Neutron star mergers eject neutron-rich matter in which heavy elements are synthesised. The decay of these freshly synthesised elements powers electromagnetic transients (“macronovae” or “kilonovae”) whose luminosity and colour strongly depend on their nuclear composition. If the ejecta are very neutron-rich (electron fraction Ye < 0.25), they contain fair amounts of lanthanides and actinides which have large opacities and therefore efficiently trap the radiation inside the ejecta so that the emission peaks in the red part of the spectrum. Even small amounts of this high-opacity material can obscure emission from lower lying material and therefore act as a “lanthanide curtain”. Here, we investigate how a relativistic jet that punches through the ejecta can potentially push away a significant fraction of the high opacity material before the macronova begins to shine. We use the results of detailed neutrino-driven wind studies as initial conditions and explore with 3D special relativistic hydrodynamic simulations how jets are propagating through these winds. Subsequently, we perform Monte Carlo radiative transfer calculations to explore the resulting macronova emission. We find that the hole punched by the jet makes the macronova brighter and bluer for on-axis observers during the first few days of emission, and that more powerful jets have larger impacts on the macronova.

On the ground of the large number of gamma-ray bursts (GRBs) detected with cosmological redshift, we have introduced a new classification of GRBs in seven subclasses, all with binary progenitors originating gravitational waves (GWs). Each binary is composed by a different combination of carbonoxygen cores (CO core ), neutron stars (NSs), black holes (BHs) and white dwarfs (WDs). This opens an ample new scenario for the role of GWs both as detectable sources and as a determining factor in the coalescence process of the GRB binary progenitors. The long bursts, traditionally assumed to originate from a single BH with an ultra-relativistic jetted emission, not expected to emit GWs, have instead been subclassified as (I) X-ray flashes (XRFs), (II) binary-driven hypernovae (BdHNe), and (III) BH-supernovae (BH-SNe). They are framed within the induced gravitational collapse (IGC) paradigm with progenitor a tight binary composed of a CO core and a NS or BH companion. The supernova (SN) explosion of the CO core triggers a hypercritical accretion process onto the companion NS or BH. If the accretion is not sufficient for the NS to reach its critical mass, an XRF occurs, while when the BH is already present or formed by the hypercritical accretion, a BdHN occurs. In the case these binaries are not disrupted by the mass-loss process, XRFs lead to NS-NS binaries and BdHNe lead to NS-BH ones. The short bursts, originating in NS-NS mergers, are subclassified as (IV) short gamma-ray flashes (S-GRFs) and (V) short GRBs (S-GRBs), the latter when a BH is formed. Two additional families are (VI) ultra-short GRBs (U-GRBs) and (VII) gamma-ray flashes (GRFs), respectively formed in NS-BH and NS-WD mergers. We use the estimated occurrence rate of the above subclasses and their GW emission to assess their detectability by Advanced LIGO and Virgo, eLISA, and resonant bars. We also discuss the consequences of our results in view of the recent announcement of the LIGO-Virgo Collaboration of the source GW 170817 as being originated by a NS-NS merger.

We present a new, multi-dimensional implementation of the Advanced Spectral Leakage (ASL) scheme with the purpose of modelling neutrino-matter interactions in neutron star mergers. A major challenge is the neutrino absorption in the semi-transparent regime which is responsible for driving winds from the merger remnant. Such winds are thought to be behind the blue emission component in the recently observed macronova following GW170817. Compared to the original version, we introduce an optical-depthdependent flux factor to model the average angle of neutrino propagation, and a modulation that accounts for flux anisotropies in non-spherical geometries. We scrutinise our approach by first comparing the new scheme against the original one for a spherically symmetric core-collapse supernova snapshot, both in 1D and in 3D, and additionally against a two-moment (M1) scheme as implemented in 1D into the code GR1D. The luminosities and mean energies agree to a few percents in most tests. Finally, we compare the new ASL scheme with the M1 scheme that is implemented in the Eulerian adaptive mesh refinement code FLASH. We find that the neutrino absorption distribution in the semi-transparent regime is overall well reproduced. Both approaches agree to within 15% for the average energies and to better than ∼ 35% in the total luminosities.