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NASA NTRS2015

Fermi: The Gamma-Ray Large Area Telescope

Following its launch in June 2008, high-energy gamma-ray observations by the Fermi Gamma-ray Space Telescope have unveiled over 1000 new sources and opened an important and previously unexplored window on a wide variety of phenomena. These have included the discovery of an population of pulsars pulsing only in gamma rays; the detection of photons up to 10s of GeV from gamma-ray bursts, enhancing our understanding of the astrophysics of these powerful explosions; the detection of hundreds of active galaxies; a measurement of the high energy cosmic-ray electron spectrum which may imply the presence of nearby astrophysical particle accelerators; the determination of the diffuse gamma-ray emission with unprecedented accuracy and the constraints on phenomena such as supersymmetric dark-matter annihilations and exotic relics from the Big Bang. Continuous monitoring of the high-energy gamma-ray sky has uncovered numerous outbursts from active galaxies and the discovery of transient sources in our galaxy. In this talk I will describe the current status of the Fermi observatory and review the science highlights from Fermi.

telescope↗

NASA NTRS2014

Fermi: The Gamma-Ray Large Area Space Telescope

telescope↗

NASA NTRS2014

Fermi: The Gamma-Ray Large Area Space Telescope Mission Status

Following its launch in June 2008, high-energy gamma-ray observations by the Fermi Gamma-ray Space Telescope have unveiled over 1000 new sources and opened an important and previously unexplored window on a wide variety of phenomena. These have included the discovery of a population of pulsars pulsing only in gamma rays; the detection of photons up to 10s of gigaelectronvolts from gamma-ray bursts, enhancing our understanding of the astrophysics of these powerful explosions; the detection of hundreds of active galaxies; a measurement of the high energy cosmic-ray electron spectrum which may imply the presence of nearby astrophysical particle accelerators; the determination of the diffuse gamma-ray emission with unprecedented accuracy and the constraints on phenomena such as super-symmetric dark-matter annihilations and exotic relics from the Big Bang. Continuous monitoring of the high-energy gamma-ray sky has uncovered numerous outbursts from active galaxies and the discovery of transient sources in our galaxy. In this talk I will describe the current status of the Fermi observatory and review the science highlights from Fermi.

telescope↗

NASA NTRS2014

Fermi: The Gamma-Ray Large Area Telescope

Following its launch in June 2008, high-energy gamma-ray observations by the Fermi Gamma-ray Space Telescope have unveiled over 1000 new sources and opened an important and previously unexplored window on a wide variety of phenomena. These have included the discovery of an population of pulsars pulsing only in gamma rays; the detection of photons up to 10 seconds of gigaelectronvolts from gamma-ray bursts, enhancing our understanding of the astrophysics of these powerful explosions; the detection of hundreds of active galaxies; a measurement of the high energy cosmic-ray electron spectrum which may imply the presence of nearby astrophysical particle accelerators; the determination of the diffuse gamma-ray emission with unprecedented accuracy and the constraints on phenomena such as super-symmetric dark-matter annihilations and exotic relics from the Big Bang. Continuous monitoring of the high-energy gamma-ray sky has uncovered numerous outbursts from active galaxies and the discovery of transient sources in our galaxy. In this talk I will describe the current status of the Fermi observatory and review the science highlights from Fermi.

fermi↗

NASA NTRS1994

An EXOSAT detection of the transient X-ray pulsar GRO J1008-57

The hard X-ray transient, GRO J1008-57, was discovered during a bright outburst in 1993 July by the Burst and Transient Source Experiment (BATSE) instrument on board the Compton Gamme-Ray Observatory (CGRO). There are no published reports of previous emission from this 93.6 sec X-ray pulsar. Recent optical results have suggested a Be star as the companion. A search of the EXOSAT archives shows that an ME observation centered on the star HD 88661 includes GRO J1008-57 within the field of view. The characteristics of the medium-energy detection including a hard spectrum and pulsed emission at 91.36 sec (with chance probability of 3 x 10(exp -4)) indicates that EXOSAT detected GRO J1008-57 rather than the field star. The estimated flux is 2.4 x 10(exp -11) ergs/cm sq/sec for a luminosity of 1.1 x 10(exp 34) (D/2 kpc)(exp 2) ergs/sec. The X-ray spectrum is hard (photon index approximately equals 1.2) and highly absorbed (N(sub H) approximately equals 0.7 x 10(exp 22)). The detection of this transient suggests that there is a pulse shape dependence on luminosity, a spectral shape independent of luminosity, a large period derivative of P-dot/P = 2.3 x 10(exp -3)/yr, and a dynamic range of at least 100 in L(sub chi). We discuss GRO J1008-57 data in the context of wind-accretion models for this new member of the Be class of X-ray binaries.

Macomb, D. J.↗

NASA NTRS1995

Observations of the X-ray Nova GRO J0422+32. 1: Outburst and the decay to quiescence

We present optical photometry and spectroscopy and Burst and Transient Source Experiment (BATSE) observations of the X-ray nova GRO J0422+32, obtained during outburst and its subsequent decay to quiescence. Although the X-ray and optical properties of GRO J0422+32 are broadly similar to those of other X-ray novae, it is unique in several respects. The unusually protracted decay to quiescence of the optical light curve has been punctuated by at least two minioutbursts of approximately 4 mag. The BATSE and optical outbursts are each separated by approximately 120 days. We find that the optical luminosity of GRO J0422+32 during the primary outburst is dominated by reprocessing of E greater than 10 keV X-rays. In contrast, the optical minioutbursts are most likely generated by an intrinsically bright disk rather than X-ray reprocessing: they do not appear to have any X-ray counterparts. Extremely broad (up to 6000 km/s FWZI) absorption lines have also been observed during both primary outbursts and minioutbursts. During the second minioutburst, H-alpha and H-beta emission was observed superposed on redshifted absorption features. We find that the interoutburst light curve of GRO J0422+32 may be inconsistent with an accretion disk instability as the origin of the minioutbursts. Finally, a transient 5.1/10.2 hr modulation, which may be related to the orbital period, has been observed during roughly half of our observations. However, confirmation of the orbital period must await observations in quiescence.

Callanan, Paul J.↗

NASA NTRS1978

Transient X-ray sources in the galactic plane

Uhuru observations of the galactic plane indicate the presence of four X-ray sources not previously characterized as transient: MX 0836-42, A1918+14, 4U 1730-22, and 4U 1807-10. X-ray light curves as well as positional and spectral information are presented for these sources and for 4U 1908+00, a recurrent transient source. The frequency, duration, and intensity of galactic-plane transients during the Uhuru lifetime are discussed. Transient X-ray sources appear to be divided into two classes based primarily on an observed bimodal spectral temperature distribution.

Cominsky, L.↗

NASA NTRS1974

Theoretical study of the effects of refraction on the noise produced by turbulence in jets

The production of noise by turbulence in jets is an extremely complex problem. One aspect of that problem, the transmission of acoustic disturbances from the interior of the jet through the mean velocity profile and into the far field is studied. The jet (two-dimensional or circular cylindrical) is assumed infinitely long with mean velocity profile independent of streamwise location. The noise generator is a sequence of transient sources drifting with the surrounding fluid and confined to a short length of the jet.

Graham, E. W.↗

NASA NTRS1975

Results from the Ariel-5 all-sky X-ray monitor

A summary of results obtained from the first year of Ariel-5 all-sky monitor operation is presented. Transient source observations, as well as the results of long term studies of Sco X-1, Cyg X-3, and Cyg X-1 are described. By example, the included results are indicative of the temporal effects to which the all-sky monitor remains sensitive as it begins its second year of observation.

Holt, S. S.↗

NASA NTRS1975

X-Ray Binaries

This publication of proceedings presents workshop papers in the order of topics on the agenda of the symposium. Introductory and/or summarizing comments by each panel chairman are given at the beginning of the collection of papers from the corresponding panel. Those brief remarks by workshop participants which were submitted in written form are grouped together for each panel and presented after the collection of associated papers. The many comments end questions not exhibited here are covered, to a large extent, by the reviews given by panel chairmen. Most of the formal presentations at the symposium are represented In this publication of the proceedings either by self-contained papers or by abstracts. Some of the major contributions to the general sessions opening and closing the workshop are not represented here, but involved material which may be found in papers included under the specialized panels. Satellite X-ray experiments and ground-based programs aimed at observation of X-ray binaries are discussed. Experiments aboard OAO-3, OSO-8, Ariel 5, Uhuru, and Skylab are included along with rocket and ground-based observations. Major topics covered are: Her X-1, Cyg X-3, Cen X-3, Cyg X-1, the transient source A0620-00, other possible X-ray binaries, and plans and prospects for future observational programs.

Elihu Boldt↗

NASA NTRS1976

All-sky monitor observations of flares from Aquila X-1

The All-Sky Monitor on Ariel 5 has observed the Aquila-Serpens region on a quasi-continuous basis since launch in 1974 October. During this time Aql X-1 exhibited major flares in 1975 June and 1976 June, with the measured X-ray intensities increasing more than an order of magnitude to approximately that measured from the Crab nebula, and remaining above the experiment threshold (approximately 0.1 x s crab) for almost two months in both instances. These outbursts resemble the X-ray light curves of transient sources such as A0620-00 and are interpreted in terms of episodic accretion in a dwarf nova-like binary. Combination of the epoch of phase minimum for the 1.3d period (1976) with the 1975 data yields a value of P = 1.28d + or - 0.02d with a corresponding modulation of approximately 3% (3-6 keV). Modulation at this period is not apparent in the 1976 data, with an upper limit of 2% during that time.

Kaluzienski, L. J.↗

NASA NTRS1978

Gamma ray spectroscopy in astrophysics: An observational overview (50 keV-20 MeV)

The observational status of gamma ray astronomy based on results reported prior to April 1978 is discussed. Specific line observations are reviewed from the Sun, the galactic plane, the Galactic Center region, the active Galaxy NGC 5128 (Cen A), the Crab Nebula region, and a transient source in the general direction of the anti-Galactic Center region. A statistical method is described which determines the relative probability that a given, reported observation is due to an external source as compared to a random fluctuation in the experimental background counting rate. Only a few of the many reported observations can be considered likely extraterrestrial observations of an extraterrestrial source made with a confidence level of 99%.

Chupp, E. L.↗

NASA NTRS1978

Fine structure and time variation of the quiet sun at 1.3 cm

The Hat Creek two-element interferometer has been used to study the quiet sun at 22 GHz. A statistical analysis of output of the interferometer clearly shows the existence of time variations on the quiet sun with time scales of approximately 180 s. The observations suggest that the fine structure on the quiet sun might consist of two components - one which varies with the time scales of approximately 3 min and the other being relatively stable. The average visibility amplitude indicates that the fine structure on the sun has a typical angular size of approximately 6 sec. The observation that the variance and the mean of the visibility amplitudes depend in the same way on the projected baseline suggests that the transient sources have angular size similar to the average size of the fine structure on the quiet sun. Power spectra of the output of the interferometer show no significant periodicity.

Rao, A. P.↗

NASA NTRS1981

Performance of photomultiplier tubes and sodium iodide scintillation detector systems

The performance of photomultiplier tubes (PMT's) and scintillation detector systems incorporating 50.8 by 1.27 cm NaI (T l) crystals was investigated to determine the characteristics of the photomultiplier tubes and optimize the detector geometry for the Burst and Transient Source Experiment on the Gamma Ray Observatory. Background information on performance characteristics of PMT's and NaI (T l) detectors is provided, procedures for measurement of relevant parameters are specified, and results of these measurements are presented.

Meegan, C. A.↗

NASA NTRS1982

Observations of a weak gamma ray burst, A0535 plus 26, NP0532 and solar flare events by a balloon-borne detector array

Observations of a cosmic gamma ray burst of about 10 to the -6 erg/sq cm, pulsed emission profiles of A0535 plus 26 and NP0532, and two solar flare events are reported for several energy intervals in 45-500 keV. The measurements were made with a NaI (Tl) detector array flown on a balloon to 4 g/sq cm residual atmosphere from Palestine, Texas Oct. 6-8, 1980 for 28 hours. The detector is a prototype of the Burst and Transient Source Experiment to be flown on the Gamma Ray Observatory.

Wilson, R. B.↗

NASA NTRS1985

Simultaneous Solar Maximum Mission and Very Large Array (VLA) observations of solar active regions

Simultaneous observations of solar active regions with the Solar Maximum Mission (SMM) Satellite and the Very Large Array (VLA) have been obtained and analyzed. Combined results enhance the scientific return for beyond that expeted from using either SMM or VLA alone. A total of two weeks of simultaneous SMM/VLA data were obtained. The multiple wavelength VLA observations were used to determine the temperature and magnetic structure at different heights within coronal loops. These data are compared with simultaneous SMM observations. Several papers on the subject are in progress. They include VLA observations of compact, transient sources in the transition region; simultaneous SMM/VLA observations of the coronal loops in one active region and the evolution of another one; and sampling of the coronal plasma using thermal cyclotron lines (magnetic field - VLA) and soft X ray spectral lines (electron density and electron temperaure-SMM).

Lang, K. R.↗

NASA NTRS1986

Development of the instruments for the Gamma Ray Observatory

The Gamma Ray Observatory (GRO) is to be launched in 1988 by the STS. The GRO will feature four very large instruments: the Oriented Scintillation Spectrometer Experiment (OSSE), the Imaging Compton Telescope (COMPTEL), the Energetic Gamma Ray Experiment Telescope (EGRET) and the Burst and Transient Source Experiment (BATSE). The instruments weigh from 900-1200 kg each, and required the development of specialized lifting and dolly devices to permit their assembly, manipulation and testing. The GRO is intended a{s a tool for studying discrete celestial objects such as black holes, neutron stars and other gamma-ray emitting objects, scanning for nucleosynthesis processes, mapping the Galaxy and other, high energy galaxies in terms of gamma rays, searching for cosmological effects and observing gamma ray bursts. The instruments will be sensitive from the upper end mof X-rya wavelengths to the highest energies possible. Details of the hardware and performance specifications of each of the instruments are discussed.

Madden, J. J.↗

NASA NTRS1986

Some atmospheric scattering considerations relevant to BATSE: A model calculation

The orbiting Burst and Transient Source Experiement (BATSE) will locate gamma ray burst sources by analysis of the relative numbers of photons coming directly from a source and entering its prescribed array of detectors. In order to accurately locate burst sources it is thus necessary to identify and correct for any counts contributed by events other than direct entry by a mainstream photon. An effort is described which estimates the photon numbers which might be scattered into the BATSE detectors from interactions with the Earth atmosphere. A model was developed which yielded analytical expressions for single-scatter photon contributions in terms of source and satellite locations.

Young, John H.↗