Monthly Images of Gamma-Ray Blazars with the VLBA at 43 GHz
Data products available: Individual images in total intensity and polarized intensity, model fits (analysis of each image with main features approximated as components with elliptical Gaussian brightness distributions), and calibrated visibility (uv) data files.
Click on the source of interest to connect to the images and data files.
Cardiff U., UK: Prof. Walter Gear, Graduate Student David Porter
Description of program: We will observe about once per month with the Very Long Baseline Array (VLBA) to obtain images of 29 blazar jets at 43 GHz. The images and polarization will be used by us in concert with light curves (brightness vs. time) obtained with NASA's GLAST (gamma-rays, scheduled to start in early 2008) and RXTE (X-rays, ongoing through at least the end of 2008 for several of the objects; see our X-ray research page). We hope to match the direction of polarization of a feature in the VLBA image with the direction of polarization seen during an outburst in visible light to identify where on the image the visible light is generated. If, as is often the case, events in the visible light curve are seen also in the X-ray and gamma-ray light curves, we can associate the X-ray and gamma-ray emission site with the same feature on the VLBA image. In this way, we hope to map the emission across the electromagnetic spectrum onto the VLBA images, which have a resolution of about 100 microarcseconds, or about 1000 times finer than can be achieved with the Hubble Space Telescope.
In most blazars, events near (but not inside!) the supermassive black hole inject extra energy into the jet. As this energetic disturbance propagates downstream away from the black hole, it energizes electrons, probably through the formation of a shock wave. This causes the disturbance to become bright at microwave, infrared, and visible wavelengths through the emission of synchrotron radiation. The electrons can also knock (scatter) up to X-ray and gamma-ray energies the synchrotron photons and other photons produced, for example, in nearby hot clouds. The order in which the blazar becomes brighter at different wavelengths probes the physical conditions in the jet on scales even finer than we can resolve in the VLBA images. But we need the images to tell us where in the jet the brightened region is located: in the part of the jet that we see on the images or even closer to the black hole. Our comprehensive program of imaging with the VLBA and densely sampled light curves with RXTE, GLAST, AGILE (an Italian gamma-ray satellite already in orbit), Swift (a NASA satellite that can observe X-rays from blazars), and various ground-based observatories at visible, infrared, and microwave wavelengths, will provide the information necessary to figure out where the electrons get energized and perhaps also how gas falling onto a black hole creates such high-speed, high-energy jets.
For more information on blazars, see our research page.
The VLBA is an instrument of the National Radio Astronomy Observatory (NRAO). NRAO is a facility of the National Science Foundation, operated by Associated Universities Inc.
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Go to the personal web pages of: Alan Marscher ---- Svetlana Jorstad