "Active Galaxies". The combination of the black hole and the accretion disk is called the "central engine" of the Active Galaxy. Some of these Active Galaxies are very powerful emitters of radio waves, light, X-rays and gamma-rays that are produced when material in the accretion disk gets accelerated by the electromagnetic forces of the black hole and accretion disk into two oppositely directed jets of material that are shot out of the galactic nucleus at speeds close to the speed of light - in other words at relativistic speeds. About one percent of these jets are pointing towards the earth and we see the radiation from the relativistic material beamed towards us, and varying in strength as the fueling of the central engine varies. Because the radiation from these objects varies strongly at radio, optical, X-ray and gamma-ray wavelengths they are called "Blazars". In our project we monitored ~1600 blazars at radio wavelengths (2 centimeters) with the 40 Meter Telescope of the Owens Valley Radio Observatory twice a week for three years, and we compared the radio emission with the gamma-ray emission observed with the Fermi-GST satellite. We were able to demonstrate conclusively for the first time that the gamma-ray emission and the radio emission in blazars are strongly correlated. There are two competing theories for where the gamma-ray emission originates: on the Blandford-Levinson theory the gamma-ray emission originates in a "gamma-sphere" at the base of the jet, and in the Jorstad-Marscher theory it originates in shocks a long way out along the jet, and therefore distant from the base of the jet. We were able to show that previous claims that the gamma-ray emission comes from way out along the jet are not supported by the observations, and that the question of where the gamma-ray emission originates is still unanswered, but that it will be answerable by these observations over the next few years as we continue to accumulate the statistics of the flaring behavior in blazars. This is an important result because if the gamma-rays originate from the base of the jet they should be able to tell us a lot about how these jets are formed and also the composition of the jets (are they electron-positron jets or electron-proton jets or electromagnetic jets?). Our results also showed, for the first time, that blazars that are bright gamma-ray sources are also very powerful radio sources. We also developed an entirely new statistical analysis of the flaring behavior in blazars that enables us to calculate the physical significance of the flares and of any correlations between gamma-ray flares and radio flares. Our method thus deals in a rigorous way with any observational selection effects that can cause spurious correlations that look statistically significant but that are not physically significant. This higher level of rigor is absolutely essential if we are to interpret the observations correctly. We also built a new polarimetric radio receiver for the 40 M Telescope for observing these blazars. The broader impacts of this work are as follows: (i) We have trained a number of undergraduates, graduate students, and post-doctoral fellows, including women and under-represented minority students in both astrophysics and instrumentation; (ii) we have participated in, and further developed, a program with the Jet Propulsion Laboratory and the Lewis Center for Educational Research (LCER) for bringing school teachers to the LCER and teaching them about the Goldstone Apple Valley Radio Telescope (GAVRT) program in which two 34 Meter Telescopes at Goldstone are used as outreach instruments, and school children can access these telescopes via the internet from the classroom, thus bringing forefront research in astrophysics right into the classroom. Six teachers were trained on this program and they have returned to their schools and carried out many successful observing sessions in their classrooms. We are now expanding this program.
