Engineering topics

Hurley, K.

Publications and source records attributed to Hurley, K..

At least 55 records · Page 3

NASA NTRS1997

Radio and Optical Follow-Up Observations and Improved IPN Position of GRB 970111

We report on Westerbork 840 MHz, 1.4 and 5 GHz radio observations of the improved IPN-WFC error box of the gamma ray burst GRB 970111, between 26.4 hours and 120 days after the event onset. In the approximately 16 sq arcmin area defined by the IPN (BATSE and Ulysses) annulus and the published refined BeppoSAX Wide Field Camera (WFC) error box we detected no steady sources brighter than 0.56 mJy (4sigma), and no varying radio emission, down to 1.0 mJy (4sigma). We also report on B, V, R and I band observations of the error box with the 4.2 m William Herschel Telescope at La Palma. Subject headings: gamma rays: bursts - gamma rays: individual (GRB 9701 1 1)

Galama, T. J.↗

NASA NTRS1995

The first search for a gamma-ray burst quiescent counterpart in the extreme ultraviolet with EUVE

The opening of the extreme ultraviolet window by the Extreme Ultraviolet Explorer (EUVE) satellite has provided the unique opportunity to perform the first search for a quiescent gamma-ray burst counterpart at these wavelengths. Such emission might be expected if some bursts are related to nearby hot neutron stars or neutron stars with accretion disks, among other objects. We report here on a 40 ks observation on the 1992 March 25 gamma-ray burst error box, determined by triangulation with the Third Interplanetary Network. No quiescent 40-190 A Extreme Ultraviolet (EUV) source was identified using the Deep Survey instrument, and a 3 sigma upper limit of 2.9 x 10(exp -14) erg/sq cm/s was obtained. Similarly, upper limits to the 140-380 and 280-760 A fluxes were obtained with the medium- and long-wavelength spectrometers; they are 1.1 x 10(exp -12) and 5.0 x 10(exp -13) erg/sq cm/s, respectively. We discuss the constraints which these limits impose on thermally radiating quiescent counterparts.

Hurley, K.↗

NASA NTRS1995

The application of network synthesis to repeating classical gamma-ray bursts

It has been suggested that the Burst and Transient Source Experiment (BATSE) gamma-ray burst catalog contains several groups of bursts clustered in space or in space and time, which provide evidence that a substantial fraction of the classical gamma-ray burst sources repeat. Because many of the bursts in these groups are weak, they are not directly detected by the Ulysses GRB experiment. We apply the network synthesis method to these events to test the repeating burst hypothesis. Although we find no evidence for repeating sources, the method must be applied under more general conditions before reaching any definite conclusions about the existence of classical gamma-ray burst repeating sources.

Hurley, K.↗

NASA NTRS1994

Simultaneous observations of gamma-ray bursts with Phebus/Granat and Ulysses GRB

We compare the characteristics of 35 gamma-ray bursts (GRBs) detected simultaneously by Phebus aboard Granat and the Ulysses GRB experiment. Phebus observes a medium to high energy range (100 keV - 100 MeV), while the Ulysses GRB detector is sensitive to lower energy photons (25 - 150 keV). Comparison of the peak counts recorded by these two instruments shows that the variation in burst intensities is more extended for Phebus (above approximately 150 keV) than for Ulysses GRB. This result confirms similar observations from other instruments (Atteia et al. 1991; Mitrofanov et al. 1992; Belli 1992). We discuss the consequences of this behavior for the statistical properties of GRBs, and for the searches for a possible cosmological redshift.

Atteia, J.-L.↗

NASA NTRS1994

The optical and X-ray content of the 1992 May 1 gamma-ray burst error box

A gamma-ray burst which occurred on 1992 May 1 was observed by three spacecraft in the third interplanetary network, and rapidly localized to a small error box. The coordinates were promptly circulated to a wide astronomical community, and radio, optical, and X-ray counterpart searches were carried out. A weak X-ray source was found in the error box, and two radio sources are discovered outside the error box, but in alignment with the X-ray source. The X-ray source position contains approximately 25 optical objects down to 23d magnitude. We discuss the prospects for identifying the burster counterpart.

Hurley, K.↗

NASA NTRS1994

Directivity of 100-500 keV solar flare hard X-ray emission

We have identified 28 solar flares simultaneously observed by a SIGNE detector aboard the Venera 13 and Venera 14 spacecraft and the Hard X-Ray Burst Spectrometer (HXRBS) aboard the Solar Maximum Mission (SMM), over a wide range of observing angles. Fourteen of them were also observed by the Gamma Ray Spectrometer (GRS) on SMM and were included in a study of the directivity of solar X-radiation. The SIGNE and HXRBS energy coverages overlap in the 50-500 keV range, allowing a detailed comparison of energy spectra. Using this database, we have conducted stereoscopic studies of flare hard X-ray anisotropy. It is found that the 100-500 keV directivity is less than 3, both for the entire set of 28 flares and for the 14 flares which gave evidence for directivity in the SMM GRS study. We conclude that solar flare X-ray directivity can only be marginally present in our energy/observing angle range.

Li, P.↗

NASA NTRS1994

High-energy gamma rays from the intense 1993 January 31 gamma-ray burst

The intense gamma-ray burst of 1993 January 31 was detected by the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Observatory. Sixteen gamma rays above 30 MeV were imaged in the telescope when only 0.04 gamma rays were expected by chance. Two of these gamma rays have energies of approximately 1 GeV, and the five bin spectrum of the 16 events is fitted by a power law of photon spectral index -2.0 +/- 0.4. The high-energy emission extends for at least 25 s. The most probable direction for this burst is determined from the directions of the 16 gamma rays observed by Egret and also by requiring the position to lie on annulus derived by the Interplanetary Network.

Sommer, M.↗

NASA NTRS1993

Upper limits to Jovian hard X radiation from the Ulysses gamma ray burst experiment

We describe the first in situ search for Jovian X radiation with a dedicated X ray instrument. Upper limits to Jupiter's X ray power in the 27 - 48 keV range are presented using data taken by the gamma ray burst experiment on the experiment on the inbound Ulysses trajectory, at distances between 163 and 110 R(sub J). The data were analyzed using three methods for detection of (1) a steady flux, (2) a flux linked to System III rotation, and (3) a sporadic flux. The 3 sigma upper limits lie between 1.1 x 10(exp 8) and 5.6 x 10(exp 8) W. The results are consistent with the idea that the bulk of the Jovian UV auroral emissions are due to energetic electrons, while the previously observed low-energy X radiation is due to ion precipitation.

Hurley, K.↗

NASA NTRS1993

Compton-backscattered annihilation radiation from the Galactic Center region

On 1989 May 22, the High Energy X-ray and Gamma-ray Observatory for Nuclear Emissions, a balloon-borne high-resolution germanium spectrometer with an 18-deg FOV, observed the Galactic Center (GC) from 25 to 2500 keV. The GC photon spectrum is obtained from the count spectrum by a model-independent method which accounts for the effects of passive material in the instrument and scattering in the atmosphere. Besides a positron annihilation line with a flux of (10.0 +/- 2.4) x 10 exp -4 photons/sq cm s and a full width at half-maximum (FWHM) of (2.9 + 1.0, -1.1) keV, the spectrum shows a peak centered at (163.7 +/- 3.4) keV with a flux of (1.55 +/- 0.47) x 10 exp -3 photons/sq cm s and a FWHM of (24.4 +/- 9.2) keV. The energy range 450-507 keV shows no positronium continuum associated with the annihilation line, with a 2-sigma upper limit of 0.90 on the positronium fraction. The 164 keV feature is interpreted as Compton backscatter of broadened and redshifted annihilation radiation, possibly from the source 1E 1740.7-2942.

Smith, D. M.↗

NASA NTRS1992

Gamma-ray bursts and radio pulsar glitches

Upper limits to gamma-ray fluxes produced in conjunction with a radio pulsar glitch are presented. The glitch occurred on the Vela pulsar on December 24, 1988 and was the first to be observed as it occurred. Sensitive gamma-ray burst detectors aboard the Phobos 2 spacecraft were operating at this time, but recorded no significant burst at the time of the glitch. It is concluded that if a gamma-ray burst was generated in the energy range to which the Phobos detectors were sensitive, and if it was not beamed away from the spacecraft, the efficiency of glitch energy conversion into gamma-rays could not have exceeded 10 exp -4.

Hartmann, D.↗

NASA NTRS1992

Ulysses/BATSE observations of cosmic gamma ray bursts

The gamma ray burst detector aboard the ESA-NASA Ulysses spacecraft, in operation since Nov. 1990, has detected numerous gamma bursts in conjunction with the BATSE experiment aboard the Compton Observatory. Initial results are presented on burst locations for three events (21 April, 2 May, and 3 May, 1991) obtained by arrival time analysis, and they are compared with the BATSE locations. The arrival time analysis annuli have typical widths of 5'. The preliminary analysis indicates that both experiments are likely to have unresolved systematic errors, but that further work will improve the location accuracy substantially.

Hurley, K.↗

NASA NTRS1992

Stereoscopic observations of hard x ray sources in solar flares made with GRO and other spacecraft

Since the launch of the Gamma Ray Observatory (GRO) in Apr. 1991, the Burst and Transient Source Experiment (BATSE) instrument on GRO has recorded a large number of solar flares. Some of these flares have also been observed by the Gamma-Ray Burst Detector on the Pioneer Venus Orbiter (PVO) and/or by the Solar X-Ray/Cosmic Gamma-Ray Burst Experiment on the Ulysses spacecraft. A preliminary list of common flares observed during the period May-Jun. 1991 is presented and the possible joint studies are indicated.

Kane, S. R.↗

NASA NTRS1992

The solar X-ray/cosmic gamma-ray burst experiment aboard Ulysses

The scientific objectives of the Ulysses solar X-ray/cosmic gamma-ray burst experiment, and the unique features of the Ulysses mission which will help to achieve them are described. After a discussion of the special design constraints imposed by the mission, the sensor systems, consisting of two CsI scintillators and two Si surface barrier detectors covering the energy range 5-150 keV are described. Their operating modes and inflight performance are also given.

Hurley, K.↗

NASA NTRS1992

A high resolution gamma-ray and hard X-ray spectrometer (HIREGS) for long duration balloon flights

The elements of a high resolution gamma-ray spectrometer, developed for observations of solar flares, are described. Emphasis is given to those aspects of the system that relate to its operation on a long duration balloon platform. The performance of the system observed in its first flight, launched from McMurdo Station, Antarctica on 10 January, 1992, is discussed. Background characteristics of the antarctic balloon environment are compared with those observed in conventional mid-latitude balloon flights and the general advantages of long duration ballooning are discussed.

Pelling, M.↗

NASA NTRS1991

New constraints on neutron star models of gamma-ray bursts. II - X-ray observations of three gamma-ray burst error boxes

Exosat observations are presented for 3 gamma-ray-burst error boxes, one of which may be associated with an optical flash. No point sources were detected at the 3-sigma level. A comparison with Einstein data (Pizzichini et al., 1986) is made for the March 5b, 1979 source. The data are interpreted in the framework of neutron star models and derive upper limits for the neutron star surface temperatures, accretion rates, and surface densities of an accretion disk. Apart from the March 5b, 1979 source, consistency is found with each model.

Boer, M.↗

NASA NTRS1991

SIGHT - A balloon borne hard X-ray telescope

The authors report on progress toward developing a large-area, high-pressure xenon gas scintillator for use in hard X-ray astrophysics. Proof test results for a low-mass pressure vessel are presented. The design of a high-voltage multiplier board operating inside the scintillation chamber is discussed. The development of tetrakis-dimethylamine-thylene (TMAE)-based proportional tubes for detecting primary scintillation in the xenon is described. Finally, Monte Carlo tests of a scheme to use conventional photomultiplier tubes are discussed.

Wilkerson, J.↗

NASA NTRS1991

Cosmic gamma-ray bursts

A review of the cosmic gamma-ray burst phenomenon is presented. Both the light curves and the energy spectra of these short transient events display a great diversity. However, rapid rise times and periodicities sometimes observed in the light curves suggest a compact object origin. Similarly, absorption and emission features in the energy spectra argue strongly in favor of this interpretation. Counterparts to gamma-bursters in other energy ranges, such as optical and sort x-ray, have still not been identified, however, leading to a large uncertainty in the distances to bursters. Although gamma-ray burst sources have not yet been observed to repeat, numerous bursts from three objects which may be related to the gamma-bursters, called Soft Gamma Repeaters, have been recorded; there is weak evidence that they may be relatively distant on a galactic scale. Future missions, particularly those emphasizing high energy, time, and/or spatial resolution, as well as a multiwavelength approach, are likely to advance our understanding of this enigmatic phenomenon.

Hurley, K.↗

NASA NTRS1990

Active neutron stars

A review of some hard X-ray and gamma-ray sources is presented. These objects are strongly suspected to be associated with neutron stars. Examples include gamma ray bursters, soft gamma repeaters, the June 10, 1974 transient, and Geminga. It is argued that such objects probably constitute the majority of observable galactic neutron stars.

Hurley, K.↗