We compute the kinematical dependence of the peak luminosity, the pulse width and the spectral lag of the peak luminosity on the viewing angle θv of a jet. For appropriate model parameters we obtain the peak luminosity-spectral lag relation similar to the observed one including GRB980425. A bright (dim) peak with short (long) spectral lag corresponds to a jet with small (large) viewing angle. T...

Two different luminosity indicators have been recently proposed for Gamma Ray Bursts that use the lag between light curve peaks with hard and soft photons as well as the variability (’spikiness’) of the burst light curve. Schaefer, Deng, & Band have proven that both of these luminosity indicators are valid by finding a lag/variability relation for 112 BATSE bursts. Here, I provide simple and ge...

We have estimated JHKs magnitudes corrected to mean intensity for LMC type II Cepheids found in the OGLE-III survey. Period-luminosity relations (PLRs) are derived in JHKs as well as in a reddening-free V I parameter. The BL Her stars (P < 4 d) and the W Vir stars (P = 4 to 20 d) are co-linear in these PLRs. The slopes of the infrared relations agree with those found previously for type II Ceph...

We study the spectra of all long Gamma Ray Bursts (GRBs) of known redshift detected by the Fermi satellite. Their fluxes and fluences are large enough to allow a time dependent study of their spectral characteristics in the 8 keV-1 MeV energy range. We find that the peak energy E peak of their EL(E) spectrum correlates with the luminosity in a remarkable tight way within individual bursts. This...

The theoretical period-luminosity relation for Cepheids was deduced from stellar evolution and pulsation computations. Questions concerning the metallicity dependence of the relation as well as the constancy of the pulsation ‘constant’ Q in the instablility strip were addressed. We found no significant metallicity dependence of either the slope or of the zero-point of the period-luminosity rela...

We have investigated the influence of nuclear parameters such as black hole mass and photoionizing luminosity on the FRI/FRII transition in a sample of nearby (z < 0.2) radio galaxies from the 3CR catalogue. The sample was observed with medium-resolution, optical spectroscopy and contains some galaxies with unpublished velocity dispersion measurements and emission-line fluxes. The measured velo...