Please use this identifier to cite or link to this item: http://hdl.handle.net/1959.3/211895

Title

Optical polarization and spectral variability in the M87 jet

Author(s)

Perlman, Eric S.;  Adams, Steven C.;  Cara, Mihai;  Bourque, Matthew;  Harris, D. E.;  Madrid, Juan P.;  Simons, Raymond C.;  Clausen-Brown, Eric;  Cheung, C. C.;  Stawarz, Lukasz;  Georganopoulos, Markos;  Sparks, William B.;  Biretta, John A.

Abstract

During the last decade, M87's jet has been the site of an extraordinary variability event, with one knot (HST-1) increasing by over a factor 100 in brightness. Variability has also been seen on timescales of months in the nuclear flux. Here we discuss the optical-UV polarization and spectral variability of these components, which show vastly different behavior. HST-1 shows a highly significant correlation between flux and polarization, with P increasing from ~20% at minimum to >40% at maximum, while the orientation of its electric vector stayed constant. HST-1's optical-UV spectrum is very hard (αUV-O ~ 0.5, F νν–α), and displays "hard lags" during epochs 2004.9-2005.5, including the peak of the flare, with soft lags at later epochs. We interpret the behavior of HST-1 as enhanced particle acceleration in a shock, with cooling from both particle aging and the relaxation of the compression. We set 2σ upper limits of 0.5δ pc and 1.02c on the size and advance speed of the flaring region. The slight deviation of the electric vector orientation from the jet position angle (P.A.) makes it likely that on smaller scales the flaring region has either a double or twisted structure. By contrast, the nucleus displays much more rapid variability, with a highly variable electric vector orientation and "looping" in the (I, P) plane. The nucleus has a much steeper spectrum (αUV-O ~ 1.5) but does not show UV-optical spectral variability. Its behavior can be interpreted as either a helical distortion to a steady jet or a shock propagating through a helical jet.

Publication type

Journal article

Research centre

Swinburne University of Technology. Faculty of Information and Communication Technologies. Centre for Astrophysics and Supercomputing

Source

Astrophysical Journal, Vol. 743, no. 2 (Dec 2011), article no. 119

Publication year

2011

FOR Code(s)

0201 Astronomical and Space Sciences;  0305 Organic Chemistry;  0306 Physical Chemistry (Incl. Structural)

Keyword(s)

Galaxies;  Jets;  M87;  Nuclei

Publisher

Institute of Physics Publishing

ISSN

0004-637X

Publisher URL

http://dx.doi.org/10.1088/0004-637x/743/2/119

Copyright

Copyright © 2011 The American Astronomical Society. All rights reserved. The American Astronomical Society does not allow institutions to archive either the accepted manuscript or the published version of the article. However, you can find an earlier version of the full text here: http://arxiv.org/abs/1109.6252

Additional information

The authors acknowledge support from NASA under LTSA program Grant NNX07AM17G and HST Grant GO-11138.01, a NASA Fermi Grant NNX10AO46G and SARA REU fellowships, funded by the National Science Foundation Research Experiences for Undergraduates (REU) program through grant NSFAST-1004872.

Peer reviewed