Narrow Results

The evolution of compact stars is believed to be able to produce various violent phenomena in our universe. In this paper, we discuss the possibility that gamma-ray bursts (GRBs) might result from the phase transition of a neutron star to a quark star and calculate the energy released from the conversion. In our study, we utilize the relativistic mean field (RMF) theory to describe the hadronic phase of neutron stars, while an improved quasi-particle model is adopted to describe the quark phase of quark stars. With quark matter equation-of-state (EOS) more reliable than models used before, it is found that the energy released is of the order of 10${}^{52}$ erg, which confirms the validity of the phase transition model.

The Large High Altitude Air Shower Observatory (LHAASO) reported observation of photons with energies above 10TeV from gamma-ray burst GRB 221009A. A suggestion was proposed that this result may contradict our knowledge of special relativity (SR) and the standard model (SM), according to which photons of about 10TeV from such a distant object should be severely suppressed because of the absorption by extragalactic background light. As a result, a number of mechanisms have been proposed to solve this potential puzzle, including Lorentz invariance violation (LIV). In this work, we perform a detailed numerical calculation and show the feasibility to constrain LIV of photons from the LHAASO observation of GRB 221009A quantitatively.

We present a unified, quantitative synthesis of analytical and numerical calculations of the effects caused on an Earth-like planet by a Gamma-Ray Burst (GRB), considering atmospheric and biological implications. The main effects of the illumination by a GRB are classified in four distinct phenomena and analyzed separately, namely: direct γ radiation transmission, UV flash, ozone layer depletion and cosmic rays. The "effectiveness" of each of these effects is compared and lethal distances for significant biological damage are given for each one. We find that the first three effects have potential to cause global environmental changes and biospheric damages, even if the source is located at a great distance (perhaps 100 kpc). In contrast, cosmic rays would only be a serious threat for very close sources.

This paper presents a gamma-ray down-going induced muon analysis combining the Gamma-ray bursts Coordinates Network (which announces a possible GRB event) with a blind strategy. The goal of this analysis is to find an astrophysical source through the ability of distinguishing between a real alert (signal) and a fake one (background), through comparisons between the position of an Antares event and the position of the alert, leading us to a better understanding of gamma-ray bursts.

Gamma-ray Bursts (GRBs) are one of the most promising tools in the study of cosmology. The luminosity, energy, light curve parameters and spectral measures could yield to the calibration of standard candles in the Universe. Nevertheless, cosmological and non-cosmological effects are not well understood. Aiming to clarify the possible effects, we started to study the autocorrelation function (ACF) of a sample of GRBs with known redshift in the combined band of Swift (15–150 keV) and Suzaku (50 keV–5 Mev) satellites. We first confirmed the bimodal distribution of the cosmological corrected ACF reported by Borgonovo et al., then looking at the energy evolution we found a bimodal distribution of the decay index of the ACF. For the next step we explored the intrinsic effects of the pulses within GRBs, determining the ACF of individual pulses at two different energy bands, as well as the skewness of the pulse. We found two kinds of internal effects, the increase of the asymmetry of the pulse with energy and the variability-dependence on energy. Two types of pulses are distinguished, suggesting more than one physical process during the prompt emission.

This contribution is a brief report on the IceCube kilometer cubed neutrino telescope located at the geographical South Pole. IceCube construction is on schedule to be completed in 2011. The full detector will consist of 86 strings, each with 60 digital optical modules. At the time of writing 59 strings of IceCube are taking data. Based on the data taken to date, the telescope meets its design goals. Selected results of ongoing analysis of IceCube detector data are presented.

The ARGO-YBJ experiment is an Extensive Air Shower (EAS) array which combines high altitude location and full coverage active area in order to reach low energy threshold at a level of few hundred of GeV. The large field of view (≈ 2 sr) and the high duty cycle (≥ 90%) allow the continuous monitoring of the sky searching for unknown sources and unpredictable events, such as flares in blazar emissions and high energy Gamma-Ray Bursts (GRBs). In this paper I will briefly report on the detector performance and on some preliminary results achieved in γ-ray astronomy.

With the first detection of gravitational waves expected in the next decade, increasing efforts are made toward the electromagnetic follow-up observations of gravitational wave events. In this paper, I discuss the prospect of real-time detection and source localization for gravitational waves from neutron star–neutron star binary or neutron star–black hole binary coalescences before their merger. I show that several low-latency search pipelines are already under intensive development with the aim to provide real-time detections of these events. There will also be fast responding and/or wide-field electromagnetic telescopes available to help catch the electromagnetic or particle flashes possibly occurring during or immediately after their merger. It has been shown that a few coalescence events per year can be detected by advanced LIGO-VIRGO detector network tens of seconds before their merger. However, most of these events will have poor sky direction localization for the existing gravitational-wave detector network, making it extremely challenging for follow up observations by astronomical telescopes aiming at catching events around the merger time. A larger detector network including the planned detectors in Japan and in India will play an important role in improving the angular resolution and making prompt follow up observations much more realistic. A new detector at the Southern Hemisphere AIGO will further contribute significantly to this aspect.

High energy transients make up a diverse and exotic class of objects, from terrestrial lightning to $\gamma$-ray bursts at cosmological distances. In this review, we provide a detailed look at some of the more exciting transients observed over the last few years by Swift and other high energy missions.

The number of gamma-ray bursts (GRBs) detected at high energies ($\sim 0.1-100$GeV) has seen a rapid increase over the last decade, thanks to observations from the Fermi-Large Area Telescope. The improved statistics and quality of data resulted in a better characterization of the high-energy emission properties and in stronger constraints on theoretical models. In spite of the many achievements and progresses, several observational properties still represent a challenge for theoretical models, revealing how our understanding is far from being complete. This paper reviews the main spectral and temporal properties of $\sim 0.1-100$GeV emission from GRBs and summarizes the most promising theoretical models proposed to interpret the observations. Since a boost for the understanding of GeV radiation might come from observations at even higher energies, the present status and future prospects for observations at very-high energies (above $\sim$100GeV) are also discussed. The improved sensitivity of upcoming facilities, coupled to theoretical predictions, supports the concrete possibility for future ground GRB detections in the high/very-high energy domain.

Neutron star mergers have been long considered as promising sites of heavy $r$-process nucleosynthesis. We overview the observational evidence supporting this scenario including: the total amount of $r$-process elements in the galaxy, extreme metal-poor stars, geological radioactive elemental abundances, dwarf galaxies and short gamma-ray bursts (sGRBs). Recently, the advanced LIGO and Virgo observatories discovered a gravitational-wave signal of a neutron star merger, GW170817, as well as accompanying multi-wavelength electromagnetic (EM) counterparts. The ultra-violet, optical and near infrared (n/R) observations point to $r$-process elements that have been synthesized in the merger ejecta. The rate and ejected mass inferred from GW170817 and the EM counterparts are consistent with other observations. We however, find that, within the simple one zone chemical evolution models (based on merger rates with reasonable delay time distributions as expected from evolutionary models, or from observations of sGRBs), it is difficult to reconcile the current observations of the Eu abundance history of galactic stars for [Fe/H] $\gtrsim -1$. This implies that to account for the role of mergers in the galactic chemical evolution, we need a galactic model with multiple populations that have different spatial distributions and/or varying formation rates.

Binary-driven hypernova (BdHN) models long gamma-ray burst (GRB) as occurring in the binary systems involving a carbon–oxygen core (CO${}_{\mathrm{\text{core}}}$) and a companion neutron star (NS) or a black hole (BH). This model, first proposed in 2012, succeeds and improves upon the fireshell model and the induced gravitational collapse (IGC) paradigm. After nearly a decade of development, the BdHN model has reached a nearly complete structure, giving explanation to all the observables of long bursts into its theoretical framework, and has given a refined classification of long GRB according to the original properties of the progenitors. In this paper, we present a summary of the BdHN model and the physical processes at work in each of the envisaged Episodes during its occurrence and lifetime, duly contextualized in the framework of GRB observations.

We discuss the implications of Fermi/LAT observations on several aspects of gamma-ray burst (GRB) physics, including the radiation process, the emission sites, the bulk Lorentz factor, and the pre-shock magnetic field: (1) MeV-range emission favors synchrotron process but the highest energy (> 10 GeV) emission may not be synchrotron origin, more likely inverse Compton origin; (2) GRB should have multi-zone emission region, with MeV emission produced at smaller radii while optical and > 100 MeV emission at larger radii; (3) the bulk Lorentz factor can be a few 100's, much lower than 10³, in multi-zone model; (4) the upstream magnetic field of afterglow shock is strongly amplified to be at least in mG scale.

In this paper we give a brief review of our recent studies on the long and short gamma-ray bursts (GRBs) detected Swift, in an effort to understand the puzzle of classifying GRBs. We consider that it is still an appealing conjecture that both long and short GRBs are drawn from the same parent sample by observational biases.

The radiation of relativistic electrons in random and small-scale magnetic field is called jitter radiation. We apply jitter process to study the polarization feature of GRB prompt emission. A two-dimensional compressed slab which contains stochastic magnetic field is applied in our model. If jitter condition is satisfied, the high degree polarization can be achieved when the angle between line-of-sight and slab plane is small. Moreover, micro-emitters with mini-jet structure and jet off-axis effect are considered.

COLIBRÍ will be a Franco-Mexican 1.3-m telescope and imager for observing the visible and near infrared counterparts of transient events detected by the future SVOM mission. The imager is divided into two instruments: DDRAGO, with two 4k$\times$4k CCDs observing in $gri$ and $zy$, respectively, and CAGIRE, with one 2k$\times$2k LYNRED or H2RG detector observing in $JH$. DDRAGO will directly image the telescope focal plane with a field of view (FoV) of 26$\times$26 arcmin. CAGIRE will reimage the focal plane to make a pupil image available for a cold stop and adjust the plate scale to deliver a similar FoV. CAGIRE will not use a conventional collimator-camera configuration but rather an arrangement of lenses that sends the pupil image close to the focal plane after all of the reimaging optics. This allows most of the optics, including the infrared filters, to be at ambient temperature and avoids the complexity of having mechanisms and powered optics within the cryostat (CR). We present here the optical design of the system and a thorough analysis on the expected image quality of the instruments and the telescope.

The mechanism of the gamma-ray burst is uncertain while the current candidates, respectively, for short and long GRBs are rather accepted. They conflict with some observed facts. Here we examine in detail the process for an energy circulation to separate to two ones by the energy circulation theory. We derive the equations of the force and the potential energy for the separation of a galactic seed. A galactic seed divides to two seeds orthogonally. If the receding speed is high enough, two seeds separate away orthogonally. If not enough, they are trapped at the energy trough, from where a subsequent flat separation occurs. The difference in the potential energy is partly emitted as gamma-ray radiations. The proposed process nicely meets the observed features of the GRBs, which the standard cosmology cannot explain. The GRBs are an important evidence to support our proposed model of galactic evolution, which includes galactic seed separations, as well as its basis; the energy circulation theory. Another key evidence, which we reported previously, is that the model predicts a constant speed of a galaxy rotation at any radial distances without dark matter.

Binary driven hypernova (BdHN) models long gamma-ray burst (GRBs) as occurring in the binary systems involving a carbon-oxygen core (CO_core) and a companion neutron star (NS) or a black hole (BH). This model, first proposed in 2012, succeeds and improves upon the fireshell model and the induced gravitational collapse (IGC) paradigm. After nearly a decade of development, the BdHN model has reached a nearly complete structure, giving explanation to all the observables of long bursts into its theoretical framework, and has given a refined classification of long GRBs according to the original properties of the progenitors. In this article, we present a summary of the BdHN model and the physical processes at work in each of the envisaged Episodes during its occurrence and lifetime, duly contextualized in the framework of GRB observations.

In this work we consider the effects of vertical self-gravity on a magnetized neutrino-dominated accretion disk, which is supposed to be a candidate for central engine of gamma-ray bursts (GRBs). We study some of the physical timescales that are considered to play a crucial role in the disk’s late-time activity, such as viscous, cooling, and diffusion timescales. We are also interested to probe the emission of X-ray flares’ probability, observed in GRBs’ extended emission by an investigation on the “magnetic barrier” and “fragmentation”. Our results approve the self-gravity as an amplifier for Blandford–Payne luminosity (BP power) and the magnetic field produced through the accretion process, but a suppressor for neutrino luminosity and magnetic barrier. The latter takes place as a result of the fragmentation enhancement in the outer disk, which is more likely to happen for the higher mass accretion rates.

The detailed continuous fast optical photometry analysis obtained by MASTER Global Network for the GRB160625B optical counterpart MASTER OT J203423.51+065508.0 is presented. There are also hard X-ray and gamma-ray emission obtained by the Lomonosov and Konus-Wind spacecrafts detectors. We detected quasiperiodic emission components in the intrinsic optical emission of GRB160625B and propose a three-stage collapse scenario for this long and bright GRB. We associate quasiperiodic fluctuations with forced precession of a Spinar, i.e. self-gravitating rapidly rotating super dense body, whose evolution is determined by a powerful magnetic field. The spinar’s mass lead it to collapse into a black hole at the end of an evolution.