Boston University  Blazar Group
Large VLBA Project: Total & Polarized Intensity Images of Gamma-Ray Bright Blazars at 43 GHz
 Movie of 3C 273 
 Left: Movie of 3C273; contours: 43 GHz VLBA; red: gamma-ray light curve
 Right: movie of 3C 279; contours: 43 GHz VLBA; red: R-band optical light curve; green: X-ray light curve
 Center: sketch of physical features of a blazar with black hole & accretion disk on left; size scale (on bottom) increases logarithmically with distance from black hole

Monthly Images of Gamma-Ray Blazars with the VLBA at 43 GHz + Gamma-ray & Optical Light Curves


List of publications from this program

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. (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 the Perkins Telescope of Lowell Observatory, and our 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 43 GHz VLBA data from the VLBA-BU Blazar Monitoring Program (VLBA-BU-BLAZAR;, 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.

0219+428 (3C66A) 0235+164 0316+413 (3C84) 0336-019 (CTA26)
0415+37 (3C111) 0420-014 (OA129) 0430+05 (3C120) 0528+134
0716+714 0735+178 0827+243 (OJ248) 0829+046
0836+710 0851+202 (OJ287) 0954+658 1055+018 (4C+01.28)
1101+384 (Mrk421) 1127-145 1156+295 (4C+29.45) 1219+285 (WCom,ON+231)
1222+216 (4C+21.35) 1226+023 (3C273) 1253-055 (3C279) 1308+326
1406-076 1510-089 1611+343 (DA406) 1622-297
1633+382 (4C+38.41) 1641+399 (3C345) 1652+398 (Mrk501) 1730-130 (NRAO 530)
1749+096 (OT081) 2200+420 (BLLac) 2223-052 (3C446) 2230+114 (CTA102)
2251+158 (3C454.3)
Boston U.: Prof. Alan Marscher, Dr. Svetlana Jorstad, Dr. Manasvita Joshi, Graduate Students Michael Malmrose, Nicholas MacDonald, & Mason Keck, recent Master of Astronomy Karen Williamson, & Undergraduate Student Vishal Bala

Insistuto de Astrofisica de Andalucia (Granada, Spain): Drs. Jose Luis Gomez & Ivan Agudo, and graduate student Carolina Casadio

Sobolev Astronomical Institute, St. Petersburg State University (Russia): Dr. Valeri M. Larionov, Dr. Darya Morozova, and researcher Ivan Troitskiy

National Radio Astronomy Observatory (Socorro, NM): Dr. Jonathan Romney


Description of program: We observe about once per month with the Very Long Baseline Array (VLBA) to obtain images of 33 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 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