Monthly Images of Gamma-Ray Blazars with the VLBA at 43 & 86 GHz + Gamma-ray & Optical Light Curves
Publications describing program and presenting overall results: Jorstad & Marscher (2016, Galaxies, vol. 4, article no. 47), Jorstad et al. (2017, Astrophysical Journal, vol. 846, article no. 98), and Weaver et al. (2022, Astrophysical Journal Supplement Series, vol. 260, article no. 12).
Data products available: (1)
Individual images in total intensity and polarized intensity, CLEAN
model files, and calibrated visibility (uv) data files. The images were
all made with the Very
Long Baseline Array at a frequency of 43 GHz or 86 GHz. (See the
bottom of
this page for proper acknowledgment of the VLBA.)
(2) Flux and polarization data from the Boston University blazar
monitoring program, which includes our group's analysis of public data from the
Large Area Telescope on the Fermi
Gamma-ray Space Telescope, our observations with Boston
University's Perkins
Telescope,
and our previous program of photometric observations with the robotic Liverpool Telescope, in
collaboration with Professor Ian McHardy of the University of
Southampton.
A plot of multi-waveband flux and linear polarization vs. time
since 2008 is also displayed for each object. Click on the source of
interest to connect to the images, data files, and plots. If
you need any of the optical data files for your research, send email to
Dr. Svetlana Jorstad.
Spectral energy distributions: Full version of paper by K.E. Williamson et al. (2014, Astrophysical Journal, vol. 789, article no. 135), including figures and data tables for all blazars studied. The paper, entitled "Comprehensive Monitoring of Gamma-ray Bright Blazars. I. Statistical Study of Optical, X-ray, and Gamma-ray Spectral Slopes," examines changes in the near-IR/optical/UV, X-ray, and gamma-ray spectral energy distributions at different flux states of 33 of the objects listed below (all of the quasars and BL Lac objects; not included are the radio galaxies 3C 84, 3C 111, and 3C 120).
Note: If you use any of these images or data
in a publication, please acknowledge via the statements:
This study makes use of VLBA data from the VLBA-BU
Blazar Monitoring Program (BEAM-ME and VLBA-BU-BLAZAR;
http://www.bu.edu/blazars/BEAM-ME.html), funded by NASA through the
Fermi Guest Investigator Program. The VLBA is an instrument of the
National Radio Astronomy Observatory. The National Radio Astronomy
Observatory is a facility of the National Science Foundation operated
by Associated Universities, Inc.
Please
note: The VLBA had pointing problems, especially at millimeter
wavelengths, from May to September 2019. Because of this, the flux
calibration for each epoch during this period needs to be verified with
37 GHz data from colleagues at the Metsaehovi Radio Observatory in
Finland. This has slowed the imaging process. The flux scales may still
be inaccurate even after correction, since pointing errors introduce
different flux errors for different objects, so an accurate global
correction is not possible. If you need images that are not yet
available on this website, feel free to contact Alan Marscher to request them.
Instituto de
Astrofisica de Andalucia (Granada, Spain): Drs. José Luis Gómez & Iván Agudo, and graduate student
Antonio Fuentes
Sobolev
Astronomical Institute, St. Petersburg State University (Russia):
Dr.
Valeri M. Larionov (deceased), Dr. Sergei Savchenko, Dr. Darya
Morozova, and
researcher Ivan Troitskiy
Description of program [see also the paper by Jorstad & Marscher (2016)]: We observe about once per month with the Very Long Baseline Array (VLBA) to obtain images of 34 blazar and 3 radio galaxy jets at 43 GHz. The images and polarization are used by us in concert with light curves (brightness vs. time) obtained with NASA's Fermi Gamma-ray Space Telescope (gamma-rays) and RXTE (to the end of 2012) and Swift (X-rays); see our X-ray research page. We can sometimes 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 can 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 Fermi, AGILE (an Italian gamma-ray satellite) , RXTE, Swift, and various ground-based observatories at visible, infrared, and microwave wavelengths, are providing 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 Very Long Baseline Array (VLBA) is an instrument of the National Radio Astronomy Observatory. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated by Associated Universities, Inc.
Back to the blazar group's home page
Go to the personal web pages of: Alan Marscher ---- Svetlana Jorstad