Tuesday, 18 April 2017

The Lynx X-Ray Mission: Defining the Next Great X-ray Observatory

Speaker: Dr. Jessica Gaskin (NASA MSFC)
Location: OPB 234, 2:30pm
Abstract: The Lynx mission is one of 4 Large Mission concepts being studied for the 2020 Astrophysics Decadal Survey. The concept is led by the NASA HQ appointed Lynx Science and Technology Definition Team (STDT) who is tasked with developing a comprehensive science case, design reference mission and mission feasibility. The science case is currently focused on 4 themes: Understanding the formation and evolution of galaxies, the evolution of the cosmic structure, the creation and local interactions of the first black holes (black hole seeds), and the impact of the stellar lifecycle to its environment. Essential observations stemming from these topics require at least a factor of 2 improvement in sensitivity over existing X-ray observatories, combined with high-angular resolution and high resolution spectroscopy. We will discuss key science observations and the related Lynx technologies that are crucial for their realization.

Tuesday, 11 April 2017

No Seminar. UAH Honors Day.

Tuesday, 4 April 2017

Turbulence and AGN Feedback in the Cores of Galaxy Clusters

Speaker: Dr. Irina Zhuravleva (Stanford)
Location: OPB 234, 2:30pm
Abstract: Despite significant progress in understanding radio-mechanical feedback in galaxy clusters and massive elliptical galaxies, we still cannot answer many important questions, e.g. what is the dominant mechanism of energy transport from supermassive black holes to the gas, how the energy is dissipated, how to maintain cooling-heating balance between within the cluster/galaxy cores? I will address these questions by considering gas fluctuations present in the high-resolution X-ray images of galaxy clusters provided by the Chandra observatory and using high-resolution spectral data from Hitomi and grating spectrometer on XMM-Newton. In particular, I will discuss the nature and energetics of AGN-driven perturbations in the hot gas, gas turbulence in clusters and massive ellipticals and its role in AGN feedback.

Tuesday, 28 March 2017

Reconnecting with Solar Flares

Speaker: Dr. Sabrina Savage (NASA MSFC)
Location: OPB 234, 2:30pm
Abstract: Because the Earth resides in the atmosphere of our nearest stellar neighbor, events occurring on the Sun's surface directly affect us by interfering with satellite operations and communications, astronaut safety, and in extreme circumstances, power grid stability. Solar flares, the most energetic events in our solar system, are a substantial source of hazardous space weather affecting our increasingly technology-dependent society. While flares have been observed using ground-based telescopes for over 150 years, modern space-bourne observatories have provided nearly continuous multi-wavelength flare coverage that cannot be obtained from the ground. We can now probe the origins and evolution of flares by tracking particle acceleration, changes in ionized plasma, and the reorganization of magnetic fields. I will walk through our current understanding of why flares occur, show several examples of these fantastic explosions, and describe the technology and instrumentation being developed at Marshall Space Flight Center to observe these phenomena.

Tuesday, 21 March 2017

No Seminar.

Tuesday, 14 March 2017

UAH Spring Break. No Seminar.

M.S. Defense: Friday, 10 March 2017

Analysis of Rediscovered Data from Apollo 17's Lunar Seismic Profiling Experiment

Speaker: Ms. Deanna Phillips (UAH Physics)
Location: OPB 234, 10:30am
Abstract: Rediscovered data from Apollo 17’s Lunar Seismic Profiling Experiment (LSPE) are a new untapped resource for probing lunar structure. LSPE, the last seismic instrument deployed on the Moon, was designed to detect artificial seismic signatures, but also listened passively from 1976 to 1977. This 40-year-old data went unstudied due to the cancellation of the Apollo program. The analyses presented here show no evidence for correlations with the Apollo 12-16 seismic event catalog. However, the LSPE geophones have also been used as a small-aperture seismic array to identify local thermally-induced events. Supporting evidence comes from a strong association with Apollo 17 heat probe data. Seismic event rate enhancements are consistent with lunar sunrise, and include a secondary rate increase delayed by nine-hours, whose origin is currently unknown. These results extend our knowledge of lunar seismology and facilitate future comparative studies, such as those anticipated for the InSight mission to Mars.

Tuesday, 7 March 2017

High-Energy Atmospheric Physics: Gamma-ray Emission from Thunderstorms

Speaker: Dr. Eric Cramer (UAH CSPAR)
Location: OPB 234, 2:30pm
Abstract: Although lightning is one of the most commonly known and destructive natural phenomena on Earth, it remains poorly understood in terms of the most basic physics. Adding to the mystery has been the discovery that lightning emits x-rays and gamma rays. Terrestrial Gamma-ray Flashes (TGFs) are sub millisecond intense bursts of gamma-ray radiation (up to 40 MeV) associated with thunderstorms and lightning. TGFs have been observed from ground instrumentation, aircraft, and satellites, such as the Gamma-ray Burst Monitor (GBM) onboard NASA Fermi. The fact that these lightning related events can affect the upper atmosphere and lower ionosphere has reshaped the scientific field to the study of high energy atmospheric physics. The research done on lightning has thus fused many areas of physics including plasma physics, atmospheric physics, and quantum electrodynamics. This talk will give a review of the field, including the current theoretical models for the generation and propagation of TGFs, as well as current and future missions to study their physical properties. I will also discuss the current research effort here at UAH to model spectral properties of observed GBM events to put constraints on TGF production altitude and beaming width.

Ph.D. Defense: Thursday, 2 March 2017

Searching for Prompt Gamma-Ray Signals Around Gravitational Wave Triggers

Speaker: Mr. Eric Burns (UAH Physics)
Location: OPB 234, 10:00am
Abstract: One of the next great discoveries in astrophysics will be the first detection of an event in both gravitational waves and photons. I investigate the most promising event for a joint detection: the merging of a neutron star with another neutron star or a black hole, thought to produce short gamma ray bursts. We investigate the possibility of sub-populations of short gamma-ray bursts by comparing the bursts observed by the Swift Burst Alert Telescope and the Fermi Gamma-ray Burst Monitor. We find no evidence that these instruments are observing different short gamma-ray bursts, allowing us to use the Swift redshift distribution for the population observed by the Fermi Gamma-ray Burst Monitor. I discuss expected rates, joint localizations, and prospects for joint science between Advanced LIGO and the Fermi Gamma-ray Burst Monitor. Additionally, I discuss the unexpected candidate GBM gamma-ray counterpart to the first detection of gravitational waves, a binary black hole merger, the likelihood that these events are associated, and the possibility of short gamma-ray bursts arising from the merging of black holes.

Tuesday, 28 February 2017

Modeling Meteor Flares for Spacecraft Safety

Speaker: Dr. Steven Ehlert (Qualis Corp/NASA MSFC)
Location: OPB 234, 2:30pm
Abstract: NASA’s Meteoroid Environment Office (MEO) is tasked with assisting spacecraft operators and engineers in quantifying the threat the meteoroid environment poses to their individual missions. A more complete understanding of the meteoroid environment for this application requires extensive observations. One manner by which the MEO observes meteors is with dedicated video camera systems that operate nightly. Connecting the observational data from these video cameras to the relevant physical properties of the ablating meteoroids, however, is subject to sizable observational and theoretical uncertainties. Arguably the most troublesome theoretical uncertainty in ablation is a model for the structure of meteoroids, as observations clearly show behaviors wholly inconsistent with meteoroids being homogeneous spheres. Further complicating the interpretation of the observations in the context of spacecraft risk is the ubiquitous process of fragmentation and the flares it can produce, which greatly muddles any attempts to estimating initial meteoroid masses. In this talk a method of estimating the mass distribution of fragments in flaring meteors using high resolution video observations will be discussed. Such measurements provide an important step in better understanding of the structure and fragmentation process of the parent meteoroids producing these flares, which in turn may lead to better constraints on meteoroid masses and reduced uncertainties in spacecraft risk.

Tuesday, 21 February 2017

Fading Active Galaxies, Feedback, and the Demographics of Growing black holes

Speaker: Dr. Bill Keel (UA Physics & Astronomy)
Location: OPB 234, 2:30pm
Abstract: Roughly 1/1000 of nearby active galactic nuclei (AGN), and a larger fraction of AGN with tidal features in stars or cool gas, are accompanied by extended emission-line regions on scales 10 kpc and larger (beyond the normal interstellar medium of the host galaxy). In about 40% of these, the AGN falls short of the energy budget needed to photoionize these clouds by 1-3 orders of magnitude, implying that the AGN have faded over the relevant light-travel times. All these are in interacting or postmerger systems, possibly needed for sufficient distant, cold neutral hydrogen to trace the AGN's ionization history. In many of the fading candidates, low abundances and quiescent kinematics indicate that we see photoionized gaseous debris from tidal interactions, rather than outflowing material; separate signatures of sub-kiloparsec outflows are seen in some cases, giving an intriguing hint that the mode of energy output incidental to accretion (and thus the dominant source of feedback to the surrounding material) may be changing, and not just the accretion rate itself. Luminosity histories derived from recombination balance show e-folding timescales from centuries to a few millennia, short compared to simple accretion-disk expectations. These rapid, large-amplitude changes may be associated with supermassive black holes in binary systems or with local feedback processes. These results suggest that the demographics of accreting supermassive black holes are broader than derived from surveys of ongoing AGN signatures alone, a conclusion supported by new samples of analogous objects in both very nearby and moderate-redshift systems. These discoveries have been an important byproduct of citizen engagement in the Galaxy Zoo project.

Ph.D. Defense: Tuesday, 14 February 2017

Shocking Features in Merging Galaxy Clusters

Speaker: Mr. Sarthak Dasadia (UAH Physics)
Location: OPB 234, 11:00am
Abstract: Shocks are the most important sources of heating in galaxy clusters. Despite their rarity, they have been studied extensively on individual scales. However, a systematic sample study is necessary to recognize any general pattern in merger shocks. With this goal, we constructed a Sample of Chandra ClustErs with Robust Shocks (SoCCERS) to study shock properties, the related merger phenomena, and particle acceleration. The sample includes 16 galaxy clusters where shocks are robustly detected with the Chandra X-ray data, from the surface brightness jumps and the changes on thermodynamic properties. The sample can be further divided into two categories: with or without di use radio emission (DRE).

We begin by studying merger shocks in 3C89 and Abell 665. 3C89 is a unique bow shock system associated with a wide angle tail (WAT) radio galaxy and several intriguing substructures. The bow shock is this system is consistent with the Mach number M ~1.6. Abell 665 hosts a bright radio halo. Our study found a very strong merger shock with the Mach number M 3 in Abell 665 which is weakly correlated with the radio relic. This newly discovered strong shock provides a great opportunity to study the re-acceleration model with the X-ray and radio data combined.

We compared several shock parameters from SoCCERS clusters such as i) shock strength vs. system temperature vs. o set from the cluster centroid, ii) cold front vs shock shape. We found that the clusters with DRE tend to have higher system temperature than clusters without DRE. Also, from all known shock front/cold front pairs, it appears that the physical scale of the shock front is correlated with their respective cold front. A comparison between the shock standoff distance and the Mach number suggests that cores are continuously shrinking in size by ram pressure stripping. Finally, we analyzed cool core strength and conclude that it correlates with projected X-ray - BCG offset (a disturbance indicator).

Tuesday, 14 February 2017

Ex Luna, Scientia: The Lunar Occultation Explorer

Speaker: Dr. Richard Miller (UAH Physics)
Location: OPB 234, 2:30pm
Abstract: The Lunar Occultation Explorer (LOX) is a paradigm shift - a next-generation mission concept that will provide new capabilities in time-domain astrophysics and established the Moon as a platform for nuclear astrophysics. Currently under review by NASA’s Explorer Program, LOX's performance requirements are driven by focused science goals designed to resolve the enigma of Type-Ia supernova (SNeIa) and their role in galactic evolution and cosmology. The proposed investigations will reveal details of these profoundly radioactive objects using long-term (>100 day) monitoring of the emergent nuclear gamma-ray spectra and their corresponding light curves. Primary science objectives include, but are not limited to, probing the fundamental thermonuclear physics processes, performing a census of progenitors and their explosion mechanisms, and evaluating the environmental conditions and intrinsic systematics of these enigmatic objects. LOX provides new capabilities for all-sky, continuous monitoring in the MeV regime (0.1-10 MeV) by leveraging the Lunar Occultation Technique (LOT). Key benefits of the LOX/LOT approach include maximizing the ratio of sensitive-to-total deployed mass, low implementation risk, and demonstrated operational simplicity that leverages extensive experience with planetary orbital geochemistry investigations. LOX will also deliver a time-domain survey of the nuclear cosmos. Proof-of-principle efforts have validated all aspects of the mission using previously deployed lunar science assets, including the first high-energy gamma-ray source detected at the Moon. LOX mission design, performance, and science will be presented.

Tuesday, 7 February 2017

Design and Evaluation of AlGaAs/GaAs Photocathodes with Varying Doping Concentrations and Doping Compositions

Speaker: Dr. Liang Chen (Jiliang University)
Location: OPB 234, 2:30pm
Abstract: In recent decades, III-V semiconductor negative electron affinity (NEA) photocathodes have been widely used in night-vision image intensifiers, ultraviolet detection, and potential electron sources for the next-generation electron accelerators due to their high quantum efficiency, low-energy spread, low dark current emission, and fast response. Some special vacuum detectors with NEA photocathodes can also be used in desert detection, ocean submarine detection, ocean communication, cosmic ray detection, high energy physics detection etc. In this talk, I will discuss the following aspects related to NEA: using the first-principles calculations to study the electronic and atomic structures of photocathode, the effects of doping concentration and doping composition in structure design, the Cs-O activation technique, the comparative characteristic evaluation for cathodes before and after activation, the decay mechanism, and the reactivation technique.

Tuesday, 31 January 2017

Atomistic Design of Nanostructured Architecture with Atomic Layer Deposition

Speaker: Dr. Yu Lei (UAH Chemical Engineering)
Location: OPB 234, 2:30pm
Abstract: We have been working on developing atomic layer deposition (ALD) as a promising method to tailor size and composition of nanostructured materials for a wide range of applications. The size and composition of nanomaterials play important roles in achieving high performance in these applications. Benefiting from self-limiting surface reactions, ALD enables conformal coatings of materials on three-dimensional substrates. The atomic level control of depositions makes it attractive to precisely control the size and composition of nanomaterials. In this talk, we will discuss nanomaterials synthesized using ALD and their applications in catalysis and batteries.

Tuesday, 24 January 2017

Clusters of Galaxies: Laboratories for Probing the Interplay between Baryons and Dark Matter

Speaker: Dr. Esra Bulbul (MIT Kavli Institute)
Location: OPB 234, 2:30pm
Abstract: As the most massive collapsed structures in the Universe, galaxy clusters are unique laboratories for studying the evolution of baryons in concert with dark matter particles, as well as for exploring the nature of dark matter, and dark energy. The thermodynamical state of the intra-cluster gas has been extensively studied through multi-wavelength X-ray and radio (Sunyaev Zel'dovich effect) observations. I will highlight the most recent measurements of a) the evolution of baryons in the deep potential wells of clusters, b) the potential of utilizing clusters in cosmological studies and indirect searches for dark matter with a particular focus on the candidate 3.5 keV emission line.

Tuesday, 17 January 2017

Transforming Galaxies in Extreme Environments

Speaker: Dr. Rukmani Vijayaraghavan (UVA Physics & Astronomy)
Location: OPB 234, 2:30pm
Abstract: Clusters of galaxies are harsh, hostile environments for their host galaxies. Gas rich, star forming galaxies are stripped of their gas, dark matter, and stars before eventually being transformed to passive and gas poor galaxies. The process of transformation can be dramatic and varied; mergers between clusters or groups and clusters can accelerate these galaxy transformation processes. Galaxy transformation processes do not behave as simply as expected; a significant fraction of cluster galaxies retain hot X-ray compact coronae that resist stripping and evaporation, form stars in stripped tails, and have AGN. Galaxies themselves can generate turbulence and amplify magnetic fields in the intracluster medium in the process of being stripped. Using numerical simulations, I will provide some physical insight into the dramatic death of galaxies in group and cluster environments.

Tuesday, 10 January 2017

Supersolid with Emergent SU(2) Symmetry

Speaker: Mr. Simon Lieu (Imperial College)
Location: OPB 234, 2:30pm
Abstract: We present a model of a supersolid on a 2D triangular lattice with non-Abelian ground-state symmetry generators and examine the low-energy behavior using Bogoliubov theory. A general mean-field phase diagram is found in terms of interaction parameters of the model and a region with an emergent SU(2) symmetry is identified at a phase boundary between a time-reversal (TR) symmetric and TR-broken supersolid. The enlarged degeneracy manifests itself via the acquisition of a quadratic Goldstone mode and the topological instability of global phase vortices. This latter point implies that such a supersolid is not expected to undergo a BKT superfluid transition. The zero-temperature superfluid fraction is calculated using linear response.