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  • Arias, M.Univ Amsterdam, Netherlands (author)

Low-frequency radio absorption in Cassiopeia A

  • Article/chapterEnglish2018

Publisher, publication year, extent ...

  • 2018-05-08
  • EDP Sciences,2018
  • printrdacarrier

Numbers

  • LIBRIS-ID:oai:DiVA.org:lnu-76769
  • https://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-76769URI
  • https://doi.org/10.1051/0004-6361/201732411DOI

Supplementary language notes

  • Language:English
  • Summary in:English

Part of subdatabase

Classification

  • Subject category:ref swepub-contenttype
  • Subject category:art swepub-publicationtype

Notes

  • Context. Cassiopeia A is one of the best-studied supernova remnants. Its bright radio and X-ray emission is due to shocked ejecta. Cas A is rather unique in that the unshocked ejecta can also be studied: through emission in the infrared, the radio-active decay of Ti-44, and the low-frequency free-free absorption caused by cold ionised gas, which is the topic of this paper. Aims. Free-free absorption processes are affected by the mass, geometry, temperature, and ionisation conditions in the absorbing gas. Observations at the lowest radio frequencies can constrain a combination of these properties. Methods. We used Low Frequency Array (LOFAR) Low Band Antenna observations at 30-77 MHz and Very Large Array (VLA) L-band observations at 1-2 GHz to fit for internal absorption as parametrised by the emission measure. We simultaneously fit multiple UV-matched images with a common resolution of 17 '' (this corresponds to 0.25 pc for a source at the distance of Cas A). The ample frequency coverage allows us separate the relative contributions from the absorbing gas, the unabsorbed front of the shell, and the absorbed back of the shell to the emission spectrum. We explored the effects that a temperature lower than the similar to 100-500 K proposed from infrared observations and a high degree of clumping can have on the derived physical properties of the unshocked material, such as its mass and density. We also compiled integrated radio flux density measurements, fit for the absorption processes that occur in the radio band, and considered their effect on the secular decline of the source. Results. We find a mass in the unshocked ejecta of M = 2.95 +/- 0.48 M-circle dot for an assumed gas temperature of T = 100 K. This estimate is reduced for colder gas temperatures and, most significantly, if the ejecta are clumped. We measure the reverse shock to have a radius of 114 '' +/- 6 '' and be centred at 23:23:26, +58:48:54 (J2000). We also find that a decrease in the amount of mass in the unshocked ejecta (as more and more material meets the reverse shock and heats up) cannot account for the observed low-frequency behaviour of the secular decline rate. Conclusions. To reconcile our low-frequency absorption measurements with models that reproduce much of the observed behaviour in Cas A and predict little mass in the unshocked ejecta, the ejecta need to be very clumped or the temperature in the cold gas needs to be low (similar to 10 K). Both of these options are plausible and can together contribute to the high absorption value that we find.

Subject headings and genre

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  • Vink, J.Univ Amsterdam, Netherlands;SRON Netherlands Inst Space Res, Netherlands (author)
  • de Gasperin, F.Leiden Univ, Netherlands;Netherlands Inst Radio Astron, Netherlands (author)
  • Salas, P.Leiden Univ, Netherlands (author)
  • Oonk, J. B. R.Leiden Univ, Netherlands;Netherlands Inst Radio Astron, Netherlands (author)
  • van Weeren, R. J.Leiden Univ, Netherlands (author)
  • van Amesfoort, A. S.Netherlands Inst Radio Astron, Netherlands (author)
  • Anderson, J.Helmholtz Zentrum Potsdam, Germany (author)
  • Beck, R.Max Planck Inst Radio Astron, Germany (author)
  • Bell, M. E.Univ Technol Sydney, Australia (author)
  • Bentum, M. J.Netherlands Inst Radio Astron, Netherlands;Eindhoven Univ Technol, Netherlands (author)
  • Best, P.Univ Edinburgh, UK (author)
  • Blaauw, R.Netherlands Inst Radio Astron, Netherlands (author)
  • Breitling, F.Leibniz Inst Astrophys Potsdam AIP, Germany (author)
  • Broderick, J. W.Netherlands Inst Radio Astron, Netherlands (author)
  • Brouw, W. N.Netherlands Inst Radio Astron, Netherlands;Kapteyn Astron Inst, Netherlands (author)
  • Brueggen, M.Univ Hamburg, Germany (author)
  • Butcher, H. R.Australian Natl Univ, Australia (author)
  • Ciardi, B.Max Planck Inst Astrophys, Germany (author)
  • de Geus, E.Netherlands Inst Radio Astron, Netherlands;SmarterVision BV, Netherlands (author)
  • Deller, A.Netherlands Inst Radio Astron, Netherlands;Swinburne Univ Technol, Australia (author)
  • van Dijk, P. C. G.Netherlands Inst Radio Astron, Netherlands (author)
  • Duscha, S.Netherlands Inst Radio Astron, Netherlands (author)
  • Eisloeffel, J.Thuringer Landessternwarte, Germany (author)
  • Garrett, M. A.Leiden Univ, Netherlands;Univ Manchester, UK (author)
  • Griessmeier, J. M.Univ Orleans, France (author)
  • Gunst, A. W.Netherlands Inst Radio Astron, Netherlands (author)
  • van Haarlem, M. P.Netherlands Inst Radio Astron, Netherlands (author)
  • Heald, G.Netherlands Inst Radio Astron, Netherlands;Kapteyn Astron Inst, Netherlands;CSIRO Astron & Space Sci, Australia (author)
  • Hessels, J.Univ Amsterdam, Netherlands;Netherlands Inst Radio Astron, Netherlands (author)
  • Horandel, J.Radboud Univ Nijmegen, Netherlands (author)
  • Holties, H. A.Netherlands Inst Radio Astron, Netherlands (author)
  • van der Horst, A. J.George Washington Univ, USA (author)
  • Iacobelli, M.Netherlands Inst Radio Astron, Netherlands (author)
  • Juette, E.Ruhr Univ Bochum, Germany (author)
  • Krankowski, A.Univ Warmia & Mazury, Poland (author)
  • van Leeuwen, J.Univ Amsterdam, Netherlands;Netherlands Inst Radio Astron, Netherlands (author)
  • Mann, G.Leibniz Inst Astrophys Potsdam AIP, Germany (author)
  • McKay-Bukowski, D.Univ Tromsö, Norway;STFC Rutherford Appleton Lab, UK (author)
  • McKean, J. P.Netherlands Inst Radio Astron, Netherlands;Kapteyn Astron Inst, Netherlands (author)
  • Mulder, H.Netherlands Inst Radio Astron, Netherlands (author)
  • Nelles, A.Univ Calif Irvine, USA (author)
  • Orru, E.Netherlands Inst Radio Astron, Netherlands (author)
  • Paas, H.Univ Groningen, Netherlands (author)
  • Pandey-Pommier, M.Observ Lyon, France (author)
  • Pandey, V. N.Netherlands Inst Radio Astron, Netherlands;Kapteyn Astron Inst, Netherlands (author)
  • Pekal, R.Poznan Supercomp & Networking Ctr PCSS, Poland (author)
  • Pizzo, R.Netherlands Inst Radio Astron, Netherlands (author)
  • Polatidis, A. G.Netherlands Inst Radio Astron, Netherlands (author)
  • Reich, W.Max Planck Inst Radio Astron, Germany (author)
  • Rottgering, H. J. A.Leiden Univ, Netherlands (author)
  • Rothkaehl, H.Space Res Ctr PAS, Poland (author)
  • Schwarz, D. J.Univ Bielefeld, Germany (author)
  • Smirnov, O.Rhodes Univ, South Africa;SKA South Africa, South Africa (author)
  • Soida, M.Jagiellonian Univ, Poland (author)
  • Steinmetz, M.Leibniz Inst Astrophys Potsdam AIP, Germany (author)
  • Tagger, M.Univ Orleans, France (author)
  • Thoudam, SatyendraLinnéuniversitetet,Institutionen för fysik och elektroteknik (IFE)(Swepub:lnu)sathaa (author)
  • Toribio, M. C.Leiden Univ, Netherlands;Netherlands Inst Radio Astron, Netherlands (author)
  • Vocks, C.Leibniz Inst Astrophys Potsdam AIP, Germany (author)
  • van der Wiel, M. H. D.Netherlands Inst Radio Astron, Netherlands (author)
  • Wijers, R. A. M. J.Univ Amsterdam, Netherlands (author)
  • Wucknitz, O.Max Planck Inst Radio Astron, Germany (author)
  • Zarka, P.Observ Paris, France;Observ Paris, France (author)
  • Zucca, P.Netherlands Inst Radio Astron, Netherlands (author)
  • Univ Amsterdam, NetherlandsUniv Amsterdam, Netherlands;SRON Netherlands Inst Space Res, Netherlands (creator_code:org_t)

Related titles

  • In:Astronomy and Astrophysics: EDP Sciences6120004-63611432-0746

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