Last update: January 15, 2015.
We are currently studying the energetic jets emerging from radio-loud quasars (in particular, from the subcategory known as blazars) using the radio-astronomy technique of Very Long Baseline Interferometry (VLBI). This technique combines data recorded by widely separated radio telescopes to obtain the same angular resolution as a single radio telescope with a size equal to the maximum separation between individual telescopes. VLBI produces the highest angular resolution images in astronomy, allowing us to see closer to the supermassive black hole at the quasar's center. Our work has mainly used the National Radio Astronomy Observatory's Very Long Baseline Array (VLBA) to make these observations.
Over forty high-frequency peaked blazars (HBLs) have been observed to emit very high-energy gamma-rays (> 1 TeV) by ground-based TeV gamma-ray telescopes (see TeVCat for a current list). We have been studying the parsec-scale structures of these TeV blazars using VLBA monitoring for several years.
Our current project involves imaging the parsec-scale structure of 20 relatively newly discovered TeV blazars with the VLBA at multiple epochs. Many of these are relatively faint in the radio, and we are taking advantage of the recently upgraded sensitivity of the VLBA to produce high dynamic range images of these fainter sources. This project is approximately tripling the number of TeV blazers for which parsec-scale structural information is available, and this information should lead to new insights into the astrophysics of these extreme objects. See the Gallery of Images of New TeV Blazars below.
Read the 2014 Astrophysical Journal Paper on first epoch observations of these 20 sources.
|SHBL J001355.9-185406||KUV 00311-1938||1ES 0033+595||RGB J0136+391||RGB J0152+017|
|1ES 0229+200||RBS 0413||1ES 0347-121||1ES 0414+009||1ES 0502+675|
|PKS 0548-322||RX J0648.7+1516||1ES 0647+250||RGB J0710+591||1RXS J101015.9-311909|
|MS 1221.8+2452||1ES 1440+122||H 1722+119||1ES 1741+196||B3 2247+381|
Read the 2012 Fermi & Jansky Conference Paper on multi-epoch observations of five additional TeV blazars (1ES 1101-232, Markarian 180, 1ES 1218+304, PG 1553+113, and H 2356-309).
Read the 2010 Astrophysical Journal Paper about high-resolution 43 GHz VLBA observations of the six original TeV blazars (Markarian 421, Markarian 501, H 1426+428, 1ES 1959+650, PKS 2155-304, and 1ES 2344+514).
Read the 2009 Astrophysical Journal Letter about high-resolution VLBA observations showing limb-brightening in the jet of the TeV blazar Markarian 501.
This was a large project designed to study the jet structure and kinematics of sources observed in the RDV series of astrometric and geodetic VLBA experiments. It was done in collaboration with Alan Fey (U.S. Naval Observatory), Patrick Charlot (Observatoire de Bordeaux), Alexander Pushkarev (MPIfR), Yuri Kovalev (Astro Space Center), and others. The RDV series of experiments observes about 100 sources each at 8 and 2 GHz every two months for the purposes of astrometry and geodesy. Because of the dense time sampling of the observations, this database can also provide detailed measurements of jet kinematics. Many of the VLBI images from these experiments are available at The Radio Reference Frame Image Database. Others are available at The Bordeaux VLBI Image Database and at Astrogeo.org.
Our most recent project involved studying the kinematics of all sources observed at 20 or more epochs over the first 50 experiments in the database (from 1994-2003), for the purpose of measuring jet accelerations. It entailed the production and analysis of 2753 global VLBI images of 68 sources. Results from this project were published in 2012.
Read the 2012 Astrophysical Journal Paper on this project.
Download the model-fit table (Table 3) from this paper.
Download the accelerations table (Table 6) from this paper.
A past project investigated the kinematics of all sources observed at 3 or more epochs over the first five years of the database (from 1994-1998), and entailed the production and analysis of 966 images of 87 sources. The results of this phase of the project were published in 2007.
Read the 2007 Astronomical Journal Paper on that project.
The MOJAVE survey, the VLBA 2cm survey, the VIPS survey, the VCS survey, and the Caltech-Jodrell Bank Survey.
Whittier undergraduates Suzanne Fodor, Deyan Tabakov, Mehreen Mahmud, Jeremy Milne, Kalina Gospodinova, Ghalib Bello, Dipesh Bhattarai, Niraj Pant, Corey Nichols, Christopher Marvin, Joshua Arenson, Vivian Tiet, Faraz Zaerpoor, Jon-Paul Cook, and Amanda Harrison have all participated in the Quasar Research Program at Whittier College.