Probing the Ultra-high-energy Jets of Blazars across the Electromagnetic Spectrum

NASA Press Release: http://www.nasa.gov/mission_pages/GLAST/news/aas-flares.html

Blazars – the most extreme class of active nuclei of galaxies – are the most luminous long-lived objects in the universe. They contain supermassive (up to 20 billion times the mass of the Sun) black holes that accrete gas from the central regions of the host galaxy. Jets stream out of the nucleus at near-light speeds and emit radiation profusely across the entire electromagnetic spectrum. In order to probe the jets, Professor Alan Marscher and Senior Research Scientist Svetlana Jorstad have developed a comprehensive program to monitor changes in their brightness and polarization at microwave, infrared, visible, ultra-violet, X-ray, and gamma-ray frequencies. Their project involves monthly radio frequency observations with the Very Long Baseline Array (which produces images of the jets of blazars with angular resolution 1000 times finer than that of the Hubble Space Telescope) of a sample of 35 blazars, as well as optical polarimetric and photometric observations with PRISM and Mimir on the Perkins Telescope.  Graduate students Michael Malmrose, Nicholas MacDonald, Terri Scott, and Karen Williamson, and undergraduates Adi Foord, Claudio DeMutiis, and Vishal Bala participated in the analysis of the data from these extensive observations. The data collected by the group are combined with observations by collaborators using numerous other space- and ground-based telescopes around the world.

 Time sequence of microwave images by Jorstad and Marscher of the bright “core” region jet of the jet  (which is yellow in the upper image). The color, which represents intensity of polarized emission, accentuates the new knot of high-energy plasma that strongly emits gamma-rays as it speeds away from the core. The ability of the Boston University group to use polarization and changes in brightness at microwave, visible, and gamma-ray frequencies to locate the gamma-ray outburst in the core out to 70 light-years away from the black hole (which cannot be seen, but lies to the upper left in the lower images), represents a major breakthrough in the field.

Time sequence of microwave images by Jorstad and Marscher of the bright “core” region of the jet (which is yellow in the upper image). The color, which represents intensity of polarized emission, accentuates the new knot of high-energy plasma that strongly emits gamma-rays as it speeds away from the core. The ability of the Boston University group to use polarization and changes in brightness at microwave, visible, and gamma-ray frequencies to locate the gamma-ray outburst in the core out to 70 light-years away from the black hole (which cannot be seen, but lies to the upper left in the lower images), represents a major breakthrough in the field.  Credit: NASA/DOE/Fermi LAT Collaboration

 

In FY13, the group reported at the January 2013 American Astronomical Society meeting their new finding that associates an outburst of gamma-rays with a bright “knot” of high-energy plasma ejected from the nucleus of the quasar 4C+71.07 at a speed of 99.875% the speed of light.  Such comprehensive observations of blazars have provided extremely rich data sets that reveal both complexities and patterns that challenge current theoretical models. Professor Marscher, Senior Postdoctoral Associate Joshi, and graduate students Michael Valdez and Nicholas MacDonald are developing new theoretical paradigms and numerical codes that are potentially capable of explaining the observational results. Professor Marscher has completed a 3-year project to create the Turbulent Extreme Multi-Zone computer model that calculates the time variations of radiation emitted when turbulent high-energy plasma crosses a standing cone-shaped shock wave in a blazar jet. Graduate student Valdez has translated the code to the C++ language and will optimize and parallelize it to run on a supercomputer, after which he will develop the code further. Dr. Joshi is modifying her own time-dependent code to take into account various sources of photons in the nucleus of an active galaxy that can be scattered to gamma-ray energies. Graduate student MacDonald is calculating the time-dependent emission from an energetic plasma passing through photons from a slower sheath of a jet.