DECEMBER 3 - 7, 2007

MONDAY, DECEMBER 3

1:00 pm: High Energy Astrophysics Division Lunch Talk. "Possible Nonthermal Nature of the Excess Soft X-ray Emission in the Cluster of Galaxies Sersic 159-03," Dr. Norbert Werner, SRON, The Netherlands. Classroom A-101.

Abstract: We studied new Suzaku data and two archival XMM-Newton data sets of the cluster of galaxies Sersic 159-03, which has a strong excess soft X-ray emission component. The Suzaku observation confirms the presence of the soft excess emission, but it does not confirm the presence of redshifted O VII lines in the cluster. We derived radial profiles and 2D maps which show that the soft excess emission has a strong peak at the position of the central cD galaxy and has no significant azimuthal variations. We concluded that the spatial distribution of the soft excess is neither consistent with the models of inter-cluster warm-hot filaments, nor with models of clumpy warm intra-cluster gas associated with infalling groups. Moreover, the XMM-Newton RGS observation does not show OVII line emission, which we would expect to see if the centrally peaked soft emission was of thermal origin. We concluded that a non-thermal model provides the best explanation for the observed properties of the soft excess in Sersic 159-03. This non-thermal emission might be due inverse-Compton scattering of the cosmic microwave background photons on relativistic electrons. The total energy in relativistic electrons needed to explain the excess emission within the radius of 600 kpc does not exceed 1x10^61 erg, while the total thermal energy within the same radius is 3x10^63 erg.  Furthermore, we discuss the prospects of a search for the missing baryons in the warm-hot phase of the inter-cluster filaments with the current instruments using pairs of clusters of galaxies, in which the filament connecting them has a favorable geometry.

TUESDAY, DECEMBER 4

2:00 pm: Institute for Theory and Computation (ITC) Seminar. "Primordial Black Holes in the Dark Ages," Katie Mack, Princeton University. Phillips Auditorium.

Abstract: I will discuss the effect of evaporating primordial black holes on the ionization history of the universe, with an emphasis on the limits derivable from future 21-cm observations of high-redshift neutral hydrogen.

WEDNESDAY, DECEMBER 5

12:30 pm: High Energy Astrophysics Division Lunch Talk. "Particle-in-Cell Simulations of Collisionless Reconnection in GRB Outflows," Dr. Joachim Moortgat, University of Rochester. Phillips Auditorium.

Abstract: One of the open issues in GRB models is whether the outflow dynamics are dominated by the particles or by the electromagnetic Poynting flux, and the related question of the jet composition, i.e. a pure pair plasma or a plasma loaded with a certain fraction of baryons. Few observational diagnostics exist to constrain either the magnetic fields or the jet composition. Whichever is the case close to the source, observations indicate that at larger distances the particles are accelerated to highly relativistic velocities and dominate the energy budget. Magnetic reconnection is a likely mechanism to operate in the magnetized GRB jet plasma and is known to efficiently accelerate particles at the expense of the free magnetic energy. This is fairly well studied in the less energetic environments of the solar corona and the Earth's magnetotail, but to a much lesser extend in the relativistic regime and for pair plasmas. To address some of these issues, we are developing numerical simulations of magnetic reconnection under conditions applicable to GRB outflows. Here we present some of our first results using a fully explicit and highly parallelized relativistic particle-in-cell code, Osiris. We study a double Harris current sheet configuration in 2 dimensions with periodic boundary conditions on all sides and high spatial and temporal resolutions. By tuning the plasma velocity from non-relativistic to highly relativistic values and, similarly, studying both a pure electron-positron plasma and a plasma with an increasing proton fraction we intend to obtain different particle acceleration spectra that could be used as distinguishing observational diagnostics of the jet's nature.

4:00 pm: Initiative in Innovative Computing (IIC) Seminar. "Many Eyes: Democratizing Visualization," Martin Wattenberg and Fernanda Viegas, Research Staff Members, IBM. Preceded by refreshments at 3:45 pm. Room 330, 60 Oxford Street, Cambridge. Event parking is available at the 52 Oxford Street Garage [map]. Please inform the parking attendant you are attending the IIC seminar. (The IIC seminar series schedule is updated often with additional information and seminars.)

Abstract: Data visualization has historically been accessible only to the elite in academia, business, and government. To democratize visualization, we have built Many Eyes, a web site where people upload their data, create interactive visualizations, and carry on conversations. The goal is a social style of data analysis in which visualizations spur discussion and collaboration. We present Many Eyes, describe patterns of usage on the site, and discuss what those patterns suggest about the future of visualization.

4:30 pm: Joint CfA/Harvard University Atomic Physics Colloquium. "Microscopic Study of Fermi Gases at Unitarity," Prof. Doerte Blume, Washington State University. Preceded by tea at 4:00 pm. Jefferson 356, Harvard University.

THURSDAY, DECEMBER 6

11:00 am: Science Education Seminar and Open Discussion. Weekly sessions focus on current department programs, literature reviews, and recent trends in science education and assessment. Some sessions feature outside speakers or guests. All members of the CfA community are welcome. Please contact Bruce Ward at bward@cfa, if you wish to attend any session. Phillips Auditorium.

4:00 pm: Colloquium. "How Luminous Was the Galactic Supermassive Black Hole in the Past?" Dr. Frederick K. Baganoff, MIT. Preceded by tea at 3:30 pm. Phillips Auditorium.

Abstract: Repeated deep Chandra monitoring of Sgr A* over the past few years has revealed rapidly variable Fe fluorescence features within 6' (14 pc in projection) of the supermassive black hole, suggesting that its X-ray luminosity may have been greater than 10^38 erg/s for at least 2-3 years about 60 years ago, before the first X- ray satellites were launched. These results will be discussed in the context of X-ray observations of Fe fluorescence in Sgr B2 and Sgr C, and arguments will be presented against the alternative hypotheses of irradiation by local X-ray binaries or excitation by low-energy cosmic ray electrons. In addition, some results from the latest multiwavelength monitoring campaigns on Sgr A* will be presented, including the first clear detection of a sub-mm counterpart with the SMA to a flare seen in the X-ray and IR bands by Chandra and Keck.

7:00 pm: Family Friendly Night. "A Star is Born," Meredith Hughes, CfA. Family Friendly Night features a fun, interactive program followed by telescopic observing from the observatory roof, if weather permits. All ages are welcome to attend. Seating is limited and available on a first-come, first-served basis. Doors open at 6:30 pm. Phillips Auditorium.

Abstract: How are stars made, and what happens when their lives are over? Join us as we use our telescopes to watch stars forming trillions of miles away in the night sky, and look at what happens to stars after they die. If it's cloudy, we'll check out the constellations in our inflatable planetarium and make models of asteroids out of things you can find in your kitchen.

FRIDAY, DECEMBER 7

12:30 pm: Institute for Theory and Computation (ITC) Seminar. "Stellar Feedback and Galaxy Formation," Norm Murray, CITA. Phillips Auditorium.

Abstract: Star formation in galaxies is remarkably inefficient; naively one might expect that gas would cool rapidly, and collapse to form stars on a dynamical time. Observations, on the other hand, show that only two percent of the gas in a galaxy is turned into stars per dynamical time. Similar comments apply to star formation in individual giant molecular clouds. In the case of galaxies, current models attribute the low efficiency to turbulence induced by energy input from supernovae. In giant molecular clouds, the low efficiency is attributed to turbulent stirring by ionized gas (HII regions or shocked stellar winds). I will argue that the low efficiency in both cases is driven primarily by radiation pressure, from light produced by massive star clusters, on dust. I will present models that reproduce the Carina and Westerlund I clusters in the Milky Way, the 20 or so massive clusters in M82, and argue that yet more massive clusters, with masses up to 100 million solar masses, dominate the dynamics of the ISM in ultraluminous galaxies like Arp 220. I will describe the formation and evolution of such massive clusters, which should have a well defined mass-radius relation and mass-to-light ratios that vary with cluster mass, and compare the results to observations of massive clusters in the nearby universe.

CfA-WIDE RECEPTION FOR THE CfA VISITING COMMITTEE

Tuesday, December 4, 5:00 - 6:00 pm, Perkin Lobby: The CfA Visiting Committee will be meeting at the CfA from Monday, December 3 to Wednesday, December 5. Chaired by Martha Haynes (Cornell University), the committee includes: John Gallagher (University of Wisconsin), Richard McCray (University of Colorado), Sean Solomon (Carnegie Institution of Washington), David Spergel (Princeton University), Charles Steidel (California Institute of Technology), and Alan Title (Lockheed Martin Space Systems). We look forward to seeing you at the reception. Questions? Call or email Amanda Preston, 5-7321, preston@cfa

SAO HUMAN RESOURCES NOTES

Open Season Reminder

The 2008 Health Benefits Open Season for both Federal and Trust Fund employees is from November 12 to December 10, 2007. During this period, employees eligible for health benefits have an opportunity to enroll in a plan if not currently enrolled, change to a new provider, or make changes to their current coverage. If you do not wish to make changes during this open enrollment period, your current coverage will remain in force through the 2008 health plan year.

In addition, two Flexible Spending Accounts (FSAs) - a Health Care FSA and a Dependent Care FSA - are available for the first time to Trust Fund employees in 2008. For information about these new benefit options, go to the HR Homepage and click on the What's New link.

Plan changes and new enrollments for Federal employees will become effective on January 6, 2008. For Trust Fund employees, 2008 health plan changes and new enrollments will be effective on January 1, 2008.

Please note that Human Resources must receive your plan change forms or new enrollments by close of business on December 10, 2007.

If you have questions or need a health plan brochure, please contact Anne LeBlanc, ext. 5-7371, or Linda McDonald, ext. 6-7605.

Leave Donations Requested

Due to a medical emergency, Joyce Janjigian of the Solar, Stellar and Planetary Science Division has been approved as a leave donor recipient in the Leave Transfer Program. Donna Coletti of the Library is also an approved leave donor recipient. Any SAO Trust Fund employee who wishes to donate annual leave to Joyce and/or Donna should complete a Leave Donor Form and send it to MS 17.

Under the Leave Transfer Program, Trust Fund employees may only donate annual leave to other Trust Fund employees and Federal employees may donate annual leave only to other Federal employees. If you should have any questions or are not able to access the form, please contact Anne LeBlanc, ext. 5-7371.

Job Vacancies

An online listing of all current SAO job openings is available. For more information, please call Human Resources, ext. 5-7371, or view your nearest bulletin board.