LOFAR detections of low-frequency radio recombination lines towards Cassiopeia A

Ashish Asgekar 1 J. B. R. Oonk 1 S. Yatawatta 2 R. J. Van Weeren 1, 3 J. P. Mckean 1 G. White 4 N. Jackson 5 J. Anderson 6 I. M. Avruch 7 F. Batejat 6 R. Beck 8 M. E. Bell 9 M. R. Bell 9 I. Van Bemmel 1 M. J. Bentum 1 G. Bernardi 10 P. Best 11 L. Birzan 12 A. Bonafede 13 R. Braun 14 F. Breitling 15 R. H. Van de Brink 1 J. Broderick 9 W. N. Brouw 2 M. Bruggen 13 H. R. Butcher 1 W. Van Cappellen 16 B. Ciardi 6 J. E. Conway 17 F. De Gasperin 18 E. De Geus 19 A. De Jong 1 M. De Vos 1 S. Duscha 1 J. Eisloffel 20 H. Falcke 21, 22, 1 R. A. Fallows 23 C. Ferrari 24 W. Frieswijk 1 M. A. Garrett 12, 1 Jean-Mathias Grießmeier 25, 26 T. Grit 1 A. W. Gunst 1 T. E. Hassall 27 G. Heald 1 J. W. T. Hessels 28 M. Hoeft 20 M. Iacobelli 29, 30 H. Intema 12 E. Juette 31 A. Karastergiou 32 J. Kohler 33 V. I. Kondratiev 1 M. Kuniyoshi 22 G. Kuper 1 C. Law 34 J. Van Leeuwen 28 P. Maat 1 G. Macario 24 G. Mann 35 S. Markoff 34 D. Mckay-Bukowski 36 M. Mevius 1 J. C. A. Miller-Jones 34 J. D. Mol 1 R. Morganti 37, 38 D. D. Mulcahy 9 H. Munk 1 M. J. Norden 1 E. Orru 1 H. Paas 1 M. Pandey-Pommier 39 V. N. Pandey 40 R. Pizzo 1 A. G. Polatidis 1 W. Reich 22 H. Rottgering 12 B. Scheers 34 A. Schoenmakers 1 J. Sluman 1 O. Smirnov 41 C. Sobey 22 M. Steinmetz 35 Michel Tagger 25 Y. Tang 1 C. Tasse 42, 41 R. Vermeulen 1 C. Vocks 43 R. A. M. J. Wijers 34 M. W. Wise 1, 34 O. Wucknitz 44 P. Zarka 45
1 ASTRON - Netherlands Institute for Radio Astronomy
2 KAPTEYN ASTRONOMICAL INSTITUTE - Kapteyn Astronomical Institute
3 CfA - Harvard-Smithsonian Center for Astrophysics
4 SLAC National Accelerator Laboratory
5 Jodrell Bank Cent. for Astrophysics
6 Max Planck Institute for Astrophysics
7 SRON - SRON Netherlands Institute for Space Research
8 LCPM - Laboratoire de Chimie Physique Moléculaire
9 University of Southampton [Southampton]
10 LPNHE - Laboratoire de Physique Nucléaire et de Hautes Énergies
11 University of Edinburgh
12 Leiden Observatory [Leiden]
13 Jacobs University [Bremen]
14 TUD - Technische Universität Dresden
15 Leibniz Inst Astrophys Potsdam AIP
16 Max Planck Institute for Astrophysics
17 Onsala Space Observatory
18 Hamburger Sternwarte/Hamburg Observatory
19 Medstar Research Institute
20 TLS - Thüringer Landessternwarte Tautenburg
21 Radboud university [Nijmegen]
22 MPIFR - Max-Planck-Institut für Radioastronomie
23 Institute of Mathematical and Physical Sciences
24 LAGRANGE - Joseph Louis LAGRANGE
25 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace
26 USN - Unité Scientifique de la Station de Nançay
27 Jodrell Bank Centre for Astrophysics
28 UvA - University of Amsterdam [Amsterdam]
29 Sapienza University of Rome - Dipartimento di Matematica "Guido Castelnuovo" [Roma I]
30 CMLS - Centre de Mathématiques Laurent Schwartz
31 Ruhr-Universität Bochum [Bochum]
32 Astrophysics, University of Oxford
33 KIT - Karlsruhe Institute of Technology
34 AI PANNEKOEK - Astronomical Institute Anton Pannekoek
35 AIP - Leibniz-Institut für Astrophysik Potsdam
36 University of Oulu
37 Kapteyn Astronomical Institute
38 ASTRON - Netherlands Institute for Radio Astronomy
39 CRAL - Centre de Recherche Astrophysique de Lyon
40 NRAO - National Radio Astronomy Observatory [Charlottesville]
41 Rhodes University
42 SKA South Africa
43 Astrophysikalisches Institut Potsdam
44 Argelander Institut für Astronomie
45 OP - Observatoire de Paris - Site de Paris
Abstract : 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 datasets. The derived line velocities (v_LSR ~ -50 km/s) and integrated optical depths (~ 13 s^-1) of the RRLs in our spectra, extracted over the whole supernova remnant, are consistent within each LOFAR dataset 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 %) integrated optical depths, indicating that there is small-scale angular structure on the order of ~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.
Keywords : radio lines : ISM ISM: individual objects: Cas siopeia A ISM: clouds
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Article dans une revue
Astronomy and Astrophysics - A&A, EDP Sciences, 2013, 551 (L11), 5 p. 〈10.1051/0004-6361/201221001〉
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Ashish Asgekar, J. B. R. Oonk, S. Yatawatta, R. J. Van Weeren, J. P. Mckean, et al.. LOFAR detections of low-frequency radio recombination lines towards Cassiopeia A. Astronomy and Astrophysics - A&A, EDP Sciences, 2013, 551 (L11), 5 p. 〈10.1051/0004-6361/201221001〉. 〈insu-01286281〉

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