D. A. Smith
A5047474127- Astrophysics and Cosmic Phenomena
- Gamma-ray bursts and supernovae
- Pulsars and Gravitational Waves Research
- Astrophysical Phenomena and Observations
- Dark Matter and Cosmic Phenomena
- Quantum Chromodynamics and Particle Interactions
- Particle physics theoretical and experimental studies
- Nuclear physics research studies
- Nuclear Physics and Applications
- Particle Detector Development and Performance
- Radio Astronomy Observations and Technology
- High-Energy Particle Collisions Research
- Galaxies: Formation, Evolution, Phenomena
- Astronomy and Astrophysical Research
- Atomic and Subatomic Physics Research
- Advanced NMR Techniques and Applications
- Stellar, planetary, and galactic studies
- Geophysics and Gravity Measurements
- Superconducting Materials and Applications
- Particle Accelerators and Free-Electron Lasers
- Quantum, superfluid, helium dynamics
- Neutrino Physics Research
- Astronomical Observations and Instrumentation
- Solar and Space Plasma Dynamics
- High-pressure geophysics and materials
Université de Bordeaux
2009-2024
Duke University
1996-2024
Centre National de la Recherche Scientifique
2015-2024
Laboratoire d'Astrophysique de Bordeaux
2021-2024
Laboratoire de Physique des deux infinis Bordeaux
2014-2023
Institut National de Physique Nucléaire et de Physique des Particules
2014-2023
The University of Texas at Dallas
2017
Nagoya University
2016
University of Massachusetts Amherst
2004-2014
Goddard Space Flight Center
1998-2013
We reanalyse archival Ginga data of the soft X-ray transient source GS 2023+338 covering beginning its 1989 May outburst. The showed a number rather unusual features: very high and apparently saturated luminosity, dramatic flux spectral variability (often on ∼1 s time-scale), generally hard spectrum, with no obvious thermal component characteristic for soft/high state. describe spectrum obtained at maximum we demonstrate that it is different from spectra other transients similar luminosity....
Abstract We present 294 pulsars found in GeV data from the Large Area Telescope (LAT) on Fermi Gamma-ray Space Telescope. Another 33 millisecond (MSPs) discovered deep radio searches of LAT sources will likely reveal pulsations once phase-connected rotation ephemerides are achieved. A further dozen optical and/or X-ray binary systems colocated with also harbor gamma-ray MSPs. This catalog thus reports roughly 340 and candidates, 10% all known pulsars, compared to ≤11 before Fermi. Half...
We present an analysis and decomposition of the broad-band optical/UV/X-ray/γ-ray spectrum Seyfert 1 galaxy NGC 5548. The consists average simultaneous optical/IUE/Ginga observations accompanied by ROSAT/CGRO/OSSE data from non-simultaneous observations. show that overall can be deconvolved into three basic continuum components: a cool multitemperature blackbody, hard thermal Comptonized component EUV/soft X-ray well described Comptonization continuum. Assuming optical/IUE comes cold disc,...
We report the discovery of eight gamma-ray pulsars in blind frequency searches using LAT, onboard Fermi Gamma-ray Space Telescope. Five are young (tau_c<100 kyr), energetic (Edot>10^36 erg/s), and located within Galactic plane (|b|<3 deg). The remaining three older, less energetic, off plane. associated with sources included LAT bright source list, but only one, PSR J1413-6205, is clearly an EGRET source. J1023-5746 has smallest characteristic age (tau_c=4.6 kyr) most (Edot=1.1E37 erg/s) all...
We searched for radio pulsars in 25 of the non-variable, unassociated sources Fermi LAT Bright Source List with Green Bank Telescope at 820 MHz. report discovery three and gamma-ray millisecond (MSPs) from a high Galactic latitude subset these sources. All are binary systems, which would have made them virtually impossible to detect blind pulsation searches. They seem be relatively normal, nearby (<=2 kpc) pulsars. These observations, combination detection gamma-rays other known MSPs, imply...
We present a summary of the Fermi Pulsar Search Consortium (PSC), an international collaboration radio astronomers and members Large Area Telescope (LAT) collaboration, whose goal is to organize follow-up observations pulsars pulsar candidates among LAT gamma-ray source population. The PSC includes observers with expertise using world's largest telescopes that together cover full sky. have performed very deep all 35 discovered in blind frequency searches data, resulting discovery pulsations...
view Abstract Citations (180) References (64) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Multiwavelength Observations of Short-Timescale Variability in NGC 4151. IV. Analysis Continuum Edelson, R. A. ; Alexander, T. Crenshaw, D. M. Kaspi, S. Malkan, Peterson, B. Warwick, Clavel, J. Filippenko, V. Horne, K. Korista, Kriss, G. Krolik, H. Maoz, Nandra, O'Brien, P. Penton, Yaqoob, Albrecht, Alloin, Ayres, Balonek, Barr, Barth, Bertram, Bromage, E. Carini,...
view Abstract Citations (217) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Average X-Ray/Gamma-Ray Spectra of Seyfert Galaxies from GINGA and OSSE the Origin Cosmic X-Ray Background Zdziarski, Andrzej A. ; Johnson, W. Neil Done, Chris Smith, David McNaron-Brown, Kellie We have obtained first average 2-500 keV spectra galaxies, using data Ginga Compton Gamma-Ray Observatory's OSSE. Our sample contains three classes objects with markedly...
Sixteen pulsars have been discovered so far in blind searches of photons collected with the Large Area Telescope on Fermi Gamma-ray Space Telescope. We here report discovery radio pulsations from two them. PSR J1741-2054, period P=413ms, was detected archival Parkes telescope data and subsequently has at Green Bank (GBT). Its received flux varies greatly due to interstellar scintillation it a very small dispersion measure DM=4.7pc/cc, implying distance ~0.4kpc possibly smallest luminosity...
Long-term monitoring of PSR J2021+4026 in the heart Cygnus region with Fermi Large Area Telescope unveiled a sudden decrease flux above 100 MeV over timescale shorter than week. The "jump" was near MJD 55850 (2011 October 16), decreasing from (8.33 ± 0.08) × 10−10 erg cm−2 s−1 to (6.86 0.13) s−1. Simultaneously, frequency spindown rate increased (7.8 0.1) 10−13 Hz (8.1 Significant (>5σ) changes pulse profile and marginal (<3σ) emission spectrum occurred at same time. There is also evidence...
Using the Parkes Radio Telescope, we have carried out deep observations of 11 unassociated gamma-ray sources. Periodicity searches these data discovered two millisecond pulsars, PSR J1103−5403 (1FGL J1103.9−5355) and J2241−5236 J2241.9−5236), a long-period pulsar, J1604−44 J1604.7−4443). In addition, searched for but did not detect any radio pulsations from six pulsars by Fermi satellite to level ∼0.04 mJy (for with 10 per cent duty cycle). The timing pulsar has shown that its position is 9...
The nearby Large Magellanic Cloud (LMC) provides a rare opportunity of spatially resolved view an external star-forming galaxy in gamma-rays. LMC was detected at 0.1-100GeV as extended source with CGRO/EGRET and using early observations the Fermi-LAT. emission found to correlate massive regions be particularly bright towards 30 Doradus. Studies origin transport cosmic rays (CRs) Milky Way are frequently hampered by line-of-sight confusion poor distance determination. offers complementary way...
Abstract Reliable neutron star mass measurements are key to determining the equation of state cold nuclear matter, but such rare. Black widows and redbacks compact binaries consisting millisecond pulsars semi-degenerate companion stars. Spectroscopy optically bright companions can determine their radial velocities, providing inclination-dependent pulsar estimates. Although inclinations be inferred from subtle features in optical light curves, estimates may systematically biased due...
The results from a recent Chandra ACIS-S study of the cluster surrounding Cygnus A are presented. We have deprojected X-ray spectra taken various elliptical shells in order to derive run temperature, density, pressure, and abundance for ICM as function radius. confirm drop temperature emitting gas $\sim 8$ keV more than 2^{\prime}$ center $\simeq 5$ some $30^{\prime\prime}$ center, with coolest immediately adjacent radio galaxy. ``Belts'' slightly cooler ($\simeq 4$ keV) around minor...
We describe a comprehensive pulsar monitoring campaign for the Large Area Telescope (LAT) on {\em Fermi Gamma-ray Space Telescope} (formerly GLAST). The detection and study of pulsars in gamma rays give insights into populations neutron stars supernova rates Galaxy, particle acceleration mechanisms star magnetospheres, "engines" driving wind nebulae. LAT's unprecedented sensitivity between 20 MeV 300 GeV together with its 2.4 sr field-of-view makes many gamma-ray likely, justifying over two...
We report the discovery of two millisecond pulsars in a search for radio pulsations at positions Fermi-Large Area Telescope sources with no previously known counterparts, using Nançay Radio Telescope. The pulsars, PSRs J2017+0603 and J2302+4442, have rotational periods 2.896 5.192 ms are both binary systems low-eccentricity orbits orbital 2.2 125.9 days, respectively, suggesting long recycling processes. Gamma-ray were subsequently detected objects, indicating that they power associated...
We report on the discovery of gamma-ray pulsations from five millisecond pulsars (MSPs) using Fermi Large Area Telescope (LAT) and timing ephemerides provided by various radio observatories. also present confirmation a sixth source, PSR J2051-0827. Five these six MSPs are in binary systems: PSRs J1713+0747, J1741+1351, J1600-3053 two black widow J0610-2100 2051-0827. The only isolated MSP is nearby J1024-0719, which known to emit X-rays. X-ray observations direction While latter firmly...
We have re-analysed the Ginga 2–18 keV X-ray observations of Seyfert 2 galaxies, and find that their mean spectrum can be described by a power law index ± ∼ 1, reflection from an optically thick accretion disc and/or molecular torus, absorption cold material. These objects then intrinsic similar to 1s, so support predictions orientation-dependent unification schemes. There is also dispersion about this which seen in 1s. demonstrate explicitly several with data high signal-to-noise ratio,...
We study X-ray and soft gamma-ray spectral properties of BLRGs using data from Ginga, ASCA, OSSE EXOSAT. The spectra are well fitted by an intrinsic power-law continuum with energy index alpha ~ 0.7, moderately absorbed a cold medium. In addition, the Ginga show Fe K-alpha lines average equivalent width 100 eV, and, in some cases, Compton reflection humps. However, latter components significantly weaker than both those seen radio-quiet Seyferts expected if were due to reflection. Some ASCA...
In this Letter, we focus on the limb-brightened, prolate spheroidal cavity of radio galaxy Cygnus A, as revealed by Chandra X-Ray Observatory. We use shock-heated, thermal intracluster medium around expanding to infer properties synchrotron-emitting gas inside cavity. The along north and south edges is found have an average temperature 6.0 keV, which hotter than (4.6 keV) adjacent gas. It proposed that shocked shock thus inferred be weak (Mach number 1.3, a value also from density jump at...
We report a 5.4σ detection of pulsed gamma rays from PSR B1821−24 in the globular cluster M28 using ∼44 months Fermi Large Area Telescope (LAT) data that have been reprocessed with improved instrument calibration constants. constructed phase-coherent ephemeris, post-fit residual rms 3 μs, radio spanning ∼23.2 yr, enabling measurements multi-wavelength light-curve properties at milliperiod level. fold RXTE observations 1996 to 2007 and discuss implications on emission zones. The gamma-ray...
Millisecond pulsars (MSPs) represent nearly half of the more than 160 currently known $\gamma$-ray detected by Large Area Telescope on \textit{Fermi} satellite, and a third all MSPs are seen in $\gamma$ rays. The least energetic enable us to probe so-called deathline for high-energy emission, i.e., spin-down luminosity limit under which (PSRs) cease produce detectable radiation. Characterizing MSP distribution helps determine their contribution Galactic diffuse emission. We made use...