The BATSE experiment on the Compton Gamma-ray Observatory was the first large detectorsystem designed for the study of gamma-ray bursts. The eight large-area detectors allowedfull-sky coverage and were optimized to operate in the primary energy region of emissionof most GRBs. BATSE provided detailed observations of the temporal and spectralcharacteristics of several thousand GRBs, and it was the first experiment to provide rapidnotifications of the coarse location of many them. It also provided strong evidence forthe cosmological distances to GRBs through the observation of the sky distribution andintensity distribution of numerous GRBs. The large number of GRBs observed with the high-sensitivity BATSE detectors continues to provide a database of GRB spectral and temporalproperties in the primary energy range of GRB emission that will likely not be exceededfor at least another decade. The origin and development of the BATSE experiment, somehighlights from the mission and its continuing legacy are described in this paper.

By 1975 the hunt for GRB counterparts had been on for almost ten years without success.Gamma burst instruments of that day provided little or no directional data in themselves.Positions could be extracted only using the time delay technique – potentially accuratebut very slow. Triggered by a japanese report of a balloon instrument for GRB studiesbased on a Rotation Modulation Collimator we at the Danish Space Research Institutestarted the development of an RMC detector for GRBs, the WATCH wide field monitor.

Four WATCH units were flown on the Soviet Granat satellites, and one on ESA’s EURECAsatellite. The design and results will be summarized. Now, 35 years later, recent detectordevelopments may allow the construction of WATCH-type instruments able to fit weight,power and data-wise into 1 kg cubesats. This could provide the basis for a true all-skymonitor with 100 percent duty cycle for rare, bright events.

The short review of GRB studies performed for many years by Ioffe Institute is presented.An important breakthrough in GRB studies became possible owing to four Konus experimentscarried out by the Ioffe Institute onboard the Venera 11 to 14 interplanetary missionsfrom 1978 to 1983. The joint Russian-American Konus-Wind experiment, which has alreadybeen operating for more than 18 years, provides important and often unique data regardingGRB characteristics in 20 keV – 15 MeV energy range. These investigations werecomplemented by several Konus and Helicon experiments onboard Russian near-Earthspacecraft. A short description of future Konus-UF and Konus-M experiments are alsogiven.

The Fermi and Swift satellites offer unique, andcomplementary capabilities for the study of short GRBs. Here, I briefly summarize thecurrent status of Fermi and Swift observations of shortGRBs, and outline some highlights, focusing on the prompt emission phase.

Gamma-ray bursts (GRB) are extremely energetic events and produce highly diverse lightcurves. Light curves are believed to be resulting from internal shocks reflecting theactivities of the GRB central engine. Hence their temporal studies can potentially lead tothe understanding of the GRB central engine and its evolution. The light curve variabilitytime scale is an interesting parameter which most models attribute to a physical origine.g., central engine activity, clumpy circum-burst medium, orrelativistic turbulence. We develop a statistical method to estimate the GRB minimumvariability time scale (MVT) for long and short GRBs detected by GBM. We find that the MVTof short bursts is distinctly shorter than that for long GRBs supporting the possibilityof a more compact central engine of the former. We find that MVT estimated by this methodis consistent with the shortest rise time of the fitted pulses. Hence we use the fittedpulse rise times to study the evolution of burst variability time scale. Variability timeis in turn related to the minimum bulk Lorentz factor. Using this we relate the GRBspectral evolution to the evolution of the variability time scale.

In spite of extensive research over the past decades, a complete physical picture of theorigin of the prompt gamma-ray burst emission is still lacking. During recent years,evidence has been accumulating that the jet photosphere plays an important role. In thispaper we summarize the lessons learned from Fermi observations regardingthe behavior of the photosphere and discuss why photospheric emission does not necessarilyappear as blackbody radiation. We concentrate on two strong and important bursts, GRB090902B and GRB 110721A, which serve as examples of the standard appearance photosphericemission may have in gamma-ray burst spectra.

Monitor of All-sky X-ray Image (MAXI) on board International Space Station is capable ofobserving gamma-ray bursts (GRBs) and sending notices of GRBs or other transient events,using real time connection to the ground. MAXI observed 32 GRBs or short X-ray transientsas of the end of September 2012. Among them, eleven events were simultaneously detected byother satellites. The observed rate of the MAXI GRBs is about one event per month. Thisrate is comparable to a past observation with larger effective area and larger field ofview. The fact indicates that MAXI has better sensitivity to observe GRBs because of lowbackground. The distribution of the spectral hardness of MAXI GRBs is similar to theresults of a past instrument, which is sensitive to similar energy range.

Since the early 90s Gamma Ray Bursts have been accepted to be of extra-galactic originthanks to the isotropic distribution observed by BATSE and the redshifts observed in someof their optical or infrared counterparts. Nevertheless, there have been a few cases thatupon further examination have turned out to be of galactic origin. Several of thesegalactic sources have presented a Fast Rise, Exponential Decay structure which leads us tobelieve that there could be an underlying correlation. In this work we do severalstatistical analyses to determine the degree of contamination by galactic sources thatcertain subsample of known FREDs have. And find that certain subsamples have a mostprobable contamination between 27% and 34%.

The exceptionally intense long GRB 110918A was discovered by several GRB observingmissions: INTEGRAL (SPI-ACS), Konus-WIND, MarsOdyssey (HEND), and MESSENGER (GRNS) on September 18, 2011.This GRB was localized by the Interplanetary Network (IPN) and its bright X-raycounterpart was found in close vicinity of the IPN box in the Swift/XRTfollow-up observations starting 1.2 days after the trigger. The optical afterglow wasdiscovered by the Isaac Newton Telescope and its spectroscopic redshift z = 0.982 wasmeasured with the GMOS spectrograph mounted on the Gemini-N telescope. GRB 110918A is thebrightest burst detected by Konus-WIND for more than 17 years of itscontinuous observations. The instrument’s light curves in three energy bands covering22–1450 keV range show an extremely bright, short, hard pulse followed by three weaker,softer, partly overlapping pulses within next 25 seconds. A spectral lag between thelight-curves is determined, showing a substantial increase in the course of the burst. Theemission is detected up to 12 MeV. Modeling the time-integrated energy spectrum with theBand function yields a moderate value ofEpeak = 340keV, while the time-resolvedspectral analysis reveals strong hardness-intensity correlation and a hard-to-softevolution of the emission: Epeak falls from ~ 4 MeV at the onset of the huge initial pulse to ~50 keV at the final stage of theburst. The total 20 keV–10 MeV energy fluence amounts toS = (7.8 ± 0.4) × 10-4erg cm-2 and a 64-ms peakflux Fmax = (9.2 ± 0.4) × 10-4erg cm-2s-1, which corresponds to a huge isotropic-equivalent energy release Eiso = (2.1 ± 0.1) × 1054erg andthe record-breaking peak luminosity Liso;max = (4.7 ± 0.2) × 1054erg s-1.

We investigated the dependence of a spectral lag against energy band based on 28 brightGRBs registered by SPI and IBIS/ISGRI of INTEGRAL observatory. It was found that forsimple structure bursts or well separated pulses of multipulse bursts the spectral lag canbe approximated by the relation ofτ ~ Alg(E), where A is a positiveparameter, which correlates with pulse duration. We have not found any negative lag insimple structure bursts or in well separated pulses. While investigating the time profileof the whole burst negative lag may appear due to different spectral parameters of thepulses.

A sample of 427 gamma-ray bursts (GRBs) was observed by the RHESSIsatellite in Feb. 2002 - Apr. 2008. We calculated spectral lags and peak-countrates for the first time and constructed a new observational database. This database isstatistically studied completing an earlier analysis of durations and hardness ratios.First, we discuss properties of short-, intermediate-, and long-duration GRBs in terms ofpeak-count rates and spectral lags. Second, we investigate the number of GRB groups usingmodel-based clustering method together with Kolmogorov-Smirnov (K-S) and Anderson-Darling(A-D) tests. The results are: The inter. bursts have properties similar to short bursts.The groups of inter. and long bursts appear to be different. The inter. GRBs in theRHESSI and Swift databases seem to be differentphenomena. This work is summary of Řípa et al. (2012).

We report γ-ray afterglow observations of GRB 110625A using Fermi’sLarge Area Telescope (LAT) above 100 MeV. Gamma-ray emission was clearly detected usingdata taken between 180 s and 580 s after the burst. The GeV light curve differs from apower-law decay, and probably consists of two emission periods. Simultaneous Swift/XRTobservations did not show flaring behaviors, distinguishing its origin of the extended GeVemission from the case of GRB 100728A.

We performed a statistical analysis of the intrinsic properties of long gamma-ray bursts(GRBs) observed by Swift. The intrinsic quantities are the rest-frame durationT90,rest, the rest-frame peak energyEp,rest, the isotropic equivalent energyEiso and the peak luminosityLiso of the prompt emission. We find that the distributionsof T90,rest,Ep,rest, Eisoand Liso all span a wide range and the central values of theseintrinsic quantities of long GRBs areT90,rests10s,Ep,rests520keV,Eisos1053 erg andLisos4 × 1052 erg/s. We also find bothEp,rest andLiso are independent with T90,but Eiso is correlated withT90.

Gamma-ray burst (GRB) light curves generally are energy dependent, i.e.,the higher the photon energy, the narrower the pulse. In addition, the peak of the pulseat lower energies is usually delayed compared with that in higher energy. The phenomenoneven exists in some X-ray flares and following optical flares. However, its origin isstill unclear. Here we calculate the emission in different bands produced fromdifferent-thickness shocked shell due to radiative cooling, with the equal arrival timevolume effect considered. We find the emission profile is energy dependent and that thelight curves show spectral lag, which are consistent with the observations. This can be anexplanation of the energy dependence of light curve and spectral lag in GRB, X-ray flareand following optical flare.

We introduce a new model of gamma ray burst (GRB) that explains its observed promptsignals, namely, its primary quasi-thermal spectrum and high energy tail. This mechanismcan be applied to either assumption of GRB progenitor: coalescence of compact objects orhypernova explosion. The key ingredients of our model are: (1) The initial stage of a GRBis in the form of a relativistic quark-gluon plasma lava; (2) The expansion and cooling ofthis lava results in a QCD phase transition that induces a sudden gravitational stoppageof the condensed non-relativistic baryons and form a hadrosphere; (3) Acoustic shocks andAlfven waves (magnetoquakes) that erupt in episodes from the epicenter efficientlytransport the thermal energy to the hadrospheric surface and induce a rapid detachment ofleptons and photons from the hadrons; (4) The detachede + e −  and γform an opaque, relativistically hot leptosphere, which expands and cools toT ~ mc2, or 0.5 MeV,wheree + e −  → 2γand its reverse process becomes unbalanced, and the GRB photons are finally released; (5)The mode-conversion of Alfven waves into electromagnetic waves in the leptosphere providesa snowplow acceleration and deceleration that gives rise to both the high energy spectrumof GRB and the erosion of its thermal spectrum down to a quasi-thermal distribution.According to this model, the observed GRB photons should have a redshifted peak frequencyatEp ~ Γ(1 + β/2)mc2/(1 + z),where Γ ~ O(1) is the Lorentz factor of the bulk flow of the lava,which may be determined from the existing GRB data.

Motivated by the Fermi gamma-ray space telescope results, in recentyears immense efforts were given to understanding the mechanism that leads to the promptemission observed. The failure of the optically thin emission models (synchrotron andsynchrotron self Compton) increased interest in alternative models. Optically thickmodels, while having several advantages, also face difficulty in capturing several keyobservables. Theoretical efforts are focused in two main directions: (1) mechanisms thatact to broaden the Planck spectrum; and (2) combining the optically thin and opticallythick models to a hybrid model that could explain the key observables.

The Fermi observatory has detected GeV photons from several GRBs. Some of them show anextra spectral component, which is a hint for emission mechanism of GRBs. Here we discussthe GeV emission mechanism according to several promising models. The difference betweenmodels will appear in temporal evolution of the photon spectrum. To verify this,instruments that can obtain high photon statistics like CTA are desired. We also discussthe photosphere model, which is recently supported by wide-band observations withFermi.

In three years of observations the Large Area Telescope (LAT) on board the FermiGamma Ray Space Telescope has observed high-energy γ-rayemission from 35 gamma-ray bursts (GRBs). The first Fermi-LAT catalog ofGRBs is in preparation within the Fermi LAT collaboration and willprovide a systematic study of high-energy emission from GRBs. In this paper we presentsome of the main results, briefly discussing durations, energetics, time-resolved and timeintegrated LAT spectral analysis. We also discuss characteristics of LAT-detected emissionsuch as its delayed onset and longer duration compared to emission detected by the GBM,and its power-law temporal decay at late times.

We propose a model for the spectral formation of Gamma Ray Burst (GRB) prompt emission,where the phenomenological Band function is usually applied to describe the GRB promptemission. We suggest that the GRB prompt emission is mainly a result of the Comptonizationof relatively soft photons of the star off electrons of a hot shell of plasma oftemperature of the order of 109 K (or ~100 keV) that movessub-relativistically with the bulk velocity substantially less than the speed of light. Inthis case, the Comptonization parameter is high and the interaction between ablackbody-like soft seed photon population and hot electrons leads to formation of asaturated Comptonization spectrum. We give an interpretation of the Amati relation betweenthe intrinsic spectral peak photon energy and radiated energy or luminosity.