Infrared Jet of the Galactic Superluminal Source Grs 1915+105

A near-infrared jet emanating from the galactic superluminal source GRS 1915 + 105, discovered at λ = 2.2 µm by Sams et al. 8 on 18-21 July 1995, was not seen later anymore, neither in the Mirabel et al. 6 images, taken on 4 August 1995 and that we analyze here, nor by Eikenberry & Fazio 2 on 16-17 October 1995. Therefore, the radiative lifetime of the electrons which have created this emission is τ < 17 days. The detection, and the later non-detection, of this infrared jet is consistent with a synchrotron emission, provided that the magnetic field in the ejected clouds is B > ∼ 160 mG, and that the Lorentz factor of the internal motions of the electrons in the jet is γ < ∼ 10 4. The lower limit for the magnetic field suggests a magneto-hydrodynamic mechanism for the acceleration and collimation of the ejecta. 1 The Observations Sams et al. 8 observed the counterpart of the galactic superluminal source GRS 1915+105, by near-infrared speckle imaging, at λ = 2.2 µm (K band). These observations were done on 18– 21 July 1995, using the Max Planck Institut fr Extraterrestrische Physik near-infrared speckle camera SHARP at the New Technology Telescope of the European Southern Observatory. The main characteristics, of all the instruments and observations reported in this paper, are given in the Table 1. The high-spatial resolution images show that GRS 1915 + 105 appears extended to the SouthWest: this jet has a total near-infrared magnitude of K = 13.9 magnitude, and is separated from the central source by 0.3 ′′. No extension is seen to the NorthEast. The jet structure, the flux ratio between the SW jet and the NE residuals, and the position angle of the SW jet, are consistent to that observed in a radio outburst of the source (Mirabel & Rodrguez 4).