14655295
Modeling the Hard States of XTE J1550–564 during Its 2000 Outburst
We study the hard states of the black hole binary XTE J1550-564 during its 2000 outburst. In order to explain those states at their highest luminosities, L similar to 10% of the Eddington luminosity, L-E, we propose a specific hot accretion flow model. We point out that the highest values of the hard-state L are substantially above the L that an advection-dominated accretion flow can produce, similar to 0.4 alpha L-2(E), which is only similar to 3%-4% of L-E even for alpha as high as 0.3. On the other hand, we successfully explain the hard states with L similar to 0.04-0.10 using the luminous hot accretion flow (LHAF) model. As 0.10L(E) is also roughly the highest luminosity an LHAF can produce, such agreement between the predicted and observed highest luminosities itself provides strong support for this model. We then study multiwaveband spectral variability during the 2000 outburst. In addition to the primary maxima in the optical light curves, secondary maxima were detected after the transition from the very high state to the hard state. We show that the secondary maxima are well modeled as synchrotron emission from a jet formed during the state transition. We argue that the absence of a corresponding secondary peak in the X-ray light curve indicates that the X-ray jet emission, regardless of its radiative process, synchrotron or Comptonization, is not important in the hard state as compared with the emission from the accretion flow.
2227030
Testing the transition layer model of quasi-periodic oscillations in neutron star X-ray binaries
We compare the theoretical predictions of the transition layer model with some observational features of quasi-periodic oscillations (QPOs) in neutron star X-ray binaries. We found that the correlation between horizontal branch oscillation (HBO) frequencies and kilohertz (kHz) QPO frequencies, the difference between the low-frequency QPOs in atoll sources and HBOs in Z sources, and the correlation between the frequencies of low-frequency QPOs and break frequencies can be well explained by the transition layer model, provided the neutron star mass is around 1.4 M☉ and the angle between magnetosphere equator and accretion disk plane is around 6°. The observed decrease of peak separation between the two kHz QPO frequencies with the increase of the kHz QPO frequencies and the increase of QPO frequencies with the increase of inferred mass accretion rate are also consistent with the theoretical predictions of the transition layer model. In addition, we derive a simple equation that can be adopted to estimate the angle (δ) between magnetosphere equator and accretion disk plane by use of the simultaneously observed QPO frequency data. We estimate this angle, in the range of 4°-8°, for five Z sources and two atoll sources. The nearly constant δ value for each source, derived from the different sets of simultaneously observed QPO frequency data, provides a strong test of the theoretical model. Finally, we suggest that similar transition layer oscillations may be responsible for the observed QPOs in accretion-powered millisecond X-ray pulsars and Galactic black hole candidates.
118357880
ON THE STRUCTURE OF ACCRETION DISKS WITH OUTFLOWS
To study the outflows from accretion disks, we solve the set of hydrodynamic equations for accretion disks in spherical coordinates (rθ) to obtain the explicit structure along the θ-direction. Using self-similar assumptions in the radial direction, we change the equations to a set of ordinary differential equations about the θ-coordinate, which are then solved with symmetrical boundary conditions in the equatorial plane; the velocity field is then obtained. The α viscosity prescription is applied and an advective factor f is used to simplify the energy equation. The results display thinner, quasi-Keplerian disks for Shakura-Sunyaev disks; thicker, sub-Keplerian disks for advection-dominated accretion flows; and slim disks which are consistent with previous popular analytical models. However, an inflow region and an outflow region always exist, except when the viscosity parameter α is too large, which supports the results of some recent numerical simulation works. Our results indicate that the outflows should be common in various accretion disks and may be stronger in slim disks, where both advection and radiation pressure are dominant. We also present the structure's dependence on the input parameters and discuss their physical meanings. The caveats of this work and possible improvements for the future are discussed.
2377462
Galaxy bulge formation: Interplay with dark matter halo and central supermassive black hole
We present a simple scenario where the formation of galactic bulges was regulated by the dark halo gravity and regulates the growth of the central supermassive black hole. Assuming the angular momentum is low, we suggest that bulges form in a runaway collapse due to the "gravothermal" instability once the central gas density or pressure exceeds a certain threshold. We emphasize that the threshold is nearly universal, set by the background NFW dark matter gravity gDM ~ 1.2 × 10-8 cm s-2 in the central cusps of halos. Unlike known thresholds for gradual formation of galaxy disks, we show that the universal "halo-regulated" star formation threshold for spheroids matches the very high star formation rate and star formation efficiency seen in high-redshift observations of central starburst regions. The starburst feedback also builds up a pressure shortly after the collapse. This large pressure could act both outward to halt further infall of gas from larger scales and inward to counter the Compton-thick wind launched from the central black hole in an Eddington accretion. Assuming the feedback balances inward and outward forces, our scenario naturally gives rise to the black hole-bulge relationships observed in the local universe.
2132712
Inclinations and black hole masses of Seyfert 1 galaxies
A tight correlation between black hole mass (MBH) and central velocity dispersion (σ) has been found recently for both active and quiescent galaxies. By applying this correlation, we develop a simple method to derive the inclination angles for a sample of 11 Seyfert 1 galaxies that have both measured central velocity dispersions and black hole masses estimated by reverberation mapping. These angles, with a mean value of 36° that agrees well with the result obtained by fitting the iron Kα lines of Seyfert 1 galaxies observed with ASCA, provide further support to the orientation-dependent unification scheme of active galactic nuclei (AGNs). A positive correlation of the inclinations with observed FWHMs of the Hβ line and a possible anticorrelation with the nuclear radio loudness have been found. We conclude that more accurate knowledge of inclinations and broad-line region dynamics is needed to improve the black hole mass determination of AGNs with the reverberation mapping technique.
199676816
Discovering the missing bright quasars at intermediate redshifts based on the optical/near-IR color selections
118447242
Heavy and light meson wavefunctions
We present a short review on the properties of heavy and light mesons’ light-cone wavefunctions (LCWFs), and their distribution amplitudes (DAs). The $$B$$B meson LCWFs can be treated by taking the heavy quark limit ($$m_b\rightarrow \infty $$mb→∞) and by using the heavy quark effective theory. Furthermore, we propose a simple model for the $$B$$B meson wavefunctions with 3-particle Fock states’ contributions, whose behaviors are controlled by two parameters $$\bar{\varLambda }$$Λ¯ and $$\delta $$δ. Using such model, the form factors $$F^{B\rightarrow \pi }_{+,0,{\text{T}}}$$F+,0,TB→π and $$F^{B\rightarrow K}_{+,0,{\text{T}}}$$F+,0,TB→K in large recoil region are studied up to $$\mathcal{O}(1/m_b^2)$$O(1/mb2) within the $$k_{{\mathrm{T}}}$$kT factorization approach. On the other hand, we adopt Brodsky-Huang-Lepage (BHL) prescription for constructing the WFs of the lighter pseudoscalars as $$\eta _c, D$$ηc,D-meson, pion, kaon, $$\eta ^{(\prime )}$$η(′) and etc. Such BHL-like model can be conveniently extended to construct the LCWFs for light scalar or vector mesons. Within such model the longitudinal distributions of those WFs are basically determined by a parameter $$B$$B, whose value can be determined via a global fit of experimental data.
197452857
Renormalization group improved QCD prediction for $\Upsilon(1S)$ leptonic decay
The complete next-to-next-to-next-to-leading order short-distance and bound-state QCD corrections to $\Upsilon(1S)$ leptonic decay rate $\Gamma(\Upsilon(1S)\to \ell^+\ell^-)$ has been finished by Beneke {\it etal.} [5]. Based on those improvements, we present a renormalization group (RG) improved pQCD prediction for $\Gamma(\Upsilon(1S)\to \ell^+\ell^-)$ by applying the principle of maximum conformality (PMC). The PMC is based on RG-invariance and is designed to solve the renormalization scheme and scale ambiguities. After applying the PMC for $\Upsilon(1S)$ leptonic decay, all known-type of $\beta$-terms at all orders, which are controlled by the RG-equation, are resummed to determine optimal renormalization scales for its strong running coupling at each perturbative order. We then achieve a more convergent pQCD series, a scheme-independent and more accurate pQCD prediction, i.e. $\Gamma_{\Upsilon(1S) \to e^+ e^-}|_{\rm PMC} = 1.361^{+0.154}_{-0.214}$ keV, where the uncertainty is squared average of the mentioned pQCD error sources. This RG-improved pQCD prediction agrees well with the experimental measurement within errors.
45563375
Pion form factor in the k(T) factorization formalism
Based on the light-cone (LC) framework and the k{sub T} factorization formalism, the transverse momentum effects and the different helicity components' contributions to the pion form factor F{sub {pi}}(Q{sup 2}) are recalculated. In particular, the contributions to the pion form factor from the higher-helicity components ({lambda}{sub 1}+{lambda}{sub 2}={+-}1), which come from the spin-space Wigner rotation, are analyzed in the soft and hard energy regions, respectively. Our numerical results show that the right power behavior of the hard contribution from the higher-helicity components can only be obtained by fully keeping the k{sub T} dependence in the hard amplitude, and that the k{sub T} dependence in LC wave function affects the hard and soft contributions substantially. As an example, we employ a model LC wave function to calculate the pion form factor and then compare the numerical predictions with the experimental data.
118446028
Z0 boson decays to $B^{(*)}_{c}$ meson and its uncertainties
The planned new e+e− collider with high luminosity shall provide another useful platform to study the properties of the doubly heavy Bc meson in addition to the hadronic colliders as LHC and TEVATRON. In the ‘New Trace Amplitude Approach’, we calculate the production of the spin-singlet Bc and the spin-triplet $B^{*}_{c}$ mesons through the Z0 boson decays, where uncertainties for the production are also discussed. Our results show $\varGamma_{(^{1}S_{0})}=81.4^{+102.1}_{-40.5}$ KeV and $\varGamma_{(^{3}S_{1})}=116.4^{+163.9}_{-62.8}$ KeV, where the errors are caused by varying mb and mc within their reasonable regions.
119293270
Kaon electromagnetic form factor within the kT factorization formalism and it's light-cone wave function
We present a systematical study on the kaon electromagnetic form factors F-K +/-,K-0,(K) over bar (0)(Q(2)) within the k(T) factorization formalism, where the transverse momentum effects, the contributions from the different helicity components and different twist structures of the kaon light-cone (LC) wave function are carefully analyzed for giving a well understanding of the hard contributions at the energy region where pQCD is applicable. The right power behavior of the hard contribution from the higher helicity components and from the higher twist structures can be obtained by keeping the kT dependence in the hard amplitude. Our results show that the kT dependence in LC wave function affects the hard and soft contributions substantially and the power-suppressed terms (twist-3 and higher helicity components) make an important contribution below Q(2) similar to several GeV2 although they drop fast as Q(2) increasing. The parameters of the proposed model wave function can be fixed by the first two moments of its distribution amplitude and other conditions. By varying the first two moments a(1)(K) (1GeV) and a(2)(K) (1GeV) with the region of 0.05 +/- 0.02 and 0.10 +/- 0.05 respectively, we find that the uncertainty of the kaon electromagnetic form factor is rather small.