Narrow Results

By applying a method of virtual quanta we derive formulae for relativistic non-thermal bremsstrahlung radiation from relativistic electrons as well as from protons and heavier particles with power-law momentum distribution N(p)dp = k p^-qdp. We show that emission which originates from an electron scattering on an ion, represents the most significant component of relativistic non-thermal bremsstrahlung. Radiation from an ion scattering on electron, known as inverse bremsstrahlung, is shown to be negligible in overall non-thermal bremsstrahlung emission. These results arise from theory refinement, where we introduce the dependence of relativistic kinetic energy of an incident particle, upon the energy of scattered photon. In part, it is also a consequence of a different mass of particles and relativistic effects.

We start with a brief introduction to the historical background in the early pioneering days when the first neutron star thermal evolution calculations predicted the presence of neutron stars hot enough to be observable. We then report on the first detection of neutron star temperatures by ROSAT X-ray satellite, which vindicated the earlier prediction of hot neutron stars. We proceed to present subsequent developments, both in theory and observation, up to today. We then discuss the current status and the future prospect, which will offer useful insight to the understanding of basic properties of ultra-high density matter beyond the nuclear density, such as the possible presence of such exotic particles as pion condensates.

The first detection of gravitational waves on 2015 with the Advanced LIGO and Advanced Virgo interferometers has opened a new observational window in the Universe. The last decade has also welcomed decisive discoveries in neutrino astronomy. Expected advances of gravitational wave and neutrino detectors by the end of the 2020s will mark the start of a golden era of multi-messenger astrophysics. The most promising multi-messenger sources in the high-energy sky, e.g. GRBs, AGNs, magnetars, are among the main targets for the enhanced X-ray Timing and Polarimetry (eXTP). In this proceeding, we describe the possible role of eXTP in the context of multi-messenger astronomy and in particular on the synergies with gravitational wave interferometers at the sensitivity expected by the end of the twenties.

We start with a brief introduction to the historical background in the early pioneering days when the first neutron star thermal evolution calculations predicted the presence of neutron stars hot enough to be observable. We then report on the first detection of neutron star temperatures by ROSAT X-ray satellite, which vindicated the earlier prediction of hot neutron stars. We proceed to present subsequent developments, both in theory and observation, up to today. We then discuss the current status and the future prospect, which will offer useful insight to the understanding of basic properties of ultra-high density matter beyond the nuclear density, such as the possible presence of such exotic particles as pion condensates.

The recent discovery of a neutron star accretor in the ultra-luminous X-ray (ULX) source M82 X-2 challenges our understanding of high-mass X-ray binary formation and evolution. By combining binary population synthesis and detailed mass-transfer models, however, we show that the binary parameters of M82 X-2 are not surprising provided non-conservative mass transfer is allowed. Specifically, the donor-mass lower limit and orbital period measured for M82 X-2 lie near the most probable values predicted by population synthesis models, and systems such as M82 X-2 exist in approximately 13% of the galaxies with star formation history similar to M82. This work is presented in detail in Fragos et al.

We present observations of the extended optical counterpart of the bright, elongated ULX in the interacting galaxy pair NGC 5953/54 using the FLAMES-ARGUS integral field spectrograph on the VLT. We describe spectroscopic and spatial information of the ionized surroundings of this ULX in order to distinguish between two possible scenarios: a stellar-mass black hole binary or an intermediate-mass (~ 50 solar masses) black hole.