We present optical spectroscopy secured at the 10 m Gran Telescopio Canarias of the counterparts of 20 extragalactic γ-ray sources detected by the Fermi satellite. The observations allow us to investigate the nature of these sources and to determine their redshift. We find that all optical counterparts have a spectrum that is consistent with a BL

We present new results from the analysis of 55 high-resolution spectra of V404 Cyg (the optical counterpart of the X-ray transient GS 2023+338) taken in 1991 July-August which, added to our 1990 July Hα spectra, establish the most complete spectroscopic data base in quiescence of this new black hole candidate. In addition, we present multicolour

We present the identification and characterization of the optical counterpart to 2XMM J011942.7+032421, one of the most luminous and distant ultra-luminous X-ray sources (ULXs). The counterpart is located near a star-forming region in a spiral arm of the galaxy NGC 470 with u, g, and r magnitudes of 21.53, 21.69, and 21.71 mag, respectively. The

We present the results of optical photometry of the X-ray transient XTE J2123-058. CCD R-band images, have been obtained since 2 Jul until 29 Sep 1998. Following the behaviour of the XTE/ASM lightcurve, the system decline optically from the begining of August at approximately 0.1 mag/day. Despite the drop in luminosity, we observe a dramatic

An international collaboration of fourty scientists have been involved in multifrequency observations of the blazar OJ 287, as well as of a few other complementary objects, taken both photometrically and spectroscopically. We present the optical light curve of OJ 287 obtained between the fall of 1993 through the present. Over 1200 photometric

To asses stability against 1/f noise, the Low Frequency Instrument (LFI) on-board the Planck mission will acquire data at a rate much higher than the data rate allowed by the science telemetry bandwith of 35.5 Kbps. The data are processed by an on-board pipeline, followed on-ground by a decoding and reconstruction step, to reduce the volume of data