Hercules A

Hercules A
Radio-Optical View of the Galaxy Hercules A - Many thanks to: NASA, ESA, S. Baum and C. O'Dea (RIT), R. Perley and W. Cotton (NRAO/AUI/NSF), and the Hubble Heritage Team (STScI/AURA)

Saturday, February 9, 2013

Jupiter imaging with LOFAR below 200 MHz, in November 2011, for one full rotation

I refer to Girard Zarka Tasse Hess 2012:

I copy below Figures 1 and 2.

"Since its detection in the mid-fifties, the synchrotron radiation, emitted by the Jupiter radiation belts at decimeter wavelengths (``DIM''), has been extensively observed over a wide spectrum (from >300 MHz to 22 GHz) by various instruments (VLA, ATCA, WSRT). They provided accurate flux measurements and resolved images of the emission that reveal spatial, temporal and spectral variabilities. However, no instrument was able to image the radiations belts below 100 MHz (at meter and decametre wavelength). The LOw Frequency ARray (LOFAR) (van Haarlem et al. 2012), which is a phased-array interferometer operating in the [30-80] & [110-250] MHz bandwidth, observed for the first time the Jupiter synchrotron emission. The antenna distribution provided baselines from 70 m up to ˜20 km that resolved the emission at low frequencies (127-172 MHz) during its commissioning phase. In November 2011, a single 10-hour track enabled to cover an entire planetary rotation in a bandwidth of 24 MHz. We present here the specific methods and steps implemented to reduce and to image the planetary data at low frequencies. At this stage of the commissioning, the smoothness of the synchrotron spectrum enabled the direct comparison between the expected flux density and the measurements from VLA data obtained in 1994 and 1998 (Kloosterman et al. 2008). We measured a total flux density of 3.5-4± [0.1-0.3] Jy, slightly lower to what was obtained from VLA observations and models (˜ 5-6 Jy). Future joint observations that cover the whole spectrum of the emission will enable the tracking of its temporal short- and long-term variability. The study of this variability brings information about the source, loss and transport processes taking place in the inner Jovian magnetosphere, improving in the same time the existing radiative code and magnetospheric models."