LOFAR detections of low-frequency radio recombination lines towards Cassiopeia A
Journal article, 2013
Cassiopeia A was observed using the low-band antennas of the LOw Frequency ARray (LOFAR) with high spectral resolution. This allowed a search for radio recombination lines (RRLs) along the line-of-sight to this source. Five carbon alpha RRLs were detected in absorption between 40 and 50 MHz with a signal-to-noise ratio of >5 from two independent LOFAR data sets. The derived line velocities (v(LSR) similar to -50 km s(-1)) and integrated optical depths (similar to 13 s(-1)) of the RRLs in our spectra, extracted over the whole supernova remnant, are consistent within each LOFAR data set and with those previously reported. For the first time, we are able to extract spectra against the brightest hotspot of the remnant at frequencies below 330 MHz. These spectra show significantly higher (15-80 percent) integrated optical depths, indicating that there is small-scale angular structure of the order of similar to 1 pc in the absorbing gas distribution over the face of the remnant. We also place an upper limit of 3 x 10(-4) on the peak optical depths of hydrogen and helium RRLs. These results demonstrate that LOFAR has the desired spectral stability and sensitivity to study faint recombination lines in the decameter band.
ISM: individual objects: Cassiopeia A
Radio lines: ISM
ISM: clouds
Author
A. Asgekar
Shell Technology Center
J. B. R. Oonk
Leiden University
S. Yatawatta
Netherlands Institute for Radio Astronomy (ASTRON)
R. J. van Weeren
Leiden University
J. P. McKean
University of Groningen
G. White
Open University
N. Jackson
University of Manchester
J. Anderson
Technische Universität Berlin
I. M. Avruch
University of Groningen
Fabien Batejat
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
R. Beck
Max-Planck Institute for Radio Astronomy
M. E. Bell
University of Technology Sydney
M. R. Bell
Max Planck Institute for Astrophysics
I. van Bemmel
Joint Institute for VLBI in Europe (JIVE)
M. J. Bentum
University of Twente
G. Bernardi
Istituto di Radioastronomia
P. Best
University of Edinburgh
L. Birzan
University of Hamburg
A. Bonafede
Istituto di Radioastronomia
R. Braun
SKA Organisation
F. Breitling
Leibniz Institute for Astrophysics Potsdam
R. H. van de Brink
Netherlands Institute for Radio Astronomy (ASTRON)
J. Broderick
Curtin University
W. N. Brouw
University of Groningen
M. Brüggen
University of Hamburg
H. R. Butcher
Australian National University
W. van Cappellen
Netherlands Institute for Radio Astronomy (ASTRON)
B. Ciardi
Max Planck Institute for Astrophysics
John Conway
Chalmers, Earth and Space Sciences, Onsala Space Observatory
F. De Gasperin
University of Hamburg
E. de Geus
SmarterVision BV
A. de Jong
Netherlands Institute for Radio Astronomy (ASTRON)
M. de Vos
Netherlands Institute for Radio Astronomy (ASTRON)
S. Duscha
Netherlands Institute for Radio Astronomy (ASTRON)
J. Eisloffel
Thüringer Landessternwarte Tautenburg
H. Falcke
Max-Planck Institute for Radio Astronomy
R. A. Fallows
Netherlands Institute for Radio Astronomy (ASTRON)
C. Ferrari
Observatoire de la Cote d'Azur
W. Frieswijk
Netherlands Institute for Radio Astronomy (ASTRON)
M. A. Garrett
Leiden University
J. M. Griessmeier
University of Orléans
T. Grit
Netherlands Institute for Radio Astronomy (ASTRON)
A. W. Gunst
Netherlands Institute for Radio Astronomy (ASTRON)
T. E. Hassall
University of Southampton
G. Heald
Commonwealth Scientific and Industrial Research Organisation (CSIRO)
J. W. T. Hessels
University of Amsterdam
M. Hoeft
Thüringer Landessternwarte Tautenburg
M. Iacobelli
Netherlands Institute for Radio Astronomy (ASTRON)
H. Intema
Curtin University
E. Juette
Ruhr-Universität Bochum
A. Karastergiou
University of Oxford
J. Kohler
Max-Planck Institute for Radio Astronomy
V. I. Kondratiev
Russian Academy of Sciences
M. Kuniyoshi
National Astronomical Observatory of Japan
G. Kuper
Netherlands Institute for Radio Astronomy (ASTRON)
C. Law
California Institute of Technology (Caltech)
J. van Leeuwen
University of Amsterdam
P. Maat
Netherlands Institute for Radio Astronomy (ASTRON)
G. Macario
Arcetri Astrophysical Observatory
G. Mann
Leibniz Institute for Astrophysics Potsdam
S. Markoff
University of Amsterdam
D. McKay-Bukowski
STFC Rutherford Appleton Laboratory
M. Mevius
Netherlands Institute for Radio Astronomy (ASTRON)
J. C. A. Miller-Jones
Curtin University
J. D. Mol
Netherlands Institute for Radio Astronomy (ASTRON)
R. Morganti
University of Groningen
D. D. Mulcahy
University of Southampton
H. Munk
Netherlands Institute for Radio Astronomy (ASTRON)
M. J. Norden
Netherlands Institute for Radio Astronomy (ASTRON)
E. Orru
Netherlands Institute for Radio Astronomy (ASTRON)
H. Paas
University of Groningen
M. Pandey-Pommier
Université de Lyon
V. N. Pandey
University of Melbourne
R. Pizzo
Netherlands Institute for Radio Astronomy (ASTRON)
A. G. Polatidis
Netherlands Institute for Radio Astronomy (ASTRON)
W. Reich
Max-Planck Institute for Radio Astronomy
H. Rottgering
Leiden University
B. Scheers
Stichting Centrum voor Wiskunde & Informatica (CWI)
A. Schoenmakers
Netherlands Institute for Radio Astronomy (ASTRON)
J. Sluman
Netherlands Institute for Radio Astronomy (ASTRON)
O. Smirnov
South African Radio Astronomy Observatory (SARAO)
C. Sobey
Commonwealth Scientific and Industrial Research Organisation (CSIRO)
M. Steinmetz
Leibniz Institute for Astrophysics Potsdam
M. Tagger
University of Orléans
Y. Tang
Netherlands Institute for Radio Astronomy (ASTRON)
C. Tasse
Observatoire de Paris-Meudon
R. Vermeulen
Netherlands Institute for Radio Astronomy (ASTRON)
C. Vocks
Leibniz Institute for Astrophysics Potsdam
Ramj Wijers
University of Amsterdam
M. W. Wise
University of Amsterdam
O. Wucknitz
Max-Planck Institute for Radio Astronomy
P. Zarka
LESIA - Laboratoire d'Etudes Spatiales et d'Instrumentation en Astrophysique
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 551 L11Subject Categories
Astronomy, Astrophysics and Cosmology
DOI
10.1051/0004-6361/201221001