New Analytical Formula for Supercritical Accretion Flows

We examine a new family of global analytic solutions for optically thick accretion disks, which includes the supercritical accretion regime. We found that the ratio of the advection cooling rate, $Q_{\rm adv}$, to the viscous heating rate, $Q_{\rm vis}$, i.e., $f=Q_{\rm adv}/Q_{\rm vis}$, can be represented by an analytical form dependent on the radius and the mass accretion rate. The new analytic solutions can be characterized by the photon-trapping radius, \rtrap, inside which the accretion time is less than the photon diffusion time in the vertical direction; the nature of the solutions changes significantly as this radius is crossed. Inside the trapping radius, $f$ approaches $f \propto r^0$, which corresponds to the advection-dominated limit ($f \sim 1$), whereas outside the trapping radius, the radial dependence of $f$ changes to $f \propto r^{-2}$, which corresponds to the radiative-cooling-dominated limit. The analytical formula for $f$ derived here smoothly connects these two regimes. The set of new analytic solutions reproduces well the global disk structure obtained by numerical integration over a wide range of mass accretion rates, including the supercritical accretion regime. In particular, the effective temperature profiles for our new solutions are in good agreement with those obtained from numerical solutions. Therefore, the new solutions will provide a useful tool not only for evaluating the observational properties of accretion flows, but also for investigating the mass evolution of black holes in the presence of supercritical accretion flows.Comment: 14 pages, 7 figures, accepted for publication in the Astrophysical Journa

Model for Relaxation Oscillations of Luminous Accretion Disk in GRS1915+105: Variable Inner Edge

To understand the bursting behavior of the microquasar GRS 1915+105, we calculate time evolution of a luminous, optically thick accretion disk around a stellar mass black hole undergoing limit-cycle oscillations between the high- and low- luminosity states. We, especially, carefully solve the behavior of the innermost part of the disk, since it produces significant number of photons during the burst, and fit the theoretical spectra with the multi-color disk model. The fitting parameters are \Tin (the maximum disk temperature) and \Rin (the innermost radius of the disk). We find an abrupt, transient increase in \Tin and a temporary decrease in \Rin during a burst, which are actually observed in GRS 1915+105. The precise behavior is subject to the viscosity prescription. We prescribe the radial-azimuthal component of viscosity stress tensor to be $T_{r \phi}=-\alpha \Pi (p_{\rm gas}/p)^{\mu}$, with $\Pi$ being the height integrated pressure, $\alpha$ and $\mu$ being the parameter, and $p$ and $p_{\rm gas}$ being the total pressure and gas pressure on the equatorial plane, respectively. Model with $\mu=0.1$ can produce the overall time changes of \Tin and \Rin, but cannot give an excellent fit to the observed amplitudes. Model with $\mu=0.2$, on the other hand, gives the right amplitudes, but the changes of \Tin and \Rin are smaller. Although precise matching is left as future work, we may conclude that the basic properties of the bursts of GRS 1915+105 can be explained by our ``limit-cycle oscillation'' model. It is then required that the spectral hardening factor at high luminosities should be about 3 at around the Eddington luminosity instead of less than 2 as is usually assumed.Comment: 11 pages, 5 figures, accepted for publication in Ap

The X-ray Luminosity Function of "The Antennae" Galaxies (NGC4038/39) and the Nature of Ultra-Luminous X-ray Sources

We derive the X-ray luminosity function (XLF) of the X-ray source population detected in the Chandra observation of NGC4038/39 (the Antennae). We explicitly include photon counting and spectral parameter uncertainties in our calculations. The cumulative XLF is well represented by a flat power law ($\alpha=-0.47$), similar to those describing the XLFs of other star-forming systems (e.g. M82, the disk of M81), but different from those of early type galaxies. This result associates the X-ray source population in the Antennae with young High Mass X-ray Binaries. In comparison with less actively star-forming galaxies, the XLF of the Antennae has a highly significant excess of sources with luminosities above 10^{39} erg\s (Ultra Luminous Sources; ULXs). We discuss the nature of these sources, based on the XLF and on their general spectral properties, as well as their optical counterparts discussed in Paper III. We conclude that the majority of the ULXs cannot be intermediate mass black-holes (M > 10-1000 \msun) binaries, unless they are linked to the remnants of massive Population III stars (the Madau & Rees model). Instead, their spatial and multiwavelength properties can be well explained by beamed emission as a consequence of supercritical accretion. Binaries with a neutron star or moderate mass black-hole (up to 20\msun), and B2 to A type star companions would be consistent with our data. In the beaming scenario, the XLF should exibit caracteristic breaks that will be visible in future deeper observations of the Antennae.Comment: 15 pages, submitted to Ap

Observations of Rapid Disk-Jet Interaction in the Microquasar GRS 1915+105

We present evidence that ~ 30 minute episodes of jet formation in the Galactic microquasar GRS 1915+105 may sometimes entirely be a superposition of smaller, faster phenomena. We base this conclusion on simultaneous X-ray and infrared observations in July 2002, using the Rossi X-ray Timing Explorer and the Palomar 5 meter telescope. On two nights, we observed quasi-periodic infrared flares from GRS 1915+105, each accompanied by a set of fast oscillations in the X-ray light curve (indicating an interaction between the jet and accretion disk). In contrast to similar observations in 1997, we find that the duration of each X-ray cycle matches the duration of its accompanying infrared flare, and we observed one instance in which an isolated X-ray oscillation occurred at the same time as a faint infrared "subflare" (of duration ~ 150 seconds) superimposed on one of the main flares. From these data, we are able to conclude that each X-ray oscillation had an associated faint infrared flare and that these flares blend together to form, and entirely comprise, the ~ 30 minute events we observed. Part of the infrared emission in 1997 also appears to be due to superimposed small flares, but it was overshadowed by infrared-bright ejections associated with the appearance of a sharp "trigger" spike in each X-ray cycle that were not present in 2002. We also study the evolution of the X-ray spectrum and find significant differences in the high energy power law component, which was strongly variable in 1997 but not in 2002. Taken together, these observations reveal the diversity of ways in which the accretion disk and jet in black hole systems are capable of interacting and solidify the importance of the trigger spike for large ejections to occur on ~ 30 minute timescales in GRS 1915+105.Comment: 17 pages, 9 figures; accepted for publication in The Astrophysical Journa

M 33 X-7: ChASeM33 reveals the first eclipsing black hole X-ray binary

The first observations conducted as part of the Chandra ACIS survey of M 33 (ChASeM33) sampled the eclipsing X-ray binary M 33 X-7 over a large part of the 3.45 d orbital period and have resolved eclipse ingress and egress for the first time. The occurrence of the X-ray eclipse allows us to determine an improved ephemeris of mid-eclipse and binary period as HJD (2453639.119+-0.005) +- N x (3.453014+-0.000020) and constrain the eclipse half angle to (26.5+-1.1) degree. There are indications for a shortening of the orbital period. The X-ray spectrum is best described by a disk blackbody spectrum typical for black hole X-ray binaries in the Galaxy. We find a flat power density spectrum and no significant regular pulsations were found in the frequency range of 10^{-4} to 0.15 Hz. HST WFPC2 images resolve the optical counterpart, which can be identified as an O6III star with the help of extinction and colour corrections derived from the X-ray absorption. Based on the optical light curve, the mass of the compact object in the system most likely exceeds 9 M_sun. This mass, the shape of the X-ray spectrum and the short term X-ray time variability identify M 33 X-7 as the first eclipsing black hole high mass X-ray binary.Comment: 14 pages, 5 figures, ApJ accepte

Does the Slim-Disk Model Correctly Consider Photon-Trapping Effects?

We investigate the photon-trapping effects in the super-critical black hole accretion flows by solving radiation transfer as well as the energy equations of radiation and gas. It is found that the slim-disk model generally overestimates the luminosity of the disk at around the Eddington luminosity (L_E) and is not accurate in describing the effective temperature profile, since it neglects time delay between energy generation at deeper inside the disk and energy release at the surface. Especially, the photon-trapping effects are appreciable even below L ~ L_E, while they appear above ~ 3L_E according to the slim disk. Through the photon-trapping effects, the luminosity is reduced and the effective temperature profile becomes flatter than r^{-3/4} as in the standard disk. In the case that the viscous heating is effective only around the equatorial plane, the luminosity is kept around the Eddington luminosity even at very large mass accretion rate, Mdot>>L_E/c^2. The effective temperature profile is almost flat, and the maximum temperature decreases in accordance with rise in the mass accretion rate. Thus, the most luminous radius shifts to the outer region when Mdot/(L_E/c^2) >> 10^2. In the case that the energy is dissipated equally at any heights, the resultant luminosity is somewhat larger than in the former case, but the energy-conversion efficiency still decreases with increase of the mass accretion rate, as well. The most luminous radius stays around the inner edge of the disk in the latter case. Hence, the effective temperature profile is sensitive to the vertical distribution of energy production rates, so is the spectral shape. Future observations of high L/L_E objects will be able to test our model.Comment: 10 pages, 7 figures, accepted for publication in Ap

Dynamics of spin correlations in the spin-1/2 isotropic XY chain in a transverse field

Dynamic xx spin pair correlation functions for the isotropic spin-1/2 XY chain are calculated numerically for long open chains in the presence of a transverse magnetic field at finite temperature. As an application we discuss the temperature dependence of the spin-spin relaxation time in PrCl_3.Comment: 2 pages, latex, 2 figures, abstract of the paper presented at Ampere Summer School ``Applications of Magnetic Resonance in Novel Materials'' Nafplion, Greece, 3-9 September, 2000, partially published in J. Phys. A: Math. Gen. 33, 3063 (2000

Vertically Self-Gravitating ADAFs in the Presence of Toroidal Magnetic Field

Force due to the self-gravity of the disc in the vertical direction is considered to study its possible effects on the structure of a magnetized advection-dominated accretion disc. We present steady-sate self similar solutions for the dynamical structure of such a type of the accretion flows. Our solutions imply reduced thickness of the disc because of the self-gravity. It also imply that the thickness of the disc will increase by adding the magnetic field strength.Comment: Accepted for publication in Astrophysics and Space Science

An Optical Source Catalog of the North Ecliptic Pole Region

We present a five (u*,g',r',i',z') band optical photometry catalog of the sources in the North Ecliptic Pole (NEP) region based on deep observations made with MegaCam at CFHT. The source catalog covers about 2 square degree area centered at the NEP and reaches depths of about 26 mag for u*, g', r' bands, about 25 mag for i' band, and about 24 mag for z' band (4 sigma detection over an 1 arcsec aperture). The total number of cataloged sources brighter than r'= 23 mag is about 56,000 including both point sources and extended sources. From the investigation of photometric properties using the color-magnitude diagrams and color-color diagrams, we have found that the colors of extended sources are mostly (u*-r') 0.5. This can be used to separate the extended sources from the point sources reliably, even for the faint source domain where typical morphological classification schemes hardly work efficiently. We have derived an empirical color-redshift relation of the red sequence galaxies using the Sloan Digital Sky Survey data. By applying this relation to our photometry catalog and searching for any spatial overdensities, we have found two galaxy clusters and one nearby galaxy group.Comment: 34 pages, 15 figures, 2 tables. Accepted for publication in ApJS. The pdf file with high resolution figures can be downloaded from http://astro.snu.ac.kr/~nhwang/index.files/nep.htm

Mass-losing accretion discs around supermassive black holes

We study the effects of outflow/wind on the gravitational stability of accretion discs around supermassive black holes using a set of analytical steady-state solutions. Mass-loss rate by the outflow from the disc is assumed to be a power-law of the radial distance and the amount of the energy and the angular momentum which are carried away by the wind are parameterized phenomenologically. We show that the mass of the first clumps at the self-gravitating radius linearly decreases with the total mass-loss rate of the outflow. Except for the case of small viscosity and high accretion rate, generally, the self-gravitating radius increases as the amount of mass-loss by the outflow increases. Our solutions show that as more angular momentum is lost by the outflow, then reduction to the mass of the first clumps is more significant.Comment: Accepted for publication in Astrophysics & Space Scienc