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1.
《New Astronomy》2003,8(2):141-153
In many GRB inner engine models the highly relativistic GRB jets are engulfed by slower moving matter. This could result in different beaming for the prompt γ-ray emission and for the lower energy afterglow. In this case we should expect that some observer will see on-axis orphan afterglows: X-ray, optical and radio afterglows within the initial relativistic ejecta with no preceding GRB; the prompt γ-ray emission is pointing elsewhere. We show that the observations of the WFC on BeppoSAX constrain with high certainty the prompt X-ray beaming factor to be less than twice the prompt γ-ray beaming. The results of Ariel 5 are consistent with this interpretation. The RASS from ROSAT and HEAO-1 constrain the X-ray beaming factor at 400 and 20 min after the burst, respectively, to be comparable and certainly not much larger than the γ-ray beaming factor. There is no direct limit on the optical beaming. However, we show that observations of several months with existing hardware could result in a useful limit on the optical beaming factor of GRB afterglows.  相似文献   

2.
《New Astronomy》2003,8(5):495-505
We present general analytic expressions for GRB afterglow light curves arising from a variable external density profile and/or a variable energy in the blast wave. The former could arise from a clumpy ISM or a variable stellar wind; The latter could arise from refreshed shocks or from an angular dependent jet structure (patchy shell). Both scenarios would lead to a variable light curve. Our formalism enables us to invert the observed light curve and obtain possible density or energy profiles. The optical afterglow of GRB 021004 was detected 537 s AB (after the burst) [GCN (2002) 1564]. Extensive follow up observations revealed a significant temporal variability. We apply our formalism to the R-band light curve of GRB 021004 and we find that several models provide a good fit to the data. We consider the patchy shell model with p=2.2 as the most likely explanation. According to this model our line of sight was towards a ‘cold spot’ that has lead to a relativity low γ-ray flux and an initially weak afterglow (while the X-ray afterglow flux after a day was above average). Observations above the cooling frequency, νc, could provide the best way to distinguish between our different models.  相似文献   

3.
We investigate the relation between the optical (g-band) and X-ray (0.5–10 keV) luminosities of accreting nonmagnetic white dwarfs. According to the present-day counts of the populations of star systems in our Galaxy, these systems have the highest space density among the close binary systems with white dwarfs. We show that the dependence of the optical luminosity of accreting white dwarfs on their X-ray luminosity forms a fairly narrow one-parameter curve. The typical half-width of this curve does not exceed 0.2–0.3 dex in optical and X-ray luminosities, which is essentially consistent with the amplitude of the aperiodic flux variability for these objects. At X-ray luminosities L x ～ 1032 erg s?1 or lower, the optical g-band luminosity of the accretion flow is shown to be related to its X-ray luminosity by a factor ～2–3. At even lower X-ray luminosities (L x ? 1030 erg s?1), the contribution from the photosphere of the white dwarf begins to dominate in the optical spectrum of the binary system and its optical brightness does not drop below M g ～ 13–14. Using the latter fact, we show that in current and planned X-ray sky surveys, the family of accreting nonmagnetic white dwarfs can be completely identified to the distance determined by the sensitivity of an optical sky survey in this region. For the Sloan Digital Sky Survey (SDSS) with a limiting sensitivity m g ～ 22.5, this distance is ～400–600 pc.  相似文献   

4.
We describe the first results of our observations of the exceptionally bright optical afterglow from the cosmic gamma-ray burst (GRB) of March 29, 2003 (030329), with the 1.5-m Russian-Turkish telescope (RTT150) installed at the TUBITAK National Observatory (Turkey) at Mount Bakyrlytepe. RTT150 was one of the first medium-class telescopes pointed at the afterglow. The observations began as early as about six hours after the GRB. During the first five hours of our observations, the BV RI flux fell off exactly as a power law with the same slope ?1.19±0.01. Subsequently, in all of the BV RI bands, we observed the same increase in the power-law slope of the light curve to a value that was later recorded during the observations at observatories in the western hemisphere. The break in the power-law light curve occurs at t ? t 0 ≈ 0.57 days (13.5 h) and lasts for about 0.2 days. Apart from this smooth decrease in the flux, the afterglow exhibited no flux variability. The upper limits on the variability are 10–1% on time scales of 0.1–1000 s, respectively. The BV RI spectral flux distribution during the first night of our observations closely corresponds to a power-law spectrum with a spectral index α=0.66±0.01. The change in the power-law slope of the light curve at the end of our observations is probably attributable to the deceleration of the ultrarelativistic jet to a gamma factor when its structural features begin to show up in the light curve. The radio, optical, and X-ray broadband spectrum is consistent with the assumption about the synchrotron radiation of the ultrarelativistic jet. This unique object continues to be observed with RTT150.  相似文献   

5.
The existence or otherwise of X-ray luminous star-forming galaxies has been an open question since the era of the Einstein satellite. Various authors have claimed the discovery of X-ray luminous star-forming galaxies but in many cases more careful spectroscopic studies of these objects have shown that many of them are in fact obscured AGN. In order to investigate the possibility that such a class of galaxies do exist, we have carried out a cross-correlation between optical and IRAS samples of galaxies which are known to contain large numbers of star-forming galaxies and catalogues of sources detected in X-ray surveys. The selection criteria for the optical follow-up observations was based on their X-ray and infrared (IRAS) colours and their X-ray luminosities. We note that this sample is by no means complete or uniformly selected and hence cannot be used for statistical studies; nevertheless, confirmation of the existence of such a class of objects would be an important step and would require us to understand the physical process responsible for such powerful X-ray emission. We have initiated an optical spectroscopic survey in order to obtain accurate spectroscopic classifications for all the objects which are claimed to be starburst galaxies. Here we present preliminary results from this survey. We have discovered a number of starburst galaxies with X-ray luminosities above ～ 1041 erg s-1 (for H 0=50 km s-1 Mpc-1).We investigate possible origins for the X-ray emission in individual cases.  相似文献   

6.
Based on our UBV RI observations and X-ray data from the RXTE satellite, we have investigated the variability of the galaxy 3C 120 over the period 1996–2008. The relative variability amplitude in the U and B bands without any subtraction of the contribution from the underlying galaxy is 23 and 22%, respectively, against 21% in the X-ray band. The autocorrelation function based on the B-band data is considerably wider than that based on the X-ray data. The structure functions on a time scale from 1 to ～100–300 days in the X-ray and optical spectral ranges have the form of a power law (SF ～ τ b ). However, their indices differ significantly: b = 0.42 in the X-ray band and b = 1.36 in the B band. Considering the X-ray and optical variabilities as a superposition of independent flares in a wide range of durations, we may conclude that the amplitudes of short flares in the X-ray band are higher than those in the optical one and, conversely, the relative amplitudes of long flares in the X-ray band are slightly lower than those in the optical one, i.e., short events dominate in the X-ray band. The optical flux variations in the R c and I c bands lag significantly behind those in the B band, by 3.9 ?0.7 +1.0 and 6.2 ?0.6 +1.1 days, respectively, if the lag is estimated from the centroid of the cross-correlation function. The X-ray variability on a time scale of about 1800 days (～5 yr) lags behind the B-band variations by 5.3 ?3.3 +2.7 days, but the confidence level of this estimate is only 87%. A more detailed analysis of the correlation between the X-ray and optical emissions has revealed a fairly complex picture: different degrees of correlation between the optical and X-ray fluxes are observed at different times.  相似文献   

7.
The afterglow of GRB 050401 presents several novel and interesting features. (i) An initially faster decay in optical band than in X-rays. (ii) A break in the X-ray light curve after ∼0.06 d with an unusual slope after the break. (iii)The X-ray afterglow does not show any spectral evolution across the break while the R -band light curve does not show any break. We have modelled the observed multiband evolution of the afterglow of GRB 050401 as originating in a two-component jet, and interpreting the break in X-ray light curve as due to lateral expansion of a narrow collimated outflow which dominates the X-ray emission. The optical emission is attributed to a wider jet component. Our model reproduces all the observed features of multiband afterglow of GRB 050401. We present optical observations of GRB 050401 using the 104-cm Sampurnanand Telescope at the Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital. Results of the analysis of multiband data are presented and compared with GRB 030329, the first reported case of double jet.  相似文献   

8.
A sample of cataclysmic variables (CVs) detected among the X-ray sources of the 400 square degree (400d) survey performed based on ROSAT pointings is presented. A technique for selecting CVs among the X-ray sources using additional optical and infrared data, based on Sloan Digital Sky Survey andWISE data, is described. We present the optical observations of the selected objects carried out mainly with the Russian–Turkish 1.5-m telescope (RTT-150) and the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences (BTA). Some observations have also been performed with the 1.6-m AZT-33IK telescope of the Institute of Solar–Terrestrial Physics, the Siberian branch of the Russian Academy of Sciences. Eight CVs, four of which were detected in our work, have been selected by now. Based on this sample, we have obtained preliminary constraints on the X-ray luminosity function of CVs in the solar neighborhood in the range of low luminosities, L X ~ 1029–1030 erg s?1 (0.5–2 keV). The logarithmic slope of the CV luminosity function in this luminosity range is shown to become gentler than that at L X > 1031 erg s?1. It follows from our estimates of the CV luminosity function that several thousand CVs will be detected in the SRG all-sky survey at high Galactic latitudes, which will allow much more accurate measurements of their X-ray luminosity function to be obtained.  相似文献   

9.
《New Astronomy Reviews》2000,44(7-9):491-496
We report on a three-year program of coordinated X-ray and optical monitoring of the narrow-line Seyfert 1 galaxy NGC 4051. The rapid continuum variations observed in the X-ray fluxes are not detected in the optical, although the X-ray and optical continuum fluxes are correlated on time scales of many weeks and longer. Variations in the flux of the broad Hβ line are found to lag behind the optical continuum variations by approximately 6 days (with an uncertainty of 2–3 days), and combining this with the line width yields a virial mass estimate of ∼1.1×106 M⊙, at the very low end of the distribution of AGN masses measured by line reverberation. Strong variability of HeII λ4686 is also detected, and the response time measured is similar to that of Hβ, but with a much larger uncertainty. The HeII λ4686 line is almost five times broader than Hβ, and it is strongly blueward asymmetric, as are the high-ionization UV lines recorded in archive spectra of NGC 4051. The data are consistent with the Balmer lines arising in a low-inclination (nearly face-on) disk-like configuration, and the high-ionization lines arising in an outflowing wind, of which we observe preferentially the near side. During the third year of monitoring, both the X-ray continuum and the HeII λ4686 line went into extremely low states, although the optical continuum and the Hβ broad line were both still present and variable. We suggest that the inner part of the accretion disk may have gone into an advection-dominated state, yielding little radiation from the hotter inner disk.  相似文献   

10.
We derive a conservative coincidence time window for joint searches of gravitational-wave (GW) transients and high-energy neutrinos (HENs, with energies ?100 GeV), emitted by gamma-ray bursts (GRBs). The last are among the most interesting astrophysical sources for coincident detections with current and near-future detectors. We take into account a broad range of emission mechanisms. We take the upper limit of GRB durations as the 95% quantile of the T90’s of GRBs observed by BATSE, obtaining a GRB duration upper limit of ∼150 s. Using published results on high-energy (>100 MeV) photon light curves for 8 GRBs detected by Fermi LAT, we verify that most high-energy photons are expected to be observed within the first ∼150 s of the GRB. Taking into account the breakout-time of the relativistic jet produced by the central engine, we allow GW and HEN emission to begin up to 100 s before the onset of observable gamma photon production. Using published precursor time differences, we calculate a time upper bound for precursor activity, obtaining that 95% of precursors occur within ∼250 s prior to the onset of the GRB. Taking the above different processes into account, we arrive at a time window of tHEN − tGW ∈ [−500 s, +500 s]. Considering the above processes, an upper bound can also be determined for the expected time window of GW and/or HEN signals coincident with a detected GRB, tGW − tGRB ≈ tHEN − tGRB ∈ [−350 s, +150 s]. These upper bounds can be used to limit the coincidence time window in multimessenger searches, as well as aiding the interpretation of the times of arrival of measured signals.  相似文献   

11.
We have computed a spherically symmetric model for the interaction of matter ejected during the outburst of a classical nova with the stellar wind from its optical component. This model is used to describe the intense X-ray outburst (the peak 3–20 keV flux was ～2 Crab) of the binary system CI Camelopardalis in 1998. According to our model, the stellar wind from the optical component heated by a strong shock wave produced when matter is ejected from the white dwarf as the result of a thermonuclear explosion on its surface is the emission source in the standard X-ray band. Comparison of the calculated and observed time dependences of the mean radiation temperature and luminosity of the binary system during its outburst has yielded very important characteristics of the explosion. We have been able to measure the velocity of the ejected matter immediately after the onset of the explosion for the first time: it follows from our model that the ejected matter had a velocity of ～2700 km s?1 even on 0.1–0.5 day after the outburst onset and it flew with such a velocity for the first 1–1.5 day under an external force, possibly, the radiation pressure from the white dwarf. Subsequently, the matter probably became transparent and began to decelerate. The time dependence of the mean radiation temperature at late expansion phases has allowed us to estimate the mass of the ejected matter, ～10?7–10?6 M ⊙. The mass loss rate in the stellar wind required to explain the observed peak luminosity of the binary system during its outburst has been estimated to be \(\dot M\) ～ (1 ? 2) × 10?6 M ⊙ yr?1.  相似文献   

12.
Observational parameters of the optical and gamma-ray emissions from 58 gamma-ray bursts (GRBs) with discovered afterglows and known redshifts are analyzed. The distributions of these parameters and pair correlations between them are studied. Approximately half of the objects exhibit a relatively slow decrease in the optical flux at initial afterglow phases (with a power-law index in the decay law α < 1). Correlations have been found between the luminosities, energies, and durations of the optical and gamma-ray emissions, which can be explained by the presence of universal features in the light curves. A correlation of the peak luminosity for afterglows with the redshift and an anticorrelation of their durations with the redshift have been found for the first time. Against the background of a weak z dependence of the total afterglow energy, this effect can be explained by cosmological evolution of the GRB environment, which determines the rate of optical energy release.  相似文献   

13.
Multicolor photometric observations of the optical afterglow from GRB 060526 with the Russian-Turkish 1.5-m RTT-150 telescope (Mount Bakyrlytepe, Turkey) are presented. The afterglow light curve was measured in detail starting from about 5 h after the GRB and over five ensuing nights. In addition, upper limits were obtained on the rapid variability of the afterglow on the first night of observations and the history of afterglow color variations was measured in detail. In the time interval from 6 to 16 h after the burst, the flux gradually decreased approximately as a power law with a slope of ?1.14 ± 0.02. Subsequently, variability was observed on a time scale δt < t and the afterglow began to decay much faster. The afterglow color was approximately constant (V?R ≈ 0.5) throughout the observations, despite the flux variability. Variability time scales up to δt/t ≈ 0.0055 were observed at ΔF ν/F ν ≈ 0.3, which violates many constraints on the variability of the observed emission from an ultrarelativistic jet obtained by Ioka et al. (2005). We suggest explaining this variability by the fact that the shell motion is no longer ultrarelativistic at this time.  相似文献   

14.
We describe the technique and results of our numerical simulation of the effects related to the heating of the circumstellar medium by hard gamma-ray burst radiation using a modified STELLA radiation-hydrodynamics code. The code modification allows the processes of nonstationary heating and change in the state of the matter to be taken into account. We present the computed light curves and emergent gamma-ray, X-ray, and optical spectra for several models of the circumstellar medium (shells) with different geometrical sizes, densities, density profiles, chemical compositions, and temperatures. Depending on the model parameters, the total thermal and optical luminosities of the heated shell can reach 1047 and 1043 erg s−1, respectively. The presence of bumps in the X-ray and optical GRB afterglow light curves can be explained by such effects.  相似文献   

15.
The RELEC scientific instrumentation onboard the Vernov spacecraft launched on July 8, 2014, included the DRGE gamma-ray and electron spectrometer. This instrument incorporates a set of scintillation phoswich detectors, including four identical X-ray and gamma-ray detectors in the energy range from 10 keV to 3 MeV with a total area of ~500 cm2 directed toward the nadir, and an electron spectrometer containing three mutually orthogonal detector units with a geometry factor of ~2 cm2 sr, which is also sensitive to X-rays and gamma-rays. The goal of the space experiment with the DRGE instrument was to investigate phenomena with fast temporal variability, in particular, terrestrial gammaray flashes (TGFs) and magnetospheric electron precipitations. However, the detectors of the DRGE instrument could record cosmic gamma-ray bursts (GRBs) and allowed one not only to perform a detailed analysis of the gamma-ray variability but also to compare the time profiles with the measurements made by other instruments of the RELEC scientific instrumentation (the detectors of optical and ultraviolet flashes, the radio-frequency and low-frequency analyzers of electromagnetic field parameters). We present the results of our observations of cosmicGRB 141011A and GRB 141104A, compare the parameters obtained in the GBM/Fermi and KONUS–Wind experiments, and estimate the redshifts and E iso for the sources of these GRBs. The detectability of GRBs and good agreement between the independent estimates of their parameters obtained in various experiments are important factors of the successful operation of similar detectors onboard the Lomonosov spacecraft.  相似文献   

16.
During the GRIF experiment onboard the Mir orbiting station, cosmic gamma-ray bursts (GRBs) were observed in the photon energy range 10–300 keV. We developed a technique for selecting events, cosmic GRB candidates, based on output readings from the PX-2 scintillation spectrometer, the main astrophysical instrument. Six events interpreted as cosmic GRBs were identified at a threshold sensitivity level of ≥10?7 erg cm?2. The GRIF burst detection rate recalculated to all the sky is ～103 yr?1 (fluence ≥10?7 erg cm?2). This rate matches the BATSE/CGRO estimate and significantly differs from the value predicted by the S?3/2 dependence, which holds for a spatially uniform source distribution. The GRB detection rate at low peak fluxes is compared with the results of analysis for BATSE/CGRO “nontriggered” events and with predictions of major cosmological models. We conclude that the PX-2 observational data on faint cosmic GRBs are consistent with predictions of models with the highest frequency of GRB occurrence at z ≥1.5–2.  相似文献   

17.
The central compact object for some gamma-ray bursts (GRBs) may be a strongly magnetized millisecond pulsar. It can inject energy to the outer shock of the GRB by through the magnetic dipole radiation, and therefore causes the shallow decay of the early afterglow. Recently, from a large number of GRB X-ray afterglows observed by Swift/XRT(X-ray telescope), it is revealed that many of them exhibit the shallow decay about 102∼104 s after the burst prompt emission. We have fitted the X-ray afterglow light curves of 11 GRBs by using the energy injection model of a magnetar with the rotation period in the millisecond order of magnitude. The obtained result shows the validity and universality of the magnetar energy injection model in explaining the shallow decay of afterglows, and simultaneously provides some constraints on the magnetic field strength and rotation period of the central magnetar.  相似文献   

18.
We present a preliminary analysis of multiple X-ray (0.1–2.5 keV) observations of HD 50896 andγ Velorum obtained with theROSAT satellite. For HD 50896, our 8 observations show variability at the 30% level on timescales of ～ 1 day, together with larger (× 1.7) epoch-changes, but no evidence for rapid variability. No phase-dependent modulation is apparent on the 3d.766 optical period. The mean PSPC spectrum gives kT = 0.28 keV, log N(H) = 20.6, and Lx = 3.8 × 1032 erg s?1, and implies that the observed X-rays have undergone little absorption in the WN5 wind. Forγ Velorum, we have 13 observations secured over several cycles in the 78d.5 binary period. At most binary phases, the X-ray emission is relatively constant, with kT ? 0.19 keV, log N(H) = 20.2, and Lx = 2.5 × 1031 erg s?1. Near orbital phase 0.5, the X-ray emission is enhanced by a factor of 4, due almost entirely to an additional harder component with kT ≥ 2 keV. We believe this is due to X-ray emission produced in the collision of the two stellar winds.  相似文献   

19.
We analyze in detail the ASCA observations of the hard X-ray source IGR J16318-4848, which was recently discovered by the INTEGRAL observatory (Courvoisier et al. 2003). The source has an anomalously hard spectrum in the energy range 0.5–10 keV and is virtually undetectable below 4 keV because of strong photoabsorption (n H L>4×1023 cm?2). The Kα line of neutral or weakly ionized iron with an equivalent width of ～2.5 keV dominates in the energy range 4–10 keV. There is also evidence for the presence of a second line at energy ～7 keV. Our analysis of archival observational data for the infrared counterpart of IGR J16318-4848 that was discovered by Foschini et al. (2003) revealed the source in the wavelength range 1–15 µm. Available data suggest that the object can be an X-ray binary system surrounded by a dense envelope. The source may be a high-mass X-ray binary similar to GX 301-2. We believe that IGR J16318-4848 can be the first representative of a hitherto unknown population of strongly absorbed Galactic X-ray sources that could not be detected by previous X-ray observatories.  相似文献   

20.
An intense outburst of hard radiation (with a peak flux of ～50 mCrab) was detected from the X-ray transient AX J1749.1-2733 by the IBIS/ISGRI gamma-ray telescope onboard the INTEGRAL observatory when the Galactic center field was monitored on September 8–10, 2003. Previously, this source had never been observed in a bright X-ray state. During the outburst, the source’s radiation spectrum was gently sloping and hard (extended to ～100 keV), followed a power law in the standard X-ray energy range, and had an exponential cutoff above 40–50 keV. The spectral hardness decreased with increasing flux. These and other properties described here and the shortness of the outburst (<2 days) allow the source to be attributed to the group of fast X-ray transients many representatives of which have an early O-B supergiant as their optical counterpart. Possible causes of the outbursts of fast transients are discussed. We show that accretion from the supergiant’s stellar wind should have led to intense persistent radiation from transients. The absence of radiation can be explained by the ejection of accreting matter from the system (propeller effect) during its contact with the magnetosphere of a rapidly rotating neutron star. Transient outbursts could originate in sources of this type if the spin period of their neutron star P s differed only slightly from the critical period P s * ? 3 s at which the propeller effect is still possible. The outburst is triggered by an insignificant rise in the local stellar wind density, by a factor of (P s * /P s)7/3. The entire outburst profile cannot be explained by an individual inhomogeneity in the wind, but is the reflection of a long-term (～2 days for AX J1749.1-2733) change in the rate of wind outflow from the supergiant’s surface facing the compact source. The rate of wind outflow could be enhanced through X-ray heating of the supergiant’s surface.  相似文献   

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