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.     

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.     

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.     

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.     

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.     

The flux-E p relation within GRB060218 in comparison with typical GRB pulses

The prompt gamma-ray/X-ray emission of gamma-ray burst (GRB) 060218 was simultaneously observed by the Burst Alert Telescope (BAT) and X-ray Telescope (XRT) onboard Swift. Its peak energy of the joint vf _v spectrum (E _p) clearly evolves with time from tens of keV to ∼1 keV, crossing both the BAT and XRT bands. The best fit yields log E _p=(4.61±0.23)+(−1.29±0.08) log t, with a correlation coefficient of 0.98 and a chance probability of p<10⁻⁴. We derive its bolometric flux (F) in the 0.01–10⁴ keV band, and find that its F-E _p relation, with a power-law index of 0.37, is much shallower than that observed in typical GRB pulses. Discussion of this shallowness is presented.

     

γ射线暴的最新研究进展:火球模型、余辉及前身星

γ射线暴（称简γ暴）的研究在最近几年里有了巨大的突破。观测上，人们发现了γ暴的低能余辉以及与γ射线发同时的光学爆发，还发现了它位于宇学距离的寄主星系。越来越多的观测证据还表明长时标γ暴与恒星形成区、甚至可能与超新星成协。在γ暴的相对论火球模型框架下，人们对γ暴以及余辉的产生机制的认识也有了进展。进而人们对γ暴的前身星以及环境效应等有了新的认识。本文旨在对这些进展和认识给一个扼要的评述。     

Tachyonic γ-ray bursts generated by nonlocal plasma currents

The dispersion relations of superluminal wave propagation in electron plasmas are derived, and the tachyonic energy flux, the velocity of energy transport, and the relaxation time asymptotics of the conductivity are studied. The formalism is based on Maxwell-type equations for Proca fields with negative mass-square in dispersive and dissipative media. Specifically, superluminal radiation fields generated by the ultra-relativistic electronic source plasma of γ-ray bursts (GRBs) are investigated. The radiation field is coupled to the shock-heated electron gas by a frequency-dependent fine-structure constant. The varying coupling constant generates long-range dispersion in the charge and current densities. At high energy, the coupling strength approaches a finite limit, so that the Proca field becomes minimally coupled to the electron current. The tachyonic fine-structure constant scales with the frequency-dependent superluminal velocity of the radiated modes. This scaling is manifested in the tachyonic flux densities of the GRB plasma, so that the scaling exponent can be extracted from spectral maps in the soft γ-ray band. To this end, tachyonic spectral fits of GRB 930506, GRB 950425, and GRB 910503 are performed. The scaling amplitude of the fine-structure constant is inferred from the burst duration. The transversal and longitudinal tachyonic luminosity of the source plasma is calculated in the high-temperature regime. Estimates of the plasma temperature and the internal energy of the ultra-relativistic electron gas are obtained.     

A black hole preying on the star for a gamma-ray burst of GRB080503: Evidence for the second event in this new class

In this paper, we critically assess GRB080503, a short gamma-ray burst with very bright extended emission (about 30 times the gamma-ray fluence of the initial spike). The light curve of the prompt γ-ray emission of GRB080503 resembles that of GRB 060614 which has been suggested to be due to an event from an intermediate mass black hole (IMBH) preying on a star. We therefore propose that GRB080503 is also due to a similar event; the mass of the IMBH is estimated to be about 4.6×10⁴ solar masses, and the engulfed star had about the same mass and size as the Sun. We also estimate that the total burst energy is about 7.67 × 10⁵⁰ ergs.

     

Neutrinos of energy approximately 10(16) eV from gamma-ray bursts in pulsar wind bubbles

The supranova model for gamma-ray bursts (GRBs) is becoming increasingly more popular. In this scenario the GRB occurs weeks to years after a supernova explosion, and is located inside a pulsar wind bubble (PWB). Protons accelerated in the internal shocks that emit the GRB may interact with the external PWB photons producing pions which decay into approximately 10(16) eV neutrinos. A km(2) neutrino detector would observe several events per year correlated with the GRBs.     

Nearby stars as sources of gamma-ray bursts

Observations of ground-based telescopes and the Hubble space telescope made it possible to identify a part of gamma-ray bursts with far objects (redshift parameter Z ≥ 1).However, it remains unclear what are other bursts and what are their sources. The possibility of identifying other bursts with close sources known as small-mass flare stars is considered. The coordinates of space gamma-ray bursts (GRBs) for 2008–2013 and close stars (within the radius r < 25 pc) were compared by the correlation analysis method. Six coincidences were found with an accuracy of ～0.1°. The probability of accidental coincidence of GRBs with stars is 4 · 10^?8, which undoubtedly proves their stellar origin.     

Neutrinos from pulsar wind bubbles as precursors to gamma-ray bursts

The supranova model for gamma-ray bursts (GRBs) has recently gained popularity. In this scenario the GRB occurs weeks to years after a supernova explosion, and is located inside a pulsar wind bubble (PWB). High energy protons from the PWB can interact with photons from the rich radiation field inside the PWB or collide with cold protons from the supernova remnant, producing pions which decay into approximately 10-10(3) TeV neutrinos. The predicted neutrino flux from the PWBs that host the GRBs should be easily detectable by planned 1 km(2) detectors.     

Cosmic γ-ray bursts: Observations and modeling

It is now commonly accepted that cosmic γ-ray bursts (GRBs) are of cosmological origin. This conclusion is based on the statistical analysis of GRBs and the measurements of line redshifts in GRB optical afterglows, i.e., in the so-called long GRBs. In this review, the models of radiation and models of GRB sources are considered. In most of these models, if not in all of them, the isotropic radiation cannot provide the energy release necessary for the appearance of a cosmological GRB. No correlation is noted between the redshift, the GRB-spectrum shape, and the total detected energy. The comparison between data obtained in the Soviet experiment KONUS and the American experiment BATSE shows that they substantially differ in statistical properties and the detection of hard x-ray lines. The investigation of hard gamma (0.1–10 GeV) afterglows, the measurement of prompt optical spectra during the GRB detection, and the further investigation of hard x-ray lines is of obvious importance for gaining insight into the GRB origin. Observations of two bright optical GRB afterglows point to the fact that an initially bright optical flare is directly related to the GRB itself, and the subsequent weak and much more continuous optical radiation is of a different nature. The results of observations of optical GRB afterglows are discussed. They point to the fact that the GRBs originate in distant galaxies with a high matter density, where intense star formation takes place. The interaction of the cosmological GRB radiation with a dense surrounding molecular cloud results in the appearance of long-duration (up to 10 years) weak optical afterglows associated with the heating and reradiation of gas. Results of 2D numerical simulation of the heating and reradiation of gas in various variants of the relative disposition of GRB and molecular clouds are presented. In conclusion, the possible relation between the so-called short GRBs and recurrent sources of soft γ rays in our Galaxy, the so-called “soft gamma repeaters,” is discussed.     

Ultra-high energy cosmic rays and prompt TeV gamma rays from gamma ray bursts

Gamma ray bursts (GRBs) have been proposed as one possible class of sources of the ultrahigh energy cosmic ray (UHECR) events observed up to energies ≳ 10²⁰ eV. The synchrotron radiation of the highest energy protons accelerated within the GRB source should produce gamma rays up to TeV energies. Here we briefly discuss the implications on the energetics of the GRB from the point of view of the detectability of the prompt TeV γ-rays of proton-synchrotron origin in GRBs in the up-coming ICECUBE muon detector in the south pole.     

Spectral properties of Fermi/GBM gamma-ray bursts and the GeV emission detection rate with Fermi/LAT

With a sample of 58 Fermi/GBM GRBs detected before 2009 May, we compare the spectral properties of GBM GRBs with those detected by CGRO/BTASE and HETE-2. Our results show that the spectral index distributions are very consistent with those observed by BATSE. However, the E _p distribution is quite different from that observed with BATSE and HETE-2. The GBM GRBs tend to be softer than the BATSE sample, but harder than the HETE-2 sample. This may be due to the instrumental selection effects and artificial sample effect on the BATSE sample. The distribution of the pseudo redshifts derived from the luminosity indicator based on the Amati-relation shows rough consistency with the spectroscopic redshifts of Swift GRBs. We estimate the detection rate of GBM GRBs with LAT based on the observed spectrum in the GBM band, and the inferred burst ratio of LAT detection with over 5 photons to GBM detection is 6%, yielding a detection rate pf 12 GRBs/yr with over 5 photons in the 1–300 GeV band. This is roughly consistent with the results in the first half year of Fermi operation. The low detection rate compared with theoretical predictions is a key for revealing the radiation mechanisms and particle acceleration of the prompt gamma-rays.     

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.     

The gamma-ray burst monitor on board the SAX satellite

Summary The anticoincidence lateral shields of the high-energy ((15÷200) keV) detector PDS aboard the SAX satellite will be used to detect celestial gamma-ray bursts. As a gamma-ray burst monitor (GRBM), the shields have a 5σ sensitivity in the (60÷600) keV nominal energy band about 10⁻⁶ erg/cm², and a capability of determining the burst location to an accuracy of a few tenths of degree to several degrees, depending on burst direction and strength. The GRBM will be mainly devoted to study the burst time profile with a time resolution down to 0.5 ms. Its expected performances are evaluated by means of Monte Carlo simulations. To speed up publication, the proofs were not sent to the authors and were supervised by the Scientific Committee.     

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     

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.     

Investigation of65Cu by means of the average resonance proton capture method

The⁶⁴Ni(p, γ)⁶⁵Cu reaction has been studied in the proton energy rangeE _p =2.05–2.55 MeV. The gamma-ray spectra were recorded with a three-crystal pair spectrometer at proton energy differences of 19 keV covering the proton energy range. An average gamma-ray spectrum was formed by adding all the individual spectra after proper adjustment as a result of the alterations in proton energy. The intensities of the gamma rays to final states with knownJ ^π-values were tested against theoretical calculations based on the Hauser-Feshbach theory. The gamma-ray strength function for energies lower than 9 MeV has been extracted from the experiment.