We present details of the ISON network for GRB follow-up and complete list of observations in 2010–2012.

We present an overview of top internet technologies that can be used to build webtools and rich internet applications for astronomy. The aim is to simplify the data handling, reduction and access, in particular of optical/infrared images collected by traditional, automatic or robotic telescopes. These tools are particularly suitable for real-time management of GRB afterglow observations. Using these technologies we are developing a web-based images database management system. We present available features and discuss further improvements to the mentioned system.

GRB 110715A had a bright afterglow that was obscured in the optical by a high Galactic extinction. We discovered the submillimeter counterpart with APEX and followed it in radio with ATCA for over 2 months. Additional submm observations were performed with ALMA as a test of the ToO procedures during commissioning, becoming the first GRB afterglow to be detected by the observatory. UV, optical and NIR observations were performed with Swift/UVOT and 2.2 m/GROND in La Silla and X-ray data were obtained by Swift/XRT. The dataset is complemented with spectroscopic data from the VLT/X-shooter spectrograph. The absorption features present in the intermediate resolution optical/nIR spectra reveal a redshift of 0.8224 and a host galaxy environment with low ionization. We fit in the host galaxy absorption features two velocity components separated by 30 km/s, implying a host galaxy with low dynamical activity.

We show the power of the method of the color indices that uses the commonly availablemultiband photometry of optical afterglows (OAs) of long GRBs detected bySwift. Our study shows that for most OAs, in the observer frame, thesecolors, corrected for the Galactic reddening, display prominent clustering in thecolor-color diagrams. The color indices enable us to distinguish OAs from other types ofobjects even without available gamma-ray emission. The color-color diagrams can be used toassess the extinction inside the host galaxy. Our approach is also generally important forinvestigating the numerous faint OAs for which obtaining spectra with good S/N ratio isoften impossible.

We present multi-wavelength observations of the dark GRB 051008. The burst was notdetected in the optical bands, however we discover the host galaxy and secured theredshift of the host with following campaign of multicolor observations of Shajn, NOT,Gemini North and Keck telescopes. We provide arguments that the galaxy could be in acomplex of gravitationally bound galaxies. Our investigation of the GRB 051008 alsoconfirms a tendency of host galaxies of dark bursts to be more dusty.

Since 1997, and following our detection of the first mm afterglow, we have followed-up 70GRBs, mainly with the IRAMś Plateau de Bure Interferometer, what can be considered as theIRAM Legacy GRB Sample. 66 events were observed at 3 mm, with 19 of them being detected(with another 3 having marginal detections). 32 GRBs were followed up at 1 mm, with 6 ofthem being detected. Redshifts for the GRB afterglows lie in the range z = 0.03–8.3, withmeasured flux densities (at 3 mm) varying between 0.25 and 60 mJy (but usually <1.5mJy) with first observations taking place around 1–2 days after the GRB. Forward shockemission expleains the observations with the exception of one particular case (GRB 090423at z = 8.2) for which reverse shock emission is required.

Recent observations of broad-band afterglow of gamma-ray bursts (GRBs) suggest that thestandard external shock model cannot account for all the data. The observed “afterglow” ofsome GRBs includes the contributions from at least three emission components.Theoretically, there are naturally three emission sites. Besides the traditional externalforward shock, the existence of X-ray flares demands late central engine activities of theGRB central engine, so that an “internal dissipation” region of the late wind is anotheremission site. After dissipation, this late wind would inevitably catch up with theblastwave, giving rise to a third emission site at a long-lasting reverse shock. Somerecent efforts in understanding the broadband afterglow are reviewed.

Collisionless shocks are a key ingredient of the Fireball scenario. Yet, their formationfrom the encounter of two collisionless plasma shells is not understood from firstprinciples. When the shells interpenetrate, the overlapping region turns unstable,triggering the shock formation. As a first step towards a microscopic understanding of theprocess, we analyze here in details the initial instability phase. On the one hand, 2Drelativistic PIC simulations are performed where two symmetric initially cold pair plasmascollide. On the other hand, the instabilities at work are analyzed, as well as the fieldat saturation and the seed field which gets amplified. For mildly relativistic motions andonward, Weibel modes with ω = 0+iδ govern the linearphase. We derive an expression for the duration of the linear phase in reasonableagreement with the simulations.

Few GRBs clearly present distinct High-Energy (HE) component that evolve independent ofthe usual Band function that describes the prompt keV-emission. This component can be longor short lasting compared to the burst duration. However, most of models only explain thelong duration HE component. We have developed a leptonic model on the external shockframework to describe the HE components. We propose that the short HE component that fallsin the MeV regime in coincidence with the prompt phase and, the second long lastingGeV-emission could be understood as synchrotron self-Compton (SSC) emission from thereverse and forward shock respectively. This model requires a magnetized jet and a reverseshock in the thick shell case. This model already has been proven in GRB 980923 and GRB090926A, the former with a short duration MeV-component and the latter with both long GeV-and short MeV- HE components. All fluxes, energies and durations are consistent with theobserved values. Here, we apply this model to GRB 940217 that presented similarities withGRB 090926A and GRB 980923.

The number of detections as well as significantly deep non-detections of optical/NIRafterglows of Type I (compact-object-merger population) Gamma-Ray Bursts (GRBs) has becomelarge enough that statistically meaningful samples can now be constructed. I presentwithin some recent results on the luminosity distribution of Type I GRB afterglows incomparison to those of Type II GRBs (collapsar population), the issue of the existence ofjet breaks in Type I GRB afterglows, and the discovery of dark Type IGRBs.

Assuming that the extended emission (EE) with broad dynamic range is a common property ofshort duration bursts, we propose a two-jet model which can describe both short mainepisode of hard spectra emission, specific for short bursts, and softer spectra EE by thedifferent off axis position of the observer. The model involves a short-duration jet,which is powered by heating due to νν̅ annihilation, and a long-lived Blandford–Znajek (BZ)jet with a significantly narrow opening angle. We also discuss observational tests oftwo-jet model.

We report on follow-up observations of 20 short-duration gamma-ray bursts(T90 < 2s) performed ing′r′i′z′JHKswith the Gamma-Ray Burst Optical Near-Infrared Detector (GROND) between mid-2007 and theend of 2010. This is the most homogeneous and comprehensive data set on GRB afterglowobservations of short bursts. In three cases, GROND was on target within less than 10 minafter the trigger, leading to the discovery of the afterglow of GRB 081226A and its faintunderlying host galaxy. In addition, GROND was able to image the optical afterglow andfollow the light curve evolution in five further cases: GRBs 090305, 090426, 090510,090927, and 100117A. Three of the aforementioned six bursts with optical light curves showa break: GRBs 090426 and 090510 as well as GRB 090305. For GRB 090927, no break is seen inthe optical/X-ray light curve until about 150 ks/600 ks after the burst. A decay slope ofthe optical afterglow of GRB 100117A could be measured. Using these data supplemented byabout ten events taken from the literature, we compare the jet half-opening angles of longand short bursts. We find a tentative evidence that short bursts have wider opening anglesthan long bursts. However, the statistics are still very poor and follow-up observationsof these events are therefore very important to gain as much observational data aspossible.

In this contribution we briefly introduce a mechanism for short gamma ray burst emissiondifferent from the usually assumed compact objects binary merger progenitor model. It isbased on the energy release in the central regions of neutron stars. This energy injectionmay be due to internal self-annihilation of dark matter gravitationally accreted from thegalactic halo. We explain how this effect may trigger its full or partial conversion intoa quark star and, in such a case, induce a gamma ray burst with isotropic equivalentenergies in agreement with those measured experimentally. Additionally, we show how theejection of the outer crust in such events may be accelerated enough to produce Lorentzfactors over those required for gamma ray emission.

There has been growing consensus that short and long GRBs are associated with twodifferent populations of astrophysical sources: mergers and SN explosions, respectively.While temporal properties of short and long GRBs could be considered with similar depthand accuracy, patterns of spectral variability of the 2 classes of GRBs are much harder tocompare. This is due to the fact, that short GRBs exhibit variability on time scalesshorter than 1 ms and count rate, measured at such short time scales, is not sufficientfor reliable spectroscopy even for the brightest events.

In this situation, any new possibility to look at spectral evolution of short GRBs onsub-millisecond time scales in terms of spectral parameters, may provide more solidbackground for theoretical analysis. In this paper we present analysis of spectralevolution of short GRBs in terms of Band spectral function parameters, using the earlierdeveloped Global Fit approach (GFA).

We investigate the vertical structure and element distribution of neutrino-dominatedaccretion flows around black holes in spherical coordinates with reasonable nuclearstatistical equilibrium. According to our calculations, heavy nuclei tend to be producedin a thin region near the disk surface. In this thin region, we find that 56Niis dominant in the flow with low accretion rate (e.g.,0.05M⊙s-1). The solutions indicate that56Ni comes from the central engine, whose decay may drive the bumps in thelight curve of core-collapse supernova.

We present the results from an optical monitoring campaign aimed at studying theafterglow properties of the short GRB 100816A. We implemented a new way of processing theSwift-BAT data, and based on it we reclassified this burst as short,discarding the initial classification as long. Observations were carried out mainly withthe GTC Telescope within the four following days after the burst to investigate theoptical photometry of its afterglow, and a year later to localize the host. We completedthe optical imaging with the 1.23 m and 3.5 m CAHA Telescopes. We built and fitted thenIR-optical SED for the characterization of the host. The best fit of the SED(χ2/d.o.f. = 1.656) obtained for assumed values of a solarmetallicity, and an extinction of AV = 0.2mag is obtained fora starburst galaxy with a dominant stellar population aging about 360 Myr.

A significant number of long Gamma-ray Bursts (GRBs) detected by the SwiftSatellite have a plateau phase signifying ongoing energy injection. Using BAT andXRT observations, we find that many short GRBs show similar behavior which challenges thetypical short GRB progenitor model. We suggest the remnant of neutron star - neutron starmergers may not collapse immediately to a black hole (or even collapse at all) forminginstead a magnetar. This model predicts that there would be a plateau phase in the X-raylightcurve followed by a shallow decay phase, if it is a stable magnetar, or a steep decayif the magnetar collapses to a black hole within a few hundred seconds. By fitting thismodel to all short GRB BAT-XRT lightcurves, we show that a magnetar could power theobserved energy injection. This model can be tested using the next generationgravitational wave observatories.

GRB’s environment can be studied through the imprint (i.e. absorption)it leaves on the afterglow emission. Fast optical observations allowed us to observe linevariability and to derive the distance and composition of the absorbing medium. However,given the huge GRB ionizing flux, this medium starts showing up in the optical spectraonly at relatively large distances (100 pc). A complementary view comes from the X-rayband, where the overall contribution of all metals bends the power law X-ray afterglowspectrum. We will review and compare optical and X-ray studies of the circumbustmedium.

We propose an alternative explanation for the post-breakout emission of SN 2008D thatcannot be reproduced by the explosion of a normal Wolf-Rayet star. We explored severalphysical scenarios and proposed that the early emission was enhanced by the presence of56Ni in the outermost layers of the ejecta in addition to the usual internaldistribution. This kind of double-peaked 56Ni distribution could be explainedby the formation of jets during the explosion.

Long duration Gamma Ray Bursts (LGRB) are thought to originate from massive rotatingstars and the interaction of their expanding jet will be affected by the structure oftheir circumburst medium. In this work we use rotating stellar models of massive stars todetermine the state of circumbust material in various types of progenitor scenarios and wedescribe how this external matter can appear in GRB observations.