Multi-wavelength INTEGRAL NEtwork (MINE) observations of the microquasar GRS 1915+105

We present the international collaboration MINE (Multi-lambda Integral NEtwork) aimed at conducting multi-wavelength observations of X-ray binaries and microquasars simultaneously with the INTEGRAL gamma-ray satellite. We will focus on the 2003 March-April campaign of observations of the peculiar microquasar GRS 1915+105 gathering radio, IR and X-ray data. The source was observed 3 times in the plateau state, before and after a major radio and X-ray flare. It showed strong steady optically thick radio emission corresponding to powerful compact jets resolved in the radio images, bright near-infrared emission, a strong QPO at 2.5 Hz in the X-rays and a power law dominated spectrum without cutoff in the 3-300 keV range. We compare the different observations, their multi-wavelength light curves, including JEM-X, ISGRI and SPI, and the parameters deduced from fitting the spectra obtained with these instruments on board INTEGRAL.Comment: 4 pages, 9 fig., Proc. of the 5th INTEGRAL Workshop (Feb. 16-20 2004), to be published by ES

Simultaneous multi-wavelength observations of microquasars (the MINE collaboration)

We present the international collaboration MINE (Multi-lambda INTEGRAL NEtwork) aimed at conducting multi-wavelength observations of microquasars simultaneously with the INTEGRAL satellite. The first results on GRS 1915+105 are encouraging and those to come should help us to understand the physics of the accretion and ejection phenomena around a compact object.Comment: 2 p, 3 fig., proc. of the IAU Coll. 194, ``Compact Binaries in the Galaxy and Beyond'', Nov. 2003, La Paz, Mexico, to be published in the Conf. Series of Revista Mexicana de Astronomia y Astrofisica, Eds. G. Tovmassian & E. Sio

Epidemics and percolation in small-world networks

We study some simple models of disease transmission on small-world networks, in which either the probability of infection by a disease or the probability of its transmission is varied, or both. The resulting models display epidemic behavior when the infection or transmission probability rises above the threshold for site or bond percolation on the network, and we give exact solutions for the position of this threshold in a variety of cases. We confirm our analytic results by numerical simulation.Comment: 6 pages, including 3 postscript figure

Impact of spatial inhomogeneities on on-axis pulse reconstruction in femtosecond filaments

We demonstrate a strong influence of the spatial beam profile on the vacuum-propagated on-axis pulse shapes for a femtosecond filament in argon. The effects can be minimized by transmitting the filament into the far-field by a laser-drilled pinhole setup. Using this method, we can monitor the pulse compression dynamics along the entire longitudinal extension of the filament, including the ionization-induced plasma channel

INTEGRAL-RXTE observations of Cygnus X-1

We present first results from contemporaneous observations of Cygnus X-1 with INTEGRAL and RXTE, made during INTEGRAL's performance verification phase in 2002 November and December. Consistent with earlier results, the 3-250 keV data are well described by Comptonization spectra from a Compton corona with a temperature of kT~50-90 keV and an optical depth of tau~1.0-1.3 plus reflection from a cold or mildly ionized slab with a covering factor of Omega/2pi~0.2-0.3. A soft excess below 10 keV, interpreted as emission from the accretion disk, is seen to decrease during the 1.5 months spanned by our observations. Our results indicate a remarkable consistency among the independently calibrated detectors, with the remaining issues being mainly related to the flux calibration of INTEGRAL.Comment: 6 pages, 3 figures. Figs. 2 and 3 are best viewed in color. Accepted for publication in the INTEGRAL special edition of A&A

Short-period X-ray oscillations in super-soft novae and persistent SSS

Transient short-period <100s oscillations have been found in the X-ray light curves of three novae during their SSS phase and in one persistent SSS. We pursue an observational approach to determine possible driving mechanisms and relations to fundamental system parameters such as the white dwarf mass. We performed a systematic search for short-period oscillations in all available XMM-Newton and Chandra X-ray light curves of persistent SSS and novae during their SSS phase. To study time evolution, we divided each light curve into short time segments and computed power spectra. We then constructed dynamic power spectra from which we identified transient periodic signals even when only present for a short time. From all time segments of each system, we computed fractions of time when periodic signals were detected. In addition to the previously known systems with short-period oscillations, RS Oph (35s), KT Eri (35s), V339 Del (54s), and Cal 83 (67s), we found one additional system, LMC 2009a (33s), and also confirm the 35s period from Chandra data of KT Eri. The amplitudes of oscillations are of order <15% of the respective count rates and vary without any clear dependence on the X-ray count rate. The fractions of the time when the respective periods were detected at 2-sigma significance (duty cycle) are 11.3%, 38.8%, 16.9%, 49.2%, and 18.7% for LMC 2009a, RS Oph, KT Eri, V339 Del, and Cal 83, respectively. The respective highest duty cycles found in a single observation are 38.1%, 74.5%, 61.4%, 67.8%, and 61.8%.Comment: accepted for publication in A&