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Grindlay, J. E.

Publications and source records attributed to Grindlay, J. E..

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Hard X-ray imaging from Explorer

Coded aperture X-ray detectors were applied to obtain large increases in sensitivity as well as angular resolution. A hard X-ray coded aperture detector concept is described which enables very high sensitivity studies persistent hard X-ray sources and gamma ray bursts. Coded aperture imaging is employed so that approx. 2 min source locations can be derived within a 3 deg field of view. Gamma bursts were located initially to within approx. 2 deg and X-ray/hard X-ray spectra and timing, as well as precise locations, derived for possible burst afterglow emission. It is suggested that hard X-ray imaging should be conducted from an Explorer mission where long exposure times are possible.

Grindlay, J. E.↗
NASA NTRS1981

An X-ray study of the galactic center

The results from two long observations with the Einstein Observatory Imaging Proportional Counter (IPC) of an approximately 1 x 1 deg field centered near the galactic nucleus are presented. The X-ray images reveal a complex of weak sources within 20 arcmin of the galactic nucleus (Sgr A West) together with a region of apparently diffuse emission about 25 x 15 arcmin in extent. Three of the sources are tentatively identified: two with nearby galactic objects, and a third positionally coincident with Sgr A West itself (within the arcmin-accuracy available with the IPC). The nature of this source and the implications of both the high source density and presence of diffuse emission in the galactic center region are discussed.

Watson, M. G.↗
NASA NTRS1981

Observations of SMC X-1 with the monitor proportional counter on the Einstein /HEAO 2/ X-ray Observatory - The pulse period and its history

The results of the sixth determination of the pulse period of the X-ray source SMC X-1 are presented. The observations were made in April 1979. The pulse period at this epoch was found to be (0.713683 + or - 0.000032) s referred to phase zero of the binary motion. This result together with all available historical data is utilized to quantify the observed trend toward spin-up. It is found that simple secular trends are not applicable. This finding is interpreted as evidence for additional variations in the pulse period. The obtained results are discussed in the context of present theoretical models for period variations in the binary pulsating X-ray sources. The apparent absence of spin-down episodes in the period history of SMC X-1 is also considered.

Darbro, W.↗
NASA NTRS1981

Search for high frequency pulsations in the onset of the March 5 gamma-ray burst

The onset of the March 5 Gamma-Ray burst was observed with microsecond time resolution by the Monitor Proportional Counter aboard the HEAO-2/Einstein Observatory. The data were analyzed for high frequency periodic pulsations which, if present, would be strong evidence for vibrations of a neutron star following the initial release of energy. Evidence is not found for such pulsations in the data over the period range 29.4737 to 0.0962 ms, and upper limits to the amplitude of 49-70% are set.

Weisskopf, M. C.↗
NASA NTRS1981

Einstein observations of the galactic centre

A description is presented of the X-ray observations made with the Einstein Observatory Imaging Proportional Counter of a 1 x 1 degree field centered near the galactic nucleus. In the direction of the galactic center the interstellar medium is generally opaque to all radiation between the visual and extreme ultraviolet due to the large column density of the intervening gas and dust. The importance of this X-ray study lies in the fact that it opens up a new window in which the central regions of the Milky Way Galaxy can be observed. The X-ray image is clearly dominated by a bright, central region of emission elongated along the galactic plane. Also presented are a number of unresolved sources.

Watson, M. G.↗
NASA NTRS1981

X-ray sources in globular clusters

The Einstein X-ray Observatory globular cluster observation program has completed a survey of 30 clusters, using the HRI detector. Preliminary results are reported for a more sensitive survey being conducted with the imaging proportional counter (IPC) of the satellite, which has found four possible new sources in the first 32 clusters observed. Also described are detailed studies of several luminous, globular cluster sources, including the X-ray burst from Terzan 2, and an effort is made to locate the X-ray sources with respect to cluster centers. Sources of systematic error, required optical studies of globular cluster structure, and the implications of the plausible binary systems for cluster core evolution are discussed.

Grindlay, J. E.↗
NASA NTRS1980

Time-resolved imaging and spectral studies of an X-ray burst from the globular cluster Terzan

The first image of an X-ray burst was recorded with the HRI detector at the Einstein Observatory while observing the globular cluster Terzan 2. The burst was coincident with a persistent X-ray source located near the center of the cluster (thus confirming an earlier suggested identification) and reached a peak luminosity exceeding 5 x 10 to the 38th (d/10 kpc) squared. After a rapid rise to peak luminosity, a double-peaked spectral variation was observed over the next approximately 20 s with anticorrelated changes in the apparent emission region radius and temperature derived from blackbody (and modified blackbody) spectral fits. A shell or disk geometry, which undergoes adiabatic expansion and contraction, may be implied for the burst emission region. Alternatively, Comptonization is required. It is also shown that the peak burst luminosity must exceed the Eddington limit.

Grindlay, J. E.↗
NASA NTRS1980

Discovery of low-redshift X-ray selected quasars - New clues to the QSO phenomenon

The identification of six X-ray sources discovered by the Einstein Observatory with X-ray quasars is reported, and the properties of these X-ray selected quasars are discussed. The four high-latitude fields of 1 sq deg each in which the Einstein imaging proportional counter detected serendipitous X-ray sources at intermediate exposures of 10,000 sec were observed by 4-m and 1.5-m telescopes, and optical sources with uv excesses and emission line spectra typical of many low-redshift quasars and Seyfert 1 galaxies were found within the 1-arcsec error boxes of the X-ray sources. All six quasars identified were found to be radio quiet, with low redshift and relatively faint optical magnitudes, and to be similar in space density, colors and magnitude versus redshift relation to an optically selected sample at the same mean magnitude. X-ray luminosity was found to be well correlated with both continuum and broad-line emission luminosities for the known radio-quiet quasars and Seyfert 1 galaxies, and it was observed that the five objects with the lowest redshifts have very similar X-ray/optical luminosity ratios despite tenfold variations in X-ray luminosity. It is concluded that photoionization by a continuum extending to X-ray energies is the dominant excitation mechanism in radio-quiet quasars.

Grindlay, J. E.↗
NASA NTRS1980

Observations of Cygnus X-3 with the Einstein /HEAO 2/ X-ray Observatory The period derivative and the asymmetric X-ray light curve

Cygnus X-3 was observed by the Monitor Proportional Counter on the Einstein (HEAO 2) X-ray Observatory for 2.4 days in 1978 December. The analysis of the data from these observations is used in conjunction with a self-consistent re-examination of previous results from the Uhuru, ANS, COS B, and SAS 3 satellites to investigate earlier reports that the 4.8 hour period of Cygnus X-3 is increasing. It is found that there is indeed a period derivative, P = (1.78 plus or minus 0.40) x 10 to the -9th s/s, which confirms the principal conclusion of previous authors. The possibility that the X-ray source is in an elliptical orbit and that some, or all, of the observed period derivative may be due to apsidal motion is discussed. The elliptic orbit hypothesis explains the observed asymmetry in the average X-ray light curve and leads to the conclusion that the most likely companion to the X-ray source is a helium star, possibly with a light hydrogen envelope

Elsner, R. F.↗
NASA NTRS1980

Discovery of the optical counterpart of the transient X-ray burster Centaurus X-4

The paper deals with the discovery and subsequent study of the optical counterpart to an X-ray nova which is almost certainly the historical transient Centaurus X-4, first discovered in 1969 and then dormant for the past decade. It is shown that Cen X-4 is a clear example of a soft, transient X-ray burster. The most important consequence of the connection between bursters and soft transients is the support it gives to the hypothesis that bursters are accreting neutron stars in binary systems. The observations support the hypothesis that at least some of the light comes from an accretion disk, and that X-ray heating plays an important role in the optical emission.

Canizares, C. R.↗
NASA NTRS1980

Simultaneous X-ray and optical observations of the 7.7 second X-ray pulsar 4U 1626-67

Simultaneous X-ray and optical observations of the 7.7-s X-ray pulsar 4U 1626-67, obtained during May 29-31, 1978, reveal the presence of (1) intense, correlated optical and X-ray flares and (2) 7.7-s optical pulsations which agree in phase with the 1-3 keV X-ray pulsations to within 0.5 s (two standard deviations) and which agree in period to within 0.001 s (one standard deviation). From these data it is concluded that a substantial fraction (a minimum of 8%) and possibly all of the optical emission is produced from within approximately 0.5 light sec or 1.5 x 10 to the 10th cm of the neutron star. Furthermore, the data rule out the possibility that this optical emission comes from the X-ray heated surface of a degenerate or nondegenerate dwarf companion. It most likely comes from an accretion disk.

Mcclintock, J. E.↗
NASA NTRS1979

A spectroscopic study of the optical counterparts of three X-ray bursters

One of the major puzzles in galactic X-ray astronomy is the nature of the galactic bulge sources in general and the X-ray burst sources in particular. The answer to this puzzle is likely to come from studies of the faint blue optical counterparts which have been identified with several of these sources. As part of such a study, some results of a detailed investigation of the spectroscopic properties of the optical counterparts to three X-ray bursters - 4U 1735-44, 4U 1636-53, and MXB 1659-29.

Canizares, C. R.↗
NASA NTRS1979

The optical counterpart of GX 339-4, a possible black hole X-ray source

Optical studies of the galactic X-ray source GX 339-4 (4U 1658-48), which led to its recent identification as reported by Doxsey et al. (1979), are presented. Reddening and distance estimates are given, as well as evidence for optical variability on differing time scales. The emission-line spectra and UBV photometry suggest that GX 339-4 may be at about 8 kpc and have a main-sequence B star binary companion. Both the optical spectrum and optical/X-ray luminosity ratio for GX 339-4 may be similar to Cir X-1.

Grindlay, J. E.↗
NASA NTRS1979

A 3-s delay in an optical burst from X-ray burst source MXB1735-44

Analysis of the arrival times of X-ray and optical bursts from the X-ray burst source MXB1735-44 shows that the onset of one optical burst was delayed 2.8 sec with respect to the X-ray burst. Observations of the pulses are accurate to less than or equal to five ms. The delay in the optical pulse may be attributed to light travel time in the system and/or the time needed to reprocess X-rays into light.

Mcclintock, J. E.↗
NASA NTRS1978

Si XIII and Si XIV line emission search with the ANS crystal spectrometer

The final results of the search for Si XIII and Si XIV line emission, using the ANS Bragg crystal spectrometer, are presented. No positive line detection was achieved in any of the measurements made on several types of cosmic object; i.e., a transient X-ray source, close binary systems, supernova remnants, GX sources, and clusters of galaxies. Three-sigma upper limits for discrete line emission from these objects are reported and compared with line strengths inferred from other proportional-counter and Bragg spectrometer data. The present upper limit of 1.0 eV for the equivalent width of a narrow Si XIV line emission from the X-ray nova A0620-00 is an order of magnitude lower than previous limits set by other experiments.

Parsignault, D. R.↗
NASA NTRS1978

Intensity and spectral variability of strong galactic X-ray sources observed by ANS

Hard X-ray observations by the ANS are used to analyze the energy spectrum and intensity fluctuations on time scales of seconds to days for 20 luminous galactic sources, of which 11 are galactic-bulge (GX) sources having no obvious identification with source categories. It is found that: (1) most GX sources are best fitted in the energy range from about 1 to 20 keV by exponential spectra with a source temperature (kT) of approximately 5 keV; (2) iron line emission around 6.7 keV is always detected as a persistent spectral feature of at least six and possibly seven of the sources studied; (3) most of the iron-line sources exhibit a direct correlation between kT and intensity (I) in the band from 1.4 to 7.2 keV; (4) no burst source counterparts or candidates show a direct correlation between kT and I, at least two show an inverse correlation, and no iron line emission is detected at a 3-sigma level from burster counterparts during burst-active states. A classification scheme for GX sources is proposed, and several observational tests for this scheme and for possible source models are described.

Parsignault, D. R.↗
NASA NTRS1978

Photometric study of the X-ray pulsar 4U 1626-67

Results are reported for UBVR photometric observations of the optical candidate for the pulsating X-ray source 4U 1626-67. The data are found to be consistent with a constant V magnitude of approximately 19.00 and marginally consistent with constant B-V and U-B colors, but two averaged measures obtained about 2 hr apart suggest that the B-V and U-B colors are variable and that this variability may be entirely in U and B. Additional evidence for variability of the optical candidate is examined, and it is shown that the optical object is probably variable with a B amplitude of no more than about 0.5 mag and time scales as short as less than the order of 1 min. A power spectrum analysis reveals no significant peaks at or near the X-ray pulse period of 7.68 sec or its harmonics. It is concluded that although the optical data do not provide any additional evidence that 4U 1626-67 is a binary, a short-period binary system with the optical emission strongly dominated by an accretion disk is probably favored.

Grindlay, J. E.↗