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Jernigan, J. G.

Publications and source records attributed to Jernigan, J. G..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

Observations of Gamma-Ray Bursts by HETE-2

The High Energy Transient Explorer 2 (HETE-2), launched in October 2000, is currently localizing gamma-ray bursts (GRBs) at a rate of approximately 20/yr, many in real time. As of August 2003, HETE-2 had localized 43 GRBs; 16 localizations had led to the detection of an X-ray, optical, or radio afterglows. The prompt position notification of HETE-2 enabled probing the nature of so-called "dark bursts" for which no optical afterglows were found despite of accurate localizations. In some cases, the optical afterglow was found to be intrinsically faint , and its flux declined rapidly. In another case, the optical emission was likely to be extinguished by the dust in the vicinity of the GRB source. The bright afterglows of GRB021004 and GRB030329 were observed in unprecedented details by telescopes around the world. Strong evidence for the association of long GRBs with the core-collapse supernovae was found. HETE-2 has localized almost as many X-ray rich GRBs as classical GRBs. The nature of the X-ray rich GRBs and X-ray flashes have been studied systematically with HETE-2, and they are found to have many properties in common with the classical GRBs, suggesting that they are a single phenomenon.

Kawai, N.↗
NASA NTRS2000

X-Ray Imaging-Spectroscopy of Abell 1835

We present detailed spatially-resolved spectroscopy results of the observation of Abell 1835 using the European Photon Imaging Cameras (EPIC) and the Reflection Grating Spectrometers (RGS) on the XMM-Newton observatory. Abell 1835 is a luminous (10(exp 46)ergs/s), medium redshift (z = 0.2523), X-ray emitting cluster of galaxies. The observations support the interpretation that large amounts of cool gas are present in a multi-phase medium surrounded by a hot (kT(sub e) = 8.2 keV) outer envelope. We detect O VIII Ly(alpha) and two Fe XXIV complexes in the RGS spectrum. The emission measure of the cool gas below kT(sub e) = 2.7 keV is much lower than expected from standard cooling-flow models, suggesting either a more complicated cooling process than simple isobaric radiative cooling or differential cold absorption of the cooler gas.

Peterson, J. R.↗
NASA NTRS1989

Telescience at the University of California, Berkeley

The University of California at Berkeley (UCB) is a member of a university consortium involved in telescience testbed activities under the sponsorship of NASA. Our Telescience Testbed Project consists of three experiments using flight hardware being developed for the Extreme Ultraviolet Explorer project at UCB's Space Sciences Laboratory. The first one is a teleoperation experiment investigating remote instrument control using a computer network such as the Internet. The second experiment is an effort to develop a system for operation of a network of remote workstations allowing coordinated software development, evaluation, and use by widely dispersed groups. The final experiment concerns simulation as a method to facilitate the concurrent development of instrument hardware and support software. We describe our progress in these areas.

Telemetry/instrumentation/methods↗
NASA NTRS1988

Telescience at the University of California, Berkeley

The University of California at Berkeley (UCB) is a member of a university consortium involved in telescience testbed activities under the sponsorship of NASA. The Telescience Testbed Project consists of three experiments using flight hardware being developed for the Extreme Ultraviolet Explorer project at UCB's Space Sciences Laboratory. The first one is a teleoperation experiment investigating remote instrument control using a computer network such as the Internet. The second experiment is an effort to develop a system for operation of a network of remote workstations allowing coordinated software development, evaluation, and use by widely dispersed groups. The final experiment concerns simulation as a method to facilitate the concurrent development of instrument hardware and support software. Progress in these areas is described.

Chakrabarti, S.↗
NASA NTRS1983

Discovery of 13.5 s X-ray pulsations from LMC X-4 and an orbital determination

X-ray pulsations with a 13.5-sec period have been detected from the 1.4-d X-ray binary LMC X-4. By measuring the apparent pulse period at several binary orbital phases, and assuming the orbit to be nearly circular, the semimajor axis of the orbit is determined to be 30 + or - 5 ly-sec. This result, together with a revised orbital velocity amplitude of 37.9 + or - 2.4 km/sec, and other available information, suffice for the determination of the component masses of the binary system and the radius of the companion star. The mass of the neutron star is found to be 1.6 +1.0 -0.5 solar masses, while the mass, radius, and effective temperature of the companion star indicate that it may be undermassive for its luminosity.

Kelley, R. L.↗
NASA NTRS1982

X-ray spectroscopy of the galaxy M87 - Radiative accretion of the hot plasma halo

Canizares et al. (1979) have reported the detection of the O VIII Lyman-alpha line from the vicinity of the giant elliptical galaxy M87 in the Virgo cluster. The detection is based on high-resolution X-ray spectroscopy studies performed with the Focal Plane Crystal Spectrometer on the Einstein Observatory. The presence of a strong O VIII line indicates the existence of some material which is cooler than the bulk of the X-ray emitting gas surrounding M87. The result is interpreted as favoring models which call for radiative accretion of the hot gas onto M87. The present investigation is concerned with further high-resolution X-ray spectroscopy of M87. Seven additional emission line blends due primarily to ionized iron have been detected. These data make it possible to derive the approximate distribution of the quantity of emitting material over more than a decade in temperature for the central part of the M87 source. The obtained results are in excellent agreement with expectations for radiative, pressure driven accretion.

Canizares, C. R.↗
NASA NTRS1982

On the orbital phase dependence of the turn-on times of Hercules X-1

The present investigation is concerned with the dynamics of tilted accretion disks in binary systems. It is shown that the expected motion of a ring of matter in an accretion disk is more complicated than simple precession at a uniform rate. The motion is found to be better described by a vector normal to the plane of the ring of matter whose tip periodically traces out a small ellipse centered on the tip of a uniformly precessing vector. It is also demonstrated that this 'wobble' can be utilized to explain why the turn-ons of Hercules X-1 preferentially occur around orbital phases 0.2 and 0.7. If an accretion disk in a binary system is tilted with respect to the binary orbital plane, then it must undergo forced precession with the corresponding 'wobble'. This 'wobble' may be, at least, partially responsible for the phase dependence of the distribution of X-ray turn-on times of Hercules X-1.

Levine, A. M.↗
NASA NTRS1981

Discovery of X-ray pulsations from 2S 1417-624

X-ray pulsations having a period of 17.64 sec are detected from the hard, variable galactic X-ray source 2S 1417-624. It is noted that the pulsations were found through a Fourier analysis of 40 satellite orbits of data taken with the rotation modulation collimators aboard SAS 3 in July 1978. The pulse profile shows detailed interpulse structure that is similar in character to the pulse profiles of 4U 0900-40 and A0535+26. Significant changes in pulse period are detected over the eight-day observing interval. It is suggested that these changes may be the result of a large intrinsic spin-up rate for the neutron star or from binary orbital motion, with orbital periods longer than approximately 15 days.

Kelley, R. L.↗
NASA NTRS1980

High resolution X-ray spectroscopy from the Einstein Observatory

Results obtained from the Focal Plane Crystal Spectrometer (FPCS) are presented with particular reference to supernova remnants Puppis A and Cas A in the Galaxy, and N132D and N63A in the Large Magellanic Cloud. A schematic diagram of the FPCS is given, and spectrum reconstruction is outlined, noting that the final spectrum consists of a histogram of counting rate vs. energy corrected for the exposure time in each energy bin. Consideration is also given to the Virgo cluster and its two X-ray components: the hot exponent extending throughout much of the cluster and a cooler, 'halo', component centered on M87. FPCS observations of central M87 are presented, and it is postulated that the central portion of the M87 'halo' source contains material with a dominant temperature near 10 to the 7th K or below about 2 x 10 to the 6th K.

Winkler, P. F.↗
NASA NTRS1979

The locations of X-ray sources in globular clusters

The SAS 3 X-ray observatory has been used to measure the positions of the X-ray sources in the globular clusters NGC 1851, 6441, 6624, 6712, and 7078. The derived positions have error circles with 90% confidence radii of 10 or 30 arcsec, which, in each case, include the optical center of the cluster. The results of a statistical analysis demonstrate that the X-ray sources are more concentrated toward the cluster centers than the visible stars and are therefore more massive than those stars.

Jernigan, J. G.↗
NASA NTRS1979

A0535+26 - Refined position measurement and new pulse period data

The hard, pulsing, transient X-ray source A0535+26 has been observed with SAS 3 on three occasions during 1977-1978. These observations have yielded a precise position measurement (20 arcsec error radius), which renders the identification of A0535+26 with the Be star HDE 245770 virtually certain. The pulse phase was tracked for about 9 days in April 1978 and clearly showed both first and second derivatives in the pulse period. An analysis of these timing data, combined with data from previous observations, leads to the following conclusions: (1) a significant fraction of the observed changes in pulse period is probably intrinsic to the compact X-ray star (e.g., accretion torques on a neutron star), and (2) conservative limits on binary orbital parameters tend to further confirm a long orbital period (at least about 20 days).

Li, F.↗
NASA NTRS1979

Discovery of soft X-ray flux from 2A 1102+384 = Markarian 421

During April 1976 a soft X-ray flux was detected with SAS 3 from the vicinity of 2A 1102+384. The average flux densities were 4.3 x 10 to the -11th and 14 x 10 to the -11th erg/sq cm per sec in the energy bands 0.1-0.28 keV and 1-6 keV, respectively. There is an indication of variability over about 0.5 day in the lowest energy band. An upper limit of 3 x 10 to the 20th H atoms per sq cm is found for the gas column density to the X-ray source. In May 1978, observations with the modulation collimators of SAS 3 yielded an accurate (40 arcsec error radius) position for the X-ray source (2-6 keV) at right ascension 11 h 1 m 39.7 s, declination + 38 deg 28 min 51 sec (equinox 1950). The earlier tentative identification by Ricketts et al. (1976) with the BL Lacertae object B2 1101+38 = Markarian 421 is thus confirmed.

Hearn, D. R.↗
NASA NTRS1979

Positions and identifications of galactic X-ray sources

A catalog of compact Galactic X-ray sources with precise positions is presented together with a large bibliography. The catalog provides available X-ray, optical, and radio data for the 96 compact Galactic sources that have been identified and contains the most precise of the available optical, X-ray, or radio positions, the maximum and minimum published intensities, references to finding charts, and a comprehensive referenced list of X-ray, optical, and radio characteristics. The catalog also includes X-ray sources in the Magellanic clouds as well as all unidentified hard (greater than 2 keV) compact sources with an error radius of less than 60 arcsec and a Galactic latitude of less than 10 deg (absolute value). The sources list includes 14 X-ray Doppler or eclipsing binaries, seven or eight other X-ray pulsators, 23 transients or X-ray novae, 15 persistent bright bulge sources, seven X-ray sources associated with globular clusters, nine bursters, seven Galactic Center sources, and 18 other identified sources.

Bradt, H. V.↗
NASA NTRS1979

Observations of an X-ray QSO

This paper reports X-ray, optical, radio, and IR measurements of the z = 0.068 QSO MR2251-178, which was initially discovered on the basis of its X-ray emission. Data are provided on the position, optical colors, and 2-10-keV X-ray luminosity of this low-redshift QSO. An absolute V magnitude of -24.2 is implied, and the X-ray/optical luminosity ratio is estimated to be about 3:1 at peak X-ray brightness. It is shown that the optical spectrum of MR2251-178 is quite normal for a QSO, except for an extremely broad H-alpha emission line with a FWZI of 30,000 to 40,000 km/s. The overall spectrum of MR2251-178 from the radio to the X-ray region is plotted, and the photometric history of this QSO since 1889 is briefly discussed.

Ricker, G. R.↗
NASA NTRS1978

Discovery and optical identification of 2S0921-630

The discovery of a faint X-ray source at approximately 282 deg galactic longitude, -9 deg galactic latitude with the rotation modulation collimator X-ray detectors aboard SAS 3 is reported. The source is designated 2S 0921-630 and is tentatively identified, on the basis of an optical search, with a 17th magnitude star exhibiting the He II line at 4686 A and H-beta in emission. The optical spectrum of this star is shown to be similar to those of the optical counterparts of Sco X-1 and other such galactic X-ray sources. It is suggested that 2S 0921-630 may belong to the class of low-luminosity galactic X-ray binaries.

Li, F. K.↗
NASA NTRS1978

An energy-dependent map of the X-ray emission of the Perseus cluster

Results are discussed for X-ray scans of the Perseus cluster with the SAS 3 slat detectors. Counting rates in two broadband channels (1.5 to 5.5 keV and 5.5 to 15.5 keV) are compared as a function of the instrument scan angle measured from the center of emission, and it is found that the emission in the higher energy range is broader in extent. Tests for a systematic energy-dependent error in the background demonstrate that the discovered energy dependence of the Perseus cluster emission is valid. Iron line emission is determined by two methods, various models are fitted to the data, and the total cluster emission in the two energy ranges is computed. The iron line emission is determined to be 0.003 photon/sq cm per sec. It is concluded that the diffuse emission increases in the range from 1.5 to 15.5 keV within the bounds of a model involving a point source with a radius not exceeding about 3 arcmin plus a diffuse source.

Ulmer, M. P.↗