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.     

A search for high-energy cosmic gamma-ray bursts

Summary A search has been made for excesses of cosmic-ray counting rates at primary energiesE ₀₁>5 GeV andE ₀₄>2·10⁴ GeV over the time scalet=(1÷100) ms. The measurement was performed by means of a small extensive air shower array operating at mountain altitude (3500 m a.s.l.). During the running time 111 cosmic gamma-ray bursts were detected by satellites; 10 of them certainly (55 probably) above the horizon of the detector. No significant counting rate excess has been recorded out of the statistical fluctuations. Also the search for correlations with satellite events has given a negative result. The upper limit for high-energy cosmic gamma-ray flux in bursts isϕ ₁(E>E ₀₁)<4·10⁻⁵ (t = time scale in ms),ϕ ₄(E>E ₀₄)<1.6·10⁻⁵erg/cm². Paper presented at the 2^o Convegno Nazionale di Fisica Cosmica, held at L'Aquila, 29 May–2 June 1984.     

Duration distributions for different softness groups of gamma-ray bursts

Gamma-ray bursts(GRBs) are divided into two classes according to their durations.We investigate if the softness of bursts plays a role in the conventional classification of the objects.We employ the BATSE(Burst and Transient Source Experiment) catalog and analyze the duration distributions of different groups of GRBs associated with distinct softness.Our analysis reveals that the conventional classification of GRBs with the duration of bursts is influenced by the softness of the objects.There exists a bimodality in the duration distribution of GRBs for each group of bursts and the time position of the dip in the bimodality histogram shifts with the softness parameter.Our findings suggest that the conventional classification scheme should be modified by separating the two well-known populations in different softness groups,which would be more reasonable than doing so with a single sample.According to the relation between the dip position and the softness parameter,we get an empirical function that can roughly set apart the short-hard and long-soft bursts:SP =(0.100 ± 0.028) T-(0.85 0.18) 90,± where SP is the softness parameter adopted in this paper.     

Sensitive polarimetric search for relativity violations in gamma-ray bursts

We show that the recent measurements of linear polarization in gamma rays from GRB 930131 and GRB 960924 constrain certain types of relativity violations in photons to less than parts in 10(37), representing an improvement in sensitivity by a factor of 100,000.     

Preliminary investigation to test extragalactic hypothesis for gamma-ray bursts

Summary Recent observations of CGRO satellite challenged the almost universally accepted galactic origin of gamma-ray bursts and have revived the extragalactic, cosmological models. This hypothesis should imply some variations of the morphological and energetic characteristics of the weaker events to which we think the farthest ones might belong. The existence of such variations due to the cosmological red-shift should be tested. In this paper we examine the possible correlations between temporal morphology of the gamma-ray bursts, peak intensity and photon energy spectra when the red-shift effects do not yet occur. We examine the peak intensities and the energy spectral-hardness distributionversus rise times for events observed by previous space missions, with a logN-logS shape free of cosmological effects. The results of this analysis suggest that a wide range of values of the temporal and spectral characteristic parameters is an intrinsic property of the sources. Paper presented at the 6th Cosmic Physics National Conference, Palermo, 3–7 November 1992.     

Experimental search for gamma-ray bursts from evaporating primordial black holes

The energy spectra and temporal characteristics of high-energy gamma-ray bursts from evaporating primordial black holes have been calculated using various evaporation models. The currently existing theoretical uncertainties in the shape of the evaporated photon spectrum are discussed. The data from the Andyrchy and Carpet-2 arrays of the Baksan Neutrino Observatory (Institute for Nuclear Research, Russian Academy of Sciences) obtained in the mode of detection of a single cosmic-ray component are used to search for cosmic gamma-ray bursts with a primary photon energy of about 8 GeV. New upper limits have been obtained for the number density of evaporating black holes in a local region of space with a characteristic size of ～10^?3 pc for various evaporation models.     

Spectral loudness summation for sequences of short noise bursts

Recent loudness data of single noise bursts indicate that spectral loudness summation depends on signal duration. To gain insight into the mechanisms underlying this duration effect, loudness was measured as a function of signal bandwidth centered around 2 kHz for sequences of 10-ms noise bursts at various repetition rates and, for comparison, for single noise bursts of either 10- or 1000-ms duration. The test-signal bandwidth was varied from 200 to 6400 Hz. For the repeated noise bursts, the reference signal had a bandwidth of 400 Hz. For the single noise bursts, data were obtained for two reference bandwidths: 400 and 3200 Hz. In agreement with previous results, the magnitude of spectral loudness summation was larger for the 10-ms than for the 1000-ms noise bursts. The reference bandwidth had no significant effect on the results for the single noise bursts. Up to repetition rates of 50 Hz, the magnitude of spectral loudness summation for the sequences of noise bursts was the same as for the single short noise burst. The data indicate that the mechanism underlying the duration effect in spectral loudness is considerably faster than the time constant of about 100 ms commonly associated with the temporal integration of loudness.     

Jet precession in neutrino-cooled disks for gamma-ray bursts: The effects of the mass and spin of a black hole

We present a model of jet precession driven by a neutrino-cooled disk around a spinning black hole to explain the quasi-periodic features observed in some gamma-ray burst light curves.The different orientations of the rotational axes between the outer part of a neutrino-cooled disk and a black hole result in precessions of the central black hole and the inner part of the disk.Hence,the jet arising from the neutrino annihilation above the inner disk is driven to precession.We find that the period of precession is positively correlated with the mass as well as the spin of a black hole.     

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)     

The search for neutrino bursts from core collapse Supernovae at the Baksan Underground Scintillation Telescope

The current status of the experiment on recording neutrino bursts from core collapse stars is presented. The actual observational time T (from June 30, 1980 until December 31, 2009) is 25.58 years. An upper bound of the mean frequency of gravitational collapse in our Galaxy f _col < 0.090 year^?1 at a 90% confidence level. The results of studying single events at the facility in the case of muon inelastic interaction of cosmic rays with the matter of the detector are presented.     

STAR CLUSTER: a tracking array for gamma-ray astronomy

Summary A new type of extensive air shower array-telescope is being constructed, close to the GREX scintillator array at Haverah Park. The design of the new instrument is based on identification and measurement of individual shower particles by means of pattern recognition techniques applied to data from LST chambers above and below a thin sheet of high-Z material. Air showers will be detected in the range from 10¹⁴ eV to 10¹⁸ eV. The directions of the shower primaries will be reconstructed with an accuracy of a few tenths of a degree using triangulation between tracks of detected shower particles: >1 GeV electrons, photons and muons. Particle densities measured at the detector locations will be used to calculate shower sizes and core locations. Information about the height of production of the high-energy secondaries will be obtained for each shower. This information will be taken into account in calculating the primary energies. It will be used together with the observed muon content (ratio of muons to all particles), to draw conclusions about the nature of the primary particles. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

Gain requirement for a gamma-ray laser

A simple expression for gain saturation is presented for a laser filament emitting in a single transverse mode. Values of the gain exponent in the range 20 ? αl ? 30 are found, giving a maximum increase of ～ 10¹¹ in axial intensity.     

A neutron star collapse induced by a primordial black hole as the source of cosmological γ-ray bursts

A novel scenario is proposed for the origin of cosmological γ-ray bursts relating them with the induced collapse of an isolated neutron star under the action of a primordial black hole inside it. A mechanism is pointed out for black hole capturing into bounded orbits in a contracting protostellar cloud (which further evolves to a neutron star), and it is shown that this mechanism is most efficient in the pregalactic epoch. The qualitative results of neutrino transfer calculations are presented; these neutrinos originate from the quark phase transition in the nucleon matter which takes place in the accretion flow in the interior of the star. The neutrinos and antineutrinos escaping from a dense nucleon matter are degenerate and annihilate in the immediate vicinity of the star surface where an inverse temperature layer in the outstreaming electron-positron wind is produced. This layer acts as a natural barrier against baryon pollution and gives rise to a very high (≈ 10³) value of the Lorentz factor in the expanding plasma, in agreement with the observed energy and duration of the process. This makes it possible to explain the main properties of the γ-ray bursts. We also consider other important features of this scenario, including the predominantly extragalactic origin of the bursts, the apparent absence of the cosmological time dilation, the excess drop in the number of bursts—luminosity dependence for z>0.7, and the unlikely corrllation between the burst and the gravitational wave pulse.     

Twenty years of Galactic observations in searching for bursts of collapse neutrinos with the Baksan underground scintillation telescope

The results of twenty-year-long Galactic observations in neutrino radiation are summarized. Except for the recording of a neutrino signal from the supernova SN 1987A, no Galactic bursts of collapse neutrinos have been detected. An upper bound on the mean frequency of gravitational collapses in our Galaxy was obtained, f _collapse (at 90% confidence) <0.13 yr^?1.     

双向隐形传态方案及安全性分析

基于位函数的引入与介质参量无关,将各向异性目标内外的电场展为级数形式,得到了任意各向异性目标n阶散射场、目标内场的递推表达式,给出了介电常量张量的变换关系,在平面波任意入射的条件下,并给出了传播单位矢量与极化单位矢量的一般关系.以磁化冷等离子体为例,给出了一阶散射场的具体表达式,并对二阶散射场引起的误差进行了评估.在THz波段和光波段,对所得结果进行了部分仿真.结果表明:微分散射对电波频率和极化状态等因素的影响较为敏感,介电常量张量的非对角元素对散射的影响不大,当波长与目标尺寸一定时,仿真结果不仅适用于THz波段,对其它波段也成立.     

磁化冷等离子体球的太赫兹散射特性

基于位函数的引入与介质参量无关,将各向异性目标内外的电场展为级数形式,得到了任意各向异性目标n阶散射场、目标内场的递推表达式,给出了介电常量张量的变换关系,在平面波任意入射的条件下,并给出了传播单位矢量与极化单位矢量的一般关系.以磁化冷等离子体为例,给出了一阶散射场的具体表达式,并对二阶散射场引起的误差进行了评估.在THz波段和光波段,对所得结果进行了部分仿真.结果表明:微分散射对电波频率和极化状态等因素的影响较为敏感,介电常量张量的非对角元素对散射的影响不大,当波长与目标尺寸一定时,仿真结果不仅适用于THz波段,对其它波段也成立.     

Proposal for a nuclear gamma-ray laser of optical range

A possibility of the amplification of the 7.6 eV γ radiation by the stimulated γ emission of the ensemble of the (229m)Th isomeric nuclei in a host dielectric crystal is proved theoretically. This amplification is a result of (1) the excitation of a large number of (229m)Th isomers by laser radiation, (2) the creation of the inverse population of nuclear levels in a cooled sample owing to the interaction of thorium nuclei with the crystal electric field or with an external magnetic field, (3) the emission or absorption of the optical photons by thorium nuclei in the crystal without recoil, and (4) the nuclear spin relaxation through the conduction electrons of the metallic covering.     

Bump time-frequency toolbox: a toolbox for time-frequency oscillatory bursts extraction in electrophysiological signals

Background  

oscillatory activity, which can be separated in background and oscillatory burst pattern activities, is supposed to be representative of local synchronies of neural assemblies. Oscillatory burst events should consequently play a specific functional role, distinct from background EEG activity – especially for cognitive tasks (e.g. working memory tasks), binding mechanisms and perceptual dynamics (e.g. visual binding), or in clinical contexts (e.g. effects of brain disorders). However extracting oscillatory events in single trials, with a reliable and consistent method, is not a simple task.