The Square Kilometre Array (SKA)

Abstract:

We present the discovery of a new type of explosive X-ray flash in Chandra images of the old elliptical galaxy M86. This unique event is characterized by the peak luminosity of 6 × 1042 erg s-1 for the distance of M86, the presence of precursor events, the timescale between the precursors and the main event (∼4000 s), the absence of detectable hard X-ray and γ-ray emission, the total duration of the event, and the detection of a faint associated optical signal. The transient is located close to M86 in the Virgo cluster at the location where gas and stars are seen protruding from the galaxy probably due to an ongoing wet minor merger. We discuss the possible mechanisms for the transient and conclude that the X-ray flash could have been caused by the disruption of a compact white dwarf star by a ∼104 M black hole. Alternative scenarios such that of a foreground neutron star accreting an asteroid or the detection of an off-axis (short) γ-ray burst cannot be excluded at present. © 2013. The American Astronomical Society. All rights reserved..

Abstract:

The low frequency array (LOFAR), is the first radio telescope designed with the capability to measure radio emission from cosmic-ray induced air showers in parallel with interferometric observations. In the first ~2 years of observing, 405 cosmic-ray events in the energy range of 1016-1018 eV have been detected in the band from 30-80 MHz. Each of these air showers is registered with up to ~1000 independent antennas resulting in measurements of the radio emission with unprecedented detail. This article describes the dataset, as well as the analysis pipeline, and serves as a reference for future papers based on these data. All steps necessary to achieve a full reconstruction of the electric field at every antenna position are explained, including removal of radio frequency interference, correcting for the antenna response and identification of the pulsed signal. © ESO, 2013.