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1.
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   

2.
GRBs are the most energetic combination of jets and disks in the Universe. Observations made using Swift reveal a complex temporal and spectral behaviour. We propose that this behaviour can be used to refine the GRB classification scheme and align it better with progenitor types. The early (prompt) X-ray light curve can be well described by an exponential which relaxes into a power law. The transition time between the exponential and the power law gives a well-defined timescale, T p , for the burst duration which we use with the spectral index of the prompt emission, β p , and the prompt power law decay index, α p to define four classes of burst: short, slow, fast and soft. Short bursts tend to decline more gradually than long bursts. Most GRBs display a second “afterglow” component which can be fitted in a similar way to the early emission. During the decay of this second component, few GRBs show jet breaks in accord with pre-Swift predictions. However, the start time of the final afterglow decay, T a , correlates with the peak of the prompt γ-ray emission spectrum, E peak, in an analogous way to the Ghirlanda relation found between optical “jet-break” times, t j , and E peak. These data are inconsistent with simple achromatic jet-break models casting doubt on the reliability of using late temporal breaks to determine the jet collimation.  相似文献   

3.
Optical CCD imaging with Hα and [SII] filters and spectroscopic observations of the galactic supernova remnant G85.9-0.6 have been performed for the first time. The CCD image data are taken with the 1.5 m Russian-Turkish Telescope (RTT150) at TüBİTAK National Observatory (TUG) and spectral data are taken with the Bok 2.3 m telescope on Kitt Peak, AZ. The images are taken with narrow-band interference filters Hα, [SII] and their continuum. [SII]/Hα ratio image is performed. The ratio obtained from [SII]/Hα is found to be ∼0.42, indicating that the remnant interacts with HII regions. G85.9-0.6 shows diffuse-shell morphology. [SII]λ λ6716/6731 average flux ratio is calculated from the spectra, and the electron density N e is obtained to be 395 cm−3. From [OIII]/Hβ ratio, shock velocity has been estimated, pre-shock density of n c =14 cm−3, explosion energy of E=9.2×1050 ergs, interstellar extinction of E(B−V)=0.28, and neutral hydrogen column density of N(HI)=1.53×1021 cm−2 are reported.  相似文献   

4.
We present two new luminous blue variable (LBV) candidate stars discovered in the M33 galaxy. We identified these stars as massive star candidates at the final stages of evolution, presumably with a notable interstellar extinction. The candidates were selected from the Massey et al. catalog based on the following criteria: emission in H α , V<18./m 5 and 0.m 35 < (B - V) < 1.m 2. The spectra of both stars reveal a broad and strong H α emission with extended wings (770 and 1000 kms−1). Based on the spectra we estimated the main parameters of the stars. Object N45901 has a bolometric luminosity log(L/L⊙) = 6.0–6.2 with the value of interstellar extinction A V = 2.3 ± 0.1. The temperature of the star’s photosphere is estimated as T⋆ ∼ 13000–15000 K, its probable mass on the Zero Age Main Sequence is M∼ 60–80 M⊙. The infrared excess in N 45901 corresponds to the emission of warm dust with the temperature Twarm ∼ 1000 K, and amounts to 0.1%of the bolometric luminosity. A comparison of stellar magnitude estimates from different catalogs points to the probable variability of the object N45901. Bolometric luminosity of the second object, N125093, is log(L/L⊙) = 6.3 − 6.6, the value of interstellar extinction is A V = 2.75 ± 0.15. We estimate its photosphere’s temperature as T⋆∼ 13000–16000K, the initial mass as M ∼ 90–120 M⊙. The infrared excess in N125093 amounts to 5–6% of the bolometric luminosity. Its spectral energy distribution reveals two thermal components with the temperatures Twarm ∼ 1000K and Tcold ∼ 480 K. The [Ca II] λλ7291, 7323 lines, observed in LBV-like stars Var A and N93351 in M33 are also present in the spectrum of N 125093. These lines indicate relatively recent gas eruptions and dust activity linked with them. High bolometric luminosity of these stars and broad H α emissions allow classifying the studied objects as LBV candidates.  相似文献   

5.
We use three indicators of massive star formation, Hα, FIR and non-thermal radio luminosities, to compare estimates of the star formation rate (SFR) for a sample of 34 spiral galaxies. To adjust the SFR values obtained from these indicators, we considered the slope, α, and/or the upper mass limit M up of the initial mass function (IMF) as free parameters. The best agreement between the indicators is found for M up≈ 60-100 M⊙ and α ≈–3.1 at the high-mass end of the IMF (M>10 M⊙.Parallelwith the SFR we also estimated the FIR excess X FIR, defined as the fraction of the observed FIR not directly related to young massive stars. X FIR is found to be well correlated with types of spiral galaxies and their colours (B-V): the redder a galaxy, the higher its FIR excess. We conclude that for any parameters of the IMF the observed FIR flux of early-type spiral galaxies needs an additional source of energy apart from massive star radiation. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

6.
Based on data from the Baksan underground scintillation telescope (BUST) for the period 2001–2004, we searched for cosmic gamma-ray bursts (GRBs) at primary photon energies of 0.5 TeV or higher. We obtained constraints on the rate of bursts with durations of 1–10 s for fluences within the range 4.6 × 10−3-1.8 × 10−2 erg cm−2 in the declination band 30° ≤ δ ≤ 80°. We searched for ultrahigh-energy gamma rays from GRBs detected on spacecraft during and within ±2 h of the burst. No statistically significant excesses above the background of random coincidences were found. The derived constraints on the ultrahigh-energy gamma-ray fluence during GRBs lie within the range 4.6 × 10−3-3.7 × 10−2 erg cm−2.  相似文献   

7.
We have collected the observational data accumulated before the Swift experiment to check the possible connection of short gamma-ray bursts (GRBs) with low-redshift galaxies. The BATSE/IPN experimental data on well-localized short GRBs and the SDSS DR5 and PSCz catalogs of galaxies are used. The PSCz sky coverage has allowed us to search for host galaxies for a sample of 34 short GRBs. One or more galaxies have been found in the error boxes of six bursts, but the probability of a chance coincidence for each of them is high. No excess of nearby galaxies in the total sample has been detected. The 90% confidence limit corresponds to the fact that no more than 7%of the short GRBs could originate in nearby galaxies of the PSCz sample. The estimated upper limit of several percent may be considered to be valid in the volume z = 0.015–0.025. Based on the results of our search, we have estimated the lower limits for the isotropic energies E γiso of 31 short bursts from our sample. Their values lie within the range 1.0 × 1047–2.7 × 1049 erg. The possible fraction of the flares from magnetars in our sample of short GRBs is discussed. The SDSS sky coverage is currently insufficient to perform a similar analysis.  相似文献   

8.
Gamma‐ray bursts (GRBs) are one of the most luminous events in the Universe. In addition, the Universe itself is almost transparent to γ ‐rays, making GRBs detectable up to very high redshifts. As a result, GRBs are very suitable to probe the cosmological parameters. This work shows the potential of long‐duration GRBs for measuring the cosmological parameters ΩM and ΩΛ by comparing the observed log N ‐log P distribution with the theoretical one. Provided that the GRBs rate and luminosity function are well determined, the best values and 1σ confidence intervals obtained are ΩM = 0.22+0.05–0.03 and ΩΛ = 1.06+0.05–0.10. Finally, a set of simulations show the ability of the method to measure ΩM and ΩΛ (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

9.
We present some results based on optical photometry of an unbiased subsample of 64 sources, from a sample of radio quasars 80 per cent complete. The quasars (z=0.4-2.8) show approximately a similar spectral energy distribution (SED). Only two quasars appear clearly differenciated, exhibiting redder colours than the rest, and they have low or moderate redshifts (z=0.50 and 1.12). Composite broad-band spectra for the remaining 62 quasars reveal the presence of a break in the SED at ∼ 3000 Å, where the average slope α (defined by Sν ∝ να) changes from αblue=0.11±0.16 at λ>3000 Å to αUV=-0.66±0.15 at λ<3000 Å. Composite spectra from a low and a high redshift subsample, with the redshift separation at the median value z=1.2, yields αUV=-0.87±0.20, for z<1.2 and αUV=-0.48±0.12 for z>1.2 and the difference is 98 per cent significant. This trend could be intrinsic or could arise from a dependence between αUV and the blue/UV luminosity, since the three quantities αUV - Lblue/UV - z are correlated. Finally, an intrinsic correlation is found between blue/UV and radio luminosity. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

10.
The “blazar sequence” posits that the most powerful BL Lacertae objects and flat-spectrum radio quasars should have relatively small synchrotron peak frequencies, ν peak, and that the least powerful such objects should have the highest ν peak values. This would have strong implications for our understanding of jet formation and physics and the possible detection of powerful, moderately high-redshift TeV blazars. I review the validity of the blazar sequence by using the results of very recent surveys and compare its detailed predictions against observational data. I find that the blazar sequence in its simplest form is ruled out. However, powerful flat-spectrum radio quasars appear not to reach the ν peak typical of BL Lacs. This could indeed be related to some sort of sequence, although it cannot be excluded that it is instead due to a selection effect.   相似文献   

11.
The minimum dissipative rate (MDR) method for deriving a coronal non-force-free magnetic field solution is partially evaluated. These magnetic field solutions employ a combination of three linear (constant-α) force-free-field solutions with one being a potential field (i.e., α=0). The particular case of the solutions where the other two α’s are of equal magnitude but of opposite sign is examined. This is motivated by studying the SOLIS (Synoptic Optical Long-term Investigation of the Sun (SOLIS), a National Solar Observatory facility) vector magnetograms of AR 10987, which show a global α value consistent with an α=0 value as evaluated by (∇×B) z /B z over the region. Typical of the current state of the observing technology, there is no definitive twist for input into the general MDR method. This suggests that the special α case, of two α’s with equal magnitudes and opposite signs, is appropriate given the data. Only for an extensively twisted active region does a dominant, nonzero α normally emerge from a distribution of local values. For a special set of conditions, is it found that (i) the resulting magnetic field is a vertically inflated magnetic field resulting from the electric currents being parallel to the photosphere, similar to the results of Gary and Alexander (Solar Phys. 186:123, 1999), and (ii) for α≈(α max /2), the Lorentz force per unit volume normalized by the square of the magnetic field is on the order of 1.4×10−10 cm−1. The Lorentz force (F L) is a factor of ten higher than that of the magnetic force d(B 2/8π)/dz, a component of F L. The calculated photospheric electric current densities are an order of magnitude smaller than the maximum observed in all active regions. Hence both the Lorentz force density and the generated electric current density seem to be physically consistent with possible solar dynamics. The results imply that the field could be inflated with an overpressure along the neutral line. However, the implementation of this or any other extrapolation method using the electric current density as a lower boundary condition must be done cautiously, with the current magnetography.  相似文献   

12.
Individual tidal torque λ 2,E 2 and apsidal-motion k 2 constants were calculated for 112 close eclipsing binaries (CEBs) with Detached components belonging to the Main Sequence (DMS-type) from the catalogue by Svechnikov and Perevozkina (Catalogue of orbital elements, masses and luminosities of variable stars of DMS-type and some results of its statistical treatment, Ural State University Press, Yekaterinburg, pp. 1–5, 1999) and for 95 detached binaries taken from the catalogue by Torres et al. (Astron. Astrophys. Rev. 18:67, 2010) on the base of theoretical evolutionary stellar models including tidal torque constants by Claret (Astron. Astrophys. 424:919, 2004). A method of the inversion of model track grid into isochrones was formulated as a complex interpolation procedure for DMS-binaries data. Sets of isochrones were computed in k 2–M, k 2–R, λ 2–M, λ 2–R, E 2–M, and E 2–R planes. Calculated tidal torque constants allow to test stellar structure theory by comparing observed and estimated values of apsidal motion period and analyzing the correlation between timescales of synchronization, circularization, magnetic braking, as well as nuclear burning of DMS-components.  相似文献   

13.
The evolution of the 27-day recurrence in the series of two solar indices (Wolf number WN and 10.7 cm radio flux F) and two geomagnetic indices (Dst and ζ, variance of the geomagnetic field recorded at a magnetic observatory) have been studied over the 1957 – 2007 time span. Spectral energies contained in two period domains (25 – 27.3 and 27.3 – 31 days), designated as E 1 and E 2, have been computed. Whereas the evolution of E 1 is the same for the four indices, that of E 2 is essentially different for WN and F on the one hand, Dst and ζ on the other hand. Some general conclusions on the dynamics of the solar outer layers are inferred from these results. First the solar activity, as measured by WN, and when averaged over a few years, evolves in the same way whatever the latitude. Second, two families of coronal holes (CHs) are identified; the rapidly and the slowly rotating CHs evolve quite differently.  相似文献   

14.
Aschwanden  Markus J. 《Solar physics》1999,190(1-2):233-247
Recent observations with EUV imaging instruments such as SOHO/EIT and TRACE have shown evidence for flare-like processes at the bottom end of the energy scale, in the range of E th≈1024–1027 erg. Here we compare these EUV nanoflares with soft X-ray microflares and hard X-ray flares across the entire energy range. From the observations we establish empirical scaling laws for the flare loop length, L(T)∼T, the electron density, n e(T)∼T 2, from which we derive scaling laws for the loop pressure, p(T)∼T 3, and the thermal energy, E th∼T 6. Extrapolating these scaling laws into the picoflare regime we find that the pressure conditions in the chromosphere constrain a height level for flare loop footpoints, which scales with h eq(T)∼T −0.5. Based on this chromospheric pressure limit we predict a lower cutoff of flare loop sizes at L ∖min≲5 Mm and flare energies E ∖min≲1024 erg. We show evidence for such a rollover in the flare energy size distribution from recent TRACE EUV data. Based on this energy cutoff imposed by the chromospheric boundary condition we find that the energy content of the heated plasma observed in EUV, SXR, and HXR flares is insufficient (by 2–3 orders of magnitude) to account for coronal heating.  相似文献   

15.
The variation of the fine-structure constant α = e 2 / ħc can be probed by comparing the wavelength of atomic transitions from the redshift of quasars in the Universe and laboratory over cosmological time scales t ~ 1010 yr. After a careful selection of pairs of lines, the Thong method with a derived analytical expression for the error analysis was applied to compute the α variation. We report a new constraint on the variation of the fine-structure constant based on the analysis of the CIV, NV, MgII, AlIII, and SiIV doublet absorption lines. The weighted mean value of the variation in α derived from our analysis over the redshift range 0.4939 ≤ z ≤ 3.7 is = ( 0.09 ± 0.07)×10−5. This result is three orders of magnitude better than the results obtained by earlier analysis of the same data on the constraint on Δα/α .  相似文献   

16.
A rigorous theoretical investigation of nonlinear electron-acoustic (EA) waves in a plasma system (containing cold electrons, hot electrons obeying a Boltzmann distribution, and hot ions obeying a nonthermal distribution) is studied by the reductive perturbation method. The modified Gardner (MG) equation is derived and numerically solved. It has been found that the basic characteristics of the EA Gardner solitons (GSs), which are shown to exist for α around its critical value α c [where α is the nonthermal parameter, α c is the value of α corresponding to the vanishing of the nonlinear coefficient of the Korteweg-de Vries (K-dV) equation, e.g. α c ≃0.31 for μ=n h0/n i0=0.5, σ=T h /T i =10, n h0, n i0 are, respectively, hot electron and nonthermal ion number densities at equilibrium, T h (T i ) is the hot electron (ion) temperature], are different from those of the K-dV solitons, which do not exist for α around α c , and mixed K-dV solitons, which are valid around α∼α c , but do not have any corresponding double layers (DLs) solution. The parametric regimes for the existence of the DLs, which are found to be associated with positive potential, are obtained. The present investigations can be observed in various space plasma environments (viz. the geomagnetic tail, the auroral regions, the cusp of the terrestrial magnetosphere, etc.).  相似文献   

17.
Aschwanden  Markus J.  Alexander  David 《Solar physics》2001,204(1-2):91-120
We present an analysis of the evolution of the thermal flare plasma during the 14 July 2000, 10 UT, Bastille Day flare event, using spacecraft data from Yohkoh/HXT, Yohkoh/SXT, GOES, and TRACE. The spatial structure of this double-ribbon flare consists of a curved arcade with some 100 post-flare loops which brighten up in a sequential manner from highly-sheared low-lying to less-sheared higher-lying bipolar loops. We reconstruct an instrument-combined, average differential emission measure distribution dEM(T)/dT that ranges from T=1 MK to 40 MK and peaks at T 0=10.9 MK. We find that the time profiles of the different instrument fluxes peak sequentially over 7 minutes with decreasing temperatures from T≈30 MK to 1 MK, indicating the systematic cooling of the flare plasma. From these temperature-dependent relative peak times t peak(T) we reconstruct the average plasma cooling function T(t) for loops observed near the flare peak time, and find that their temperature decrease is initially controlled by conductive cooling during the first 188 s, T(t)∼[1+(t/τcond)]−2/7, and then by radiative cooling during the next 592 s, T(t)∼[1−(t/τrad)]3/5. From the radiative cooling phase we infer an average electron density of n e=4.2×1011 cm−3, which implies a filling factor near 100% for the brightest observed 23 loops with diameters of ∼1.8 Mm that appear simultaneously over the flare peak time and are fully resolved with TRACE. We reproduce the time delays and fluxes of the observed time profiles near the flare peak self-consistently with a forward-fitting method of a fully analytical model. The total integrated thermal energy of this flare amounts to E thermal=2.6×1031 erg. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1014257826116  相似文献   

18.
We use a sample of Swift gamma-ray bursts (GRBs) to analyze the Amati and Yonetoku correlations. The first relation is between E p,i , the intrinsic peak energy of the prompt GRB emission, and E iso , the equivalent isotropic energy. The second relation is between E p,i and L iso , the isotropic peak luminosity. We select a sample of 71 Swift GRBs that have a measured redshift and whose observed $E^{obs}_{p}$ is within the interval of energy 15–150 keV with a relative uncertainty of less than 70 %. We seek to find correlation relations for long-duration GRBs (LGRBs) with a peak photon flux P ph ≥2.6 ph/cm2/s. Uncertainties (error bars) on the values of the calculated energy flux P, the energy E iso , and the peak isotropic luminosity L iso are estimated using a Monte Carlo approach. We find 27 Swift LGRBs that satisfy all our constraints. Results of our analyses of the sample of 71 GRBs and the selected subsample (27 GRBs) are in good agreement with published results. The plots of the two relations for all bursts show a large dispersion around the best straight lines in the sample of 71 LGRBs but not so much in the subsample of 27 GRBs.  相似文献   

19.
In recent years, the Lyman-α forest in quasar spectra has been used, together with N-body simulations, to determine the underlying matter distribution in the intergalactic medium (IGM). One of the key parameters to be known in order to compare observations and numerical simulations is the mean HI absorption in the IGM. To derive the latter, one has first to fit the quasar continuum. We have observed 20 high redshift and highly luminous QSOs (m V ≤ 17.5 and 2.40 ≤ z em ≤ 3.91) at intermediate spectral resolution, with either EMMI (ESO Multi-Mode Instrument) on the ESO-NTT telescope or CARELEC at the OHP (Observatoire de Haute-Provence), and applied different methods of determining the QSO continuum to this QSO sample. We have measured the amount of absorption, known as the flux decrement, DA, in the Lyman-α forest for these different methods and compared the results. In addition, we have compared DA values measured along the same lines of sight observed at high and intermediate spectral resolutions. We discuss the systematics resulting from the use of automatic continuum fitting methods.  相似文献   

20.
We present CCD BV and JHK s 2MASS photometric data for the open cluster NGC 1513. We observed 609 stars in the direction of the cluster up to a limiting magnitude of V∼19 mag. The star-count method showed that the centre of the cluster lies at α 2000=04 h 09 m 36 s , δ 2000=49°28′43″ and its angular size is r=10 arcmin. The optical and near-infrared two-colour diagrams revealed the colour excesses in the direction of the cluster as E(B−V)=0.68±0.06, E(J−H)=0.21±0.02 and E(J−K s )=0.33±0.04 mag. These results are consistent with normal interstellar extinction values. Optical and near-infrared Zero Age Main-Sequences (ZAMS) provided an average distance modulus of (m−M)0=10.80±0.13 mag, which can be translated into a distance of 1440±80 pc. Finally, using Padova isochrones we determined the metallicity and age of the cluster as Z=0.015±0.004 ([M/H]=−0.10±0.10 dex) and log (t/yr)=8.40±0.04, respectively.  相似文献   

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