Low-Frequency Radio Absorption in Cassiopeia A
M. Arias
(1)
,
J. Vink
(1, 2)
,
F. de Gasperin
(3)
,
P. Salas
(3)
,
R.B. R. Oonk
(3)
,
R. van Weeren
(3)
,
A.S. van Amesfoort
(4)
,
J. Anderson
(5)
,
R. Beck
(6)
,
M.E. Bell
(7)
,
M.J. Bentum
(4)
,
P. Best
(8)
,
R. Blaauw
(4)
,
F. Breitling
(9)
,
J.W. Broderick
(4)
,
W.N. Brouw
(4)
,
M. Brüggen
(10)
,
H.R. Butcher
(11)
,
B. Ciardi
(12)
,
E. de Geus
(4)
,
A. Deller
(13)
,
P.C. G. van Dijk
(4)
,
S. Duscha
(4)
,
J. Eislöffel
(14)
,
M.A. Garrett
(15)
,
J.M. Griessmeier
(16, 17)
,
A.W. Gunst
(4)
,
M.P. van Haarlem
(4)
,
G. Heald
(18)
,
J. Hessels
(1)
,
J. Hörandel
(19)
,
H.A. Holties
(4)
,
A.J. van Der Horst
(20)
,
M. Iacobelli
(4)
,
E. Juette
(21)
,
A. Krankowski
(22)
,
J. van Leeuwen
(4)
,
G. Mann
(9)
,
D. Mckay-Bukowski
(23)
,
J.P. Mckean
(4)
,
H. Mulder
(4)
,
A. Nelles
(24)
,
E. Orru
(4)
,
H. Paas
(25)
,
M. Pandey-Pommier
(26)
,
V.N. Pandey
(4)
,
R. Pekal
(27)
,
R. Pizzo
(4)
,
A.G. Polatidis
(4)
,
W. Reich
(6)
,
H.J. A. Röttgering
(3)
,
H. Rothkaehl
(28)
,
D.J. Schwarz
(29)
,
O. Smirnov
(30)
,
M. Soida
(31)
,
M. Steinmetz
(9)
,
M. Tagger
(16)
,
S. Thoudam
(32)
,
M.C. Toribio
(3)
,
C. Vocks
(9)
,
M.H. D. van Der Wiel
(4)
,
R.A. M. J. Wijers
(1)
,
O. Wucknitz
(6)
,
P. Zarka
(33)
,
P. Zucca
(4)
1
AI PANNEKOEK -
Astronomical Institute Anton Pannekoek
2 SRON - SRON Netherlands Institute for Space Research
3 Leiden Observatory [Leiden]
4 ASTRON - Netherlands Institute for Radio Astronomy
5 GFZ - GeoForschungsZentrum
6 MPIA - Max-Planck-Institut für Astronomie
7 UTS - University of Technology Sydney
8 Edin. - University of Edinburgh
9 AIP - Leibniz-Institut für Astrophysik Potsdam
10 University of Hamburg, Gojenbergsweg 112, 21029, Hamburg, Germany
11 Mount Stromlo Observatory, Australian National University
12 MPA - Max-Planck-Institut für Astrophysik
13 Centre for Astrophysics and Supercomputing, Swinburne University of Technology
14 Thüringer Landessternwarte, Tautenburg Observatory
15 JBCA School of Physics and Astronomy,
16 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace
17 USN - Unité Scientifique de la Station de Nançay
18 CSIRO Astronomy and Space Science
19 Radboud University [Nijmegen]
20 George Washington University
21 Astronomisches Institut der Ruhr-Universitat Bochum, Universitaetsstrasse 150, 44780, Bochum, Germany
22 University of Warmia and Mazury [Olsztyn]
23 Department of Physics and Technology, University of Tromso, Tromso, Norway
24 Department of Physics and Astronomy, University of Missouri
25 University of Groningen [Groningen]
26 CRAL - Centre de Recherche Astrophysique de Lyon
27 Poznan University of Technology
28 Space Research Center, Polish Academy of Sciences (Torun)
29 Universität Bielefeld = Bielefeld University
30 Department of Physics and Electronics, Rhodes University
31 Astronomical Observatory, Jagiellonian University
32 Department of Physics and Electrical Engineering
33 LESIA (UMR_8109) - Laboratoire d'études spatiales et d'instrumentation en astrophysique
2 SRON - SRON Netherlands Institute for Space Research
3 Leiden Observatory [Leiden]
4 ASTRON - Netherlands Institute for Radio Astronomy
5 GFZ - GeoForschungsZentrum
6 MPIA - Max-Planck-Institut für Astronomie
7 UTS - University of Technology Sydney
8 Edin. - University of Edinburgh
9 AIP - Leibniz-Institut für Astrophysik Potsdam
10 University of Hamburg, Gojenbergsweg 112, 21029, Hamburg, Germany
11 Mount Stromlo Observatory, Australian National University
12 MPA - Max-Planck-Institut für Astrophysik
13 Centre for Astrophysics and Supercomputing, Swinburne University of Technology
14 Thüringer Landessternwarte, Tautenburg Observatory
15 JBCA School of Physics and Astronomy,
16 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace
17 USN - Unité Scientifique de la Station de Nançay
18 CSIRO Astronomy and Space Science
19 Radboud University [Nijmegen]
20 George Washington University
21 Astronomisches Institut der Ruhr-Universitat Bochum, Universitaetsstrasse 150, 44780, Bochum, Germany
22 University of Warmia and Mazury [Olsztyn]
23 Department of Physics and Technology, University of Tromso, Tromso, Norway
24 Department of Physics and Astronomy, University of Missouri
25 University of Groningen [Groningen]
26 CRAL - Centre de Recherche Astrophysique de Lyon
27 Poznan University of Technology
28 Space Research Center, Polish Academy of Sciences (Torun)
29 Universität Bielefeld = Bielefeld University
30 Department of Physics and Electronics, Rhodes University
31 Astronomical Observatory, Jagiellonian University
32 Department of Physics and Electrical Engineering
33 LESIA (UMR_8109) - Laboratoire d'études spatiales et d'instrumentation en astrophysique
M. Arias
- Fonction : Auteur
- PersonId : 755774
- ORCID : 0000-0002-1951-1105
J. Vink
- Fonction : Auteur
- PersonId : 756156
- ORCID : 0000-0002-4708-4219
F. de Gasperin
- Fonction : Auteur
- PersonId : 766669
- ORCID : 0000-0003-4439-2627
R. van Weeren
- Fonction : Auteur
- PersonId : 766683
- ORCID : 0000-0002-0587-1660
J. Eislöffel
- Fonction : Auteur
- PersonId : 761407
- ORCID : 0000-0001-6496-0252
M. Iacobelli
- Fonction : Auteur
- PersonId : 774611
- ORCID : 0000-0001-9118-2097
G. Mann
- Fonction : Auteur
- PersonId : 760232
- ORCID : 0000-0002-4452-3028
R. Pizzo
- Fonction : Auteur
- PersonId : 766670
- ORCID : 0000-0003-2816-9492
P. Zarka
- Fonction : Auteur
- PersonId : 755767
- ORCID : 0000-0003-1672-9878
- IdRef : 034944648
Résumé
Cassiopeia A is one of the best-studied supernova remnants. Its shocked ejecta emits brightly in radio and X-rays. Its unshocked ejecta can be studied through infrared emission, the radio-active decay of $^{44}$Ti, and low frequency free-free absorption due to cold gas internal to the shell. Free-free absorption is affected by the mass, geometry, temperature, and ionisation conditions in the absorbing gas. Observations at the lowest radio frequencies constrain a combination of these properties. We use LOFAR LBA observations at 30-77 MHz and L-band VLA observations to compare $u-v$-matched images with a common resolution of 17". We simultaneously fit, per pixel, for the emission measure and the ratio of the emission from the unabsorbed front of the shell versus the absorbed back of the shell. We explore the effects that low temperatures and a high degree of clumping can have on the derived physical properties, such as mass and density. We also compile published radio flux measurements, fit for the absorption processes that occur in the radio band, and consider how they affect the secular decline of the source. We find a mass in the unshocked ejecta of $M = 2.95 \pm {0.48} \,M_{\odot}$ for an assumed gas temperature of $T=100$ K. This estimate is reduced for colder gas temperatures and if the ejecta are clumped. We measure the reverse shock to have a radius of $114$" $\pm $6". We also find that a decrease in the amount of mass in the unshocked ejecta (as more and more material meets the reverse shock and heats up) cannot account for the observed low frequency behaviour of the secular decline rate. To reconcile our low frequency absorption measurements with models that predict little mass in the unshocked ejecta we need the ejecta to be very clumped, or the temperature in the cold gas to be low ($\sim10$ K). Both conditions can jointly contribute to the high absorption.
Domaines
Astrophysique [astro-ph]| Origine | Fichiers produits par l'(les) auteur(s) |
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