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Chandra Fellows Symposium 2004

Harvard-Smithsonian Center for Astrophysics

October 13, 2004

Titles and Abstracts of Talks

Doron Chelouche
Institute for Advanced Studies

Mass Loss by X-ray Winds in Active Galactic Nuclei

Abstract: We consider a small sample of five type-I active galactic nuclei (AGN) which were observed with Chandra/HETG resulting in high S/N X-ray spectrum. We are able to estimate the mass loss rates and kinetic luminosities associated with the highly ionized outflowing gas in those objects and study its physical properties. Our conclusions are as follows: 1) All objects show signatures for a very high ionization outflow. 2) There is a strong indication that the flows in all objects are multi-phase with little or no kinematic differences between different phases. 3) The X-ray spectrum is consistent with such flows being thermally driven from pc scales and are therefore not associated with the inner accretion disk. 4) The underlying hard X-ray spectrum yields a consistent photon index of ~1.6 for all objects emitting below their Eddington rate while an additional soft X-ray component is required for some of them. Also, there is no clear indication for a broad relativistic iron line in any object. 5) The physical properties of the flow are similar for all objects and a coherent picture emerges concerning its physical properties. 5) The mass loss rates are of the order of 0.1 solar masses per year and the kinetic luminosities are \<\<1\% of the bolometric luminosity of the AGN. We discuss the implications of our results to AGN structure and AGN interaction with the environment.

Taotao Fang

Feedback and Non-Equilibrium Evolution of the Warm-Hot Intergalactic Medium

Abstract: Numerical simulations have shown that at the present epoch a significant fraction of baryons should be found in the warm-hot intergalactic medium (WHIM) via UV/X-ray observations. We compute the evolution of the WHIM by (1) including galactic superwind feedback processes from galaxy/star formation, (2) explicitly computing major metal species in a non-equilibrium way, and (3) significantly increasing mass and spatial dynamic ranges in the simulation. Our simulation shows that feedback processes and non-equilibrium calculations have dramatic impact on the evolution and distribution of major metal species, and therefore provide strong constraints on the current models of the IGM when compared with observational data.

Elena Gallo
Relativistic Jets from Stellar Black Holes

Abstract: After briefly reviewing our current understanding of the radio properties of black hole X-ray binaries over different accretion regimes, I will report on the discovery of a low surface brightness jet-blown bubble around the 10 solar mass black hole in Cygnus X-1. It is estimated that, in order to sustain the observed emission of the bubble, the jet of Cyg X-1 has to carry a kinetic power that is a sizable fraction of the liberated accretion luminosity.

Gordon Garmire
ACIS IPI, Evan Pugh Professor of Astronomy and Astrophysics, Penn State University

The Development of the ACIS Instrumsnt on Chandra

Abstract: The ACIS instrument on Chandra began as a developmental offshoot of the WFPC being built for HST. I will go through the various phases of the improvements to this instrument for X-ray applications and how the X-ray work benefited the optical. Finally, I will talk about the science programs that have grown out of the GTO program.

Sebastian Heinz

Whispering through whipped cream: Dissipation of weak shocks and sound waves in a filamentary intracluster medium

Radio galaxies have long been suspected as the heat sources in Galaxy clusters that can counterbalance catastrophic cooling. However, the weak shocks and sound waves excited by sub-sonic inflation and buoyancy of radio lobes are, by themselves, very inefficient in dissipating the energy they carry. But the very presence of relativistic plasma bubbles in the cluster gas provides a simple catalyst to tap into this energy through the creation of a vortex field upon their interaction with the waves. I will show how this mechanism can contribute significantly to the heating of galaxy clusters.

Ben Maughan

Chandra and XMM observations of distant galaxy clusters

We present the results of an analysis of 67 clusters of galaxies in the redshift range 0.1-0.9 (median=0.4). We give an overview of the sample, which includes a diverse array of galaxy clusters and investigate some of its statistical properties with an emphasis the scaling relations between cluster properties. We then focus on two remarkable high redshift systems with contrasting properties.

Jan-Uwe Ness

X-ray observations through the stages of Classical Novae

A Classical Nova explosion occurs on the surface of a white dwarf accreting material from a main sequence companion. This material supplies the energy for the explosion by hydrogen burning bursting out when ignition conditions are reached. Numerical simulations of the explosion have been carried out and important constraints for the models can be obtained from X-ray observa tions. The explosion itself has never been observed in X-rays and during some months after the explosion any X-ray emission is absorbed by surrounding material ejec ted by the explosion. During a phase of constant bolometric luminosity the expandin g shell is transparent to X-rays and X-ray spectra reflect the conditions of the nuclea r burning and the expanding shell. A strong, broad emission peak originates from ongoing nuclear burning and recent Chandra high-resolution X-ray grating spectra show absorption lines from the expanding shell. Very similar spectra have been obser ved from Super-Soft X-ray Sources, likely candidates for predecessors of SN Ia expl osions. The spectra of Classical Novae and Super-Soft X-ray Sources are awaiting to be analysed with sophisticated atmospheric codes like PHOENIX. In the very late phase, afte r nuclear burning has switched off, one can see an emission line spectrum produced in the shell by collisional ionisation and excitation followed by radiative decays. I give an overview of the potential in high-resolution X-ray spectroscopy. We can learn about the velocity structure, the temperature conditions, evolution of op acity, and elemental composition. These are important ingredients to feed the numerica l models to understand the development in detail and to find out which conditions can ac tually lead to a SN Ia explosion.

Enrico Ramirez-Ruiz

Supernovae and Gamma-Ray Bursts Powered by Hot Neutrino-Cooled Coronae

Although they were discovered more than 30 years ago, short lived gamma-ray bursts are still a mystery. All that we can be confident about is that they involve compact objects and relativistic plasma. Current ideas and prospects are briefly reviewed. There are, fortunately, several new observations that could help clarify the issues.

Elena Rossi

Neutron loaded Gamma Ray Bursts fireballs

I present here the theory of a relativistic neutron-loaded outflow in gamma-ray bursts. The focus is on its early stages, before deceleration by a surrounding medium. The outflow has four components: radiation, electrons, protons and neutrons. The components interact with each other and exchange energy as the outflow expands. The presence of neutrons significantly changes the outflow evolution. Before the neutron-proton decoupling, friction between the neutron and proton components increases their temperatures by many orders of magnitude. After the decoupling, the gradual neutron decay inside the outflow has a drag effect on the protons and reduces their final Lorentz factor.

Mateusz Ruszkowski

AGN feedback in clusters

Recent observations show a multitude of physical effects that occur when AGN interact with the ambient ICM. An understanding of these effects is essential for all models of feedback, which is believed to be the crucial ingredient for the baryonic part of galaxy formation. We have performed a series of cosmological simulations of galaxy clusters on an adaptive mesh, which include physics that is usually neglected in these types of simulations. In particular, we include thermal conduction and viscosity. These effects are likely to play an important role in dissipating the mechanical energy of the AGN, and therefore have implications for the cooling flow problem. We also show synthetic data, showing how our simulations would appear when observed with Chandra, including the proper background and response functions.

David Sand

On the Distribution of Dark Matter in Galaxy Clusters

Cold dark matter simulations of structure formation predict that the dark matter density profile of halos ranging in size from dwarf galaxies all the way up to galaxy clusters have a universal, cuspy density profile. We present the results of a combined two-dimensional gravitational lensing and dynamical analysis of the dark matter density profile in several galaxy clusters in order to test this fundamental prediction of the CDM paradigm. Future work will both combine and compare results from X-ray analyses of the intracluster medium with those obtained with gravitational lensing.

Weiqun Zhang

Numerical Simulations of Relativistic Explosions: Gamma-Ray Bursts

Recent numerical simulations of relativistic explosions related to gamma-ray bursts (GRBs) are presented. The simulations are performed with RAM, a new special relativistic code with adaptive mesh refinement (AMR) based on the FLASH code. RAM includes physical equations of state, neutrino cooling, photodisintergration, alpha viscosity, and pseudo GR potential. We show that under-resolved simulations of test problems produce incorrect results and demonstrate the ability of RAM to correctly solve these problems. We present recent numerical work on the central engine of long soft gamma-ray bursts, more specifically the collapsar model, and the transition of GRB outflows from the collimated relativistic phase to somewhat isotropic Newtonian phase.

Last modified: 08/24/11

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