TY - JOUR
T1 - First detections of the cataclysmic variable AE Aquarii in the near to
far infrared with ISO and IRAS: Investigating the
various possible thermal and non-thermal contributions
AU - Abada-simon, M.
AU - Casares, J.
AU - Eyres, S.
AU - Fender, R.P.
AU - Garrington, S. T.
AU - De Jager, O.
AU - Kuno, N.
AU - Martínez-pais, I. G.
AU - De Martino, D.
AU - Matsuo, H.
AU - Mouchet, M.
AU - Pooley, G. G.
AU - Ramsay, G.
AU - Salama, A.
AU - Schulz, B.
AU - Evans, A.
PY - 2005/4/1
Y1 - 2005/4/1
N2 - We have used ISO to observe the Magnetic Cataclysmic Variable AE Aquarii in the previously unexplored range from 4.8 μm up to 170 μm in the framework of a coordinated multi-wavelength campaign from the radio to optical wavelengths. We have obtained for the first time a spectrum between 4.8 and 7.3 μm with ISOCAM and ISOPHOT-P: the major contribution comes from the secondary star spectrum, with some thermal emission from the accretion stream, and possibly some additional cyclotron radiation from the post-shock accretion material close to the magnetised white dwarf. Having reprocessed ISOPHOT-C data, we confirm AE Aqr detection at m and we have re-estimated its upper limit at 170 μm. In addition, having re-processed IRAS data, we have detected AE Aqr at 60 μm and we have estimated its upper limits at 12, 25, and 100 μm. The literature shows that the time-averaged spectrum of AE Aqr increases roughly with frequency from the radio wavelengths up to m; our results indicate that it seems to be approximately flat between ~761 and m, at the same level as the 3σ upper limit at 170 μm; and it then decreases from m to m. Thermal emission from dust grains or from a circum-binary disc seems to be very unlikely in AE Aqr, unless such a disc has properties substantially different from those predicted recently. Since various measurements and the usual assumptions on the source size suggest a brightness temperature below 109 K at mm, we have reconsidered also the possible mechanisms explaining the emission already known from the submillimetre to the radio. The complex average spectrum measured from m to the radio must be explained by emission from a plasma composed of more than one “pure” non-thermal electron energy distribution (usually assumed to be a power-law): either a very large volume (diameter ≥ 80 times the binary separation) could be the source of thermal bremsstrahlung which would dominate from m to the ~millimetre, with, inside, a non-thermal source of synchrotron which dominates in radio; or, more probably, an initially small infrared source composed of several distributions (possibly both thermal, and non-thermal, mildly relativistic electrons) radiates gyro-synchrotron and expands moderately: it requires to be re-energised in order to lead to the observed, larger, radio source of highly relativistic electrons (in the form of several non-thermal distributions) which produce synchrotron.
AB - We have used ISO to observe the Magnetic Cataclysmic Variable AE Aquarii in the previously unexplored range from 4.8 μm up to 170 μm in the framework of a coordinated multi-wavelength campaign from the radio to optical wavelengths. We have obtained for the first time a spectrum between 4.8 and 7.3 μm with ISOCAM and ISOPHOT-P: the major contribution comes from the secondary star spectrum, with some thermal emission from the accretion stream, and possibly some additional cyclotron radiation from the post-shock accretion material close to the magnetised white dwarf. Having reprocessed ISOPHOT-C data, we confirm AE Aqr detection at m and we have re-estimated its upper limit at 170 μm. In addition, having re-processed IRAS data, we have detected AE Aqr at 60 μm and we have estimated its upper limits at 12, 25, and 100 μm. The literature shows that the time-averaged spectrum of AE Aqr increases roughly with frequency from the radio wavelengths up to m; our results indicate that it seems to be approximately flat between ~761 and m, at the same level as the 3σ upper limit at 170 μm; and it then decreases from m to m. Thermal emission from dust grains or from a circum-binary disc seems to be very unlikely in AE Aqr, unless such a disc has properties substantially different from those predicted recently. Since various measurements and the usual assumptions on the source size suggest a brightness temperature below 109 K at mm, we have reconsidered also the possible mechanisms explaining the emission already known from the submillimetre to the radio. The complex average spectrum measured from m to the radio must be explained by emission from a plasma composed of more than one “pure” non-thermal electron energy distribution (usually assumed to be a power-law): either a very large volume (diameter ≥ 80 times the binary separation) could be the source of thermal bremsstrahlung which would dominate from m to the ~millimetre, with, inside, a non-thermal source of synchrotron which dominates in radio; or, more probably, an initially small infrared source composed of several distributions (possibly both thermal, and non-thermal, mildly relativistic electrons) radiates gyro-synchrotron and expands moderately: it requires to be re-energised in order to lead to the observed, larger, radio source of highly relativistic electrons (in the form of several non-thermal distributions) which produce synchrotron.
KW - stars: novae, cataclysmic variables
KW - infrared: stars
KW - radio continuum: stars
KW - stars: flare
KW - radiation mechanisms: thermal
KW - radiation mechanisms: non-thermal
U2 - 10.1051/0004-6361:20042066
DO - 10.1051/0004-6361:20042066
M3 - Article
VL - 433
SP - 1063
EP - 1077
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
SN - 0004-6361
IS - 3
ER -