Prof Patrick Roche

Abstract:

Simultaneous multiwavelength observations of BL Lacertae were performed on two occasions separated by 1 month in 1988 June and July, covering the radio, submillimeter, infrared, optical, ultraviolet, and X-ray wave bands. In the wide-band photon spectra, the X-ray flux lies clearly above the extension of radio-ultraviolet continuum as expected. The slope of the X-ray spectra is significantly flatter than that at optical-ultraviolet regimes, and its spectral index 0.7-1.0 corresponds to the slope at submillimeter band. Comparison with earlier observations, in fact, indicates that the X-ray flux is correlated with the submillimeter band, an not with the others, and supports the SSC model.

Abstract:

We present new closely sampled (∼1″) imaging polarimetry of the central 0.5 pc of the Galaxy at 12.4 μm with a 58 × 62 array camera system. The image shows a much more detailed view of the morphology of the intrinsically polarized emission (and the associated aligning magnetic field) in the ionized filaments of the Sgr A West complex than has been possible with earlier single beam studies. The new results show that the magnetic field in the northern arm is continuous on 1″ scale and is a property of the filamentary structure rather than the compact peaks of infrared emission and that it continues in a southwesterly direction from IRS 1 for several arcseconds into the east-west bar. In the southern and western part of the east-west bar the intrinsic polarization becomes complex, with small-scale variations of polarization fraction and position angle, probably due to superposition of different field directions along the line of sight. There is no evidence of perturbation of the field structure by the energetic outflows from the IRS 16 complex, and it is concluded that 1RS 16 does not lie in the plane of the northern arm, and that it cannot be at the center of the mass distribution of the Sgr A West system. We consider that the magnetic field in Sgr A West is amplified due to shearing motions in the ionized material and that the direction of the field is that of the flow. The run of magnetic field directions in the inner rim of the northern arm and east west bar then indicate a flow pattern which shows striking symmetry about the position of Sgr A*. When earlier data from outside the image area are included, an elliptical flow pattern with focus close to Sgr A* is indicated.