A5066502046- Pulsars and Gravitational Waves Research
- Astrophysics and Cosmic Phenomena
- Gamma-ray bursts and supernovae
- Astrophysical Phenomena and Observations
- Radio Astronomy Observations and Technology
- Geophysics and Gravity Measurements
- Dark Matter and Cosmic Phenomena
- Superconducting Materials and Applications
- Particle Accelerators and Free-Electron Lasers
- Advanced Frequency and Time Standards
- Cosmology and Gravitation Theories
- Radiation Therapy and Dosimetry
- Advanced Radiotherapy Techniques
- High-pressure geophysics and materials
- Particle Detector Development and Performance
- Astronomical Observations and Instrumentation
- Stellar, planetary, and galactic studies
- Radiation Detection and Scintillator Technologies
- GNSS positioning and interference
- Nuclear Physics and Applications
- Astronomy and Astrophysical Research
- Galaxies: Formation, Evolution, Phenomena
- Particle accelerators and beam dynamics
- Geophysics and Sensor Technology
- Atomic and Subatomic Physics Research
United States Naval Research Laboratory
2015-2025
The University of Texas MD Anderson Cancer Center
2013-2024
University of Tennessee at Knoxville
2014-2024
Columbia University
2024
National Postdoctoral Association
2023
Albert Einstein College of Medicine
2023
Cornell University
2023
Max Planck Institute for Radio Astronomy
2017-2023
Campbell Collaboration
2023
University of California, San Diego
2020-2023
We present the fourth Fermi Large Area Telescope catalog (4FGL) of gamma-ray sources. Based on first eight years science data from Gamma-ray Space mission in energy range 50 MeV to 1 TeV, it is deepest yet this range. Relative 3FGL catalog, 4FGL has twice as much exposure well a number analysis improvements, including an updated model for Galactic diffuse emission, and two sets light curves (1-year 2-month intervals). The includes 5064 sources above 4 sigma significance, which we provide...
PSR J0740$+$6620 has a gravitational mass of $2.08\pm 0.07~M_\odot$, which is the highest reliably determined any neutron star. As result, measurement its radius will provide unique insight into properties star core matter at high densities. Here we report based on fits rotating hot spot patterns to Neutron Star Interior Composition Explorer (NICER) and X-ray Multi-Mirror (XMM-Newton) observations. We find that equatorial circumferential $13.7^{+2.6}_{-1.5}$ km (68%). apply our measurement,...
Abstract We report on Bayesian estimation of the radius, mass, and hot surface regions massive millisecond pulsar PSR J0740+6620, conditional pulse-profile modeling Neutron Star Interior Composition Explorer X-ray Timing Instrument event data. condition informative distance, orbital inclination priors derived from joint North American Nanohertz Observatory for Gravitational Waves Canadian Hydrogen Intensity Mapping Experiment/Pulsar wideband radio timing measurements Fonseca et al. use...
Abstract We report multiple lines of evidence for a stochastic signal that is correlated among 67 pulsars from the 15 yr pulsar timing data set collected by North American Nanohertz Observatory Gravitational Waves. The correlations follow Hellings–Downs pattern expected gravitational-wave background. presence such background with power-law spectrum favored over model only independent noises Bayes factor in excess 10 14 , and this same an uncorrelated common factors 200–1000, depending on...
Designed as a high-sensitivity gamma-ray observatory, the Fermi Large Area Telescope is also an electron detector with large acceptance exceeding 2 m;{2} sr at 300 GeV. Building on analysis, we have developed efficient detection strategy which provides sufficient background rejection for measurement of steeply falling spectrum up to 1 TeV. Our high precision data show that falls energy E-3.0 and does not exhibit prominent spectral features. Interpretations in terms conventional diffusive...
Abstract Pulsar timing arrays aim to detect nanohertz-frequency gravitational waves (GWs). A background of GWs modulates pulsar arrival times and manifests as a stochastic process, common all pulsars, with signature spatial correlation. Here we describe search for an isotropic gravitational-wave (GWB) using observations 30 millisecond pulsars from the third data release Parkes Timing Array (PPTA), which spans 18 yr. Using current Bayesian inference techniques recover characterize...
We report on the first Fermi Large Area Telescope (LAT) measurements of so-called "extragalactic" diffuse gamma-ray emission (EGB). This component is generally considered to have an isotropic or nearly distribution sky with diverse contributions discussed in literature. The derivation EGB based detailed modeling bright foreground Galactic emission, detected LAT sources, and solar emission. find spectrum consistent a power law differential spectral index gamma = 2.41 +/- 0.05 intensity I(>100...
The Fermi Large Area Telescope (Fermi-LAT, hereafter LAT), the primary instrument on Gamma-ray Space (Fermi) mission, is an imaging, wide field-of-view, high-energy γ-ray telescope, covering energy range from 20 MeV to more than 300 GeV. During first years of LAT team has gained considerable insight into in-flight performance instrument. Accordingly, we have updated analysis used reduce data for public release as well response functions (IRFs), description provided analysis. In this paper,...
Abstract The 15 yr pulsar timing data set collected by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) shows positive evidence presence of a low-frequency gravitational-wave (GW) background. In this paper, we investigate potential cosmological interpretations signal, specifically cosmic inflation, scalar-induced GWs, first-order phase transitions, strings, and domain walls. We find that, with exception stable strings field theory origin, all these models can...
Placing bounds on gravitational wave detection Gravitational waves are expected to be generated by the interaction of massive bodies in black-hole binary systems. As distort spacetime, it should possible verify their existence as they interfere with pulses emitted millisecond pulsars. However, after monitoring 24 pulsars Parkes radio telescope for 12 years, Shannon et al. found no detectable variation pulsar records. This nondetection result indicates that a new strategy is needed. Science ,...
The highly stable spin of neutron stars can be exploited for a variety (astro)physical investigations. In particular, arrays pulsars with rotational periods the order milliseconds used to detect correlated signals such as those caused by gravitational waves. Three ‘pulsar timing arrays’ (PTAs) have been set up around world over past decades and collectively form ‘International’ PTA (IPTA). this paper, we describe first joint analysis data from three regional PTAs, i.e. IPTA set. We available...
ABSTRACT Following its launch in 2008 June, the Fermi Gamma-ray Space Telescope ( ) began a sky survey August. The Large Area (LAT) on three months produced deeper and better resolved map of γ-ray than any previous space mission. We present here initial results for energies above 100 MeV 205 most significant (statistical significance greater ∼10σ) sources these data. These are best characterized localized point-like (i.e., spatially unresolved) early mission
We report on the observation of bright, long gamma-ray burst, GRB 090902B, by Gamma-ray Burst Monitor (GBM) and Large Area Telescope (LAT) instruments on-board Fermi observatory. This was one brightest GRBs to have been observed LAT, which detected several hundred photons during prompt phase. With a redshift z = 1.822, this burst is among most luminous Fermi. Time-resolved spectral analysis reveals significant power-law component in LAT data that distinct from usual Band model emission seen...
Pinpointing a single fast radio burst Fast bursts (FRBs) are flashes of emission from distant astronomical sources. Two FRBs known to have repeated, but most last just few milliseconds and never seen again. Most telescopes that sensitive poor angular resolutions, so the FRB host galaxies remain unknown. Bannister et al. used dedicated observing mode on interferometer detect localize nonrepeating 180924, then followed up with optical telescope observations (see Perspective by Petroff). They...
We present an incremental version (4FGL-DR3, for Data Release 3) of the fourth Fermi-LAT catalog gamma-ray sources. Based on first twelve years science data in energy range from 50 MeV to 1 TeV, it contains 6658 The analysis improves that used 4FGL over eight data: more sources are fit with curved spectra, we introduce a robust spectral parameterization pulsars, and extend points TeV. parameters, distributions, associations updated all Light curves rebuilt yr intervals (not 2 month...
We present the results of our analysis cosmic-ray electrons using about $8\ifmmode\times\else\texttimes\fi{}{10}^{6}$ electron candidates detected in first 12 months on-orbit by Fermi Large Area Telescope. This work extends previously published spectrum down to 7 GeV, giving a spectral range approximately 2.5 decades up 1 TeV. describe detail and its validation beam-test data. In addition, we measured via subset events selected for best energy resolution as cross-check on measurement full...
The first three months of sky-survey operation with the Fermi Gamma Ray Space Telescope (Fermi) Large Area (LAT) reveals 132 bright sources at |b|>10 deg test statistic greater than 100 (corresponding to about 10 sigma). Two methods, based on CGRaBS, CRATES and BZCat catalogs, indicate high-confidence associations 106 these known AGNs. This sample is referred as LAT Bright AGN Sample (LBAS). It contains two radio galaxies, namely Centaurus A NGC 1275, 104 blazars consisting 57 flat...
A young and energetic pulsar powers the well-known Crab Nebula. Here, we describe two separate gamma-ray (photon energy greater than 100 mega-electron volts) flares from this source detected by Large Area Telescope on board Fermi Gamma-ray Space Telescope. The first flare occurred in February 2009 lasted approximately 16 days. second was September 2010 4 During these outbursts, flux nebula increased factors of four six, respectively. brevity implies that gamma rays were emitted via...
Pulsars are rapidly-rotating, highly-magnetized neutron stars emitting radiation across the electromagnetic spectrum. Although there more than 1800 known radio pulsars, until recently, only seven were observed to pulse in gamma rays and these all discovered at other wavelengths. The Fermi Large Area Telescope makes it possible pinpoint through their gamma-ray pulsations. We report detection of 16 pulsars blind frequency searches using LAT. Most coincident with previously unidentified...
We report the discovery with Fermi/LAT of gamma-ray emission from three radio-loud narrow-line Seyfert 1 galaxies: PKS 1502+036 (z=0.409), 1H 0323+342 (z=0.061) and 2004-447 (z=0.24). In addition to PMN J0948+0022 (z=0.585), first source this type be detected in gamma rays, they may form an emerging new class active galactic nuclei (AGN). These findings can have strong implications on our knowledge about relativistic jets unified model AGN.
The origin of Galactic cosmic rays is a century-long puzzle. Indirect evidence points to their acceleration by supernova shockwaves, but we know little escape from the shock and evolution through turbulent medium surrounding massive stars. Gamma can probe spreading ambient gas radiation fields. Fermi Large Area Telescope (LAT) has observed star-forming region Cygnus X. 1- 100-gigaelectronvolt images reveal 50-parsec-wide cocoon freshly accelerated that flood cavities carved stellar winds...
We present timing models for 20 millisecond pulsars in the Parkes Pulsar Timing Array. The precision of parameter measurements these has been improved over earlier results by using longer data sets and modelling non-stationary noise. describe a new noise procedure demonstrate its effectiveness simulated data. Our methodology includes addition annual dispersion measure (DM) variations to some pulsars. first significant parallax PSRs J1024−0719, J1045−4509, J1600−3053, J1603−7202, J1730−2304,...
We searched for an isotropic stochastic gravitational wave background in the second data release of International Pulsar Timing Array, a global collaboration synthesizing decadal-length pulsar-timing campaigns North America, Europe, and Australia. In our reference search power law strain spectrum form $h_c = A(f/1\,\mathrm{yr}^{-1})^{\alpha}$, we found strong evidence spectrally-similar low-frequency process amplitude $A 3.8^{+6.3}_{-2.5}\times10^{-15}$ spectral index $\alpha -0.5 \pm 0.5$,...