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Astrophysics of compact objects

The study and observation of compact objects (neutron stars and black holes) constitutes a powerful instrument in the study of ultra-dense matter, allows the measurement of many General Relativistic effects, provides a channel for studying high energy astrophysics, and provides precious information about the dynamics of globular clusters. One of the most studied manifestations of neutron stars are the pulsars. Regular monitoring of these objects (through timing studies) provides a wealth of accurate data ideal for performing various experiments in the field of fundamental physics. These range from the theory of Relativity to the direct observation of gravitational waves, the determination of the Galactic magnetic field and studies of the interstellar medium.

The Italian community has played an important role in research into compact objects, and pulsars in particular, over the last fifteen years, and has also taken a prominent role in recent years. The highlight of this research is obviously the work related to the discovery and timing observations of the binary system J0737-3039, otherwise known as the double pulsar. Italian researchers have also led a deep survey to search for pulsars in globular clusters with the Parkes telescope. To date, 12 recycled pulsars have been discovered in 6 clusters, in which none had previously been detected.

Since 2006 the Italian pulsar community has been part of EPTA (the European Pulsar Timing Array) of which it is one of the founding members. The scientific rationale is to increase the synergies between the main European research groups in this field. In the field of Pulsar Wind Nebulae, the Italian scientific community has recently developed a technique to produce synthetic spectra and maps of multi-frequency emission, based on the relativistic plasma dynamics from bi-dimensional, relativistic, magnetohydrodynamical (MHD) simulations. The work of Italian astrophysicists during the last five years has also provided an important contribution in the optical identification of the companion star of a recycled pulsar. Specifically, 3 of the only 6 optical counterparts of recycled pulsars in globular clusters have been found by the national scientific community.

Observational pulsar studies are of two types, one dedicated to the discovery of new objects and the other to timing studies of the most interesting objects. The next three years will see the development of some important international projects in both areas. The two largest projects with an Italian involvement are HTRU and LEAP. The first makes use of a 13 beam receiver that will allow a deep search for recycled pulsars over the whole southern sky (a twin experiment will be run in the northern hemisphere with the Effelsberg radio telescope). The second will make use of the combined capabilities of five major European radio telescopes, including the SRT, to carry out exceptionally accurate pulsar timing observations.

As far as the studies of Pulsar Wind Nebulae are concerned, the first new development will be a refinement of the modeling, that will also take into account the possibility of anisotropies in the particle acceleration mechanism in the shock. Over the next three years, the observational campaign on compact objects in globular clusters will focus on the cluster's central regions, with high stellar densities, in a sample of Galactic globular clusters. This will include the use of high angular resolution data obtained both from the ACS, WFPC2 and WFC3 cameras on board the Hubble Space Telescope (HST), and from instruments equipped with adaptive optics on 8-10 m class, ground-based telescopes (NACO, MAD, etc.). These data will be combined with wide-field data from other ground-based instruments (for example the Large Binocular Telescope or ESO's Wide Field Imager).

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