Speaker：Jonathan E. Grindlay (Harvard-Smithsonian Center for Astrophysics) 
Moderator： Prof. Zhang Shuangnan 
Time: 10:00 AM, Oct 19
Place: Room C305, IHEP Main Building 
Abstract:
The Digital Access to a Sky Century @ Harvard (DASCH) project has now scanned and done full photometric/astrometric reductions on half the sky (Galactic latitudes b = 0 - 90deg) when data release DR6 is enabled in December. The speaker will review the overall project, briefly, and then present initial results on the search for historic outbursts from black hole low mass X-ray binaries (BH-LMXBs) all of which are transients. This was one of the primary motivations for undertaking DASCH, and already yields interesting new results on the outburst Duty Cycles which constrain the BH-LMXB population and thus formation mechanisms. He will also discuss some examples of long-term AGN variability (3C273, OJ287 and others) which enable the study of extreme flares to be conducted on days to decades timescales.
About the speaker: 
Jonathan E.Grindlay
Robert Treat Paine Professor of Practical Astronomy 
Harvard-Smithsonian Center for Astrophysics
Research Interests: High Energy Astrophysics: Studies of accretion onto compact objects (black holes, neutron stars and white dwarfs). Development of detectors and telescopes for wide-field imaging surveys of black holes discovered in soft-to-hard X-rays. Time Domain Astrophysics: X-ray/optical/IR studies of Transients and variability of black holes in binaries and galactic nuclei to probe extreme physics phenomena and constrain black hole populations. Days-to-Century optical variability studies of stars and quasars with DASCH and follow-up spectroscopy to constrain formation and evolution of black holes.