Long gamma-ray bursts (LGRBs) and superluminous supernovae (SLSNe) are expected to result from massive star deaths. However to date, there has been no direct observational measurement of their cloud collapse timescales nor progenitor lifetimes to help constrain their mass. Our analyses of z 2 LGRB afterglow spectra and Hubble Space Telescope images find a higher fraction of host galaxies that are interacting, have a close companion, and/or may have experienced a recent galaxy ‘fly by’ as compared to the general z 2 galaxy population. A smaller set of z 2 SLSNe suggests a similar result. Under the hypothesis that galaxy interactions induce cloud collapse and star formation near their closest approach, we explore measurements of the host and companion galaxy velocities and separations at the time of the LRGB/SLSN event as a direct physical means to measure the timescale of cloud collapse plus progenitor star lifetime.

In the first observed neutron star merger, GW170817, two dynamical components, mildly- and ultra-relativistic outflows were detected independently. The first component triggered a rapidly evolving thermal transient named macronova (kilonova), while the second caused an observed short GRB where the early gamma-ray signal was followed by a multi-wavelength afterglow. These two distinct components are typically modelled independently and the observational consequences of their interplay are hardly explored. Here we summarize the results of 3D special-relativistic simulations that we have used to investigate the consequences of jet propagation through a realistic environment. We show how the presence of a jet can lead to the macronova being brighter and bluer for on-axis observers in the first few days. Then we show the consequences on the interaction on the shape of the emerging jet. Finally, we will discuss how small scale features in the emerging jet structure can impact the best-fit afterglow parameters.

Scientific synergies between Athena and some of the key multi-messenger facilities that should be operative concurrently with Athena are presented. These facilities include LIGO A+, Advanced Virgo+ and future detectors for ground-based observation of gravitational waves (GW), LISA for space-based observations of GW, IceCube and KM3NeT for neutrino observations, CTA for very high energy observations. Multimessenger synergy science themes discussed here include pressing issues in the field of Astrophysics, Cosmology and Fundamental physics such as: the central engine and jet physics in compact binary mergers, accretion processes and jet physics in SMBBHs and in compact stellar binaries, the equation of state in neutron stars, cosmic accelerators and the origin of cosmic rays, the origin of intermediate and high-Z elements in the Universe, the Cosmic distance scale and tests of General Relativity and Standard Model. Observational strategies for implementing the identified science topics are also discussed.

The hosts of binary neutron star (BNS) mergers and hence short GRBs are not only galaxies with old stellar populations, infact most short GRB hosts are at least mildly star-forming galaxies. According to theoretical studies of merger populations, both short and long merging time-scales are expected. The immediate environments of BNS mergers are not as directly related to the property of the progenitor system as for long GRBs, since the system usually travelled a significant distance from their birth place. However, studying the stellar population properties across the host can still give us vital information on the contribution of formation channels and on merger timescales. Here we review the properties of NS merger hosts in emission using integrated-light and resolved observations. The afterglows of short GRBs furthermore serve to study the interstellar medium in their host galaxies in absorption. We present our best example to date, GRB 160410A at z = 1.7, one of the highest redshift short GRBs.

We join gravitational-wave and electromagnetic data to implement a combined simultaneous fit of the GW170817 event. The LIGO-Virgo analysis includes the estimation of the inclination, the angle of the binary with respect to the gravitationa-wave detector network line of sight. From the observations of the afterglow, instead, we can recover the viewing angle. The inclination and the viewing angle are supplementary angles, and can be treated as a single parameter. The value of the inclination that we recover from the fit is in agreement with the LIGO-Virgo previous works, with an uncertainty that is 10-fold smaller, thanks to contribution of the electromagnetic data. Moreover, with the inclusion of the gravitational-wave data, the degeneracy between the viewing angle and the jet opening angle is broken. This procedure is useful not only for analyzing GW170817, but any gravitational-wave event with an electromagnetic counterpart.

We report on our observing campaign of the compact binary merger GW190814, detected by the Advanced LIGO and Advanced Virgo detectors on August 14th, 2019. This signal has the best localisation of any observed gravitational wave (GW) source, with a 90% probability area of 18.5 deg2, and an estimated distance of ≈240 Mpc. We obtained wide-field observations with the Deca-Degree Optical Transient Imager (DDOTI) covering 88% of the probability area down to a limiting magnitude of w = 19.9 AB. Nearby galaxies within the high probability region were targeted with the Lowell Discovery Telescope (LDT), whereas promising candidate counterparts were characterized through multi-colour photometry with the Reionization and Transients InfraRed (RATIR) and spectroscopy with the Gran Telescopio de Canarias (GTC). We use our optical and near-infrared limits in conjunction with the upper limits obtained by the community to constrain the possible electromagnetic counterparts associated with the merger. A gamma-ray burst seen along its jet’s axis is disfavoured by the multi-wavelength dataset, whereas the presence of a burst seen at larger viewing angles is not well constrained. Although our observations are not sensitive to a kilonova similar to AT2017gfo, we can rule out high-mass (> 0.1 M⊙) fast-moving (mean velocity ≥ 0.3c) wind ejecta for a possible kilonova associated with this merger.

The spectacular detection of the first electromagnetic counterpart of a gravitational wave event detected by the LIGO/Virgo interferometers and originated by the coalescence of a double neutron star (NS) system (GW 170817) marked the dawn of a new era for astronomy. The short GRB 170817A associated to the gravitational wave event provided the long-sought evidence that at least a fraction of short GRBs are originated by NS-NS merging and suggested the intriguing possibility that relativistic jets can be launched in the process of a NS-NS merger. The wealth of data collected provided the first compelling observational evidence for the existence of kilonovae, i.e. the emission due to radioactive decay of heavy nuclei produced through rapid neutron capture. Besides the remarkable event associated to GW 170817, kilonova signatures have been identified in a few short GRBs light curves, supporting a scenario where kilonovae are ubiquitous and can probe neutron star mergers well beyond the horizon of the gravitational wave detectors. In this paper I will review the situation and perspectives of our understanding of short GRBs progenitors and kilonovae in the multi-messenger era.

The binary neutron star merger gravitational-wave event GW170817 and observations of the subsequent electromagnetic signals at different wavelengths have helped better understand the outflows that follow these mergers. In particular, the off-axis afterglow of the jetted ejecta has allowed to probe the lateral structure of such jets, especially thanks to VLBI imagery of the source. In this work, we model this afterglow including a decelerating jet with lateral structure, while synchrotron emission and synchrotron self-Compton scatterings power the jet radiation. In particular, we extend our analysis to very high energies and predict the light curve in the energy range of H.E.S.S. and the CTA. We finally discuss how future detections of afterglows by these observatories can help break the degeneracies in some key physical parameter measurements, and allow to probe efficiently a sub-population of fast-merging binaries.

GW170817/GRB 170817A has had a huge impact on our understanding of gamma-ray burst (GRB) afterglows, and has prompted a huge sustained effort at modeling the details of the geometry and emission from GRB jets. While no additional electro-magnetic counterparts have been detected to gravitational wave emission from neutron star mergers so far, it is certainly reasonable to expect further detections in the future. Whether these will be very similar in nature to GRB 170817A or instead will provide us with samplings of afterglow model parameters across a wide parameter space remains an open question. In this presentation I will survey some of the work done by the various active groups worldwide in theoretical modeling and understanding afterglows post 170817A.

Five long gamma-ray bursts (GRBs) have been found to have very high energy (VHE, > 100GeV) counterparts. Interestingly, more than one emission mechanism has been invoked to explain the VHE counterpart from different events. As a result of this discovery, it has become apparent that we have been missing half of the energy produced in the afterglow of GRBs. We have been studying the radio afterglows in order to investigate whether these VHE GRBs have unusual jet properties. Studying these events in the radio waveband is advantageous as the emission at lower frequencies is brighter for longer enabling detailed, long term study of the jet evolution. The jet properties and environments of these GRBs vary hugely in a similar manner to that seen in the ‘regular’ long GRB population with evidence of bright reverse shock emission and multiple jet components. This work is presented on behalf of a much larger collaboration.

The hosts of long Gamma-ray bursts (GRBs) are places of intense star-formation, which, at low redshift, are primarily low-mass dwarf starburst galaxies. Spatially resolved studies of these galaxies are still sparse, even more so at high spectral resolution where we can probe gas kinematics, in- and outflows and differences in abundance between different components. Here we present the first high resolution IFU sample of six low redshift GRB hosts, all dwarf starbursts. All galaxies in our sample show evidence for excess emission or broad emission components, with velocities of 100-200 km s−1. For GRB 030329, outflowing gas had also been observed in absorption in spectra of the GRB afterglow. The high velocity emission is usually blue shifted, connected to the brightest star-forming regions and more metal rich than the narrow component associated with the emission of the general host ISM. This gives strong indications that the excess emission/broad component is indeed associated to a starburst wind as observed in many field star-burst galaxies and a sign for the intense ongoing star-formation in those galaxies.

We demonstrate how pulse structures in Short gamma-ray bursts (SGRBs), coupled with observations of GRB/GW 170817A, constrain the geometries of dying HMXRB systems composed of merging neutron stars.

The separation of the gamma-ray bursts (GRBs) into short/hard and long/soft subclasses, respectively, is well supported both theoretically and observationally. The long ones are coupled to supernovae type Ib/Ic - the short ones are connected to the merging of two neutron stars, where one or even both neutron stars can be substituted by black holes. These short GRBs - as merging binaries - can also serve as the sources of gravitation waves, and are observable as the recently detected macronovae. Since 1998 there are several statistical studies suggesting the existence of more than two subgroups. There can be a subgroup having an intermediate durations; there can be a subgroup with ultra-long durations; the long/soft subgroup itself can be divided into two subclasses with respect to the luminosity of GRBs. The authors with other collaborators provided several statistical studies in this topic. This field of the GRB-diversity is briefly surveyed in this contribution.

It is well-known that there are two types of gamma-ray bursts (GRBs): short/hard and long/soft ones, respectively. The long GRBs are coupled to supernovae, but the short ones are associated with the so called macronovae (also known as kilonovae), which can serve as the sources of gravitational waves as well. The kilonovae can arise from the merging of two neutron-stars. The neutron stars can be substituded by more massive black holes as well. Hence, the topic of gamma-ray bursts (mainly the topic of short ones) and the topic of massive binaries, are strongly connected.

In this contribution, the redshifts of GRBs are studied. The surprising result - namely that the apparently fainter GRBs can be in average at smaller distances - is discussed again. In essence, the results of Mészáros et al. (2011) are studied again using newer samples of GRBs. The former result is confirmed by the newer data.

The SALT transient follow-up programme began in 2016 and will continue for 5 semesters (until 31 Oct 2018), with an expectation of renewal thereafter. It is currently the only SALT Large Science Programme, and was awarded ~250 ksec. per semester, with a significant fraction (60%) given for the highest priority target-of-opportunity time. The aim is to characterise and study transients across a wide range of classes, currently including (from closest to most distant) cataclysmic variables, novæ and other associated eruptive variables, low- and high-mass X-ray binaries, OGLE and Gaia transients (including tidal disruption events), super-luminous and unusual core-collapse supernovæ, kilonovæ and other candidate optical counterparts to gravitational-wave events, flaring blazars and AGN, and gamma-ray bursts. This programme currently involves four SALT partners, of which South Africa is the major contributor of time (74%) and resources and includes five institutions with over 30 co-investigators. This talk reviewed the nature of the programme and highlighted some of the results to date.

The broad-lined Type Ic Supernovæ (SNe) associated with Gamma-Ray Bursts (GRBs) were long considered the most luminous class as a whole among core-collapse SNe, until the discovery of Superluminous SNe (SLSNe) during the last decade. There are many differences between the two classes, but in recent years events have been discovered which form a link between them. Associated with GRBs but more luminous and hotter, and in one case clearly dissimilar spectrally from any other known GRB-SNe, these sources point the way towards common mechanisms underlying GRBs and SLSNe.

The Space-based, multi-band, astronomical Variable Object Monitor (SVOM) is a collaborative project between China and France dedicated to the detection, localisation and study of about 60 Gamma Ray Bursts per year, and other high-energy transient phenomena. SVOM is planned to be launched in 2021, with a lifetime of 3–5 years. The poster described our construction and testing of a prototype to set up an interface between our data reduction sub-system, the global VOEvent network, and the French science centre.

Compact object mergers are promising candidates for the progenitor system of short gamma-ray bursts (GRBs). Using gravitational wave (GW) triggers to identify a merger, any electromagnetic (EM) counterparts from the jet can be used to constrain the dynamics and structure of short GRB jets. GW triggered searches could reveal a hidden population of optical transients associated with the short-lived jets from the merger object. If the population of merger-jets is dominated by low-Lorentz-factors, then a GW triggered search will reveal the on-axis orphan afterglows from these failed GRBs. By considering the EM counterparts from a jet, with or without the prompt GRB, the jet structure and dynamics can be constrained. By modelling the afterglow of various jet structures with viewing angle, we provide observable predictions for the on- and off- axis EM jet counterparts. The predictions provide an indication for the various features expected from the proposed jet structure models.

Gamma-ray bursts (GRBs) are the most powerful explosive events in the Universe. The prompt gamma emission is followed by an X-ray afterglow that is also detected for over nine hundred GRBs by the Swift BAT and XRT detectors. The X-ray afterglow spectrum bears essential information about the burst, and the surrounding interstellar medium (ISM). Since the radiation travels through the line of sight intergalactic medium and the ISM in the Milky Way, the observed emission is influenced by extragalactic and galactic components. The column density of the Galactic foreground ranges several orders of magnitudes, due to both the large scale distribution of ISM and its small scale structures. We examined the effect of local HI column density on the penetrating X-ray emission, as the first step towards a precise modeling of the measured X-ray spectra. We fitted the X-ray spectra using the Xspec software, and checked how the shape of the initially power low spectrum changes with varying input Galactic HI column density. The total absorbing HI column is a sum of the intrinsic and Galactic component. We also investigated the model results for the intrinsic component varying the Galactic foreground. We found that such variations may alter the intrinsic hydrogen column density up to twenty-five percent. We will briefly discuss its consequences.

Observing the supernovae (SNe) associated to the different types of gamma-ray bursts (GRBs) is one of the few means to study their progenitors. In the past years, it has become clear that GRB-like events are more heterogeneous than previously thought. There is a marked difference between long GRBs, which are produced by the collapse of very massive stars and are normally associated with broad-lined type Ic SNe, and short bursts, which occur when two compact objects merge and that, at least in some cases, can produce an associated kilonova. Moreover, the SNe associated with different sub-types of long GRBs are also seen to differ, especially those associated with ultra-long duration GRBs. To address this issue in a systematic way we started an observing programme in 2010 at the 10.4m GTC telescope. Here we present some results of our programme, including the detection of 12 new GRB-SNe. Highlights of our sample are the discovery of the first spectroscopic SN associated with a highly energetic (Eγ, iso ~ 1054 erg) “cosmological” burst (GRB 130427A), the study of the SN associated with a shock-breakout GRB (GRB 140606B) and the SN associated with the peculiar ultra-long GRB 101225A at z = 0.85. The sample includes also the follow-up of several short GRBs in search for kilonovae emission (GRB 130603B and GRB 160821B are important examples). Amongst our latest results we present the photometric and spectroscopic observations of the SNe associated with GRB 150818A and GRB 161219B.