Bulletin of the American Physical Society
APS April Meeting 2016
Volume 61, Number 6
Saturday–Tuesday, April 16–19, 2016; Salt Lake City, Utah
Session X4: DAP Hot TopicsInvited
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Sponsoring Units: DAP Chair: Julie McEnery, NASA Room: Ballroom C |
Tuesday, April 19, 2016 10:45AM - 11:21AM |
X4.00001: Fermi-GBM follow-up of the first gravitational-wave detection Invited Speaker: Lindy Blackburn The Advanced LIGO detectors made the first direct detection of gravitational-waves (GW) on September 14 2015 by observing the characteristic signal from a merger of two black holes, about 30 solar masses each and at a distance of 410 Mpc. The Fermi Gamma-ray Burst Monitor (GBM) covered 75% of the likely sky position of the source, and while no nearby GBM trigger was generated on-board in response to any bright gamma-ray burst (GRB), an automated offline pipeline designed to detect sub-threshold signals identified a weak event of moderate significance beginning 0.4s after the GW coalescence time and lasting for 1s. We discuss the initial detection and follow-up of the GBM event, including its plausibility as an EM counterpart when none is expected for the binary black-hole system observed. More generally, we discuss the ability for Fermi-GBM to find, characterize, and localize high-energy counterparts to GWs in the advanced LIGO era. In the coming years, detections and upper limits by Fermi-GBM for binary coalescence events involving a neutron star should reveal the progenitor behind short GRBs, aid in coordinating other targeted EM follow-up, and provide details about burst energetics and beaming. [Preview Abstract] |
Tuesday, April 19, 2016 11:21AM - 11:57AM |
X4.00002: Measuring the kinematic Sunyaev-Zel$\backslash $'dovich effect with the South Pole~ Invited Speaker: Kyle Story Inferences of the peculiar velocities of galaxy clusters can potentially constrain cosmological models and probe gravity on large length scales. Such inferences are becoming a reality with detections of the kinematic Sunyaev-Zel'dovich (kSZ) effect. The kSZ effect arises when cosmic microwave background (CMB) photons scatter off free electrons in dense clusters of galaxies that are moving with respect to the CMB; the bulk motion of clusters Doppler shifts the CMB signal. With future data sets, the kSZ signal could provide precise measurements of gravity on \textasciitilde 100 MPc scales. This talk will present a significant (\textasciitilde 4 sigma) detection of the pairwise kSZ signal using a cluster catalog from the first year of data from the Dark Energy Telescope (DES) in combination with CMB temperature maps from the South Pole Telescope. This represents the first detection of the kSZ effect from a cluster catalog with photometric redshifts and one of the first results from the DES year-one data. [Preview Abstract] |
Tuesday, April 19, 2016 11:57AM - 12:33PM |
X4.00003: A single prolific r-process event preserved in an ultra-faint dwarf galaxy Invited Speaker: Alexander Ji The heaviest elements in the periodic table are synthesized through the r-process, but the astrophysical site for r-process nucleosynthesis is still unknown. Ultra-faint dwarf galaxies contain a simple fossil record of early chemical enrichment that may determine this site. Previous measurements found very low levels of neutron-capture elements in ultra-faint dwarfs, preferring supernovae as the r-process site. I present high-resolution chemical abundances of nine stars in the recently discovered ultra-faint dwarf Reticulum II, which display extremely enhanced r-process abundances 2-3 orders of magnitude higher than the other ultra-faint dwarfs. Stars with such extreme r-process enhancements are only rarely found in the Milky Way halo. The r-process abundances imply that the neutron-capture material in Reticulum II was synthesized in a single prolific event that is incompatible with r-process yields from ordinary core-collapse supernovae. Reticulum II provides an opportunity to discriminate whether the source of this pure r-process signature is a neutron star merger or magnetorotationally driven supernova. The single event is also a uniquely stringent constraint on the metal mixing and star formation history of this ultra-faint dwarf galaxy.\\ \\In collaboration with: Anna Frebel, Anirudh Chiti - Massachusetts Institute of Technology - MIT and Joshua Simon - Observatories of the Carnegie Institution of Washington. [Preview Abstract] |
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