This program will undertake a series of observational and theoretical studies of the powerful jets which are seen to emerge at close to the speed of light from the centers of active galaxies and quasars, and also from some x-ray binary systems known as micro-quasars within our own Galaxy. It will attempt to answer basic questions about the jets and their central engines, by exploiting the information in the linear and circular polarization of the radio emission. The observations will yield other fundamental information such as the mix of positrons and protons in the jet, and the jet's kinetic luminosity.
Broader impacts of the work include training of undergraduate and graduate students, and working with local teachers and students in using the campus 24" telescope.
The outcomes achieved with this grant are described in eleven papers published or in press. They cover a series of observational and theoretical studies of the powerful jets which are seen to shoot out at close to the speed of light from the hearts of active galaxies and quasars, and also from some x-ray binary systems (dubbed "micro-quasars") within our own Galaxy. The engine at the center of both active galaxies and x-ray binaries is thought to be a massive, spinning, magnetized black hole surrounded by an accretion disk. They differ only in the mass of the black hole. I have joined the Event Horizon Telescope collaboration which seeks to image directly the emission from the vicinity of these supermassive black holes, with an angular resolution of a few Schwarzschild radii (or better!). This was not in the original proposal, but promises to be truly ground-breaking science. Significant outcomes include: (1) The east and west jets of the microquasar SS433 superficially appear very different. We have demonstrated that they are in fact very similar, if one properly takes into account projection, travel time effects, and Doppler boosting. We have used this to separate the evolution of ejected plasma blobs from variations in the power injected into the jets. The former exhibit exponential decays with a characteristic time scale of 59 days. (2) We published deep images of the kiloparsec-scale structure and polarization of the quasar 3C345. (One of the images, made by undergraduate Valerie Marchenko, was chosen as the cover image for the February 2013 edition of the Astronomical Journal. We also published a model to account for the unusual misalignment in the magnetic field of the jet. This requires the jet velocity to be greater than 95% of the speed of light, even on kiloparsec scales. (3) We published the first radio and X-ray images of the jet of the z=4.72 quasar GB 1428+4217. This is currently the most distant quasar in which an X-ray emitting jet has been discovered. (4) We published high-resolution VLA images of a complete sample of 123 high redshift (z> 2.5) quasars. This has been the stimulus for several radio and X-ray proposals by other PIs, and also several ongoing projects of our own. One of these (recently submitted with undergraduate Kyle Van Gorkom as first author) investigates several possible indicators of the orientation of a quasar with respect to the line of sight. We find that a quantity known as RV (defined as radio core flux divided by the optical continuum flux) is a demonstrably superior measure of orientation compared to other commonly used indicators. This is part of an ongoing project to develop a tool to constrain more reliably the orientation of quasars. Such a tool will have wide application, especially in understanding the geometry and the motion of gas in quasar central engines. (5) We calibrated the polarization leakage terms in the antennas of the Event Horizon Telescope (the difficulty being that there were no known calibration sources at this very high frequency (230 GHz)). This now allows the EHT to explore directly the magnetic fields surrounding supermassive black holes in the center of galaxies. Broader impact: Undergraduate research is a very high priority at Brandeis University. It is one of the best ways of encouraging students to pursue graduate studies and careers in the STEM areas, especially for women and underrepresented minorities. Of the students mention above, Kyle Van Gorkom has just taken a job with the Space Telescope Science Institute, and Valerie Marchenko is a graduate student at Brown University. Two more undergraduates have recently been authors on published papers: Phoebe Sanderbeck is a graduate student at the University of Washington and Matthew Mallory is a Program Manager at QD Vision. Current senior undergraduate Jose’ Vargas (who is Hispanic) is imaging new EVLA observations of the high redshift sample of 123 quasars mentioned above. This will also earn him a published paper. Other outreach efforts include purchasing and installing an 8" Celestron installed on the side of our 24" Cassegrain telescope, and purchasing a digital camera for it. This is used extensively by the astronomy club, which has over 300 members, almost none of which are physics majors. The club also does sterling work bringing elementary and grade school students from Waltham and neighboring towns to visit the observatory. Also, the PI has created a new first-year seminar course titled "Dark energy, dark matter and the new universe." The goal here is to engage non-science (but mathematically competent at the pre-calculus level) first year students in an intense and interactive seminar to expose them to the methods of scientific research and exploring the most exciting frontier science of our time. The PI is writing a textbook for the course, since none appears to exist for this particular audience.
