Although high-energy cosmic rays (HECRs) and gamma-ray bursts (GRBs) are the mostenergetic phenomena occurring in the universe, their origin are important enigmas in thefield of astrophysics. Today, the most studied scenario that attempts to explain them isknown as the Fireball Model. This theory assumes that the particles are accelerated by ashock developing in the interior of a relativistic plasma from a supernova (SN). Thefilamentation (sometimes called “Weibel”) instability is believed to mediate collisionlessshock formation from the collision of two plasma shells. It has been known for long that aflow aligned magnetic field can completely cancel this instability. In this work, weanalyze the robustness of the filamentation instability which develops inside a plasmaimmersed in an arbitrarily oriented magnetic field.

This is a brief review of some recent progress in our understanding of GRB jet dynamics,during the early acceleration phase and the later afterglow phase. In the accelerationphase I focus on the possible role of impulsive magnetic acceleration, and its ability toconvert most of the initial magnetic energy into kinetic energy and naturally produceefficient internal shocks at mild magnetizations. For the afterglow phase I outline newgeneralized yet simple analytic models that finally agree with numerical simulations, andpresent recent simulation results for a jet propagating into a stratified externalmedium.

The collapse of massive rotating stellar cores and the associated accretion is thought topower long Gamma ray bursts. The physical conditions make neutrino emission the maincooling agent in the flow. We have carried out an initial set of calculations of thecollapse of rotating polytropic cores in three dimensions, making use of apseudo-relativistic potential and a simplified cooling prescription. We focus on theeffects of self gravity and cooling on the overall morphology and evolution of the flowfor a given rotation rate in the context of the collapsar model. For the typical coolingtimes expected in such a scenario we observe the appearance of strong instabilities on atime scale tcool following disk formation.Such instabilities and their gravitational interaction with the black hole producesignificant variability in the obtained accretion rates, which would translate intoluminosity variations when a more realistic neutrino cooling and luminosity scheme isimplemented in future work.

We present, for the first time, three dimensional (3D) adaptive mesh refinementsimulations of a GRB jet crossing a pre-SN progenitor (with resolutions comparable to theresolutions of 2D simulations) (Lopez-Camara et al. 2012). Themorphology, Lorentz factor, and symmetries, will be discussed in this presentation.Basically the evolution is divided into three main phases: the jet moving inside theprogenitor; the jet just about break out of the progenitor; and the phase where the jethas broken out of the star and is now moving through the circumstellar medium. Theresolution and 3D effects are also discussed. Still, as with all numerical work, thecurrent investigation lacks in several aspects and needs improvement as well as furtherinvestigations.

The recent transient event Swift J1644+57 has been interpreted as resulting from arelativistic outflow, powered by the accretion of a tidally disrupted star onto asupermassive black hole. This discovery of a new class of relativistic transients opensnew windows into the study of tidal disruption events (TDEs) and offers a unique probe ofthe physics of relativistic jet formation and the conditions in the centers of distantquiescent galaxies. Unlike the rapidly-varying γ/X-ray emission fromSwift J1644+57, the radio emission varies more slowly and is well modeled as synchrotronradiation from the shock interaction between the jet and the gaseous circumnuclear medium(CNM). Early after the onset of the jet, a reverse shock propagates through anddecelerates the ejecta released during the first few days of activity, while at much latertimes the outflow approaches the self-similar evolution of Blandford and McKee. The pointat which the reverse shock entirely crosses the earliest ejecta is clearly observed as anachromatic break in the radio light curve at t ≈ 10 days. I discuss theimplications of Swift J1644+57 for the fraction of TDEs accompanied by relativistic jets;the physics of jet formation more broadly; and the prospects for detecting off-axis TDEradio emission, either via follow-up observations of TDE candidates discovered at otherwavelengths or blindly with upcoming wide-field radio surveys.

We perform two-dimensional relativistic magnetohydrodynamic simulations of a mildlyrelativistic shock propagating through an inhomogeneous medium. Simulation results showthat the postshock region becomes turbulent owing to preshock density inhomogeneity, andthe magnetic field is strongly amplified due to the stretching and folding of field linesin the turbulent velocity field. The amplified magnetic field evolves into a filamentarystructure in two-dimensional simulations. The magnetic energy spectrum is flatter than theKolmogorov spectrum and indicates that the so-called small-scale dynamo is occurring inthe postshock region.

We investigated particle acceleration and shock structure associated with an unmagnetizedrelativistic jet propagating into an unmagnetized plasma. Strong magnetic fields generatedin the trailing shock contribute to the electrons transverse deflection and acceleration.We have calculated, self-consistently, the radiation from electrons accelerated in theseturbulent magnetic fields. We found that the synthetic spectra depend on the bulk Lorentzfactor of the jet, its temperature and strength of the generated magnetic fields. We havealso investigated accelerated electrons in strong magnetic fields generated by kineticshear (Kelvin-Helmholtz) instabilities. The calculated properties of the emergingradiation will guide our understanding of the complex time evolution and/or spectralstructure in gamma-ray bursts, relativistic jets in general, and supernova remnants.

In the collapsar model of long GRBs the jet is formed at the center of the progenitorstar, propagates in its interior, and produces the observed gamma rays much after itsbreakout from the star. The loss of pressure support during breakout induces a strongrarefaction wave that propagates inside the jet and causes its bulk acceleration. Thismechanism has been already studied using axisymmetric magnetohydrodynamic (MHD)simulations assuming a prescribed shape for the surface between the jet and itsenvironment, as well as using simple rarefaction waves in planar geometry. Trying toimprove over these works, we solve the steady-state, axisymmetric, relativistic MHDequations using the method of characteristics. In this way the jet boundary is foundself-consistently and the rarefaction wave is studied in the axisymmetric geometry. Inthis poster we present our first results and a comparison with previous works.

Due to severe time constraints, the joint discussion for sessions I-IV has be beenextremely short considering the number of hot topics related to GRB prompt emissionstudies and the physics of GRB ultra-relativistic outflows. I attempt to briefly describethe main issues raised in the talks and posters presented during the conference.

Follow-up observations of large numbers of gamma-ray burst (GRB) afterglows, facilitatedby the Swift satellite, have produced a large sample of spectral energy distributions andlight curves, from which the basic micro- and macrophysical parameters of afterglows maybe derived. However, a number of phenomena have been observed that defy explanation bysimple versions of the standard fireball model, leading to a variety of new models.Polarimetry has shown great promise as a diagnosis of afterglow physics, probing themagnetic field properties of the afterglow and geometrical effects (e.g.jet breaks). Unfortunately, high quality polarimetry of a significant sample ofafterglows is difficult to acquire, requiring specialised instrumentation and observingmodes. In this talk I will review the recent successes in afterglow polarimetry, alsoshowing first results of new instruments and observing campaigns. I will particularlyfocus on jet breaks.

Optical observations of afterglows at very times are very useful towards understandingthe least known problem of GRB research field i.e. the transition fromprompt emission to early afterglows. The comparison of a subset of well-monitored GRBs andtheir early time properties at optical are compared with that seen at XRT and BATwavelengths. In most of the observed cases, the very early optical observations of GRBs donot trace the canonical decay nature seen at XRT wavelengths, suggesting different originsfor the observed early emissions in the two bands. In some of the early opticallight-curves, the decay followed by smooth rise features are consistent with the onset ofthe afterglow although such features are also expected if the emission is seen off-axisand/or the outflow is structured.

We examine 48 Swift/UVOT long Gamma-ray Burst light curves and find acorrelation between the logarithmic luminosity at 200 s and average decay rate determinedfrom 200 s onwards, with a Spearman rank coefficient of −0.58 at a significance of 99.998%(4.2σ). We determine thelog L200s − α > 200s correlation to beintrinsic and discuss two possible causes: there is a property of the central engine,outflow or external medium that effects the rate of energy release so that the brightafterglows release their energy more quickly and decay faster than the fainter afterglows;alternatively, the observers viewing angle may produce the correlation, with observers atlarge viewing angles observing fainter and slower decaying light curves.

We analyze a sample of Swift X-ray and optical GRB afterglows which werechosen so as to reduce selection effects against the weakest events. We tentativelyidentify important differences in GRBs that show a fast decay with respect to the averageGRB, in particular a tendency for the more energetic bursts to have a steeper afterglowdecline. An explanation to this finding could be bursts in a wind environment are onaverage more energetic than bursts occurring in a constant density medium.

We present the scientific analysis of the GRB afterglow data obtained by the GROND, aseven-channel imager with four optical and three near-infrared detectors. Its uniquecapability to observe in all bands simultaneously, together with rapid triggering, precisephotometry and high temporal resolution, give us the opportunity to study light curves andspectral energy distributions of GRB afterglows in unprecedented detail. This isdemonstrated using the observations of three GRB afterglows that are used to put strongconstrains on the standard GRB fireball scenario.

Starting from the Swift sample we defined a complete sub-sample of 58bright long Gamma Ray Bursts (GRB), 52 of them (90%) with a redshift determination, inorder to characterize their properties. This complete sample of bright long- GRBs allowedus to investigate their evolution with cosmic time and properties. We focused inparticular on the GRB luminosity function, on the spectral-energy correlations of theirprompt emission, on the nature of dark bursts and on possible correlations between theprompt and the X-ray afterglow properties.

We summarize the results of our programs started in 2009 with the 10.4 m Gran TelescopioCanarias (GTC) telescope. Since then its instruments have been subject of a continuousupgrade, making the GTC a competitive telescope for the GRB field. So far (Dec. 2012) theGTC have followed up 25 GRBs, measuring 10 redshifts, and discovering two SNe associatedto GRBs. The new generation of instruments foreseen for the coming years will contributesubstantially to enhance the knowledge of these puzzling explosions.

The results of investigation of 43 peaked R-band light curves of optical transients ofgamma-ray bursts with known redshifts are presented. The parameters of optical transientswere calculated in the comoving frame, and then a search for pair correlations betweenthem was conducted. As a result of the statistical analysis, a strong correlation betweenthe peak luminosity and redshift was found for pure afterglows and the events withresidual gamma activity, which can’t be explained as an effect of observational selection.It suggests the cosmological evolution of the parameters of the local interstellar mediumaround the sources of gamma-ray burst. In the models of forward and reverse shock waves, arelation between the density of interstellar medium and redshift was built for gamma-rayburst afterglows. It was shown that for GRB host galaxies the star formation rateincreases with redshift.

We analyze two X-shooter spectra of the GRB 120327A afterglow, acquired    2.1 and    30hrs after the trigger. The ISM in the GRB host galaxy at z = 2.8145 isextremely rich in absorption features, with three components contributing to the lineprofiles. The hydrogen column density associated with GRB 120327A islog NHI / cm2 = 22.01 ± 0.09,and the metallicity of the host galaxy is in the range [X/H] =  − 1.7 to  − 1 with respectto the solar values, i.e., a typical value for a GRB host galaxy. Inaddition to the ground state lines, we detect in the first observation several excitedabsorption features, which disappeared in the second observation. Using these features, wederive that component I is at dI = 200+100-60 pc from the GRB, while component II is located closer,at dII = 100+4030 pc. These values are among the lowest found in GRBs.Comparing the abundances with star formation history models, we find that the GRB 120327Ahost galaxy abundances are compatible with a star formation efficiency of 10Gyr-1, typical of spheroids (elliptical or bulge).

The Burst Observer and Optical Transient Exploring System (BOOTES), is a global roboticobservatory network, which started in 1998 with Spanish leadership devoted to studyoptical emissions from gamma ray bursts (GRBs) that occur in the Universe. We present shothistory and current status of BOOTES network. The Network philosophy, science and somedetails of 117 GRBs followed-up are discussed.

The cataclysmic variables are associated with high energy events and probably many ofthem could be potential gamma-ray sources. Up to now Fermi-LAT detected 3 gamma-raytransients, which belong to CVs and related objects: V407 Cyg, N Sco 2012 and N Mon 2012 =V959 Mon. We present the first multicolour observations of the slow classical nova V959Mon.