The cyclotron line of Gemingas atmosphere and consequences

Abstract In the panorama of Isolated Neutron Star (INS) optical astronomy new data are rapidly accumulating, especially on the recently discovered middle age (e 10 5 y) emitters. For Geminga, wide band photometry has led to the discovery of a spectral feature superimposed to the thermal continuum. Its most natural interpretion is that of emission at the ion cyclotron frequency, leading to a B-field value of H 35 10 11 G. This is the first in situ measurement of an INS surface magnetic field. Other relevant characteristics of Geminga are reviewed.