We report 31 polarimetric observations of the afterglow of GRB 030329 with
high signal-to-noise and high sampling frequency. The data imply that the
afterglow magnetic field has small coherence ...length and is mostly random,
probably generated by turbulence.
Nature 426 (2003) 257-259 We report 31 polarimetric observations of the afterglow of GRB 030329 with
high signal-to-noise and high sampling frequency. We establish the polarization
light curve, ...detect sustained polarization at the percent level, and find
significant variability of polarization degree and angle. The data imply that
the afterglow magnetic field has small coherence length and is mostly random,
probably generated by turbulence.
We report on the first simultaneous near-infrared/X-ray detection of the Sgr A* counterpart which is associated with the massive black hole at the center of the Milky Way. The observations have been ...carried out using the NACO adaptive optics (AO) instrument at the European Southern Observatory's Very Large Telescope and the ACIS-I instrument aboard the Chandra X-ray Observatory. We also report on quasi-simultaneous observations at a wavelength of 3.4 mm using the Berkeley-Illinois-Maryland Association (BIMA) array. A flare was detected in the X-domain with an excess 2-8 keV luminosity of about 6\(\times10^{33}\) erg/s. A fading flare of Sgr A* with \(>\)2 times the interim-quiescent flux was also detected at the beginning of the NIR observations, that overlapped with the fading part of the X-ray flare. Compared to 8-9 hours before the NIR/X-ray flare we detected a marginally significant increase in the millimeter flux density of Sgr A* during measurements about 7-9 hours afterwards. We find that the flaring state can be conveniently explained with a synchrotron self-Compton model involving up-scattered sub-millimeter photons from a compact source component, possibly with modest bulk relativistic motion. The size of that component is assumed to be of the order of a few times the Schwarzschild radius. The overall spectral indices \(\alpha_{NIR/X-ray}\) ($S_{\nu}$$\propto$$\nu^{-\alpha}\() of both states are quite comparable with a value of \)\sim$1.3. Since the interim-quiescent X-ray emission is spatially extended, the spectral index for the interim-quiescent state is probably only a lower limit for the compact source Sgr A*. A conservative estimate of the upper limit of the time lag between the ends of the NIR and X-ray flare is of the order of 15 minutes.
We report new simultaneous near-infrared/sub-millimeter/X-ray observations of the SgrA* counterpart associated with the massive 3-4x10**6 solar mass black hole at the Galactic Center. The main aim is ...to investigate the physical processes responsible for the variable emission from SgrA*. The observations have been carried out using the NACO adaptive optics (AO) instrument at the European Southern Observatory's Very Large Telescope and the ACIS-I instrument aboard the Chandra X-ray Observatory as well as the Submillimeter Array SMA on Mauna Kea, Hawaii, and the Very Large Array in New Mexico. We detected one moderately bright flare event in the X-ray domain and 5 events at infrared wavelengths.
We report 31 polarimetric observations of the afterglow of GRB 030329 with high signal-to-noise and high sampling frequency. The data imply that the afterglow magnetic field has small coherence ...length and is mostly random, probably generated by turbulence.
We report 31 polarimetric observations of the afterglow of GRB 030329 with high signal-to-noise and high sampling frequency. We establish the polarization light curve, detect sustained polarization ...at the percent level, and find significant variability of polarization degree and angle. The data imply that the afterglow magnetic field has small coherence length and is mostly random, probably generated by turbulence.
Precise measurements of the S-stars orbiting SgrA* have set strong constraints on the nature of the compact object at the centre of the Milky Way. The presence of a black hole in that region is well ...established, but its neighboring environment is still an open debate. In that respect, the existence of dark matter in that central region may be detectable due to its strong signatures on the orbits of stars: the main effect is a Newtonian precession which will affect the overall pericentre shift of S2, the latter being a target measurement of the GRAVITY instrument. The exact nature of this dark matter (e.g., stellar dark remnants or diffuse dark matter) is unknown. This article assumes it to be an scalar field of toroidal distribution, associated with ultra-light dark matter particles, surrounding the Kerr black hole. Such a field is a form of "hair" expected in the context of superradiance, a mechanism that extracts rotational energy from the black hole. Orbital signatures for the S2 star are computed and shown to be detectable by GRAVITY. The scalar field can be constrained because the variation of orbital elements depends both on the relative mass of the scalar field to the black hole and on the field mass coupling parameter.
