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SED Director’s Seminar

December

08

Please join us for the next SED Director’s Seminar hosted by the Gravitational Astrophysics Laboratory.

Electromagnetic chirps from neutron stars merging with black holes — Tito Dal Canton

Future detections of gravitational waves from neutron-star mergers are expected to have electromagnetic counterparts, typically in the form of prompt, short gamma-ray bursts powered by the accretion of the dispersed material on the remnant object. Recent models, however, predict the emission of a high-energy electromagnetic flare shortly before the merger. If such an emission happens close to the neutron star surface, the relativistic orbital motion of the source will imprint a “chirping" modulation on the observed light curve, closely related to the corresponding gravitational-wave signal. I will describe this modulation and how it can be used for the analysis of photon data around gravitational-wave events.

Orbitally-Modulated X-rays From Millisecond Pulsar Binaries — Alice Harding

A large number of new Black Widow (BW) and Redback (RB) rotation-powered millisecond pulsars have been discovered through radio searches of unidentified /Fermi// /sources, increasing the known number of these systems from 4 to 28. We model the high-energy synchrotron emission component from particles accelerated to several TeV in intrabinary shocks in two known BW and RB systems, and its predicted modulation at the binary orbital period. Constructing a geometric model of the shock, we use radio eclipse data in conjunction with optical constraints on the binary inclination angle to constrain the shock stagnation point distance from either the pulsar or companion star. We next model the X-ray synchrotron orbital light curves and compare them to those observed from the PSR B1957+20, where the shock surrounds the companion, and PSR J1023+0038, where the shock surrounds the pulsar, to constrain the bulk Lorentz factor of the wind flow as well as further constrain the inclination angle.

Determining the Intergalactic Photon Densities from Deep Galaxy Surveys and the Gamma-ray Opacity of the Universe — Floyd Stecker

We have calculated the extragalactic IR-UV photon density as a function of redshift, and the resulting IR-UV spectrum of the extragalactic background light. Our empirically-based approach is based on local-to-deep galaxy survey data obtained in different wavelength bands using many space-based telescopes. This approach allowed us, for the first time, to obtain a completely model independent determination of extragalactic photon densities, and also to quantify their uncertainties. Using our photon density results, we were able to place 68% confidence upper and lower limits on the opacity of the universe to gamma-rays as a function of energy and redshift. We compared our results with /Fermi/ analyses of the spectra of extragalactic gamma-ray sources.

 
Date December 08, 2017
Start/End Time 01:00 PM - 02:00 PM
Location 34/W150
Contact Amber Straughn
Email Address amber.n.straughn@nasa.gov
Event Type Seminars/Colloquia
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