Search for strong gravitational lensing effect in the current GRB data of BATSE

Because gamma-ray bursts(GRBs)trace the high-z universe,there is an appreciable probability for a GRB to be gravitational lensed by galaxies in the universe.Herein we consider the gravitational lensing effect of GRBs contributed by the dark matter halos in galaxies.Assuming that all halos have the singular isothermal sphere(SIS)mass profile in the mass range 1010h?1M?M2×1013h?1M?and all GRB samples follow the intrinsic redshift distribution and luminosity function derived from the Swift LGRBs sample,we calculated the gravitational lensing probability in BATSE,Swift/BAT and Fermi/GBM GRBs,respectively.With an derived probability result in BATSE GRBs,we searched for lensed GRB pairs in the BATSE5B GRB Spectral catalog.The search did not find any convincing gravitationally lensed events.We discuss our result and future observations for GRB lensing observation.     

Characteristics of the GAMMA-400 gamma-ray telescope for searching for dark matter signatures

The GAMMA-400 gamma-ray telescope currently under development is designed to measure fluxes of gamma rays and electron-positron cosmic-ray components, which could be associated with the annihilation or decay of dark matter particles, and to survey in detail the celestial sphere in order to search for and investigate discrete gamma-ray sources; to measure the energy spectra of Galactic and extragalactic dif- fuse gamma-ray emissions; and to study gamma-ray bursts and the gamma-ray emissions of active Sun. The GAMMA-400 energy range is 100 MeV to 3000 GeV. The gamma-ray telescope has an angular resolution of ～0.01°, an energy resolution of ～1%, and a proton rejection factor of ～10⁶. The GAMMA-400 will be installed on Russia’s Navigator space platform. Observations are planned to commence in 2018.     

SVOM gamma ray monitor

The space-based multi-band astronomical Variable Object Monitor (SVOM) mission is dedicated to the detection, localization and broad-band study of gamma-ray bursts (GRBs) and other high-energy transient phenomena. The gamma ray monitor (GRM) onboard is designed to observe GRBs up to 5 MeV. With this instrument, one of the key GRB parameters, E _peak, can be easily measured in the hard X-ray band. It can achieve a detection rate of 100 GRBs per year which ensures the scientific output of SVOM.     

X-ray flares of γ-ray bursts: Quakes of solid quark stars?

A star-quake model is proposed to understand X-ray flares of both long and short γ-ray bursts (GRBs) in a solid quark star regime. Two kinds of central engines for GRBs are available if pulsar-like stars are actually (solid) quark stars, i.e., the SNE-type GRBs and the SGR-type GRBs. It is found that a quark star could be solidified about 10³ to 10⁶ s later after its birth if the critical temperature of phase transition is a few Metga-electron-volts, and then a new source of free energy (i.e., elastic and gravitational ones, rather than rotational or magnetic energy) could be possible to power GRB X-ray flares. Supported by the National Natural Science Foundation of China (Grant Nos. 10573002, 10778611, and 10873002), the National Basic Research Program of China (Grant No. 2009CB824800), the Research Foundation of Guangxi University (Grant No. M30520), and the LCWR (Grant No. LHXZ200602)     

On the oscillations of the plasma atmosphere in gamma-ray bursts

One of the possible hypotheses implies that cosmic gamma-ray bursts can arise when two neutron stars or black holes merge together. These bursts sometimes continue for several tens of seconds, but the time dependence of their intensity often exhibits ～10²–10³ almost periodic small peaks with a period of ～10 ms. A model of oscillations in the lower plasma shell, which arises in cosmic gamma-ray bursts and is located near a neutron star, is proposed; the greater part of arising plasma in the form of an “upper” shell continues to expand into the surroundings. Other possible interpretations of periodicity of the “small peaks” are also analyzed.     

Constraining Lorentz invariance violation from the continuous spectra of short gamma-ray bursts

In some quantum gravity theories, a foamy structure of space-time may lead to Lorentz invariance violation(LIV). As the most energetic explosions in the Universe, gamma-ray bursts(GRBs) provide an effect way to probe quantum gravity effects. In this paper, we use the continuous spectra of 20 short GRBs detected by the Swift satellite to give a conservative lower limit of quantum gravity energy scale MQG. Due to the LIV effect, photons with different energy have different velocities. This will lead to the delayed arrival of high energy photons relative to low energy ones. Based on the fact that the LIV-induced time delay cannot be longer than the duration of a GRB,we present the most conservative estimate of the quantum gravity energy scales from 20 short GRBs. The strictest constraint, M_(QG) 5.05 × 10~(14) GeV in the linearly corrected case, is from GRB 140622 A. Our constraint on MQG,although not as tight as previous results, is the safest and most reliable so far.     

Very high-frequency gravitational waves from magnetars and gamma-ray bursts

Extremely powerful astrophysical electromagnetic(EM) systems could be possible sources of highfrequency gravitational waves(HFGWs). Here, based on properties of magnetars and gamma-ray bursts(GRBs), we address "Gamma-HFGWs"(with very high-frequency around 10~(20) Hz) caused by ultra-strong EM radiation(in the radiation-dominated phase of GRB fireballs) interacting with super-high magnetar surface magnetic fields(～10~(11) T).By certain parameters of distance and power, the Gamma-HFGWs would have far field energy density ?gw around10~(-6), and they would cause perturbed signal EM waves of～10~(-20) W/m~2 in a proposed HFGW detection system based on the EM response to GWs. Specially, Gamma-HFGWs would possess distinctive envelopes with characteristic shapes depending on the particular structures of surface magnetic fields of magnetars, which could be exclusive features helpful to distinguish them from background noise. Results obtained suggest that magnetars could be involved in possible astrophysical EM sources of GWs in the very high-frequency band, and Gamma-HFGWs could be potential targets for observations in the future.     

Gamma-ray bursts in the Swift-Fermi era: Confronting data with theory

With the prompt slewing capability of the X-ray and UV-optical telescopes onboard the Swift mission and with the gamma-ray large area telescope onboard the Fermi mission, gamma-ray bursts (GRBs) are now accessible in a full time window and in all electromagnetic wavelengths for the events. Many observational breakthroughs have been made in recent years. I present here a brief review of some observational breakthroughs with the two missions, focusing on how these breakthroughs have revolutionized our understanding of the nature of this phenomenon and puzzles as well as challenges of confronting the conventional models with data.     

GRB 090423: Marking the death of a massive star at z=8.2

GRB 090423 is the new high-z record holder of Gamma-ray bursts (GRBs) with z～ 8.2. We present a detailed analysis of both the spectral and temporal features of GRB 090423 observed with Swift/BAT and Fermi/GBM. We find that the T ₉₀ observed with BAT in the 15–150 keV band is 13.2 s, corresponding to ～ 1.4 s at z=8.2. It once again gives rise to the issue of whether the progenitors of high-z GRBs are massive stars or mergers since the discovery of GRB 080913 at z=6.7. In comparison with the T ₉₀ distribution in the burst frame of the current redshift-known GRB sample, we find that it is marginally grouped into the long group (Type II GRBs). The spectrum observed with both BAT and GBM is well fitted by a power-law with exponential cutoff, which yields an E _p=(50.4±7.0) keV. The event satisfies the Amati-relation well for Type II GRBs within their 3σ uncertainty range. Our results indicate that this event would be produced by the death of a massive star. Based on the Amati-relation, we derive its distance modulus, which follows the Hubble diagram of the concordance cosmology model at a redshift of ～8.2.     

Properties of intermediate GRBs subset,according to the GBM,BAT, and BATSE data

The duration of gamma ray bursts (GRBs) is usually characterized by time interval t ₉₀, in which the total number of registered counts grows from 5 to 95%. Classes of short and long GRBs were first detected in analyzing the BATSE experiment data from the Compton Gamma Ray Observatory (CGRO); burst duration separation point was found to be t _90lim ~2 s. A group of bursts of intermediate duration was first detected in analyzing the data of the same experiment in 1999 in the interval of ~1 to ~40 s with an average event duration of 〈t ₉₀〉 ~ 3.5 s. The results from analyzing the catalog of gamma-ray burst data selected while ground processing BATSE data (i.e., the catalog of nontriggered events) showed that the intensity of intermediate bursts is lower than that of short and long bursts. Preliminary results from investigating the GBM catalog (onboard the Fermi Space Observatory) and the BAT catalog (onboard the Swift satellite) confirm the detection of events with similar properties.     

Gamma-ray direct observations from space

Summary This paper is devoted to problems of gamma-ray astronomy in the energy range <10¹¹ eV. Measurements of spectra and fluxes in this energy range are carried out by means of direct observations from space. Most of the discussed results have been performed with the four telescopes of the Compton Gamma-Ray Observatory. The main topics of the paper are: diffuse galactic gamma-ray emission, point-like galactic gamma-ray sources, gamma-ray line emission, gamma-ray bursts and active galactic nuclei. Rapporteur talk given at the XXIV International Cosmic-Ray Conference, Rome, August 28–September, 8, 1995.     

Casimir Energy in Astrophysics: Gamma-Ray Bursts from QED Vacuum Transitions

Motivated by analogous applications to sonoluminescence, neutron stars mergers are examined in the context of Schwinger's dynamical Casimir effect. When the dielectric properties of the QED vacuum are altered through the introduction of dense matter, energy shifts in the zero-point fluctuations can appear as photon bursts at gamma-ray frequencies. The amount of radiation depends upon the properties and amount of matter in motion and the suddenness of the transition. It is shown that the dynamical Casimir effect can convert sufficient energy of neutron star mergers into gamma rays. Using information extracted from simulations of matter flow in neutron star mergers by Ruffert and Janka, we estimate that the total Casimir energy released can exceed 10 ⁵³ ergs in gamma-ray frequencies. The Casimir energy approach is capable of explaining the most energetic gamma-ray bursts.     

Microquasars

Microquasars are compact objects (stellar-mass black holes and neutron stars) in our Galaxy that mimic, on a smaller scale, many of the phenomena seen in quasars. Their discovery provided new insights into the physics of relativistic jets observed elsewhere in the universe, and the accretion–jet coupling. Furthermore, microquasars are opening new horizons for the understanding of ultraluminous X-ray sources observed in external galaxies, gamma-ray bursts of long duration, and the origin of stellar black holes and neutron stars. Microquasars are one of the best laboratories to probe General Relativity in the limit of the strongest gravitational fields, and, as such, have become an area of topical interest for both high energy physics and astrophysics. To cite this article: I.F. Mirabel, C. R. Physique 8 (2007).     

Gamma-ray bursts and the fireball model

Gamma-ray bursts (GRBs) have puzzled astronomers since their accidental discovery in the late 1960s. The BATSE detector on the COMPTON-GRO satellite has been detecting one burst per day for the last six years. Its findings have revolutionized our ideas about the nature of these objects. They have shown that GRBs are at cosmological distances. This idea was accepted with difficulties at first. The recent discovery of an X-ray afterglow by the Italian/Dutch satellite BeppoSAX has led to a detection of high red-shift absorption lines in the optical afterglow of GRB970508 and in several other bursts and to the identification of host galaxies to others. This has confirmed the cosmological origin. Cosmological GRBs release ∼10⁵¹–10⁵³ erg in a few seconds making them the most (electromagnetically) luminous objects in the Universe. The simplest, most conventional, and practically inevitable, interpretation of these observations is that GRBs result from the conversion of the kinetic energy of ultra-relativistic particles or possibly the electromagnetic energy of a Poynting flux to radiation in an optically thin region. This generic “fireball” model has also been confirmed by the afterglow observations. The “inner engine” that accelerates the relativistic flow is hidden from direct observations. Consequently, it is difficult to infer its structure directly from current observations. Recent studies show, however, that this “inner engine” is responsible for the complicated temporal structure observed in GRBs. This temporal structure and energy considerations indicates that the “inner engine” is associated with the formation of a compact object – most likely a black hole.     

Scientific tasks and present status of the GAMMA-400 project

The GAMMA-400 telescope is designed to investigate discrete high-energy gamma-ray sources in the energy range of 0.1–3000 GeV, to measure the energy spectra of galactic and extragalactic diffuse gammaray emissions, and to study gamma-ray bursts and gamma-ray emissions from an active Sun. The gamma-ray telescope has an angular resolution of ～0.01°, an energy resolution of ～1%, and a proton rejection factor of ～10⁶. Its special assignment is to measure fluxes of gamma rays, electrons, and positrons that could be associated with the annihilation or decay of dark matter particles.     

用羊八井ASγ实验数据寻找TeV能区的γ射线暴

γ射线暴的TeV能区辐射对研究其起源、辐射机制等是非常重要的.利用西藏羊八井ASγ实验三期阵列的重建数据,通过在给定的小天区和时间间隔内寻找较高显著性事例团的方法对TeV能区的γ射线暴进行了寻找,在计算过程中采用“等天顶角法”来估计背景.工作中采用了两种途径来寻找γ射线暴,一种是与卫星γ射线暴的符合寻找,另一种是全天区独立寻找.结果发现少量事例团对背景有明显超出,考虑试验次数后,其超出还不足以认定为γ射线暴.通过Monte Carlo模拟,给出了在95%置信水平下,到达大气顶部流强上限的估计值为3.32×10^-9—1.24×10^-7 cm^-2s^-1. 关键词： γ射线暴 TeV能区 ASγ实验 宇宙射线     

Proposed source of gravitational radiation from a torus around a black hole

Long gamma-ray bursts (GRBs) could be emitted from rapidly spinning black-hole-torus systems, resulting from either hypernovae or black-hole-neutron-star coalescence. We show that a nonaxisymmetric torus may also radiate gravitational radiation, powered by the spin energy of the black hole. The coupling to the spin energy of the black hole operates by equivalence in poloidal topology to pulsar magnetospheres. Results calculated in the suspended-accretion state indicate that GRBs are potentially the most powerful LIGO/VIRGO burst sources in the Universe, with an expected duration of 10-15 s on a horizontal branch of 1-2 kHz in the f(f) diagram.     

Search for low-energy neutrino radiation accompanying gamma-ray bursts on the Baksan subterranean scintillation telescope

An analysis aimed at finding possible neutrino radiation accompanying gamma-ray bursts in a 24-h period about them is performed on the basis of the data in the 4B BATSE Gamma-Ray Burst Catalog and data from the Baksan scintillation telescope according to a program for finding neutrinos from collapsing stars. Values significantly exceeding the background are not discovered. A lower bound for the distance to the source is established under the assumption that the anticipated radiation has characteristics similar to the characteristics of collapse neutrinos. It attests to the cosmological origin of gamma-ray bursts with a high degree of probability. Zh. éksp. Teor. Fiz. 114, 1921–1929 (December 1998)     

Extragalactic electromagnetic cascades as a possible instrument for the study of background radio emission

We analyzed the diffuse gamma-ray emission generated in the interactions between cosmic rays of ultrahigh energies and the background radiation in extragalactic space. The intensity of gamma-ray emission was calculated within a simplified model for energies E ≈ 10¹⁴ eV in different assumptions concerning the cosmic ray sources with the use of different estimates of nonthermal background radiation. It was shown that the gamma-ray radiation intensity in this energy range depends on the background radio emission and that under different assumptions concerning the radio background it can differ tens of times. It was concluded that gamma-ray emission can serve as a test for the models of background radio-frequency radiation.