Bulletin of the American Physical Society
APS April Meeting 2011
Volume 56, Number 4
Saturday–Tuesday, April 30–May 3 2011; Anaheim, California
Session L3: Astrophysical Flares |
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Sponsoring Units: DAP DPP Chair: Patrick Slane, Harvard-Smithsonian Center for Astrophysics Room: Garden 3 |
Sunday, May 1, 2011 3:30PM - 4:06PM |
L3.00001: Solar and Stellar Flares Invited Speaker: Flares in the atmosphere of the Sun and of many other stars appear to result from the sudden conversion of electromagnetic field energy into a wide array of observable forms. Of these products the definitive modern observations are the X-rays and $\gamma$-rays, signifying the common occurrence of particle acceleration to mildly relativistic or higher energies. Abundant direct (the radiation) and indirect information confirms that this particle acceleration is energetically significant, as well as common. We are thus led to the physics of particle distribution functions that may deviate radically from Maxwellian distributions. Stellar observations allow us to study these phenomena across a wide variety of environments, whereas solar and planetary observations allow us to do imaging spectroscopy and thereby get a better understanding of the global structures of the processes. In particular we have spectacular new data from satellite solar observatories such as \textit{RHESSI} (hard X-rays and $\gamma$-rays) and others, most recently the \textit{Solar Dynamics Observatory}. Of particular interest from the point of view of plasma physics is the flare environment: a low-beta corona linked to a massive body through an intermediate weakly-ionized layer (the chromosphere). The chromosphere is extraordinarily complicated; its behavior is coming again to be recognized as fundamental to the overall flare process, and in this presentation I will attempt to clarify its role. [Preview Abstract] |
Sunday, May 1, 2011 4:06PM - 4:42PM |
L3.00002: Flaring Activity of the Massive Black Hole at the Center of the Galaxy Invited Speaker: It is becoming increasing clear that an underluminous supermassive black hole (Sgr A*) lies at the center of the Galaxy. Sgr A* exhibits quiescent synchrotron emission from an accretion flow at radio and submillimeter wavelengths. Sgr A* is also known to be variable in radio, millimeter, IR and X-rays. Infrared flares appear to occur a few times a day, with a small fraction showing simultaneous flaring in X-rays. The flaring activity is thought to be arising from the inner ten Schwarzschild radii of a 4 million solar mass black hole coincident with Sgr A*. I will present highlights of recent multi-wavelength measurements to study the flaring activity of the black hole. The correlation of the variable emission in multiple wavelengths shows time delay in the peaks of flare emission. In addition, there is evidence for dimming of submillimeter and radio emission during the peak of IR flare emission. These measurements are interpreted in terms of an expanding blob of synchrotron emitting hot plasma, partially eclipsing the background quiescent emission from Sgr A*. I will also discuss the origin of X-ray flare emission in the context of inverse Compton scattering of IR flare emission. These measurements are providing us with insights on the nature of the magnetized flow very near the event horizon of a supermassive black hole. [Preview Abstract] |
Sunday, May 1, 2011 4:42PM - 5:18PM |
L3.00003: Variability of Extragalactic Very High Energy Gamma-ray Emitters Invited Speaker: The third generation of Very High Energy (VHE; E$>$100 GeV) gamma-ray telescopes (e.g. HESS, VERITAS \& MAGIC) are an order of magnitude more sensitive than their predecessors. Over the past eight years, observations with these instruments have increased the catalog of VHE emitters to more than 110 sources, of which $\sim$40 are extragalactic. While only limited variability is found from many of the newly discovered VHE emitters, the more sensitive studies of the previously known extragalactic VHE emitters have yielded unprecedented results. Recent highlights include the discovery of minute-scale VHE flux variability, significant VHE spectral changes on sub-hour time-scales, and strong correlations of these rapid VHE variations (flux \& spectrum) with those simultaneously observed at X-ray and optical energies. A summary of the variability properties of extragalactic VHE emitters and their scientific implications will be presented. [Preview Abstract] |
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