LOFAR, VLA, AND CHANDRA OBSERVATIONS OF THE TOOTHBRUSH GALAXY CLUSTER
Journal article, 2016
We present deep LOFAR observations between 120 and 181 MHz of the "Toothbrush" (RX J0603.3+ 4214), a cluster that contains one of the brightest radio relic sources known. Our LOFAR observations exploit a new and novel calibration scheme to probe 10 times deeper than any previous study in this relatively unexplored part of the spectrum. The LOFAR observations, when combined with VLA, GMRT, and Chandra X-ray data, provide new information about the nature of cluster merger shocks and their role in re-accelerating relativistic particles. We derive a spectral index of alpha = -0.8 +/- 0.1 at the northern edge of the main radio relic, steepening toward the south to alpha approximate to-2. The spectral index of the radio halo is remarkably uniform (alpha = -1.16, with an intrinsic scatter of <= 0.04). The observed radio relic spectral index gives a Mach number of M = 2.8(-0.3)(+0.5), assuming diffusive shock acceleration. However, the gas density jump at the northern edge of the large radio relic implies a much weaker shock (M approximate to 1.2, with an upper limit of M approximate to 1.5). The discrepancy between the Mach numbers calculated from the radio and X-rays can be explained if either (i) the relic traces a complex shock surface along the line of sight, or (ii) if the radio relic emission is produced by a re-accelerated population of fossil particles from a radio galaxy. Our results highlight the need for additional theoretical work and numerical simulations of particle acceleration and re-acceleration at cluster merger shocks.
Author
R. J. van Weeren
Harvard-Smithsonian Center for Astrophysics
G. Brunetti
Istituto di Radioastronomia
M. Brüggen
University of Hamburg
F. Andrade-Santos
Harvard-Smithsonian Center for Astrophysics
G. Ogrean
Harvard-Smithsonian Center for Astrophysics
W. L. Williams
University of Hertfordshire
Leiden University
Netherlands Institute for Radio Astronomy (ASTRON)
H. Rottgering
Leiden University
W. A. Dawson
Lawrence Livermore National Laboratory
W. R. Forman
Harvard-Smithsonian Center for Astrophysics
F. De Gasperin
Leiden University
University of Hamburg
M. J. Hardcastle
University of Hertfordshire
C. G. Jones
Harvard-Smithsonian Center for Astrophysics
G. K. Miley
Leiden University
D. Rafferty
University of Hamburg
L. Rudnick
University of Minnesota
J. Sabater
University of Edinburgh
C. L. Sarazin
University of Virginia
T. W. Shimwell
Leiden University
A. Bonafede
University of Hamburg
P. N. Best
University of Edinburgh
L. Birzan
University of Hamburg
R. Cassano
Istituto di Radioastronomia
K.T. Chyz̊y
Jagiellonian University in Kraków
J. H. Croston
University of Southampton
T. J. Dijkema
Netherlands Institute for Radio Astronomy (ASTRON)
T.A. Enßlin
Max Planck Society
C. Ferrari
Observatoire de la Cote d'Azur
G. Heald
University of Groningen
Netherlands Institute for Radio Astronomy (ASTRON)
M. Hoeft
Thüringer Landessternwarte Tautenburg
Cathy Horellou
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
M. J. Jarvis
University of Oxford
University of the Western Cape
R. P. Kraft
Harvard-Smithsonian Center for Astrophysics
M. Mevius
Netherlands Institute for Radio Astronomy (ASTRON)
H. T. Intema
Leiden University
National Radio Astronomy Observatory
S. S. Murray
Johns Hopkins University
Harvard-Smithsonian Center for Astrophysics
E. Orru
Netherlands Institute for Radio Astronomy (ASTRON)
R. Pizzo
Netherlands Institute for Radio Astronomy (ASTRON)
S. S. Sridhar
University of Groningen
Netherlands Institute for Radio Astronomy (ASTRON)
A. Simionescu
JAXA Institute of Space and Astronautical Science
A. Stroe
Leiden University
S. van der Tol
Netherlands Institute for Radio Astronomy (ASTRON)
G. J. White
STFC Rutherford Appleton Laboratory
Open University
Astrophysical Journal
0004-637X (ISSN) 1538-4357 (eISSN)
Vol. 818 2 204Subject Categories
Astronomy, Astrophysics and Cosmology
Roots
Basic sciences
DOI
10.3847/0004-637x/818/2/204