Weekly Calendar of Events

AUGUST 25 - 29, 2014


11:00 am: Atomic and Molecular Physics Division Seminar. "Faltering Steps into the Galaxy," Prof. Gary Zank, University of Alabama. Phillips Auditorium.

Abstract: Voyager 1 has now entered the interstellar medium, a moment of great historical import. We describe the Voyager 1 magnetic field and energetic particle observations, the initial uncertainty surrounding a possible crossing of the heliopause, and the eventual clarification by the Plasma Waves Analyzer. The interaction of the solar wind and the interstellar medium is complicated by the presence of neutral hydrogen that is coupled via charge exchange to the plasma. We present the current status of theory, models, and simulations, describing the highly non-equilibrated interaction and the underlying physics. We conclude by discussing briefly related interactions of stellar winds with their local environments.


11:00 am: Optical and Infrared Astronomy Division Seminar. "Polarization as a Diagnostic of the Emission Processes in Relativistic Jets," Markus Böttcher, North-West University, Potchefstroom, South Africa. Pratt Conference Room.

Abstract: Astrophysical sources exhibiting relativistic jets, such as active galactic nuclei (AGN) and gamma-ray bursts (GRBs) are strong emitters of radiation across the electromagnetic spectrum, from radio to gamma-rays. In spite of intensive, coordinated observing efforts over the past several decades, the nature of the radiating particles, the location of the gamma-ray emission region, and the mechanism leading to the emission of high-energy radiation, are still uncertain. As a new strategy to break the degeneracy of different models proposed for the origin of gamma-rays from relativistic jets, many observatories are now including measurements of optical polarization into multi-wavelength studies of relativistic jet sources, and a new generation of X-ray polarimeters is currently being developed. These studies have, in several instances, revealed large rotations of the position angle of the optical polarization, correlated with gamma-ray flaring activity in blazars, a highly beamed class of jet-dominated AGN. In this talk, I will summarize recent theoretical predictions of the high-energy (X-ray and gamma-ray) polarization from different blazar models, discuss the implications of high-energy polarization on gamma-gamma absorption of high-energy gamma-rays within the emission region, and present a new theoretical interpretation of the optical polarization-angle swings associated with gamma-ray flares in blazars.

12:30 pm: High Energy Astrophysics Division Lunch Talk. "Near-Infrared Observations of Ultraluminous X-ray Sources," Marianne Heida, Radboud University, The Netherlands. Pratt Conference Room.

Abstract: Are ultraluminous X-ray sources powered by stellar or intermediate mass black holes? To answer this question we need reliable mass measurements of these systems. The best way to do this would be to measure the radial velocity curves of the companion stars and thus derive the mass functions for these black holes. This has proven to be very difficult for ULXs because the optical light from these systems is dominated by the accretion disc. However, some ULXs may have red supergiant donor stars, that are intrinsically bright in the near-infrared and may enable us to measure their radial velocity curves in that part of the spectrum. We have conducted a survey of nearby ULXs to search for near-infrared counterparts. Of our 62 targets, 11 have a counterpart that could potentially be a red supergiant. I will present results of this survey and initial results of our NIR spectroscopic follow-up of several of the sources where we detected a NIR counterpart.

1:00 pm: High Energy Astrophysics Division Lunch Talk. "Clustering Properties of Type 1 and Type 2 AGN in COSMOS at z~3," Viola Allevato, University of Helsinki. Pratt Conference Room.

Abstract: Measurements of the spatial distribution of AGN in the Universe, provides a unique way to study the typical environment in which AGN preferentially reside, through the connection with their host dark matter halos and to address which physical processes are triggering AGN activity. In this presentation I will talk about the clustering properties of X-ray selected Type 1 and Type 2 AGN with moderate luminosity (logLbol~45.3 erg/s) based on XMM and Chandra data in COSMOS at z~3. I will discuss the implications in terms of previous studies at lower z and BH accretion models.

The Calendar is prepared by the Web Services Group. Entries may be submitted via email to weekly_cal@cfa.


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