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Astron. Astrophys. 347, 494-499 (1999)
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An atmospheric model for the ion cyclotron line of Geminga
A. Jacchia 1,
F. De Luca 1,2,
E. Lazzaro 1,
P.A. Caraveo 3,4,
R.P. Mignani 5 and
G.F. Bignami 6,7
1 Istituto di Fisica del Plasma "P. Caldirola", CNR, Via Cozzi 53, I-20125 Milan, Italy (jacchia@ifp.mi.cnr.it)
2 Universitá degli studi di Milano, Dipartimento di Fisica, Via Celoria 16, I-20133 Milan, Italy
3 Istituto di Fisica Cosmica "G. Occhialini", CNR, Via Bassini 15, I-20133 Milan, Italy
4 Istituto Astronomico, Via Lancisi 29, I-00161 Rome, Italy
5 STECF-ESO, Karl-Schwarzschild-Strasse 2, D-85740 Garching, Germany
6 Agenzia Spaziale Italiana, Via di Villa Patrizi 13, I-00161 Rome, Italy
7 Universitá di Pavia, Via Bassi 6, I-27100 Pavia, Italy
Received 29 October 1998 / Accepted 29 April 1999
Abstract
Recent optical/UV data of Geminga (Mignani et al. 1998) have
strengthen the significance of the emission feature present over the
thermal continuum best fitting the EUV/soft X-ray data. Here we
present a phenomenological model interpreting the data in terms of an
ion cyclotron feature, arising from a thin outer layer of hot plasma
covering Geminga's polar caps. The width of the feature favours for
Geminga the strongly oblique rotator configuration, as already deduced
from the soft X-ray data (Halpern & Ruderman 1993). Our
interpretation implies a magnetic field of
![[FORMULA]](img1.gif)
, consistent with the value deduced
from the dynamical parameters of the pulsar. This would represent the
first case of an independent measurement of the surface magnetic field
of an isolated neutron star.
The expected time modulation of Geminga's feature is also discussed.
Key words: radiation mechanisms:
thermal 
stars: pulsars: individual: Geminga = 1E 0630+1
Send offprint requests to: A. Jacchia
© European Southern Observatory (ESO) 1999
Online publication: June 30, 1999
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