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FY2013 Highlights

by Mark Adams last modified Sep 28, 2016 by Amy Mioduszewski

View Highlights from other years: Recent HighlightsFY2012

Rare Multiple Quasar Imaging Event Detected

The first detection of multiple imaging of an AGN jet due to refractive foreground scattering in our galaxy has been reported by Pushkarev et al. This rare phenomenon was first predicted several decades ago and is based on the refractive properties of AU-scale electron density enhancements in the ionized component of the Galactic interstellar medium. The predicted effect has now been seen in the low galactic latitude quasar 2023+335, one of a large sample of AGNs monitored by the MOJAVE VLBA Key Science Project. The strongest event showed a refractive image ~ 1/10th as bright as the primary image on 28 May 2009 at 15 GHz, when the source was undergoing an extreme scattering event. The VLBA image was taken serendipitously during a special phase when a caustic spike associated with the lens edge passed over the source. While the parsec-scale jet of the source normally extends along an angle of ‑20 degrees, a highly significant multi-component pattern of secondary images induced by strong refraction appears stretched out roughly along the constant galactic latitude line at an angle of +40 degrees. This suggests that the direction of relative motion of the lens is parallel to the galactic plane, as expected for an orbiting cloud.

View Publication: VLBA observations of a rare multiple quasar imaging event caused by refraction in the interstellar medium, A.B. Pushkarev (MPIfR, Pulkovo Obs, Crimean Obs), Y.Y. Kovalev (Lebedev, MPIfR), M.L. Lister (Purdue), T. Hovatta (Caltech), T. Savolainen (MPIfR), M.F. Aller (Michigan), H.D. Aller (Michigan), E. Ros (Valencia, MPIfR), J.A. Zensus (MPIfR), J.L. Richards (Purdue), W. Max-Moerbeck (Caltech), and A.C.S. Readhead (Caltech), 2013 A&A, 555, 80 (July 2013).

Added 12 Jun 2013

Accurate Distance Vindicates Disk Theory

Dwarf novae are white dwarfs accreting matter from a nearby red dwarf companion. Their regular outbursts are explained by a thermal-viscous instability in the accretion disk, which is described by the disk instability model that has since been extended to other accreting astronomical systems. However, the prototypical dwarf nova, SS Cygni, has presented a major challenge to accretion disk theory. At the distance of 159 ± 12 parsecs measured by the Hubble Space Telescope, SS Cygni is too luminous to be undergoing the regular observed outbursts. Using very long baseline interferometric radio observations acquired with the VLBA and the European VLBI Network, Miller-Jones et al. report an accurate, model-independent distance to SS Cygni of 114 ± 2 parsecs. This new distance reconciles the behavior of SS Cygni with our understanding of accretion disk theory.

View Publication: An Accurate Geometric Distance to the Compact Binary SS Cygnii Vindicates Accretion Disk Theory, J.C.A. Miller-Jones (Curtin), G.R. Sivakoff (Alberta, Virginia),C. Knigge (Southampton), E.G. Körding (Radboud), M. Templeton (AAVSO), E.O. Waggen (AAVSO), 2013 Science, 340, 950  (24 May 2013).

View 23 May 2013 Press Release

Added 12 Jun 2013

Imaging Protostellar Outflows

VLBA: Imaging Protostellar OutflowsThe VLBA has imaged water maser emission from a massive star-forming region (AFLG 2591) in unprecedented detail, revealing persistent bow shock structures that indicate outflows on 300 AU-scales. The measured proper motions imply bow shock expansion at 20 km/s, possibly driven by two different massive protostars, or two outflows from a single star.

View Publication: Formation and Evolution of the water maser outflow event in AFGL 2591 VLA 3-N, M.A. Trinidad (Guanajuato), S. Curiel (UNAM), R. Estalella (Barcelona), J. Canto (UNAM), A. Raga (UNAM), J.M. Torrelles (Barcelona), N.A. Patel (CfA), J.F. Gomez (CSIC), G. Anglada (CSIC), C. Carrasco-Gonzalez (MPIfR), and L.F. Rodriguez (UNAM), 2013 MNRAS, 430, 1309 (1 April 2013).

Added 13 Feb 2013

View Highlights from other years: Recent HighlightsFY2012