Does a merger of two neutron stars leads to the formation of a magnetar? - Assaf Horesh

The recent discovery of gravitational waves by LIGO opens a new era in astrophysics. While the event discovered by LIGO originated from the merger of two black holes, LIGO is also capable and is expected to discover mergers of Neutron stars. In a Neutron star merger, a small amount of material will be ejected at velocities of about 30,000 km/s. This material will be radioactively heated and hence will emit a weak and brief (1 day to a weak) optical/infra-red signal, named macronovae. Such a macronovae signal was first detected only a few years ago as the counterpart of short gamma-ray bursts (which are believed to also originate from compact binary mergers). The same material that is responsible for the macro novae signal, will also interact with environment, create a shockwave, and lead to radio emission. It is possible that in the merger process a magnetar will form (and not necessarily a black hole). A magnetar is a fast rotating neutron star (1 ms period) with a large magnetic field (> 10^15 Gauss). In this case, the magnetar will deposit its energy into the ejecta and will drive a much stronger shockwave, thus increasing, by at least an order of magnitude, the radio emission. We recently observed two macronoave candidates, in search for this radio emission. Our results suggest that at least in the events that we observed, no standard magnetar was formed, unless the magnetar had different properties than theory predicts. Following this results, we are conducting further radio observations of similar events, in an attempt to better characterize them and to unveil their nature.


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