Edwin M. Kellogg

Chandra Observation of Abell 2142: Survival of Dense Subcluster Cores in a Merger

We use Chandra data to map the gas temperature in the central region of the merging cluster A2142. The cluster is markedly nonisothermal; it appears that the central cooling flow has been disturbed but not destroyed by a merger. The X-ray image exhibits two sharp, bow-shaped, shocklike surface brightness edges or gas density discontinuities. However, temperature and pressure profiles across these edges indicate that these are not shock fronts. The pressure is reasonably continuous across these edges, while the entropy jumps in the opposite sense to that in a shock (i.e., the denser side of the edge has lower temperature, and hence lower entropy). Most plausibly, these edges delineate the dense subcluster cores that have survived a merger and ram pressure stripping by the surrounding shock-heated gas.

Discovery of a periodic pulsating binary X-ray source in Hercules from Uhuru.

We have discovered a new pulsating X-ray source with a 1.24-sec period in the constellation Hercules. Analysis of 5 months of data has shown the existence of periodic variations in the intensity of the source and correlated sinusoidal variations in the period of the 1.24-sec pulsations. As in the case of the pulsating X-ray source Cen X-3, we interpret this effect as due to an occulting binary system, with the intensity changes due to occultation of the X-ray source by its companion and with the sinusoidal variations in the period of the 1.24-sec pulsations due to the Doppler effect. In addition, we have observed a longer-time scale cycle in which the source is bright and pulsing for approximately 9 days during which we can observe the 1.7-day occulting, followed by approximately 27 days during which the source is not detected above background on individual 20-sec scans.

The UHURU catalog of X-ray souces.

A catalog of X-ray sources observed with the Uhuru satellite is presented. About 70 days of data have been analyzed for this catalog resulting in 125 sources. Approximately two-thirds of the sources are located within plus or minus 20 deg of the galactic plane. Some of the sources at higher galactic latitudes are identified with known extragalactic objects. Most of the strong sources near the galactic plane are found to be variable.

Discovery of the binary nature of SMC X-1 from Uhuru.

Analysis of data spanning a year of observations of the pulsating X-ray source Cen X-3 from Uhuru has revealed the existence of periodic variations in intensity of the source and correlated sinusoidal variations in the period of the 4.8-sec pulsations. We interpret this effect as due to an occulting binary system. The changes in intensity are then due to occultation of the X-ray source by a large massive companion, and the sinusoidal variations in the period of the 4.8-sec pulsations are due to Doppler effect. Physical parameters for the system are derived, and evidence for the existence and nature of an extended atmosphere surrounding the massive occulting object is discussed.

DISCOVERY OF PERIODIC X-RAY PULSATIONS IN CENTAURUS X-3 FROM UHURU.

Large amplitude periodic X ray pulsations from Centaurus X-3, observing abrupt source intensity and pulse rate changes

Further X-ray observations of Hercules X-1 from Uhuru.

Recent data are presented concerning the X-ray source Hercules X-1. Details of the 1.24-second pulse shape and its variability are shown. The 1.24- second period is observed to decrease with time, with an overall change of 4.5 mu s between 1972 January and July. The X-ray intensity shows regular on states lasting 11 or 12 days followed by 24-day off states. While ihe source turu-on is not strictly periedic, the shape of the on state can be used to determine a period of 34.88 plus or minus 0.12 days for this cycle. The source turn-ons are found to only occur at one of two well-defined phases in the 1.7-day orbit. In addition to the regular 1.7-day eclipses, regular dips in the X-ray intensity are seen, whose occurrence is related to the orbital phase. These dips are interpreted as absorption by gas in thc system. (auth)

High‐resolution imaging x‐ray detector

We describe an x‐ray detector using microchannel plates as a photocathode surface and imaging photoelectron multiplier, and a crossed wire grid as a two‐dimensional position‐sensitive detector. The position resolution is σ=10 μ. The crossed wire grid consists of 100‐μ‐diam wires on 200‐μ centers. Position sensing is accomplished by electronic interpolation to 1/20 of the wire spacing. The quantum efficiency of the microchannel plates varies from 29% at 0.28 keV to 5% at 3 keV. This detector will provide second‐of‐arc x‐ray imaging in the focal plane of the 342.9‐cm focal length grazing incidence telescope now being prepared for the HEAO‐B observatory. By addition of suitable photocathodes, it can be used for single‐photon imaging light detection in uv, visible, and near ir as well. In all cases, it gives a very low dark counting rate, allows timing of individual events to 1 μsec or less, and can handle counting rates up to 104 sec−1.

The X-Ray System R Aquarii: A Two-sided Jet and Central Source

We report Chandra ACIS-S3 X-ray imaging and spectroscopy of the R Aquarii binary system that show a spatially resolved two-sided jet and an unresolved central source. This is the first published report of such an X-ray jet seen in an evolved ∼2–3 M, stellar system. At keV, the X-ray jet extends to both the northeast E ! 1 (NE) and southwest (SW) relative to the central binary system. At keV, R Aqr is a pointlike source 1 ! E ! 7.1 centered on the star system. While both 3.5 cm radio continuum emission and X-ray emission appear coincident in projection and have maximum intensities at ∼7 .5 NE of the central binary system, the next strongest X-ray component is located ∼30 SW of the central binary system and has no radio continuum counterpart. The X-ray jets are likely shock-heated in the recent past and are not in thermal equilibrium. The strongest SW X-ray jet component may have been shocked recently since there is no relic radio emission as expected from an older shock. At the position of the central binary, we detect X-ray emission below 1.6 keV consistent with blackbody emission at K. There is also a prominent 6.4 keV feature, a possible fluorescence or collisionally 6 T ∼ 2 # 10 excited Fe Ka line from an accretion disk or from the wind of the giant star. For this excitation to occur, there must be an unseen hard source of X-rays or particles in the immediate vicinity of the hot star. Such a source would be hidden from view by the surrounding edge-on accretion disk. Subject headings: binaries: symbiotic — circumstellar matter — radio continuum: stars — stars: individual (R Aquarii) — stars: winds, outflows — white dwarfs — X-rays: general

X-ray observations of the Virgo cluster, NGC 5128, and 3C 273 from the Uhuru satellite

M87, Cen A NGC 5128 and 3C 273 X ray emission observations in Virgo cluster, using Uhuru satellite

OBSERVATIONS OF THE EXTENDED X-RAY SOURCES IN THE PERSEUS AND COMA CLUSTERS FROM UHURU.

The X-ray source in Perseus identified as NGC 1275 is found to have a finite angular extent of about 35 arc minutes. The improved location of the center of the emission is consistent with NGC 1275. An improved location for the center of the Coma X-1 source is consistent both with the kinematic center of the cluster and with NGC 4874. These extended sources - Coma, Perseus, and the source in the Virgo cluster - may be a new class of X-ray objects associated with active galaxies in rich clusters.