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1.
In this work, we report on the intense flaring activity from Mkn-421 in X-ray and γ-ray regimes simultaneously observed by Swift-XRT/BAT and Fermi-LAT satellite telescopes in February 2010. With the aim of understanding the underlying physics of the flaring state in Mkn-421, we have performed a detailed spectral analysis of Swift/XRT and Fermi/LAT observations of Mkn-421 during February 12–25, 2010 (MJD 55239–55252). Over this period, we study the daily light curves and spectral variability of the source in 1–10 keV, 0.1–1 GeV and 1–100 GeV energy bands. We have performed the spectral analysis of Swift-XRT and Fermi/LAT observations to study the spectral evolution in the X-ray and gamma-ray energy domains respectively. We also compute the fractional variability amplitude in both the energy bands during the above period. We study trends between spectral parameters and physical insights provided by the parameter responsible for X-ray and γ-ray emission from the source. We search for energetic features phenomenologically linked to the single zone SSC model for blazar emission. We also produce the broad band SED with a leptonic single zone SSC model for the source.  相似文献   

2.
The extragalactic background light (EBL) is one of the fundamental observational quantities in cosmology. All energy releases from resolved and unresolved extragalactic sources, and the light from any truly diffuse background, excluding the cosmic microwave background (CMB), contribute to its intensity and spectral energy distribution. It therefore plays a crucial role in cosmological tests for the formation and evolution of stellar objects and galaxies, and for setting limits on exotic energy releases in the universe. The EBL also plays an important role in the propagation of very high energy γ-rays which are attenuated en route to Earth by pair producing γ–γ interactions with the EBL and CMB. The EBL affects the spectrum of the sources, predominantly blazars, in the ∼10 GeV–10 TeV energy regime. Knowledge of the EBL intensity and spectrum will allow the determination of the intrinsic blazar spectrum in a crucial energy regime that can be used to test particle acceleration mechanisms and very high energy (VHE) γ-ray production models. Conversely, knowledge of the intrinsic γ-ray spectrum and the detection of blazars at increasingly higher redshifts will set strong limits on the EBL and its evolution. This paper reviews the latest developments in the determination of the EBL and its impact on the current understanding of the origin and production mechanisms of γ-rays in blazars, and on energy releases in the universe. The review concludes with a summary and future directions in Cherenkov Telescope Array techniques and in infrared ground-based and space observatories that will greatly improve our knowledge of the EBL and the origin and production of very high energy γ-rays.  相似文献   

3.
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4.
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5.
The EGRET observations have confirmed and proposed the new isotropically distributed γ-ray background, but the known objects radiating γ-rays can not supply so much radiation. Meanwhile, EGRET also reveals a population of γ-ray sources with no radio counterparts which are isotropically distributed in the sky, indicating their possible cosmological origins. Wang et al.[13] proposed a new γ-ray radiation process driven by the radiation feedback of AGNs. The energy of the radiation peaks around 1 GeV—0.1 TeV with the typical luminosity of 1042—1043 ergs · s?1. This kind of radiation process in the radio quiet quasars make them the potential γ-ray radiation sources as well as the contributors to the γ-ray background. We consider two cases in which the seed photons in the inverse-Compton processes are from the accretion disks of quasars and cosmic microwave background (CMB), respectively. We find that the former contributes 78%—92% of the background radiation around 1 GeV, while the contribution from the latter is negligible. The radio quiet quasars are highly likely to become the objects which contribute the most energy to the γ-ray background around 1 GeV.  相似文献   

6.
《Astroparticle Physics》2007,26(6):380-390
Ground-based arrays of imaging atmospheric Cherenkov telescopes have emerged as the most sensitive γ-ray detectors in the energy range of about 100 GeV and above. The strengths of these arrays are a very large effective collection area on the order of 105 m2, combined with excellent single photon angular and energy resolutions. The sensitivity of such detectors is limited by statistical fluctuations in the number of Cosmic-ray initiated air showers that resemble γ-ray air showers in many ways. In this paper, we study the performance of simple event reconstruction methods when applied to simulated data of the Very Energetic Radiation Imaging Telescope Array System (VERITAS) experiment. We review methods for reconstructing the arrival direction and the energy of the primary photons, and examine means to improve on their performance. For a software threshold energy of 300 GeV (100 GeV), the methods achieve point source angular and energy resolutions of σ63% = 0.1° (0.2°) and σ68% = 15% (22%), respectively. The main emphasis of the paper is the discussion of γ–hadron separation methods for the VERITAS experiment. We find that the information from several methods can be combined based on a likelihood ratio approach and the resulting algorithm achieves a γ–hadron suppression with a quality factor that is substantially higher than that achieved with the standard methods used so far.  相似文献   

7.
The reflex motion of a star induced by a planetary companion is too small to detect by photographic astrometry. The apparent discovery in the 1960s of planetary systems around certain nearby stars, in particular Barnard’s star, turned out to be spurious. Conventional stellar radial velocities determined from photographic spectra at that time were also too inaccurate to detect the expected reflex velocity changes. In the late 1970s and early 1980s, the introduction of solid-state, signal-generating detectors and absorption cells to impose wavelength fiducials directly on the starlight, reduced radial velocity errors to the point where such a search became feasible. Beginning in 1980, our team from UBC introduced an absorption cell of hydrogen fluoride gas in front of the CFHT coudé spectrograph and, for 12 years, monitored the radial velocities of some 29 solar-type stars. Since it was assumed that extra-solar planets would most likely resemble Jupiter in mass and orbit, we were awarded only three or four two-night observing runs each year. Our survey highlighted three potential planet hosting stars, γ Cep (K1 IV), β Gem (K0 III), and ? Eri (K2 V). The putative planets all resembled Jovian systems with periods and masses of: 2.5 years and 1.4 MJ, 1.6 years and 2.6 MJ, and 6.9 years and 0.9 MJ, respectively. All three were subsequently confirmed from more extensive data by the Texas group led by Cochran and Hatzes who also derived the currently accepted orbital elements.None of these three systems is simple. All five giant stars and the supergiant in our survey proved to be intrinsic velocity variables. When we first drew attention to a possible planetary companion to γ Cep in 1988 it was classified as a giant, and there was the possibility that its radial velocity variations and those of β Gem (K0 III) were intrinsic to the stars. A further complication for γ Cep was the presence of an unseen secondary star in an orbit with a period initially estimated at some 30 years. The implication was that the planetary orbit might not be stable, and a Jovian planet surviving so close to a giant then seemed improbable. Later observations by others showed the stellar binary period was closer to 67 years, the primary was only a sub-giant and a weak, apparently synchronous chromospheric variation disappeared. Chromospheric activity was considered important because κ1 Cet, one of our program stars, showed a significant correlation of its radial velocity curve with chromospheric activity.? Eri is a young, magnetically active star with spots making it a noisy target for radial velocities. While the signature of a highly elliptical orbit (e = 0.6) has persisted for more than three planetary orbits, some feel that even more extensive coverage is needed to confirm the identification despite an apparent complementary astrometric acceleration detected with the Hubble Space Telescope.We confined our initial analyses of the program stars to looking for circular orbits. In retrospect, it appears that some 10% of our sample did in fact have Jovian planetary companions in orbits with periods of years.  相似文献   

8.
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9.
We present the ensemble properties of 31 comets (27 resolved and 4 unresolved) observed by the Sloan Digital Sky Survey (SDSS). This sample of comets represents about 1 comet per 10 million SDSS photometric objects. Five-band (u, g, r, i, z) photometry is used to determine the comets’ colors, sizes, surface brightness profiles, and rates of dust production in terms of the Afρ formalism. We find that the cumulative luminosity function for the Jupiter Family Comets in our sample is well fit by a power law of the form N(<H) ∝ 10(0.49±0.05)H for H < 18, with evidence of a much shallower fit N(<H) ∝ 10(0.19±0.03)H for the faint (14.5 < H < 18) comets. The resolved comets show an extremely narrow distribution of colors (0.57 ± 0.05 in g ? r for example), which are statistically indistinguishable from that of the Jupiter Trojans. Further, there is no evidence of correlation between color and physical, dynamical, or observational parameters for the observed comets.  相似文献   

10.
We examine spectral properties of the SDSS quasar J093201.60 + 031858.7, in particular the presence of strong blue peaks in the Balmer emission lines offset from the narrow lines by approximately 4200 km s?1. Asymmetry in the broad central component of the Hβ line indicates the presence of a double-peaked emitter. However, the strength and sharpness of the blue Hβ and blue Hγ peaks make this quasar spectrum unique among double-peaked emitters identified from SDSS spectra. We fit a disk model to the Hβ line and compare this object with other unusual double-peaked quasar spectra, particularly candidate binary supermassive black holes (SMBHs). Under the binary SMBH scenario, we test the applicability of a model in which a second SMBH may produce the strong blue peak in the Balmer lines of a double-peaked emitter. If there were only one SMBH, a circular, Keplerian disk model fit would be insufficient, indicating some sort of asymmetry is required to produce the strength of the blue peak. In either case, understanding the nature of the complex line emission in this object will aid in further discrimination between a single SMBH with a complex accretion disk and the actual case of a binary SMBH.  相似文献   

11.
Determining the optical constants of Titan aerosol analogues, or tholins, has been a major concern for the last three decades because they are essential to constrain the numerical models used to analyze Titan’s observational data (albedo, radiative transfer, haze vertical profile, surface contribution, etc.). Here we present the optical constant characterization of tholins produced with an RF plasma discharge in a (95%N2–5%CH4) gas mixture simulating Titan’s main atmospheric composition, and deposited as a thin film on an Al–SiO2 substrate. The real and imaginary parts, n and k, of the tholin complex refractive index have been determined from 370 nm to 900 nm wavelength using spectroscopic ellipsometry. The values of n decrease from n = 1.64 (at 370 nm) to n = 1.57 (at 900 nm) as well as the values of k which feature two behaviors: an exponential decay from 370 nm to 500 nm, with k = 12.4 × e?0.018λ (where λ is expressed in nm), followed by a plateau, with k = (1.8 ± 0.2) × 10?3. The trends observed for the PAMPRE tholins optical constants are compared to those determined for other Titan tholins, as well as to the optical constants of Titan’s aerosols retrieved from observational data.  相似文献   

12.
Supernova remnants (SNRs) are among the most important targets for γ-ray observatories. Being prominent non-thermal sources, they are very likely responsible for the acceleration of the bulk of Galactic cosmic rays (CRs). To firmly establish the SNR paradigm for the origin of cosmic rays, it should be confirmed that protons are indeed accelerated in, and released from, SNRs with the appropriate flux and spectrum. This can be done by detailed theoretical models which account for microphysics of acceleration and various radiation processes of hadrons and leptons. The current generation of Cherenkov telescopes has insufficient sensitivity to constrain theoretical models. A new facility, the Cherenkov Telescope Array (CTA), will have superior capabilities and may finally resolve this long standing issue of high-energy astrophysics. We want to assess the capabilities of CTA to reveal the physics of various types of SNRs in the initial 2000 years of their evolution. During this time, the efficiency to accelerate cosmic rays is highest. We perform time-dependent simulations of the hydrodynamics, the magnetic fields, the cosmic-ray acceleration, and the non-thermal emission for type Ia, Ic and IIP SNRs. We calculate the CTA response to the γ-ray emission from these SNRs for various ages and distances, and we perform a realistic analysis of the simulated data. We derive distance limits for the detectability and resolvability of these SNR types at several ages. We test the ability of CTA to reconstruct their morphological and spectral parameters as a function of their distance. Finally, we estimate how well CTA data will constrain the theoretical models.  相似文献   

13.
The BVR photometric light curves of the eclipsing binary BD And were obtained in 2008 and 2009. We estimated the mass ratio of the system as 0.97 and the photometric solutions were derived. The results show that BD And is a detached binary system, whose components have a little temperature difference of about 40 K. By analyzing photometric available light minimum times, we also derived an update ephemeris and found for the first time a possible periodic oscillation with an amplitude of 0.011 days and a period of 9.6 years. The results indicate that the periodic oscillation could be caused by a third component physically attached to the eclipsing binary. After removing the light variations due to the eclipses and proximity effects, the light-curve distortions are further explained by the pulsation of the primary component with a dominant period of ∼1 day. In accordance with the position of the primary component on the Hertzsprung–Russell diagram and its pulsation period, the primary component of BD And could be an excellent γ Doradus candidate. It is rarely phenomenon that a component of the eclipsing binary system is a γ Doradus variable.  相似文献   

14.
In this study, we present the first Johnson BV photometry of the eclipsing binary star ET Bootis, which is member of a physically connected visual pair. Analysis of times of light minima enables us to calculate accurate ephemeris of the system via O–C analysis and observed an increase in period which we believe is a result of the light-time effect in the outer visual orbit. Secondly, we determined the total brightness and color of the system in light maxima and minima. Photometric solution of the system indicates that the contribution of the visual pair to the total light is about 40% in Johnson V band. Furthermore, photometric analysis shows that the primary star in the eclipsing binary has F8 spectral type while it confirms the G5 spectral type for the visual pair. Masses of the components in eclipsing binary are M1 = 1.109 ± 0.014 M⊙ and M2 = 1.153 ± 0.011 M⊙. Absolute radii of the components are R1 = 1.444 ± 0.007 R⊙ and R2 = 1.153 ± 0.007 R⊙. Physical properties of the components leads 176 ± 7 pc distance for the system and suggests an age of 6.5 billion years.  相似文献   

15.
To study the accretional growth of rimmed chondrules and their agglomerates in the solar nebula, we measured the restitution coefficients, ε, and the sticking velocities to a porous silica layer, vc, by impacting the silica layer with a glass ball at velocities from 0.1 to 80 m s?1. We used a porous silica layer covering a basalt block with thicknesses ranging from 1/5 of the glass ball radius to equal to the glass ball radius as a rimmed chondrule analogue, and the porosity of the silica layer was set to be 70%, 80%, 85%, and 90%. Collisional experiments were conducted by means of the free fall method or by the use of a spring gun or a gas gun, allowing us to vary the impact velocity. We used a laser displacement meter to estimate the impact and rebound velocities as well as the acceleration during the collision at impact velocities below 1 m s?1. As a result, the sticking velocity, vc, of 90%- and 85%- porosity layers with a thickness equal to 1/2 of the glass ball diameter was 0.44 and 2.4 m s?1, respectively. On the other hand, we found a distinct barrier to sticking for smaller-porosity layers: the silicate layer with a porosity smaller than 80% never exhibited sticking at any impact velocity below 1 m s?1. Instead, we observed a rebound effect with restitution coefficients larger than 0.2. In the case of a silica layer with a porosity smaller than 80%, we observed the sub-sticking condition defined by ε < 0.1 at velocities extending from 5 m s?1 to 70 m s?1.  相似文献   

16.
The recent discovery of gravitational-wave burst GW150914 marks the coming of a new era of gravitational-wave astronomy, which provides a new window to study the physics of strong gravitational field, extremely massive stars, extremely high energy processes, and extremely early universe. In this article, we introduce the basic characters of gravitational waves in the Einstein's general relativity, their observational effects and main generation mechanisms, including the rotation of neutron stars, evolution of binary systems, and spontaneous generation in the inflation universe. Different sources produce the gravitational waves at quite different frequencies, which can be detected by different methods. In the lowest frequency range (f < 10?15 Hz), the detection is mainly dependent of the observation of B-mode polarization of cosmic microwave background radiation. In the middle frequency range (10?9 < f < 10?6 Hz), the gravitational waves are detected by analyzing the timing residuals of millisecond pulsars. And in the high frequency range (10 ? 4 < f < 104 Hz), they can be detected by the space-based and ground-based laser interferometers. In particular, we focus on the main features, detection methods, detection status, and the future prospects for several important sources, including the continuous sources (e.g., the spinning neutron stars, and stable binary systems), the burst sources (e.g., the supernovae, and the merge of binary system), and the stochastic backgrounds generated by the astrophysical and cosmological process. In addition, we forecast the potential breakthroughs in gravitational-wave astronomy in the near future, and the Chinese projects which might involve in these discoveries.  相似文献   

17.
This study presents the absolute parameters of the contact binary system V376 And. CCD photometric observations were made at the Çanakkale Onsekiz Mart University Observatory in 2004. The instrumental magnitudes of all observed stars were converted into standard magnitudes. New BV light curves of the system were analysed using the Wilson–Devinney method supplemented with a Monte Carlo type algorithm. Since there are large asymmetries between maxima (i.e., O’Connell effect) in these light curves, two different models (one with a cool spot and one with a hot spot) were applied to the photometric data. The best fit, which was obtained with a large hot spot on the secondary component, gives V376 And as an A sub-type contact binary in poor thermal contact and a small value of the filling factor (f ≈ 0.07). Combining the solutions of our light curves and Rucinski et al. (2001)’s radial velocity curves, the following absolute parameters of the components were determined: M1 = 2.44 ± 0.04 M⊙, M2 = 0.74 ± 0.03 M⊙, R1 = 2.60 ± 0.03 R⊙, R2 = 1.51 ± 0.02 R⊙, L1 = 40 ± 4 L⊙ and L2 = 5 ± 1 L⊙. We also discuss the evolution of the system, which appears to have an age of 1.6 Gyr. The distance to V376 And was calculated as 230 ± 20 pc from this analysis, taking into account interstellar extinction.  相似文献   

18.
We obtained estimates of the Johnson V absolute magnitudes (H) and slope parameters (G) for 583 main-belt and near-Earth asteroids observed at Ond?ejov and Table Mountain Observatory from 1978 to 2011. Uncertainties of the absolute magnitudes in our sample are <0.21 mag, with a median value of 0.10 mag. We compared the H data with absolute magnitude values given in the MPCORB, Pisa AstDyS and JPL Horizons orbit catalogs. We found that while the catalog absolute magnitudes for large asteroids are relatively good on average, showing only little biases smaller than 0.1 mag, there is a systematic offset of the catalog values for smaller asteroids that becomes prominent in a range of H greater than ～10 and is particularly big above H ～ 12. The mean (Hcatalog ? H) value is negative, i.e., the catalog H values are systematically too bright. This systematic negative offset of the catalog values reaches a maximum around H = 14 where the mean (Hcatalog ? H) is ?0.4 to ?0.5. We found also smaller correlations of the offset of the catalog H values with taxonomic types and with lightcurve amplitude, up to ～0.1 mag or less. We discuss a few possible observational causes for the observed correlations, but the reason for the large bias of the catalog absolute magnitudes peaking around H = 14 is unknown; we suspect that the problem lies in the magnitude estimates reported by asteroid surveys. With our photometric H and G data, we revised the preliminary WISE albedo estimates made by Masiero et al. (Masired, J.R. et al. [2011]. Astrophys. J. 741, 68–89) and Mainzer et al. (Mainzer, A. et al. [2011b]. Astrophys. J. 743, 156–172) for asteroids in our sample. We found that the mean geometric albedo of Tholen/Bus/DeMeo C/G/B/F/P/D types with sizes of 25–300 km is pV = 0.057 with the standard deviation (dispersion) of the sample of 0.013 and the mean albedo of S/A/L types with sizes 0.6–200 km is 0.197 with the standard deviation of the sample of 0.051. The standard errors of the mean albedos are 0.002 and 0.006, respectively; systematic observational or modeling errors can predominate over the quoted formal errors. There is apparent only a small, marginally significant difference of 0.031 ± 0.011 between the mean albedos of sub-samples of large and small (divided at diameter 25 km) S/A/L asteroids, with the smaller ones having a higher albedo. The difference will have to be confirmed and explained; we speculate that it may be either a real size dependence of surface properties of S type asteroids or a small size-dependent bias in the data (e.g., a bias towards higher albedos in the optically-selected sample of asteroids). A trend of the mean of the preliminary WISE albedo estimates increasing with asteroid size decreasing from D ～ 30 down to ～5 km (for S types) showed in Mainzer et al. (Mainzer, A. et al. [2011a]. Astrophys. J. 741, 90–114) appears to be mainly due to the systematic bias in the MPCORB absolute magnitudes that progressively increases with H in the corresponding range H = 10–14.  相似文献   

19.
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20.
We have observed the massive star formation region W75N in 12CO J = 3 ? 2 with KOSMA. The profile of 12CO J = 3 ? 2 indicated that besides the 9 km s?1 component, there is another component of ?3 km s?1, which is associated with another star formation region, DR21N, located to the north of DR21. We derived the physical and dynamical parameters of the core and high velocity gas associated with the two components separately. Star forming activities were investigated, including outflows and infall analysis. The two regions overlap in space and are not connected in velocity. We found that the cloud–cloud collision scenario may not apply for the DR21/W75N case.  相似文献   

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