Some of the observed bursts of X-rays/Gamma-rays associated with supernovae (SNe) as well as very luminous SNe may result from the breakout of the SN shock from an optically thick wind surrounding the progenitor. We show that in such scenarios a collisionless shock necessarily forms during the shock breakout. An intense non-thermal flash of ≲1 MeV gamma rays, hard X-rays and multi-TeV neutrinos is produced simultaneously with and following the typical soft X-ray breakout emission, carrying similar or larger energy than the soft emission. The non-thermal flash is detectable by current X-ray telescopes and may be detectable out to 10's of Mpc by km-scale neutrino telescopes.

VT (Visible Telescope) is an instrument onboard SVOM (Space-based multi-band astronomical Variable Objects Monitor) satellite working in the visible band, which will play an important role in follow-up of two categories of GRBs: very distant events at higher redshift and faint/soft nearby events in SVOM mission. To fulfill these primary science requirements, decent sensitivity and wavelength coverage are fundamental for VT design. VT performance and data process strategy were successfully studied on its feasibility in Phase A, which is presented in this poster. Additionally, preliminary VT image simulator is also introduced here.

We investigate the lowest mass stars that produce Type-II supernovae, motivated by recent results showing that a large fraction of type-II supernova progenitors for which there are direct detections display unexpectedly low luminosity (for a review see e.g. Smartt 2009). There are three potential evolutionary channels leading to this fate. Alongside the standard ‘massive star’ Fe-core collapse scenario we investigate the likelihood of electron capture supernovae (EC-SNe) from super-AGB (S-AGB) stars in their thermal pulse phase, from failed massive stars for which neon burning and other advanced burning stages fail to prevent the star from contracting to the critical densities required to initiate rapid electron-capture reactions and thus the star's collapse. We find it indeed possible that both of these relatively exotic evolutionary channels may be realised but it is currently unclear for what proportion of stars. Ultimately, the supernova light curves, explosion energies, remnant properties (see e.g. Knigge et al. 2011) and ejecta composition are the quantities desired to establish the role that these stars at the lower edge of the massive star mass range play.

The first generations of stars are thought to have been more massive than Pop I stars and therefore some of these are thought to have produced pair creation supernovae (PCSNe) at the end of their life. However, the chemical signature of PCSNe is not observed in extremely metal poor stars (e.g. Umeda and Nomoto 2002) and it raises the following questions: Were stars born less (or more massive) than the mass range expected to lead to the PCSNe? Or was mass loss too strong during the evolution of these stars and prevented them from retaining enough mass to produce PCSNe? The discovery of very massive stars (VMS, M > 100 M⊙) in the Milky Way and LMC (Crowther et al. 2010) shows that VMS can form and exist. The observations of PCSN candidates (2006gy & 2007bi) also seems to indicate that such SNe may occur. Mass loss plays a crucial role in the life of VMS since the star will only die as a PCSN if the star retains a high mass throughout its life. In this paper, we shall describe the dependence of VMS evolution on metallicity and present stellar evolution models at various metallicities, including the effects of mass loss and rotation. Based on our models, we will give our predictions concerning the fate of these VMS, either a PCSN or SNIc (possibly GRBs in some cases) as a function of metallicity.

We investigate the evolution of very massive stars with Z = 0.2 Z⊙ to constrain the progenitor of the extremely luminous Type Ic SN 2007bi. In order to reproduce the 56Ni amount produced in SN 2007bi, the range of the stellar mass at the zero-age main-sequence is expected to be 515 - 575M⊙ for pair-instability supernova and 110 - 280M⊙ for core-collapse supernova. Uncertainty in the mass loss rate affects the mass range appropriate for the explosion of SN 2007bi. A core-collapse supernova of a WO star evolved from a 110 M⊙ star produces sufficient radioactive 56Ni to reproduce the light curve of SN 2007bi.

Gamma-ray bursts (GRBs) generate an afterglow with an emission peaking in the millimetre and submillimeter (mm/submm) range during the first hours to days, making the study in these wavelengths of great importance. Here we give an overview of the data that has been collected for GRB observations in this wavelengths until September 2011. The total sample includes 102 GRBs, of which 88 have afterglow observations, and the rest are only host galaxy searches. The 22 detections cover the redshift range between 0.168 and 8.2 and have peak luminosities that span 2.5 orders of magnitude. With the start of the operations at ALMA, the sensitivity with respect to previous facilities has already improved by over an order of magnitude. We estimate that, once completed, ALMA will be able to detect ~98 % of the afterglows.

This proceeding is based on the work published by de Ugarte Postigo et al. (2012).

Multiwavelength observations of gamma-ray burst afterglows are presented, in particular those in the optical and millimetre wavelengths. I will focus on the observations mostly carried out at Spanish ground-based observatories (mainly the 10.4m GTC) and at the Plateau de Bure Interferometer in the French Alps. The importance of global networks of robotic telescopes (like BOOTES, established worldwide) for early time observations in order to put constraints on the physical mechanisms of the GRB early time emission phase is also discussed. The overall observational efforts provide additional clues for a better understanding of the reverse and forward shock. Finally I will report on the Lomonosov/UFFO-p capabilities taking into account its launch in 2012.

We describe the results of our numerical simulations of the collapse of a massive stellar core to a BH, performed in the framework of full general relativity incorporating finite-temperature equation of state and neutrino cooling. We adopt a 100 M⊙ presupernova model calculated by Umeda & Nomoto (2008), which has a massive core with a high value of entropy per baryon. Changing the degree of rotation for the initial condition, we clarify the dependence of the outcome on this. When the rotation is rapid enough, the shock wave formed at the core bounce is deformed to be a torus-like shape. Then, the infalling matter is accumulated in the central region due to the oblique shock at the torus surface, hitting the hypermassive neutron star (HMNS) and dissipating the kinetic energy there. As a result, outflows can be launched. The HMNS eventually collapses to a BH and an accretion torus is formed around it. We also found that the evolution of the BH and torus depends strongly on the rotation initially given.

We report results for two epochs of spectropolarimetry on the luminous type IIn SN2010jl, taken at ≈36 and 85 days post-explosion with VLT FORS2-PMOS. The high signal-to-noise data demonstrate distinct evolution in the continuum and the broad lines point to a complex origin for the various emission components and to a potentially common polarization signal for the type IIn class even over 1-2 orders of magnitude in luminosity output.

We investigated influence of stellar oscillations on the electrodynamics of pulsars as well as magnetars magnetosphere. Besides finding noticeable modification of electromagnetic field and charge density in the polar cap vicinity of oscillating neutron stars we proposed qualitative hypotheses explaining phenomena of part time pulsars as well as sporadic radio emission from generally radio-quiet magnetars with the help of stellar oscillations.

We have performed three-dimensional (3D) hydrodynamical simulations of core-collapse supernovae (SNe) with multigroup neutrino transport to study non-axisymmetric effects in the context of neutrino heating explosion mechanism. By comparing one- (1D) and two dimensional (2D) results with those of 3D, we study how the increasing spatial multi-dimensionality affects the postbounce SN dynamics. The calculations were performed with an energy-dependent treatment of the neutrino transport that is solved by the isotropic diffusion source approximation scheme. In agreement with previous studies, our 1D model does not produce explosions for the 11.2 M⊙ star, while the neutrino-driven revival of the stalled bounce shock is obtained both in the 2D and 3D models. Our results show that convective matter motions below the gain radius become much more violent in 3D than 2D, making the neutrino luminosity larger for 3D. Enhanced by the large neutrino luminosity, the shock of the 3D model expands faster than that of the 2D. Our results show that the evolution of the shock is sensitive to the employed numerical resolutions. To draw a robust conclusion, 3D simulations with much higher numerical resolution and more advanced treatment of neutrino transport and gravity is needed.

Hard X-ray polarization is believed to be one of the most promising methods to investigate the physical processes just around the central engines by constraining the magnetic environment. For this purpose we are now developing a compact and highly sensitive hard X-ray polarimeter aboard a university class micro-satellite “TSUBAME”. We are now developing the flight model of the satellite aiming for the launch in late 2012 from Russia.

In the last few years, evidences for a long-lived and sustained engine in Gamma Ray Bursts (GRBs) have increased the attention to the so called millisecond-magnetar model, as a competitive alternative to the standard collapsar scenario. I will review here the key aspects of the millisecond magnetar model for Long Duration Gamma Ray Bursts (LGRBs). I will briefly describe what constraints present observations put on any engine model, both in terms of energetics, outflow properties, and the relation with the associated Supernova (SN). For each of these I will show how the millisecond magnetar model satisfies the requirements, what are the limits of the model, how can it be further tested, and what observations might be used to discriminate against it. I will also discuss numerical results that show the importance of the confinement by the progenitor star in explaining the formation of a collimated outflow, how a detailed model for the evolution of the central engine can be built, and show that a wide variety of explosive events can be explained by different magnetar parameters. I will conclude with a suggestion that magnetars might be at the origin of the Extended Emission (EE) observed in a significant fraction of Short GRBs.