Does an orbiting star cause periodic modulation of X-rays from NGC6814?
USING data from the Ginga satellite, Done et al.1 have confirmed an Exosat observation2 of high-amplitude periodic modulation in the X-ray emission from the Seyfert galaxy NGC6814. To within observational errors of ∼1%, the period seems to have remained constant at ∼12,100 seconds between 1985 and 1989. An obvious candidate for the phenomenon underlying the periodicity is the orbital motion of a star or low-mass compact object around the central black hole3. As we show here, the presence of an orbiting star could be verified easily by looking for the effects of Lense–Thirring precession of the orbital plane, caused by the dragging of inertia! frames around a rotating black hole. Precession-induced variations in the waveform and in the phase of the observed periodicity should have a period of between a month and a year. Such variations could account for the different waveforms present in the Ginga and Exosat data sets4, and may be detectable in existing Ginga and future Rosat, OSSE/GRO, and Astro-D data.
Investigation of optical limiting in Cobalt nanoparticles synthesized by laser ablation
Abstract We present synthesis of Cobalt nanoparticles dispersed in toluene by laser ablation and their optical limiting properties with nanosecond laser pulses. Absorption spectra and concentration dependent optical limiting studies on nanoparticles indicate it as a versatile optical limiter. Cobalt nanoparticles show better optical limiting compared to the reference optical limiter fullerene C 60 . Optical limiting threshold of Cobalt nanoparticles is about three times less than that of C 60 . Z-scan experiments, angle dependent scattering, intensity dependent transmission, and temporal profile measurements indicate that the non-linear absorption, nonlinear scattering and thermal nonlinear refraction are responsible for optical limiting behavior of Cobalt nanoparticles.
Strategies for glass based photonic system integration
There is a clear tendency to integrate more and more opto-electronic and micro-optical components like optical fibers, laser diodes, modulators, isolators, beam-splitting components and micro lenses in also increasingly dense and complex assemblies. The paper will discuss thin glass as a very promising base material for that kind of photonic packaging on interposer and board level including optical interconnection using fibers.