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Articles 451 - 480 of 832

Full-Text Articles in Astrophysics and Astronomy

Detection Methods For Stochastic Gravitational-Wave Backgrounds: A Unified Treatment, Joseph D. Romano, Neil J. Cornish Apr 2017

Detection Methods For Stochastic Gravitational-Wave Backgrounds: A Unified Treatment, Joseph D. Romano, Neil J. Cornish

Physics & Astronomy Faculty Publications

We review detection methods that are currently in use or have been proposed to search for a stochastic background of gravitational radiation. We consider both Bayesian and frequentist searches using ground-based and space-based laser interferometers, spacecraft Doppler tracking, and pulsar timing arrays; and we allow for anisotropy, non-Gaussianity, and non-standard polarization states. Our focus is on relevant data analysis issues, and not on the particular astrophysical or early Universe sources that might give rise to such backgrounds. We provide a unified treatment of these searches at the level of detector response functions, detection sensitivity curves, and, more generally, at the …

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Calibration Of The Advanced Ligo Detectors For The Discovery Of The Binary Black-Hole Merger Gw150914, B. P. Abbott, R. Abbott, T. D. Abbott, M. R. Abernathy, K. Ackley, Mario C. Diaz, Joey S. Key, Soma Mukherjee, Volker Quetschke, Malik Rakhmanov Mar 2017

Calibration Of The Advanced Ligo Detectors For The Discovery Of The Binary Black-Hole Merger Gw150914, B. P. Abbott, R. Abbott, T. D. Abbott, M. R. Abernathy, K. Ackley, Mario C. Diaz, Joey S. Key, Soma Mukherjee, Volker Quetschke, Malik Rakhmanov

Physics & Astronomy Faculty Publications

In Advanced LIGO, detection and astrophysical source parameter estimation of the binary black hole merger GW150914 requires a calibrated estimate of the gravitational-wave strain sensed by the detectors. Producing an estimate from each detector's differential arm length control loop readout signals requires applying time domain filters, which are designed from a frequency domain model of the detector's gravitational-wave response. The gravitational-wave response model is determined by the detector's opto-mechanical response and the properties of its feedback control system. The measurements used to validate the model and characterize its uncertainty are derived primarily from a dedicated photon radiation pressure actuator, with …

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Upper Limits On The Stochastic Gravitational-Wave Background From Advanced Ligo's First Observing Run, B. P. Abbott, Teviet Creighton, Mario C. Diaz, S. R. Morriss, Soma Mukherjee, Marc E. Normandin, Volker Quetschke, Malik Rakhmanov, Joseph D. Romano, Robert Stone, Darkhan Tuyenbayev, Guillermo Valdes Mar 2017

Upper Limits On The Stochastic Gravitational-Wave Background From Advanced Ligo's First Observing Run, B. P. Abbott, Teviet Creighton, Mario C. Diaz, S. R. Morriss, Soma Mukherjee, Marc E. Normandin, Volker Quetschke, Malik Rakhmanov, Joseph D. Romano, Robert Stone, Darkhan Tuyenbayev, Guillermo Valdes

Physics & Astronomy Faculty Publications

A wide variety of astrophysical and cosmological sources are expected to contribute to a stochastic gravitational-wave background. Following the observations of GW150914 and GW151226, the rate and mass of coalescing binary black holes appear to be greater than many previous expectations. As a result, the stochastic background from unresolved compact binary coalescences is expected to be particularly loud. We perform a search for the isotropic stochastic gravitational-wave background using data from Advanced Laser Interferometer Gravitational Wave Observatory's (aLIGO) first observing run. The data display no evidence of a stochastic gravitational-wave signal. We constrain the dimensionless energy density of gravitational waves …

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Directional Limits On Persistent Gravitational Waves From Advanced Ligo's First Observing Run, B. P. Abbott, Teviet Creighton, Mario C. Diaz, S. R. Morriss, Soma Mukherjee, Marc E. Normandin, Volker Quetschke, Malik Rakhmanov, Joseph D. Romano, Robert Stone, Darkhan Tuyenbayev, Guillermo Valdes Mar 2017

Directional Limits On Persistent Gravitational Waves From Advanced Ligo's First Observing Run, B. P. Abbott, Teviet Creighton, Mario C. Diaz, S. R. Morriss, Soma Mukherjee, Marc E. Normandin, Volker Quetschke, Malik Rakhmanov, Joseph D. Romano, Robert Stone, Darkhan Tuyenbayev, Guillermo Valdes

Physics & Astronomy Faculty Publications

We employ gravitational-wave radiometry to map the stochastic gravitational wave background expected from a variety of contributing mechanisms and test the assumption of isotropy using data from the Advanced Laser Interferometer Gravitational Wave Observatory’s (aLIGO) first observing run. We also search for persistent gravitational waves from point sources with only minimal assumptions over the 20–1726 Hz frequency band. Finding no evidence of gravitational waves from either point sources or a stochastic background, we set limits at 90% confidence. For broadband point sources, we report upper limits on the gravitational wave energy flux per unit frequency in the range Fα,Θ(f)

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Multiple Exciton Generation In Si And Ge Nanocrystals: An Ab Initio Comparative Study, Mahdi Gordi, Hamidreza Ramezani, Mohammad Kazem Moravvej-Farshi Mar 2017

Multiple Exciton Generation In Si And Ge Nanocrystals: An Ab Initio Comparative Study, Mahdi Gordi, Hamidreza Ramezani, Mohammad Kazem Moravvej-Farshi

Physics & Astronomy Faculty Publications

We have simulated multiexciton generation (MEG) processes in Si and Ge nanocrystals, employing the equation of motion coupled cluster single and double as a high-level ab initio approach. Simulations, consistent with the experimental results reported so far, reveal the key role of the d-polarized valence component in the chosen basis set on the accuracy and reliability of the results. Moreover, the MEG thresholds calculated with def2SVP basis set are ∼8.23(8.07) eV for seven (eight)-atom Si clusters and ∼7.58(6.84) eV for similar Ge clusters. The normalized MEG thresholds of Ge nanocrystals are 8% smaller with respect to Si. Thus, in …

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Searches For Continuous Gravitational Waves From Scorpius X-1 And Xte J1751-305 In Ligo’S Sixth Science Run, G. D. Meadors, E. Goetz, K. Riles, Teviet Creighton, F. Robinet Feb 2017

Searches For Continuous Gravitational Waves From Scorpius X-1 And Xte J1751-305 In Ligo’S Sixth Science Run, G. D. Meadors, E. Goetz, K. Riles, Teviet Creighton, F. Robinet

Physics & Astronomy Faculty Publications

Scorpius X-1 (Sco X-1) and x-ray transient XTE J1751-305 are low-mass x-ray binaries (LMXBs) that may emit continuous gravitational waves detectable in the band of ground-based interferometric observatories. Neutron stars in LMXBs could reach a torque-balance steady-state equilibrium in which angular momentum addition from infalling matter from the binary companion is balanced by angular momentum loss, conceivably due to gravitational-wave emission. Torque balance predicts a scale for detectable gravitational-wave strain based on observed x-ray flux. This paper describes a search for Sco X-1 and XTE J1751-305 in LIGO science run 6 data using the TwoSpect algorithm, based on searching for …

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All-Sky Search For Short Gravitational-Wave Bursts In The First Advanced Ligo Run, B. P. Abbott, R. Abbott, T. D. Abbott, M. R. Abernathy, Teviet Creighton, Mario C. Diaz, Soma Mukherjee, Volker Quetschke, Malik Rakhmanov Feb 2017

All-Sky Search For Short Gravitational-Wave Bursts In The First Advanced Ligo Run, B. P. Abbott, R. Abbott, T. D. Abbott, M. R. Abernathy, Teviet Creighton, Mario C. Diaz, Soma Mukherjee, Volker Quetschke, Malik Rakhmanov

Physics & Astronomy Faculty Publications

We present the results from an all-sky search for short-duration gravitational waves in the data of the first run of the Advanced LIGO detectors between September 2015 and January 2016. The search algorithms use minimal assumptions on the signal morphology, so they are sensitive to a wide range of sources emitting gravitational waves. The analyses target transient signals with duration ranging from milliseconds to seconds over the frequency band of 32 to 4096 Hz. The first observed gravitational-wave event, GW150914, has been detected with high confidence in this search; the other known gravitational-wave event, GW151226, falls below the search's sensitivity. …

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Timing Of 29 Pulsars Discovered In The Palfa Survey, A. G. Lyne, B. W. Stappers, S. Bogdanov, R. D. Ferdman, P. C.C. Freire, V. M. Kaspi, B. Knispel, R. Lynch, Fredrick A. Jenet Jan 2017

Timing Of 29 Pulsars Discovered In The Palfa Survey, A. G. Lyne, B. W. Stappers, S. Bogdanov, R. D. Ferdman, P. C.C. Freire, V. M. Kaspi, B. Knispel, R. Lynch, Fredrick A. Jenet

Physics & Astronomy Faculty Publications

We report on the discovery and timing observations of 29 distant long-period pulsars found in the ongoing Arecibo L-band Feed Array pulsar survey. Following discovery with the Arecibo Telescope, confirmation and timing observations of these pulsars over several years at Jodrell Bank Observatory have yielded high-precision positions and measurements of rotation and radiation properties. We have used multi-frequency data to measure the interstellar scattering properties of some of these pulsars. Most of the pulsars have properties that mirror those of the previously known pulsar population, although four show some notable characteristics. PSRs J1907+0631 and J1925+1720 are young and are associated …

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Two Long-Term Intermittent Pulsars Discovered In The Palfa Survey, A. G. Lyne, B. W. Stappers, P. C.C. Freire, J. W.T. Hessels, V. M. Kaspi, B. Allen, S. Bogdanov, A. Brazier, F. Camilo, Fredrick A. Jenet Jan 2017

Two Long-Term Intermittent Pulsars Discovered In The Palfa Survey, A. G. Lyne, B. W. Stappers, P. C.C. Freire, J. W.T. Hessels, V. M. Kaspi, B. Allen, S. Bogdanov, A. Brazier, F. Camilo, Fredrick A. Jenet

Physics & Astronomy Faculty Publications

We report the discovery of two long-term intermittent radio pulsars in the ongoing Pulsar Arecibo L-Band Feed Array survey. Following discovery with the Arecibo Telescope, extended observations of these pulsars over several years at Jodrell Bank Observatory have revealed the details of their rotation and radiation properties. PSRs J1910+0517 and J1929+1357 show long-term extreme bimodal intermittency, switching between active (ON) and inactive (OFF) emission states and indicating the presence of a large, hitherto unrecognized underlying population of such objects. For PSR J1929+1357, the initial duty cycle was f ON = 0.008, but two years later, this changed quite abruptly to …

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Non-Hermiticity-Induced Flat Band, Hamidreza Ramezani Jan 2017

Non-Hermiticity-Induced Flat Band, Hamidreza Ramezani

Physics & Astronomy Faculty Publications

We demonstrate the emergence of an entire flat band with no complex component embedded in dispersive bands at the exceptional point of a PT -symmetric photonic lattice. For this to occur, the gain and loss parameter effectively alters the size of the partial flat band windows and band gap of the photonic lattice simultaneously. The mode associated with the entire flat band is robust against changes in the system size and survives even at the edge of the lattice. Our proposal offers a route for controllable localization of light in non-Hermitian systems and a technique for measuring non-Hermiticity via localization.

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Search For Post-Merger Gravitational Waves From The Remnant Of The Binary Neutron Star Merger Gw170817, B. P. Abbott, R. Abbott, T. D. Abbott, F. Acernese, Teviet Creighton, Mario C. Diaz, Soma Mukherjee, Volker Quetschke, Malik Rakhmanov Jan 2017

Search For Post-Merger Gravitational Waves From The Remnant Of The Binary Neutron Star Merger Gw170817, B. P. Abbott, R. Abbott, T. D. Abbott, F. Acernese, Teviet Creighton, Mario C. Diaz, Soma Mukherjee, Volker Quetschke, Malik Rakhmanov

Physics & Astronomy Faculty Publications

The first observation of a binary neutron star (NS) coalescence by the Advanced LIGO and Advanced Virgo gravitational-wave (GW) detectors offers an unprecedented opportunity to study matter under the most extreme conditions. After such a merger, a compact remnant is left over whose nature depends primarily on the masses of the inspiraling objects and on the equation of state of nuclear matter. This could be either a black hole (BH) or an NS, with the latter being either long-lived or too massive for stability implying delayed collapse to a BH. Here, we present a search for GWs from the remnant …

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Hierarchical Follow-Up Of Subthreshold Candidates Of An All-Sky Einstein@Home Search For Continuous Gravitational Waves On Ligo Sixth Science Run Data, Maria Alessandra Papa, Heinz-Bernd Eggenstein, Sinéad Walsh, Irene Di Palma, Bruce Allen, Pia Astone, Oliver Bock, Teviet Creighton, David Keitel Dec 2016

Hierarchical Follow-Up Of Subthreshold Candidates Of An All-Sky Einstein@Home Search For Continuous Gravitational Waves On Ligo Sixth Science Run Data, Maria Alessandra Papa, Heinz-Bernd Eggenstein, Sinéad Walsh, Irene Di Palma, Bruce Allen, Pia Astone, Oliver Bock, Teviet Creighton, David Keitel

Physics & Astronomy Faculty Publications

We report results of an all-sky search for periodic gravitational waves with frequency between 50 and 510 Hz from isolated compact objects, e.g., neutron stars. A new hierarchical multistage approach is taken, supported by the computing power of the Einstein@Home project, allowing us to probe more deeply than ever before. 16 million subthreshold candidates from the initial search [LIGO Scientific and Virgo Collaborations, Phys. Rev. D 94, 102002 (2016)] are followed up in four stages. None of those candidates is consistent with an isolated gravitational wave emitter, and 90% confidence level upper limits are placed on the amplitudes of continuous …

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Timing Of Five Palfa-Discovered Millisecond Pulsars, K. Stovall, B. Allen, S. Bogdanov, A. Brazier, F. Camilo, F. Cardoso, S. Chatterjee, J. Cordes, F. Crawford, Fredrick Jenet Dec 2016

Timing Of Five Palfa-Discovered Millisecond Pulsars, K. Stovall, B. Allen, S. Bogdanov, A. Brazier, F. Camilo, F. Cardoso, S. Chatterjee, J. Cordes, F. Crawford, Fredrick Jenet

Physics & Astronomy Faculty Publications

We report the discovery and timing results for five millisecond pulsars (MSPs) from the Arecibo PALFA survey: PSRs J1906+0055, J1914+0659, J1933+1726, J1938+2516, and J1957+2516. Timing observations of the five pulsars were conducted with the Arecibo and Lovell telescopes for time spans ranging from 1.5 to 3.3 years. All of the MSPs except one (PSR J1914+0659) are in binary systems with low eccentricities. PSR J1957+2516 is likely a redback pulsar, with a ∼0.1 M⊙ companion and possible eclipses that last ∼10% of the orbit. The position of PSR J1957+2516 is also coincident with a near-infrared source. All five MSPs are distant …

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The Rate Of Binary Black Hole Mergers Inferred From Advanced Ligo Observations Surrounding Gw150914, B. P. Abbott, R. Abbott, T. D. Abbott, M. R. Abernathy, F. Acernese, K. Ackley, C. Adams, T. Adams, P. Addesso, R. X. Adhikari, V. B. Adya, C. Affeldt, M. Agathos Dec 2016

The Rate Of Binary Black Hole Mergers Inferred From Advanced Ligo Observations Surrounding Gw150914, B. P. Abbott, R. Abbott, T. D. Abbott, M. R. Abernathy, F. Acernese, K. Ackley, C. Adams, T. Adams, P. Addesso, R. X. Adhikari, V. B. Adya, C. Affeldt, M. Agathos

Physics & Astronomy Faculty Publications

A transient gravitational-wave signal, GW150914, was identified in the twin Advanced LIGO detectors on 2015 September 2015 at 09:50:45 UTC. To assess the implications of this discovery, the detectors remained in operation with unchanged configurations over a period of 39 days around the time of the signal. At the detection statistic threshold corresponding to that observed for GW150914, our search of the 16 days of simultaneous two-detector observational data is estimated to have a false-alarm rate (FAR) of <4.9×10−6yr−1, yielding a p-value for GW150914 of <2×10−7. Parameter estimation follow-up on this trigger identifies its source as a binary black hole (BBH) merger with component masses (m1,m2)=(36−4+5,29−4+4)M⊙ at redshift z=0.09−0.04+0.03 (median and 90% credible range). Here, we report on the constraints these observations place on the rate of BBH coalescences. Considering only GW150914, assuming that all BBHs in the universe have the same masses and spins as this event, imposing a search FAR threshold of 1 per 100 years, and assuming that the BBH merger rate is constant in the comoving frame, we infer a 90% credible range of merger rates between 2--53Gpc−3yr−1 (comoving frame). Incorporating all search triggers that pass a much lower threshold while accounting for the uncertainty in the astrophysical origin of each trigger, we estimate a higher rate, ranging from 13--600Gpc−3yr−1 depending on assumptions about the BBH mass distribution. All together, our various rate estimates fall in the conservative range 2--600Gpc−3yr−1.

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Structural Reinforcement Through Liquid Encapsulation, Alin Cristian Chipara, Peter Samora Owuor, Sanjit Bhowmick, Gustavo Brunetto, S. A. Syed Asif, Mircea Chipara, Robert Vajtai, Jun Lou, Douglas S. Galvao, Chandra Sekhar Tiwary Dec 2016

Structural Reinforcement Through Liquid Encapsulation, Alin Cristian Chipara, Peter Samora Owuor, Sanjit Bhowmick, Gustavo Brunetto, S. A. Syed Asif, Mircea Chipara, Robert Vajtai, Jun Lou, Douglas S. Galvao, Chandra Sekhar Tiwary

Physics & Astronomy Faculty Publications

The liquid inside a solid material is one of the most common composite materials in nature. The interface between solid–liquid plays an important role in unique deformation. Here, model systems of two polymers (polydimethylsiloxane–polyvinylidenefluoride) are used to make sphere of solid with liquid inside it.

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Supplement: The Rate Of Binary Black Hole Mergers Inferred From Advanced Ligo Observations Surrounding Gw150914, B. P. Abbott, R. Abbott, T. D. Abbott, M. R. Abernathy, Mario C. Diaz, Soma Mukherjee, Volker Quetschke, Malik Rakhmanov Dec 2016

Supplement: The Rate Of Binary Black Hole Mergers Inferred From Advanced Ligo Observations Surrounding Gw150914, B. P. Abbott, R. Abbott, T. D. Abbott, M. R. Abernathy, Mario C. Diaz, Soma Mukherjee, Volker Quetschke, Malik Rakhmanov

Physics & Astronomy Faculty Publications

This article provides supplemental information for a Letter reporting the rate of (BBH) coalescences inferred from 16 days of coincident Advanced LIGO observations surrounding the transient (GW) signal GW150914. In that work we reported various rate estimates whose 90% confidence intervals fell in the range 2-600 Gpc-3yr-1. Here we give details on our method and computations, including information about our search pipelines, a derivation of our likelihood function for the analysis, a description of the astrophysical search trigger distribution expected from merging BBHs, details on our computational methods, a description of the effects and our model for calibration uncertainty, and …

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Results Of The Deepest All-Sky Survey For Continuous Gravitational Waves On Ligo S6 Data Running On The Einstein@Home Volunteer Distributed Computing Project, B. P. Abbott, R. Abbott, T. D. Abbott, M. R. Abernathy, Teviet Creighton, Mario C. Diaz, Soma Mukherjee, Volker Quetschke, Malik Rakhmanov Nov 2016

Results Of The Deepest All-Sky Survey For Continuous Gravitational Waves On Ligo S6 Data Running On The Einstein@Home Volunteer Distributed Computing Project, B. P. Abbott, R. Abbott, T. D. Abbott, M. R. Abernathy, Teviet Creighton, Mario C. Diaz, Soma Mukherjee, Volker Quetschke, Malik Rakhmanov

Physics & Astronomy Faculty Publications

We report results of a deep all-sky search for periodic gravitational waves from isolated neutron stars in data from the S6 LIGO science run. The search was possible thanks to the computing power provided by the volunteers of the Einstein@Home distributed computing project. We find no significant signal candidate and set the most stringent upper limits to date on the amplitude of gravitational wave signals from the target population. At the frequency of best strain sensitivity, between 170.5 and 171 Hz we set a 90% confidence upper limit of 5.5×10-25, while at the high end of our frequency range, around …

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First Targeted Search For Gravitational-Wave Bursts From Core-Collapse Supernovae In Data Of First-Generation Laser Interferometer Detectors, B. P. Abbott, R. Abbott, T. D. Abbott, M. R. Abernathy, Hernan P. Daveloza, Mario C. Diaz, Joey S. Key, Soma Mukherjee, Volker Quetschke, Malik Rakhmanov, Joseph D. Romano Nov 2016

First Targeted Search For Gravitational-Wave Bursts From Core-Collapse Supernovae In Data Of First-Generation Laser Interferometer Detectors, B. P. Abbott, R. Abbott, T. D. Abbott, M. R. Abernathy, Hernan P. Daveloza, Mario C. Diaz, Joey S. Key, Soma Mukherjee, Volker Quetschke, Malik Rakhmanov, Joseph D. Romano

Physics & Astronomy Faculty Publications

We present results from a search for gravitational-wave bursts coincident with two core-collapse supernovae observed optically in 2007 and 2011. We employ data from the Laser Interferometer Gravitational-wave Observatory (LIGO), the Virgo gravitational-wave observatory, and the GEO 600 gravitational-wave observatory. The targeted core-collapse supernovae were selected on the basis of (1) proximity (within approximately 15 Mpc), (2) tightness of observational constraints on the time of core collapse that defines the gravitational-wave search window, and (3) coincident operation of at least two interferometers at the time of core collapse. We find no plausible gravitational-wave candidates. We present the probability of detecting …

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Einstein@ Home Discovery Of A Double Neutron Star Binary In The Palfa Survey, P. Lazarus, P. C.C. Freire, B. Allen, C. Aulbert, O. Bock, S. Bogdanov, A. Brazier, F. Camilo, F. Cardoso, Fredrick Jenet Nov 2016

Einstein@ Home Discovery Of A Double Neutron Star Binary In The Palfa Survey, P. Lazarus, P. C.C. Freire, B. Allen, C. Aulbert, O. Bock, S. Bogdanov, A. Brazier, F. Camilo, F. Cardoso, Fredrick Jenet

Physics & Astronomy Faculty Publications

We use time-domain electromagnetic simulations to determine the spectral characteristics of the Hydrogen Epoch of Reionization Arrays (HERA) antenna. These simulations are part of a multi-faceted campaign to determine the effectiveness of the dish's design for obtaining a detection of redshifted 21 cm emission from the epoch of reionization. Our simulations show the existence of reflections between HERA's suspended feed and its parabolic dish reflector that fall below -40 dB at 150 ns and, for reasonable impedance matches, have a negligible impact on HERA's ability to constrain EoR parameters. It follows that despite the reflections they introduce, dishes are effective …

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The Advanced Ligo Photon Calibrators, S. Karki, Darkhan Tuyenbayev, S. Kandhasamy, B. P. Abbott, T. D. Abbott, E. H. Anders, J. Berliner, J. Betzwieser, C. Cahillane, L. Canete, Volker Quetschke Nov 2016

The Advanced Ligo Photon Calibrators, S. Karki, Darkhan Tuyenbayev, S. Kandhasamy, B. P. Abbott, T. D. Abbott, E. H. Anders, J. Berliner, J. Betzwieser, C. Cahillane, L. Canete, Volker Quetschke

Physics & Astronomy Faculty Publications

The two interferometers of the Laser Interferometry Gravitational-wave Observatory (LIGO) recently detected gravitational waves from the mergers of binary black hole systems. Accurate calibration of the output of these detectors was crucial for the observation of these events and the extraction of parameters of the sources. The principal tools used to calibrate the responses of the second-generation (Advanced) LIGO detectors to gravitational waves are systems based on radiation pressure and referred to as photon calibrators. These systems, which were completely redesigned for Advanced LIGO, include several significant upgrades that enable them to meet the calibration requirements of second-generation gravitational wave …

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The Braking Index Of A Radio-Quiet Gamma-Ray Pulsar, C. J. Clark, H. J. Pletsch, J. Wu, L. Guillemot, F. Camilo, T. J. Johnson, M. Kerr, B. Allen, C. Aulbert, Andres Cuellar Nov 2016

The Braking Index Of A Radio-Quiet Gamma-Ray Pulsar, C. J. Clark, H. J. Pletsch, J. Wu, L. Guillemot, F. Camilo, T. J. Johnson, M. Kerr, B. Allen, C. Aulbert, Andres Cuellar

Physics & Astronomy Faculty Publications

We report the discovery and timing measurements of PSR J1208−6238, a young and highly magnetized gamma-ray pulsar, with a spin period of 440 ms. The pulsar was discovered in gamma-ray photon data from the Fermi Large Area Telescope (LAT) during a blind-search survey of unidentified LAT sources, running on the distributed volunteer computing system Einstein@Home. No radio pulsations were detected in dedicated follow-up searches with the Parkes radio telescope, with a flux density upper limit at 1369 MHz of 30 μJy. By timing this pulsar's gamma-ray pulsations, we measure its braking index over five years of LAT observations …

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An Eccentric Binary Millisecond Pulsar With A Helium White Dwarf Companion In The Galactic Field, John Antoniadis, David L. Kaplan, Kevin Stovall, Paulo C.C. Freire, Julia S. Deneva, Detlev Koester, Fredrick Jenet, Jose G. Martinez Oct 2016

An Eccentric Binary Millisecond Pulsar With A Helium White Dwarf Companion In The Galactic Field, John Antoniadis, David L. Kaplan, Kevin Stovall, Paulo C.C. Freire, Julia S. Deneva, Detlev Koester, Fredrick Jenet, Jose G. Martinez

Physics & Astronomy Faculty Publications

Low-mass white dwarfs (LMWDs) are believed to be exclusive products of binary evolution, as the universe is not old enough to produce them from single stars. Because of the strong tidal forces operating during the binary interaction phase, the remnant systems observed today are expected to have negligible eccentricities. Here, we report on the first unambiguous identification of an LMWD in an eccentric (e = 0.13) orbit around the millisecond pulsar PSR J2234+0511, which directly contradicts this picture. We use our spectra and radio-timing solution (derived elsewhere) to infer the WD temperature (Teff = 8600 ±190 K), and peculiar systemic …

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Physical Science Day: Design, Implementation, And Assessment, Liang Zeng, Mark A. Cunningham, Steven C. Tidrow, K. Christopher Smith, Jerry Contreras Oct 2016

Physical Science Day: Design, Implementation, And Assessment, Liang Zeng, Mark A. Cunningham, Steven C. Tidrow, K. Christopher Smith, Jerry Contreras

Physics & Astronomy Faculty Publications

Physical Science Day at The University of Texas–Pan American (UTPA), in collaboration with the Edinburg Consolidated Independent School District, has been designed, developed and implemented to address an identified fundamental shortcoming in our educational process within this primarily (90+%) Hispanic serving border region. Physical Science Day overcomes the lack of knowledge about what physics is by raising youth awareness of physics as the foundation of science, engineering and technology disciplines, through activities including hands-on laboratory experiments, career orientation, and higher educational student and graduated student testimonials. Thus, Physical Science Day encourages, attracts, and enables more Hispanic youth towards science, technology …

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Directly Comparing Gw150914 With Numerical Solutions Of Einstein's Equations For Binary Black Hole Coalescence, B. P. Abbott, R. Abbott, Mario C. Diaz, Soma Mukherjee, Volker Quetschke, Malik Rakhmanov, Joseph D. Romano, Robert Stone, Darkhan Tuyenbayev Sep 2016

Directly Comparing Gw150914 With Numerical Solutions Of Einstein's Equations For Binary Black Hole Coalescence, B. P. Abbott, R. Abbott, Mario C. Diaz, Soma Mukherjee, Volker Quetschke, Malik Rakhmanov, Joseph D. Romano, Robert Stone, Darkhan Tuyenbayev

Physics & Astronomy Faculty Publications

We compare GW150914 directly to simulations of coalescing binary black holes in full general relativity, including several performed specifically to reproduce this event. Our calculations go beyond existing semianalytic models, because for all simulations - including sources with two independent, precessing spins - we perform comparisons which account for all the spin-weighted quadrupolar modes, and separately which account for all the quadrupolar and octopolar modes. Consistent with the posterior distributions reported by Abbott et al. [Phys. Rev. Lett. 116, 241102 (2016)] (at the 90% credible level), we find the data are compatible with a wide range of nonprecessing and precessing …

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Detection And Localization Of Continuous Gravitational Waves With Pulsar Timing Arrays: The Role Of Pulsar Terms, X. J. Zhu, L. Wen, J. Xiong, Y. Xu, Y. Wang, S. D. Mohanty, G. Hobbs, R. N. Manchester Sep 2016

Detection And Localization Of Continuous Gravitational Waves With Pulsar Timing Arrays: The Role Of Pulsar Terms, X. J. Zhu, L. Wen, J. Xiong, Y. Xu, Y. Wang, S. D. Mohanty, G. Hobbs, R. N. Manchester

Physics & Astronomy Faculty Publications

A pulsar timing array is a Galactic-scale detector of nanohertz gravitational waves (GWs). Its target signals contain two components: the 'Earth term' and the 'pulsar term' corresponding to GWs incident on the Earth and pulsar, respectively. In this work we present a Frequentist method for the detection and localization of continuous waves that takes into account the pulsar term and is significantly faster than existing methods. We investigate the role of pulsar terms by comparing a full-signal search with an Earth-term-only search for non-evolving black hole binaries. By applying the method to synthetic data sets, we find that (i) a …

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Gw150914: First Search For The Electromagnetic Counterpart Of A Gravitational-Wave Event By The Toros Collaboration, Mario C. Diaz, Martin Beroiz, Tania Peñuela, Lucas M. Macri, Ryan J. Oelkers, Wenlong Yuan, Diego García Lambas, Nicolas A. Pereyra, Soma Mukherjee, Matthew Benacquista, Joey Key Sep 2016

Gw150914: First Search For The Electromagnetic Counterpart Of A Gravitational-Wave Event By The Toros Collaboration, Mario C. Diaz, Martin Beroiz, Tania Peñuela, Lucas M. Macri, Ryan J. Oelkers, Wenlong Yuan, Diego García Lambas, Nicolas A. Pereyra, Soma Mukherjee, Matthew Benacquista, Joey Key

Physics & Astronomy Faculty Publications

We present the results of the optical follow-up conducted by the TOROS collaboration of the first gravitational-wave event GW150914. We conducted unfiltered CCD observations (0.35-1 μm) with the 1.5 m telescope at Bosque Alegre starting ∼2.5 days after the alarm. Given our limited field of view (∼100 arcmin2), we targeted 14 nearby galaxies that were observable from the site and were located within the area of higher localization probability. We analyzed the observations using two independent implementations of difference-imaging algorithms, followed by a Random-Forest-based algorithm to discriminate between real and bogus transients. We did not find any bona fide transient …

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Directional Excitation Without Breaking Reciprocity, Hamidreza Ramezani, Marc Dubois, Yuan Wang, Y. Ron Shen, Xiang Zhang Sep 2016

Directional Excitation Without Breaking Reciprocity, Hamidreza Ramezani, Marc Dubois, Yuan Wang, Y. Ron Shen, Xiang Zhang

Physics & Astronomy Faculty Publications

We propose a mechanism for directional excitation without breaking reciprocity. This is achieved by embedding an impedance matched parity-time symmetric potential in a three-port system. The amplitude distribution within the gain and loss regions is strongly influenced by the direction of the incoming field. Consequently, the excitation of the third port is contingent on the direction of incidence while transmission in the main channel is immune. Our design improves the four-port directional coupler scheme, as there is no need to implement an anechoic termination to one of the ports.

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Comprehensive All-Sky Search For Periodic Gravitational Waves In The Sixth Science Run Ligo Data, B. P. Abbott, R. Abbott, T. D. Abbott, Teviet Creighton, Mario C. Diaz, Soma Mukherjee, Volker Quetschke, Malik Rakhmanov, Joseph D. Romano Aug 2016

Comprehensive All-Sky Search For Periodic Gravitational Waves In The Sixth Science Run Ligo Data, B. P. Abbott, R. Abbott, T. D. Abbott, Teviet Creighton, Mario C. Diaz, Soma Mukherjee, Volker Quetschke, Malik Rakhmanov, Joseph D. Romano

Physics & Astronomy Faculty Publications

We report on a comprehensive all-sky search for periodic gravitational waves in the frequency band 100-1500 Hz and with a frequency time derivative in the range of [-1.18,+1.00]×10-8 Hz/s. Such a signal could be produced by a nearby spinning and slightly nonaxisymmetric isolated neutron star in our galaxy. This search uses the data from the initial LIGO sixth science run and covers a larger parameter space with respect to any past search. A Loosely Coherent detection pipeline was applied to follow up weak outliers in both Gaussian (95% recovery rate) and non-Gaussian (75% recovery rate) bands. No gravitational wave signals …

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High Efficiency Near Diffraction-Limited Mid-Infrared Flat Lenses Based On Metasurface Reflectarrays, Shuyan Zhang, Myoung Hwan Kim, Francesco Aieta, Alan She, Tobias Mansuripur, Ilan Gabay, Mohammadreza Khorasaninejad, David Rousso, Xiaojun Wang, Mariano Troccoli Aug 2016

High Efficiency Near Diffraction-Limited Mid-Infrared Flat Lenses Based On Metasurface Reflectarrays, Shuyan Zhang, Myoung Hwan Kim, Francesco Aieta, Alan She, Tobias Mansuripur, Ilan Gabay, Mohammadreza Khorasaninejad, David Rousso, Xiaojun Wang, Mariano Troccoli

Physics & Astronomy Faculty Publications

We report the first demonstration of a mid-IR reflection-based flat lens with high efficiency and near diffraction-limited focusing. Focusing efficiency as high as 80%, in good agreement with simulations (83%), has been achieved at 45° incidence angle at λ = 4.6 μm. The off-axis geometry considerably simplifies the optical arrangement compared to the common geometry of normal incidence in reflection mode which requires beam splitters. Simulations show that the effects of incidence angle are small compared to parabolic mirrors with the same NA. The use of single-step photolithography allows large scale fabrication. Such a device is important in the development …

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Vanadium Pentoxide Nanobelt-Reduced Graphene Oxide Nanosheet Composites As High-Performance Pseudocapacitive Electrodes: Ac Impedanc Spectroscopy Data Modeling And Theoretical Calculations, Sanju Gupta, Bryce Aberg, Sara B. Carrizosa, Nicholas Dimakis Jul 2016

Vanadium Pentoxide Nanobelt-Reduced Graphene Oxide Nanosheet Composites As High-Performance Pseudocapacitive Electrodes: Ac Impedanc Spectroscopy Data Modeling And Theoretical Calculations, Sanju Gupta, Bryce Aberg, Sara B. Carrizosa, Nicholas Dimakis

Physics & Astronomy Faculty Publications

Graphene nanosheets and graphene nanoribbons, G combined with vanadium pentoxide (VO) nanobelts (VNBs) and VNBs forming GVNB composites with varying compositions were synthesized via a one-step low temperature facile hydrothermal decomposition method as high-performance electrochemical pseudocapacitive electrodes. VNBs from vanadium pentoxides (VO) are formed in the presence of graphene oxide (GO), a mild oxidant, which transforms into reduced GO (rGOHT), assisting in enhancing the electronic conductivity coupled with the mechanical robustness of VNBs. From electron microscopy, surface sensitive spectroscopy and other complementary structural characterization, hydrothermally-produced rGO nanosheets/nanoribbons are decorated with and inserted within the VNBs' layered crystal structure, which further …

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