An overview of the transient sky at high-energies

il giorno giovedì 03 Marzo alle ore 14.00 sulla piattaforma Zoom,
Il Professore Andrea Sanna del dipartimento di Fisica dell'Università di Cagliari, terrà un Colloquium intitolato:
"An overview of the transient sky at high-energies"
Among the numerous classes of transients, accreting millisecond X-ray pulsars (AMXPs), and gamma-ray bursts (GRBs) have direct links with most of the hottest scientific topics, such as the strong gravity regime, relativistic shocks, particle acceleration processes, equation of state of matter at nuclear density, and nucleosynthesis of heavy elements, just to mention a few.
AMXPs are extremely fast-rotating Neutron Stars (NS), that have been spun-up as the result of a long-lasting mass transfer from a low-mass companion star through an accretion disc. At the end of the mass transfer phase, a millisecond pulsar shining from radio to gamma-rays, and powered by the rotation of its magnetic field, is expected to turn on. The close link shared by radio millisecond pulsars and AMXPs has been observationally confirmed recently by the transitional binary systems IGR J18245-2452. Here I will highlight what we know and what we have still to learn about AMXPs to fully understand their (sometimes puzzling) behavior.
GRBs are extremely energetic transient emissions of gamma-rays, associated either with the death of massive stars or the merger of compact objects in binary systems. The latter scenario has been beautifully confirmed from the nearly-simultaneous detection of gravitational waves from the coalescence of the NS-NS binary system and the associated short GRB 170817A. Their huge luminosities involve the presence of a newborn stellar-mass black hole emitting a relativistic collimated outflow, which accelerates particles and produces non-thermal emissions from the radio domain to the highest energies. In this framework, I will give an overview of the HERMES Technological and Scientific pathfinders currently under development that consist of a fleet of six 3U CubeSats to be launched in equatorial Low Earth Orbits by 2023, which aim at demonstrating the feasibility to monitor the hard X-ray/soft gamma-ray sky with good localization capabilities (crucial to fully exploit the multi-messenger astronomy, currently in its infant state) taking advantage of distributed astronomy.
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Data: 03/03/2022