October 2, 2015 3:30PM BPB-207. Drew Clausen. Using Tidal Disruption Events to Study Massive Black Holes and Their Environments.

When a black hole tidally disrupts a star, accretion of the debris will produce a luminous flare and reveal the presence of a dormant black hole. Emission lines produced when the stellar debris and/or other gas in the black hole's vicinity are photoionized by the accretion flare have considerable diagnostic power. I will discuss models of the emission line spectrum produced in the debris released when evolved stars are tidally disrupted by an intermediate-mass black hole (100-10000 solar masses), and discuss the possibility of using the emission lines to identify such events and constrain the properties of the black hole. While there is some agreement between these models and observations of white dwarf tidal disruption candidates in globular clusters associated with NGC 4472 and NGC 1399, there are also drawbacks to interpreting these sources as tidally disrupted white dwarfs. I will also present results from time-dependent photoionization calculations that model the emission line spectrum produced when ambient, circumnuclear gas is illuminated by a tidal disruption flare. The emission line light curves are consistent with the transient extreme coronal line emitters recently identified in SDSS. These tidal disruption event light echoes can be used to probe the circumnuclear environments of quiescent galaxies and to constrain the extreme UV component of tidal disruption flares.

UNLV Physics & Astronomy Forum Schedule

Public Talk Thursday 9/17: Mario Livio, Brilliant Blunders.

The Russell Frank Astronomy Lecture Series

Brilliant Blunders

internationally known astrophysicist and best-selling author Dr. Mario Livio

This talk is intended for a general audience including enthusiasts of all backgrounds and ages.

Dr. Livio is the author of acclaimed popular level books including The Golden Ratio, The Equation That Couldn't Be Solved, Brilliant Blunders, and Is God a Mathematician?. He has authored many scientific publications as well. You can listen to a recent KNPR interview and see other talks he has given here.

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September 18, 2015 3:30PM BPB-102. Mario Livio, Type Ia Supernovae: Progenitors and Cosmology.

I will review the current status concerning the identification of the progenitor systems of Type Ia supernovae, in light of recent observations and theoretical developments. I will also show how current and future observations can be used to tame evolutionary effects, on the road to better constraints on the nature of dark energy.

September 11, 2015 3:30PM BPB-217. Fan Guo, Magnetic Reconnection: A Powerful Cosmic Particle Accelerator.

Astrophysical magnetic reconnection sites have long been expected to be sources of high-energy particles. Recent observations of high-energy gamma-ray flares from the Crab nebula and models of gamma-ray bursts and TeV blazars have motivated us to better understand magnetic reconnection and its associated particle acceleration in plasma conditions where the magnetic energy is dominant. We will present fully kinetic particle-in-cell simulations of anti-parallel magnetic reconnection in the highly magnetized regime (the magnetization parameter sigma >> 1). The magnetic energy is converted efficiently into kinetic energy of nonthermal relativistic particles in a power-law spectrum. For a sufficiently large system and strong magnetic field, the power-law index approaches "p=1". The dominant acceleration mechanism is a first-order Fermi process accomplished through the curvature drift motion of particles in magnetic flux tubes along the electric field induced by fast plasma flows. We will also present an analytical model for the formation of power-law distribution and show the nonthermal distribution may be a common feature of magnetically dominated reconnection.

September 4, 2015 3:30PM BPB-217. Daniel Whalen, Finding the First Cosmic Explosions.

Primordial stars formed about 200 Myr after the big bang, ending the cosmic dark ages. They were the first great nucelosynthetic engines of the universe and may be the origins of the supermassive black holes found in most massive galaxies today. In spite of their importance to the evolution of the early universe not much is known for certain about the properties of Pop III stars. Until now, observers have looked for the nucleosynthetic imprint of Pop III SNe in the chemical abundances in ancient, dim metal-poor stars to constrain the masses of the SN progenitors. But with the advent of JWST, WFIRST and the 30 m telescopes it may soon be possible to directly observe the explosions themselves in the NIR and thus unambiguously constrain the properties of the first stars. I will present radiation hydrodynamical calculations of the light curves of the first SNe in the universe and discuss strategies for their detection. I will also describe how some may already have been captured in surveys of galaxy cluster lenses such as CLASH, Frontier Fields and GLASS.

Lon Spight rememberance Friday August 28, 2015; 3:30-6:30 BPB-102

The Department of Physics & Astronomy will host an informal memorial for our recently departed friend and colleague Dr. Lon Spight -- one of the founders of our department.

August 21, 2015 10:00AM BPB-217. Wei-Hua Lei, On-beam and Off-beam Jetted TDEs.

A star or sub-stellar object will be destroyed by tidal forces when it passes close enough by a supermassive black hole (SMBH). These events, known as tidal disruption events (TDEs), are expected to produce luminous flare emission in the UV to X-ray band. Recent observations of Sw J1644+57, in particular, suggest that at least some TDEs can launch a relativistic jet. A common speculation is that these rare events are related to rapidly spinning BHs. We constrained the BH spin parameter by using the available data, and found that the BH indeed carries a moderate to high spin, suggesting that BH spin is likely the crucial factor behind the Sw J1644+57-like events. Other observational properties include the rough 2.7 day periodicity in X-ray dips and 200s QPO, which we interpret as due to precession of the jet. In addition, Sw J2058+05 and Sw J1112.2-8238 are also thought to be a TDE with an on-beam relativistic jet. It is natural to expect that there should be some events with off-beam ones. We will present the first candidate for such off-beam jetted TDEs