16029130
Line and Continuum Emission from the Galactic Center. III. Origin of 6.4 keV Line Emission from Molecular Clouds in the Galactic Center
We analyze the 6.4 keV line and continuum emission from the molecular cloud Sgr B2 and the source HESS J1745-303, which is supposed to be a complex of molecular gas. From the HESS results it follows that Sgr A is a source of high energy protons, which penetrate into molecular clouds producing there a TeV gamma-ray flux. We present arguments that Sgr A may also produce a flux of subrelativistic protons which generate the 6.4 keV line and bremsstrahlung continuum emission from the clouds.
119494719
Theoretical Aspects of Gravitational Lensing in TeVeS
Since Bekenstein's creation of his tensor-vector-scalar theory (TeVeS), the modified Newtonian dynamics (MOND) paradigm has been redeemed from the embarrassment of lacking a relativistic version. One primary success of TeVeS is that it provides an enhancement of gravitational lensing, which could not be achieved by other MOND theories. Following Bekenstein's work, we investigate the phenomena of gravitational lensing including deflection angles, lens equations, and time delay. We find that the deflection angle maintains its value, while the distance of closest approach varies in the MOND regime. We also use the deflection angle law to derive magnifications and investigate microlensing light curves. We find that the difference in the magnification of the two images in the point-mass model is not a constant, as in general relativity (GR). Besides, microlensing light curves could deviate significantly from GR in the deep MOND regime. Furthermore, the scalar field, which is introduced to enhance the deflection angle in TeVeS, contributes a negative effect on the potential time delay. Unfortunately, this phenomenon is unmeasurable in lensing systems, where we can only observe the time delay between two images for a given source. However, this measurable time delay offers another constraint on the mass ratio of the dark matter and MOND scenarios, which in general differs from that given by the deflection angle. In other words, for a lensing system, if two masses, mgN and mgM, are mutual alternatives for the deflection angles in their own paradigm, regarding the time delay they are in general in an exclusive relation.
16205821
Particle propagation in the galactic center and spatial distribution of non-thermal x-rays
We showed that if the non-thermal emission from the galactic center in the range 14–40 keV is due to inverse bremsstrahlung emission of subrelativistic protons, their interactions with hot and cold fractions of the interstellar medium are equally important. Our estimation shows that about 30% of the total non-thermal flux from the GC in the range 14–40 keV is generated in regions of cold gas while the rest is produced by proton interaction with hot plasma. From the spatial distribution of 6.7 keV iron line we concluded the spatial distribution of hot plasma is strongly non-uniform that should be taken into account in analysis of proton propagation in the GC. From the Suzaku data we got independent estimates for the diffusion coefficient of subrelativistic protons in the GC, which was in the range 10 26 –10 27 cm 2 s � 1 .
118673239
Hubble Constant, Lensing, and Time Delay in Relativistic Modified Newtonian Dynamics
The time delay in galaxy gravitational lensing systems has been used to determine the value of the Hubble constant. As with other dynamical phenomena on the galaxy scale, dark matter is often invoked in gravitational lensing to account for the "missing mass" (the apparent discrepancy between the dynamical mass and the luminous mass). Alternatively, modified gravity can be used to explain the discrepancy. In this paper, we adopt the tensor-vector-scalar gravity (TeVe S), a relativistic version of Modified Newtonian Dynamics, to study gravitational lensing phenomena and derive the formulae needed to evaluate the Hubble constant. We test our method on quasar lensing by elliptical galaxies in the literature. We focus on double-image systems with time delay measurement. Three candidates are suitable for our study: HE 2149–2745, FBQ J0951+2635, and SBS 0909+532. The Hubble constant obtained is consistent with the value used to fit the cosmic microwave background result in a neutrino cosmological model.
121843826
Hubble constant, lensing, and time delay in Te Ve S
Hubble constant can be determined by the time delay of gravitational lensing systems. As data on time delay observation accumulates, it is time to revisit this approach. As in other dynamical phenomena in scales of galaxy and cluster of galaxies, gravitational lensing in these scales is also plagued by the problem of excess acceleration or gravity (a.k.a. missing mass problem). There are always some accelerations unaccounted for by luminous matter. Usually dark matter is introduced to interpret the discrepancy. However, MOdified Newtonian Dynamics (MOND) is more successful in explaining the excess accelerations in galaxy scale. We adopt TeVeS as the relativistic version of MOND to study gravitational lensing phenomena, and we can evaluate the Hubble constant from the derived time-delay formula. To apply our method, we rely on the CASTLE quasar lensing survey and the Sloan Digital Sky Survey (SDSS). Four samples are suitable for our study. Using only the luminous part of the lensing galaxies, the average of the derived Hubble constant is 68.5 km s^-1Mpc^-1
16308661
Origin of thermal and non-thermal hard X-ray emission from the Galactic center
We analyse new results of Chandra and Suzaku Observatories which found a flux of hard X-ray emission from the compact region around Sgr A � (r � 100 pc). We suppose that this emission is generated by accretion processes onto the central supermassive blackhole when an unbound part of captured stars obtains an additional momentum. As a result a flux of subrelativistic protons is generated near the galactic center which heats the background plasma up to temperatures about 6–10 keV and produces by inverse bremsstrahlung a flux of non-thermal X-ray emission in the energy range above 10 keV.
15750292
Antikaon production and medium effects in heavy-ion collisions at AGS
Abstract Antikaon production in heavy-ion collisions at energies available from the Alternating Gradient Synchrotron (AGS) at the Brookhaven National Laboratory is studied in a relativistic transport (ART) model. We include contributions from the baryon-baryon, meson-baryon, and meson-meson interactions. The final-state interaction of antikaons via both absorption and elastic scattering by nucleons and pions are also considered. To compare with presently available or future experimental data, we have calculated the antikaon rapidity and transverse momentum distributions as well as its collective flow. Medium effects on these observables due to mean field potentials have also been investigated. It is found that both the ratio of antikaon transverse momentum spectrum to that of kaon and their transverse flow are most sensitive to the in-medium properties of kaons and antikaons.
4073106
Multiphase transport model for relativistic heavy ion collisions
We describe in detail how the different components of a multiphase transport (AMPT) model that uses the heavy ion jet interaction generator (HIJING) for generating the initial conditions, Zhang's parton cascade (ZPC) for modeling partonic scatterings, the Lund string fragmentation model or a quark coalescence model for hadronization, and a relativistic transport (ART) model for treating hadronic scatterings are improved and combined to give a coherent description of the dynamics of relativistic heavy ion collisions. We also explain the way parameters in the model are determined and discuss the sensitivity of predicted results to physical input in the model. Comparisons of these results to experimental data, mainly from heavy ion collisions at the BNL Relativistic Heavy Ion Collider, are then made in order to extract information on the properties of the hot dense matter formed in these collisions.
119326646
Medium effects on the flow of strange particles in heavy-ion collisions
Strange particles such as the kaon and lambda are useful in probing the properties of dense matter formed in heavy-ion collisions. Here we review the theoretical understanding of their properties in a nuclear medium based on both the effective chiral Lagrangian and the phenomenological hadronic model. We further review the effects due to changes in their in-medium properties on their collective flow in heavy-ion collisions.
14560383
Charmonium production from hot hadronic matter
Abstract Charmonium production from D D annihilation in the hadron gas formed in ultra-relativistic heavy-ion collisions is studied. With initial conditions taken from the HIJING parton model, we have estimated the number of J / ψ produced from an expanding hadron gas, using the J / ψ absorption and production cross sections obtained from either an effective Lagrangian or the quark-exchange model. We find that J / ψ production is negligible in heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC) but may be important at the Large Hadron Collider (LHC), where more charm mesons are produced. Similar results are obtained for ψ ′ production from the hadron gas at RHIC and LHC.
11222928
Progress Towards Determining the Density Dependence of the Nuclear Symmetry Energy Using Heavy-Ion Reactions
The latest development in determining the density dependence of the nuclear symmetry energy using heavy-ion collisions is reviewed. Within the IBUU04 version of an isospin- and momentum-dependent transport model using a modified Gogny effective interaction, recent experimental data from NSCL/MSU on isospin diffusion are found to be consistent with a nuclear sym- metry energy of Esym(ρ) ≈ 31.6(ρ/ρ0) 1.05 at subnormal densities. Predictions on several observables sensitive to the density dependence of the symmetry en- ergy at supranormal densities accessible at GSI and the planned Rare Isotope Accelerator (RIA) are also made.