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1.
We present the final part of the catalog of cosmic gamma-ray bursts (GRBs) observed in the PHEBUS experiment on the Granat orbiting astrophysical observatory. The first three parts of the catalog were published by Terekhov et al. (1994, 1995a) and Tkachenko et al. (1998). The fourth part contains information on 32 events recorded from October 1994 until December 1996. We give burst light curves in the energy range 100 keV to 1.6 MeV, integrated energy spectra, and information on the fluence and energy flux at the luminosity peak for energies above 100 keV. Over the entire period of its operation, the PHEBUS instrument detected 206 cosmic GRBs. The mean ?V/Vmax? was 0.336±0.007. The mean hardness corresponding to the ratio of count numbers in the energy ranges 400–1000 and 100–400 keV is 0.428±0.018 for events with a duration shorter than 2 s and 0.231±0.004 for events with a duration longer than 2 s.  相似文献   

2.
We examine the recent report by Prochter et al. that gamma-ray burst (GRB) sight lines have a much higher incidence of strong Mg II absorption than quasar sight lines. We propose that the discrepancy is due to the different beam sizes of GRBs and quasars, and that the intervening Mg II systems are clumpy with the dense part of each cloudlet of a similar size as the quasars, i.e. ≲1016 cm, but bigger than GRBs. We also discuss observational predictions of our proposed model. Most notably, in some cases the intervening Mg II absorbers in GRB spectra should be seen varying, and quasars with smaller sizes should show an increased rate of strong Mg II absorbers. In fact, our prediction of variable Mg II lines in the GRB spectra has been now confirmed by Hao et al., who observed intervening Fe II and Mg II lines at z=1.48 to be strongly variable in the multi-epoch spectra of z=4.05 GRB 060206.  相似文献   

3.
Of great importance in distinguishing between models for gamma-ray bursts (GRBs) is the experimental determination of the highest energy gamma rays associated with bursts. The EGRET detection of a 15 GeV gamma ray indicates that the spectra of at least some bursts extend well beyond the several MeV limit of the BATSE detectors (Hurleyet al., 1994). The low expected flux means that the collecting area of the present generation of satellite-based detectors is too small to detect gamma rays much above this energy efficiently, and such searches are currently undertaken with ground based detectors. In this paper searches made for very high energy GRBs with a southern hemisphere air shower particle array are described.  相似文献   

4.
Employing a sample presented by Kaneko et al. (2006) [Kaneko, Y. et al., 2006. ApJS 166, 298 (Paper I)] and Kocevski et al. (2003) [Kocevski, D. et al., 2003. ApJ 596, 389], we select 42 individual tracking pulses (here we defined tracking as the cases in which the hardness follows the same pattern as the flux or count rate time profile) within 36 gamma-ray bursts (GRBs) containing 527 time-resolved spectra and investigate the spectral hardness, Epeak (where Epeak is the maximum of the νFν spectrum), evolutionary characteristics. The evolution of these pulses follow soft-to-hard-to-soft (the phase of soft-to-hard and hard-to-soft are denoted by rise phase and decay phase, respectively) with time. It is found that the overall characteristics of Epeak of our selected sample are: (1) the Epeak evolution in the rise phase always start on the high state (the values of Epeak are always higher than 50 keV); (2) the spectra of rise phase clearly start at higher energy (the median of Epeak are about 300 keV), whereas the spectra of decay phase end at much lower energy (the median of Epeak are about 200 keV); (3) the spectra of rise phase are harder than that of the decay phase and the duration of rise phase are much shorter than that of decay phase as well. In other words, for a complete pulse the initial Epeak is higher than the final Epeak and the duration of initial phase (rise phase) are much shorter than the final phase (decay phase). This results are in good agreement with the predictions of [Lu, R.J. et al., 2007. ApJ 663, 1110] and current popular view on the production of GRBs. We argue that the spectral evolution of tracking pulses may be relate to both of kinematic and dynamic process even if we currently can not provide further evidences to distinguish which one is dominant. Moreover, our statistical results give some witnesses to constrain the current GRB model.  相似文献   

5.
If typical gamma-ray bursts [GRBs] have X-ray counterparts similar to those detected byGinga, then sensitive focusing X-ray telescopes will be able to detect GRBs three orders of magnitude fainter than the detection limit of the Burst and Transient Spectroscopy Experiment [BATSE]. If a substantial portion of the burst population detected byBATSE originates in a Galactic halo at distances greater than or equal to 150 kpc, existing X-ray telescopes will be able to detect GRBs in external galaxies out to a distance of at least 4.5 Mpc. As reported in Hamilton, Gotthelf and Helfand (1995) the Imaging Proportional counter [IPC] on board theEINSTEIN Observatory detected 42 transient events with pointlike spatial characteristics and timescales of less than 10 seconds. These events are distributed isotropically on the sky; in particular, they are not concentrated in the directions of nearby external galaxies. For halo models of theBATSE bursts with radii of 150 kpc or greater, we would expect to see several burst events in observations pointed towards nearby galaxies. We see none. We therefore conclude that if theGinga detections are representative of the population of GRBs sampled byBATSE, GRBs cannot originate in a Galactic halo population with limiting radii between 150 kpc and 400 kpc. Inasmuch as halos with limiting radii outside of this range have been excluded by theBATSE isotropy measurements, our result indicates that all halo models are excluded. This result is independent of whether the flashes we do detect have an astronomical origin.  相似文献   

6.
One of the most amazing phenomena in astronomy, during the last twenty years, have been cosmic gamma-ray bursts (GRBs). The duration of these events vary from a few milliseconds to hundreds of seconds. We have never been able to identify the source of these bursts in other wavelengths. These objects have also never been seen in-rays after the initial bursts although there is some very weak statistical evidence that some of the bursts will repeat (Quashnock and Lamb 1993). The standard explanation for these bursts has been that they are somehow related to neutron stars in our own Galaxy. The latest results from the Burst and Transient Source Experiment aboard the Compton Gamma-Ray Observatory (Fishmanet al. 1994) show clearly that there is no excess concentration of these events (743 bursts) in the Galactic plane. After this, a more promising explanation is that the bursts are related to the Galactic halo or that the origin is extragalactic. In this letter we show that it is very probable that the origin of these events is the QSOs and that the radiation comes from the same synchrotron source as in the other observed wavelengths.  相似文献   

7.
This talk focuses on the various aspects we learnt from multiband observations of GRBs both, before and during the afterglow era. A statistical analysis to estimate the probable redshifts of host galaxies using the luminosity function of GRBs compatible with both the afterglow redshift data as well as the overall population of GRBs is discussed. We then address the question whether the observed fields of GRBs with precise localizations from third Inter-Planetary Network (IPN3) contain suitable candidates for their host galaxies.  相似文献   

8.
    
The variation with position and view direction of heliospheric H-L scattered intensity seen by a L detector in the heliosphere is re-examined. Here, a frequency- and angle-dependent multiscattering calculation (Scherer, 1994; Scherer and Fahr, 1995) is used that takes into account the local thermodynamical conditions of the scattering agent, such as temperature, density and bulk velocity of the neutral interplanetary hydrogen, as given in a recent model by Osterbart and Fahr (1992). The calculated intensity patterns show strongly pronounced dependencies of the direction of the line of sight which are explained by effects of the Doppler shift in the resonance absorption and the dipole-phase function used in the multiscattering calculation. The theoretical results obtained with these computations nicely fit the intensities measured byPrognoz 5/6 probe (Lallement, Bertaux, and Dalaudier, 1985; Bertauxet al., 1985) without, however, assuming a latitude dependence of the solar wind mass outflow. This expresses the fact that, using an adequate radiation transport calculation, it is possible to explain thePrognoz andGalileo data without the need to specify anisotropic solar wind mass outflow from the corona preferred by several authors (Lallement, Bertaux, and Dalaudier, 1985; Lallement, 1989; Broadfoot and Kumar, 1978; Bertauxet al., 1985; Ajelloet al., 1994). In view of forthcomingUlysses solar wind measurements at polar latitudes this might be of importance to know.  相似文献   

9.
This is the first paper to consider the effects of both magnetic field and self-gravity on the pulsational instability. Our main new results are that the self-gravity enhances the instability of the magneto-acoustic mode in the outer disk strongly, and also affects the instability in the inner disk, but stabilized the viscous mode. The effect of self-gravity is much greater than that of magnetic field in the outer disk, while the effect of magnetic field on the instability is weaker than that in the previous work's (Wuet al., 1995; Yanget al., 1995), in which the self-gravity has not been considered. Finally, we discuss our results.  相似文献   

10.
We investigate quantitatively how the peak emission frequency of the overall energy spectrum is at work in distinguishing RBL-like and XBL-like objects. We employ the sample of Giommi et al. (1995) to study the distribution of BL Lacertae objects with various locations of the cutoff of the overall energy spectrum. We find that the sources with the cutoff located at lower frequency are indeed sited in the RBL region of the αro-αoxplane, while those with the cutoff located at higher frequency are distributed in the XBL region. For a more quantitative study, we employ the BL Lacerta esamples presented by Sambruna et al. (1996), where the peak emission frequency, νp, of each source is estimated by fitting the data with a parabolic function. In the plot of αrx -log νp we find that, in the four different regions divided by the αrx = 0.75 line and thelogνp = 14.7 line, all the RBL-like objects are inside the upper left region, while most XBL-like objects are within the lower right region. A few sources are located in the lower left region. No sources are in the upper right region. This result is rather quantitative. It provides an evidence supporting what Giommi et al. (1995) suggested: RBL-like and XBL-like objects can be distinguished by the difference of the peak emission frequency of the overall energy spectrum. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

11.
The variability of a gamma-ray burst (GRB) is thought to be correlated with its absolute peak luminosity, and this relation had been used to derive an estimate of the redshifts of GRBs. Recently, Amati et al. presented the results of spectral and energetic properties of several GRBs with known redshifts. Here, we analyse the properties of two groups of GRBs: one group with known redshift from afterglow observation and another group with redshift derived from the luminosity–variability relation. We study the redshift dependence of various GRBs features in their cosmological rest frames, including the burst duration, the isotropic luminosity and radiated energy, and the peak energy Ep of ν F ν spectra. We find that, for these two groups of GRBs, their properties are all redshift-dependent, i.e. their intrinsic duration, luminosity, radiated energy and peak energy Ep are all correlated with the redshift, which means that there are cosmological evolution effects on gamma-ray burst features, and this can provide an interesting clue to the nature of GRBs. If this is true, then the results also imply that the redshift derived from the luminosity–variability relation may be reliable.  相似文献   

12.
The low l solar acoustic spectrum has been measured with great accuracy (v/v 10–4), for intermediate radial order modes, 11 n 34 (Jiménez et al., 1986; Grec, Fossat, and Pomerantz, 1983; Pallé et al., 1986). The measurement of the frequencies of modes of lower n, up to the fundamental one, are very important as they depart from asymptotic behaviour and, therefore, put more severe constraints on solar models. However, their amplitudes are very low (under 2 cm s–1) and when compared to the solar velocity background noise (Jiménez et al., 1986), a S/N 1 is obtained. Taking advantage of the fact that lifetimes seem to be higher at lower frequencies (lower n values) (Jefferies et al., 1988; Elsworth et al., 1990), very long Doppler velocity measurements, obtained at Teide Observatory, have been used to increase S/N, therefore, providing the possibility to detect such modes. The frequencies observed are compared to those predicted by a solar model (Christensen-Dalsgaard, Däppen, and Lebreton, 1988), using the best equation of state yet computed (Mihalas, Däppen, and Hummer, 1988).  相似文献   

13.
Abstract— Condensation calculations for C-rich circumstellar envelopes are used to model the condensation sequence of C, TiC, and SiC, and trace-element patterns observed in circumstellar SiC grains. Some properties of carbon star envelopes are briefly discussed, and condensation temperatures for major and trace elements are computed for a wide array of total pressure, C/O-ratios, and s-process elemental abundances. The comparison of calculated patterns for trace-element solid solutions in SiC with the different observed patterns measured by Amari et al. (1995) yields an association of the grains to at least three different groups of carbon stars.  相似文献   

14.
A new procedure for smoothing a gamma-ray burst (GRB) light curve and calculating its variability is presented. Applying the procedure to a sample of 25 long GRBs, we have obtained a very tight correlation between the variability and the peak luminosity. The only significant outlier in the sample is GRB 030329. With this outlier excluded, the data scatter is reduced by a factor of ∼3 compared to that of Guidorzi et al., measured by the deviation of fit. Possible causes for the outlier are discussed.  相似文献   

15.
This work presents a possible luminosity estimator for long γ-ray bursts (GRBs) based on their light curves. We use the method of variability analysis in the time domain to calculate the power density spectrum (PDS) for each of the 12 GRBs with known redshifts observed by CGRO/BATSE. The peak of the power density spectrum P is a measure of the intensity of variability of the given light curve and a strong correlation is found between P and the isotropic peak luminosity L of the GRB. It is a successor to the lag-luminosity relation of Norris et al. (2000) and the variability-luminosity relation of Reichart et al. (2001).  相似文献   

16.
A. Skumanich  M. Semel 《Solar physics》1996,164(1-2):291-302
Using the ambiguity-free vertical current defined by Semel and Skumanich (1995) we derive a minimum-current azimuth disambiguation for the observed magnetic field in the active region NOAA 7201. A comparison of such a minimum-current azimuth resolution with those from other extant methods indicates that the resulting resolution, even though found to be limited by noise, is a useful first approximation. A comparison of our minimum current distribution with the currents we derive from an extant disambiguation (Lites et al., 1995) indicates the presence of current discontinuities in the form of linear features near the magnetic neutral line of the associated -spot.The National Center for Atmospheric Research is funded by the National Science Foundation  相似文献   

17.
A new pumping mechanism – methanol masers without population inversion is presented in this paper. It can be used to explain the formation of a series of J 0 → J -1 E methanol masers, while the 21 → 30 A + methanol masers are regarded as a driving coherent micrwave field. In the new mechanism, the intensities of J 0 - J -1 E methanol masers are increased with the decreasing transition frequencies (or with rotational number J, approximately). These results agree with Slysh et al. (1995) and Slysh et al. (1999) J ≤ 5 observations for G3345.01+1.79 and W48, in which both J 0 → J -1 E and 21 → 30 A + methanol masers are detected coincidentally. Other astronomical conditions, such as magnetic field, 21 → 30 A + coherent radition, incoherent pumping rate by thermal radition and so on are also discussed. The new mechanism can operate as a complement to other ordinary maser pumping mechanisms for some class II methonal maser sources. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

18.
Photometric observations of 11 near-Earth asteroids were made within a regular NEA CCD photometric programme at Ondejov Observatory in the first half of 1994. This paper shows obtained R lightcurves, V-R, R-I, and B-V color indices, and rotation preriods for 6 of them. Among the presented results, the most interesting are those for (4954) Eric, for which we obtained several high-quality lightcurves and which seems to indicate a surface heterogeneity, (1864) Daedalus, for which interesting comparison with older observations by Gehrelset al. (1971) can be made, and 1993 VW, for which the unusual color characteristics were observed. Two (1994 AW1 and 1994 GY) of the other three observed objects have fast rotations with periods of about 2.5 hours and relatively low amplitudes. Subsequent analysis of additional lightcurve data for 1994 AW1 has revealed a presence of two periods in its lightcurve (Pravecet al. 1995). The last object presented here is 1994 JF1, for which only lower limits on period and amplitude were determined.  相似文献   

19.
Abstract— The compelling petrographic link (Consolmagno and Drake, 1977; Gaffey, 1983) between basaltic achondrite meteorites and the ～530 km diameter asteroid 4 Vesta has been tempered by a perceived difficulty in launching rocks from this asteroid's surface at speeds sufficient to bring them to Earth (Wasson and Wetherill, 1979) without obliterating Vesta's signature crust. I address this impasse in response to recent imaging (Zellner et al, 1996; Dumas and Hainaut, 1996) of a ～450 km impact basin across Vesta's southern hemisphere (Thomas et al., 1997) and model the basin-forming collision using a detailed two-dimensional hydrocode with brittle fracture including self-gravitational compression (cf., Asphaug and Melosh, 1993). A ～42 km diameter asteroid striking Vesta's basaltic crust (atop a denser mantle and iron core) at 5.4 km/s launches multikilometer fragments up to ～600 m/s without inverting distal stratigraphy, according to the code. This modeling, together with collisional, dynamical, rheological and exposure-age timescales (Marzari et al., 1996; Welten et al., 1996), and observations of V-type asteroids (Binzel and Xu, 1993) suggests a recent (<～1 Ga) impact origin for the Vesta family and a possible Vesta origin for Earth-approaching V-type asteroids (Cruik-shank et al., 1991).  相似文献   

20.
We present a self-consistent method to determine abundance and evolutionary status for GiantHii Regions (GHR) as well as the nominal temperature of the ionizing cluster and the ionization parameter. We define the ionization parameter-free plane [,R 23] (Vilchez and Pagel, 1988) where observations are compared with the prediction of photoionization models, in order to obtain the abundance and evolutionary status for a given GHR. This new method allows us to re-calibrate the empirical relationship (R 23, O/H) by Pagelet al. (1979) up to abundances three times solar. The effects of evolution of GHR on their observed spectra are explained in terms of the cooling down of the ionizing population and some evolutionary tracks are presented.  相似文献   

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