Series: Astronomy Colloquium
Date: Wednesday 13-Sep-2017
Time: 16:05-17:00 (4:05-5:00 pm)
Location: ATL 2400
Speaker: Dr. Ke Fang (JSI Fellow) & Dr. Geoffrey Ryan (JSI Fellow) (UMD)
Title: See Abstracts
High-energy Neutrinos from Magnetars Formed from the Merger of Binary Neutron Stars-Ke Fang
The merger of a neutron star (NS) binary may result in the formation of a long-lived, or indefinitely stable, millisecond magnetar remnant surrounded by a low-mass ejecta shell. A portion of the magnetar’s prodigious rotational energy is deposited behind the ejecta in a pulsar wind nebula, powering luminous optical/X-ray emission for hours to days following the merger. Ions in the pulsar wind may also be accelerated to ultra-high energies, providing a coincident source of high energy cosmic rays and neutrinos. At early times, the cosmic rays experience strong synchrotron losses; however, after a day or so, pion production through photomeson interaction with thermal photons in the nebula comes to dominate, leading to efficient production of high-energy neutrinos. After roughly a week, the density of background photons decreases sufficiently for cosmic rays to escape the source without secondary production. We will discuss the astroparticle production resulted from these competing effects. Specifically, we will show that a neutrino flux that peaks on a few day timescale near an energy of ~ 1018 eV may be detectable for individual mergers out to ~ 10 (100) Mpc by current (next-generation) neutrino telescopes, providing clear evidence for a long-lived NS remnant and an highest-energy counterpart signal for the gravitational wave event.
Lighting Up Accretion Disks With Binary Black Holes - Geoffrey Ryan
Accretion can provide an electromagnetic counterpart, or even precursor, to binary black hole mergers seen by LIGO and eventually, LISA. Gas flows on to binary systems are highly dynamical and display a rich phenomenology. I will present a series of numerical simulations of accretion on to binary black holes, with a focus on "minidisks", the accretion disks which form around each member of the binary, and the response of a circumbinary disk to the recoiling post-merger black hole. We find minidisks display prominent spiral shock waves, excited by the tidal forces of the binary companion. These shocks efficiently heat the disk and drive accretion by purely hydrodynamic means, resulting in a thin accretion disk bright in soft x-rays. Post-merger, the recoiling remnant black hole drives a one-armed spiral shock wave through any surrounding circumbinary disk, providing a prompt x-ray counterpart to the merger. I will also briefly review the tool used to produce these simulations, the general relativistic moving-mesh hydrodynamics code Disco.
Colloquia are usually preceded by espresso and ice cream at 1:45 pm outside room PSC 1150 and are followed by an informal reception at 5:15 pm in that room. Anyone interested in talking with the speaker, or being added to the colloquium announcement email list, should contact the colloquium organizer. Lunch will normally be reserved for the speaker to talk to graduate students.
Colloquium Organizer:
Prof. L. Drake Deming
Special accommodations for individuals with disabilities can be made by calling (301) 405-3001. It would be appreciated if we are notified at least one week in advance.
