35 research outputs found
Magnetic Fields and Afterglows of BdHNe: Inferences from GRB 130427A, GRB 160509A, GRB 160625B, GRB 180728A and GRB 190114C
GRB 190114C is the first binary-driven hypernova (BdHN) fully observed from
the initial supernova appearance to the final emergence of the optical SN
signal. It offers an unprecedented testing ground for the BdHN theory and it is
here determined and further extended to additional gamma-ray bursts (GRBs).
BdHNe comprise two subclasses of long GRBs with progenitors a binary system
composed of a carbon-oxygen star (CO) and a neutron star (NS)
companion. The CO explodes as a SN leaving at its center a
newborn NS (NS). The SN ejecta hypercritically accretes both on the
NS and the NS companion. BdHNe I are the tightest binaries where the
accretion leads the companion NS to gravitational collapse into a black hole
(BH). In BdHN II the accretion onto the NS is lower, so there is no BH
formation. We observe the same structure of the afterglow for GRB 190114C and
other selected examples of BdHNe I (GRB 130427A, GRB 160509A, GRB 160625B) and
for BdHN II (GRB 180728A). In all the cases the explanation of the afterglow is
reached via the synchrotron emission powered by the NS: their magnetic
fields structures and their spin are determined. For BdHNe I, we discuss the
properties of the magnetic field embedding the newborn BH, inherited from the
collapsed NS and amplified during the gravitational collapse process, and
surrounded by the SN ejecta.Comment: 7 figures, 3 tables, submitted to Ap
Electromagnetic emission of white dwarf binary mergers
It has been recently proposed that the ejected matter from white dwarf (WD)
binary mergers can produce transient, optical and infrared emission similar to
the "kilonovae" of neutron star (NS) binary mergers. To confirm this we
calculate the electromagnetic emission from WD-WD mergers and compare with
kilonova observations. We simulate WD-WD mergers leading to a massive, fast
rotating, highly magnetized WD with an adapted version of the
smoothed-particle-hydrodynamics (SPH) code Phantom. We thus obtain initial
conditions for the ejecta such as escape velocity, mass and initial position
and distribution. The subsequent thermal and dynamical evolution of the ejecta
is obtained by integrating the energy-conservation equation accounting for
expansion cooling and a heating source given by the fallback accretion onto the
newly-formed WD and its magneto-dipole radiation. We show that magnetospheric
processes in the merger can lead to a prompt, short gamma-ray emission of up to
erg in a timescale of - s. The bulk of the ejecta
initially expands non-relativistically with velocity and then it
accelerates to due to the injection of fallback accretion energy. The
ejecta become transparent at optical wavelengths around days
post-merger with a luminosity - erg s. The X-ray
emission from the fallback accretion becomes visible around -
day post-merger with a luminosity of erg s. We also predict
the post-merger time at which the central WD should appear as a pulsar
depending on the value of the magnetic field and rotation period.Comment: 12 pages, Accepted for publication in JCA
What can we learn from GRBs?
We review our recent results on the classification of long and short gamma-ray bursts (GRBs) in different subclasses. We provide observational evidences for the binary nature of GRB progenitors. For long bursts the induced gravitational collapse (IGC) paradigm proposes as progenitor a tight binary system composed of a carbon-oxygen core (COcore) and a neutron star (NS) companion; the supernova (SN) explosion of the COcore triggers a hypercritical accretion process onto the companion NS. For short bursts a NS–NS merger is traditionally adopted as the progenitor. We also indicate additional sub-classes originating from different progenitors: (COcore)–black hole (BH), BH–NS, and white dwarf–NS binaries. We also show how the outcomes of the further evolution of some of these sub-classes may become the progenitor systems of other sub-classes
GrailQuest & HERMES: Hunting for Gravitational Wave Electromagnetic Counterparts and Probing Space-Time Quantum Foam
Within Quantum Gravity theories, different models for space-time quantisation predict an energy dependent speed for photons. Although the predicted discrepancies are minuscule, GRB, occurring at cosmological distances, could be used to detect this signature of space-time granularity with a new concept of modular observatory of huge overall collecting area consisting in a fleet of small satellites in low orbits, with sub-microsecond time resolution and wide energy band (keV-MeV). The enormous number of collected photons will allow to effectively search these energy dependent delays. Moreover, GrailQuest will allow to perform temporal triangulation of high signal-to-noise impulsive events with arc-second positional accuracies: an extraordinary sensitive X-ray/Gamma all-sky monitor crucial for hunting the elusive electromagnetic counterparts of GW. A pathfinder of GrailQuest is already under development through the HERMES project: a fleet of six 3U cube-sats to be launched by 2021/22