54197110
A COMPREHENSIVE STUDY OF GAMMA-RAY BURST OPTICAL EMISSION. II. AFTERGLOW ONSET AND LATE RE-BRIGHTENING COMPONENTS
We continue our systematic statistical study of various components of gamma-ray burst (GRB) optical light curves. We decompose the early onset bump and the late re-brightening bump with empirical fits and analyze their statistical properties. Among the 146 GRBs that have well-sampled optical light curves, the onset and re-brightening bumps are observed in 38 and 26 GRBs, respectively. It is found that the typical rising and decaying slopes for both the onset and re-brightening bumps are similar to 1.5 and similar to-1.15, respectively. No early onset bumps in the X-ray band are detected to be associated with the optical onset bumps, while an X-ray re-brightening bump is detected for half of the re-brightening optical bumps. The peak luminosity is anti-correlated with the peak time L-p proportional to t(p)(-1.81 +/- 0.32) for the onset bumps and L-p proportional to t(p)(-0.83 +/- 0.17) for the re-brightening bumps. Both L-p and the isotropic energy release of the onset bumps are correlated with E-gamma,E- iso, whereas no similar correlation is found for the re-brightening bumps. These results suggest that the afterglow onset bumps are likely due to the deceleration of the GRB fireballs. Taking the onset bumps as probes for the properties of the fireballs and their ambient medium, we find that the typical power-law index of the relativistic electrons is 2.5 and the medium density profile behaves as n proportional to r(-1) within the framework of the synchrotron external shock models. With the medium density profile obtained from our analysis, we also confirm the correlation between the initial Lorentz factor (Gamma(0)) and E-iso,E-gamma in our previous work. The jet component that produces the re-brightening bump seems to be on-axis and independent of the prompt emission jet component. Its typical kinetic energy budget would be about one order of magnitude larger than the prompt emission component, but with a lower Gamma(0), typically several tens.
119302057
REVISITING THE EMISSION FROM RELATIVISTIC BLAST WAVES IN A DENSITY-JUMP MEDIUM
Re-brightening bumps are frequently observed in gamma-ray burst afterglows. Many scenarios have been proposed to interpret the origin of these bumps, of which a blast wave encountering a density-jump in the circumburst environment has been questioned by recent works. We develop a set of differential equations to calculate the relativistic outflow encountering the density-jump by extending the work of Huang et al. This approach is a semi-analytic method and is very convenient. Our results show that late high-amplitude bumps cannot be produced under common conditions, rather only a short plateau may emerge even when the encounter occurs at an early time (< 10(4) s). In general, our results disfavor the density-jump origin for those observed bumps, which is consistent with the conclusion drawn from full hydrodynamics studies. The bumps thus should be caused by other scenarios.
54192865
A Comprehensive Study of Gamma-Ray Burst Optical Emission. I. Flares and Early Shallow-decay Component
Well-sampled optical light curves of 146 gamma-ray bursts (GRBs) are compiled from the literature. By empirical fitting, we identify eight possible emission components and summarize the results in a 'synthetic' light curve. Both optical flare and early shallow-decay components are likely related to long-term central engine activities. We focus on their statistical properties in this paper. Twenty-four optical flares are obtained from 19 GRBs. The isotropic R-band energy is smaller than 1% of E{sub {gamma},iso}. The relation between the isotropic luminosities of the flares and gamma rays follows L{sup F}{sub R,iso}{proportional_to}L {sup 1.11{+-}0.27}{sub {gamma},iso}. Later flares tend to be wider and dimmer, i.e., w{sup F} {approx} t{sup F}{sub p}/2 and L{sup F}{sub R,iso}{proportional_to}[t{sup F}{sub p}/(1 + z)]{sup -1.15{+-}0.15}. The detection probability of the optical flares is much smaller than that of X-ray flares. An optical shallow-decay segment is observed in 39 GRBs. The relation between the break time and break luminosity is a power law, with an index of -0.78 {+-} 0.08, similar to that derived from X-ray flares. The X-ray and optical breaks are usually chromatic, but a tentative correlation is found. We suggest that similar to the prompt optical emission that tracks {gamma}-rays, the optical flares are alsomore » related to the erratic behavior of the central engine. The shallow-decay component is likely related to a long-lasting spinning-down central engine or piling up of flare materials onto the blast wave. Mixing of different emission components may be the reason for the diverse chromatic afterglow behaviors.« less
111052294
Silicon photomultiplier readout system for the ECAL in the PEBS and test results from the system
Silicon photomultipliers (SiPMs) have remarkable advantages for use in photo-detection. Compared with PMT, SiPM shows advantages of high gain, excellent time resolution, insensitivity to magnetic fields and a lower operating voltage. SiPMs from Hamamatsu are used in the electromagnetic calorimeter (ECAL) sub-detector in the Positron Electron Balloon Spectrometer (PEBS) experiment, a balloon-borne spectrometer experiment aiming at the precise measurement of the cosmic-ray positron fraction. This paper introduces the evaluation and test results of several SiPM detector types, the dedicated front-end application specific integrated circuit (ASIC) electronics and the design of the data acquisition system (DAQ) system.
569169
Multitemperature Blackbody Spectrum of a Thin Accretion Disk around a Kerr Black Hole: Model Computations and Comparison with Observations
We use a ray-tracing technique to compute the observed spectrum of a thin accretion disk around a Kerr black hole. We include all relativistic effects such as frame-dragging, Doppler boost, gravitational redshift, and bending of light by the gravity of the black hole. We also include self-irradiation of the disk as a result of light deflection. Assuming that the disk emission is locally blackbody, we show how the observed spectrum depends on the spin of the black hole, the inclination of the disk, and the torque at the inner edge of the disk. We find that the effect of a nonzero torque on the spectrum can, to a good approximation, be absorbed into a zero-torque model by adjusting the mass accretion rate and the normalization. We describe a computer model, called KERRBB, which we have developed for fitting the spectra of black hole X-ray binaries. Using KERRBB within the X-ray data reduction package XSPEC, and assuming a spectral hardening factor fcol = 1.7, we analyze the spectra of three black hole X-ray binaries: 4U 1543-47, XTE J1550-564, and GRO J1655-40. We estimate the spin parameters of the black holes in 4U 1543-47 and GRO J1655-40 to be a/M ~ 0.6 and ~0.6-0.7, respectively. If fcol ~ 1.5-1.6, as in a recent study, then we find a/M ~ 0.7-0.8 and ~0.8-0.9, respectively. These estimates are subject to additional uncertainties in the assumed black hole masses, distances, and disk inclinations.
15791171
Energy transfer and its effects on the secondaries in W Ursae Majoris type contact binaries
Based on the physical parameters of 133 W Ursae Majoris (W UMa) type contact binaries, energy transfer and its effects on the secondaries in W UMa contact binaries are investigated. Relations are given between the mass ratio (q) for W UMa contact binaries and the relative energy transfer rates, i.e. U(1), the ratio of the transferred luminosity to the surface luminosity of the primary, and U(2), the ratio of the transferred luminosity to the nuclear luminosity of the secondary. The theoretical curves(U(1) versus q and U(2) versus q) are derived based on various assumptions: that the two components in each W UMa system are nearly identical in effective temperature and just fill their inner Roche lobes, and the primaries are zero-age main-sequence stars. Although these curves can reflect the distribution of U(1) and U(2) versus q, some observational systems deviate significantly from these curves. This results mainly from the difference in effective temperatures of the components of W UMa systems. The radius and the density of the secondary are related to the relative energy transfer rate U(2): the higher U(2), the greater the expansion and the lower the density of the secondary in a W UMa system. In addition, it is found that the temperature difference of W UMa binary components is correlated with the relative energy transfer rate U(1) and decreases with increasing U(1). This might suggest that there is a thermal coupling between the two components in W UMa contact binaries, and that the classification of W UMa contact binaries into A or W types depends on the energy transfer from the primary to the secondary. The temperature difference of W UMa binary components is poorly correlated with the mass of the primary. This suggests that the properties of the common envelope of a W UMa contact binary might not have a significant effect on the energy transfer between the two components.
118660988
Inclusion of sdBs in evolutionary population synthesis for binary stellar populations and the application: the determination of photo-z and galaxy morphology
Subdwarf B stars (sdBs) can significantly change the ultraviolet spectra of populations at age t∼1 Gyr, and have been even included in the evolutionary population synthesis (EPS) models by Han et al. (Mon. Not. R. Astron. Soc. 380:1098, 2007). In this study we present the spectral energy distributions (SEDs) of binary stellar populations (BSPs) by combining the EPS models of Han et al. (Mon. Not. R. Astron. Soc. 380:1098, 2007) and those of the Yunnan group (Zhang et al. in Astron. Astrophys. 415:117, 2004; Mon. Not. R. Astron. Soc. 357:1088, 2005), which have included various binary interactions (except sdBs) in EPS models. This set of SEDs is available upon request from the authors.Using this set of SEDs of BSPs we build the spectra of Burst, E, S0–Sd and Irr types of galaxies by using the package of Bruzual and Charlot (Mon. Not. R. Astron. Soc. 344:1000, 2003). Combined with the photometric data (filters and magnitudes), we obtain the photometric redshifts and morphologies of 1502 galaxies by using the Hyperz code of Bolzonella et al. (Astron. Astrophys. 363:476, 2000). This sample of galaxies is obtained by removing those objects, mismatched with the SDSS/DR7 and GALEX/DR4, from the catalogue of Fukugita et al. (Astron. J. 134:579, 2007). By comparison the results with the SDSS spectroscopic redshifts and the morphological index of Fukugita et al. (Astron. J. 134:579, 2007), we find that the photo-z fluctuate with the SDSS spectroscopic redshifts, while the Sa–Sc galaxies in the catalogue of Fukugita et al. (Astron. J. 134:579, 2007) are classified earlier as Burst-E galaxies.
119862535
Sum rules on quantum hadrodynamics at finite temperature and density
55133202
Entanglement entropy in a holographic p-wave superconductor model
In a recent paper, arXiv:1309.4877, a holographic p-wave model has been proposed in an Einstein– Maxwell-complex vector field theory with a negative cosmological constant. The model exhibits rich phase structure depending on the mass and the charge of the vector field. We investigate the behavior of the entanglement entropy of dual field theory in this model. When the above two model parameters change, we observe the second order, first order and zeroth order phase transitions from the behavior of the entanglement entropy at some intermediate temperatures. These imply that the entanglement entropy can indicate not only the occurrence of the phase transition, but also the order of the phase transition. The entanglement entropy is indeed a good probe to phase transition. Furthermore, the “retrograde condensation” which is a sub-dominated phase is also reflected on the entanglement entropy. © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP 3 .