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Ulmer, M. P.

Publications and source records attributed to Ulmer, M. P..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

A search for extended halos of hot gas in the Perseus, Virgo, and Coma Clusters

Observations of the Perseus cluster by the HEAO 1 satellite have revealed a faint X-ray halo extending at least 2.5 deg from the center and contributing between 5% and 20% to the total luminosity. This may be of nonthermal origin, but it also may be explained in terms of hot gas bound by the gravitational field of the cluster. Statistical uncertainties made it impossible to detect any such halo in the Coma cluster. Observations of the Virgo cluster confirmed the detection by the Ariel 5 satellite of a broad region of faint X-ray emission (core radius 60 arcmin). If the very extended X-ray emission from Virgo is due to hot intracluster gas, the density of this gas is lower than expected from a consideration of gas and galaxy densities in the Perseus cluster.

Ulmer, M. P.↗
NASA NTRS1980

The X-ray light curve of 4U 2129+47

The light curve of 4U 2129+47 is presented showing that it almost certainly has a period of approximately 0.22 days. This is the same period as the optical candidate proposed by Thorstensen et al. (1979). Binary X-ray source models, consisting of an M dwarf plus either a neutron star or a white dwarf, are briefly discussed.

Ulmer, M. P.↗
NASA NTRS1980

An X-ray survey of distant rich clusters of galaxies with HEAO 1

The paper presents a 1-10-keV survey of distance class 4, 5, and 6 Abell clusters using the HEAO 1 NRL large area survey experiment. The survey is a little less than 1/30 of the Abell catalog. Eleven clusters are identified with X-ray sources, and X-ray upper limits are provided for 60 others.

Ulmer, M. P.↗
NASA NTRS1979

HEAO 1 observations of 4U1232+07

An analysis of the NRL HEAO 1 observations of the Virgo cluster and 3C 273 has revealed X-ray emission from a region between these two objects. The most satisfactory explanation is the presence of two weak X-ray sources, for which error boxes have been obtained. One source is likely to be the peculiar galaxy IC 3576, suggested by Margon et al. (1972) as the source 2U 1231+07=4U 1232+07. The error box resulting from combining the present observations with the 4U data strengthen the X-ray identification with this extremely interesting galaxy. There are numerous possibilities for the other X-ray source, including the interacting pair of galaxies NGC 4410a and NGC 4410b (NGC 4410a/b).

Bhavsar, S. P.↗
NASA NTRS1979

Further analysis of SAS 3 observations of the rapid burster /MXB 1730-335/

SAS 3 observations of the rapid burster MXB 1730-335 are analyzed with specific reference to the rapidly repetitive type II bursts and also the type I bursts. It is found that: (1) there are two stable patterns in the recurrence of the rapidly repetitive type II bursts, designated modes I and II; (2) the range of type II burst energies is a factor of about 100 for mode I and a factor of about 10 for mode II; (3) type II burst spectra are best fitted by a blackbody of constant temperature (of the order of 18 million K), constant column density, and decreasing intensity; and (4) type I bursts are best fitted by a blackbody spectrum with decreasing temperature (approximately 24 million K during the first few seconds and 16 million K about 10 sec later). The spectral fits for both types of burst are shown to yield sizes for the emission region comparable to the radius of a neutron star. A model for the rapid burster is suggested.

Marshall, H. L.↗
NASA NTRS1979

Diffuse X-ray emission from Abell clusters 401 and 399 - A gravitationally bound system

The X-ray emission from the Abell 401-399 region has been studied using data obtained by the A-1 proportional counter aboard HEAO 1 in two different ways. The first involved routine scanning of the region during the all-sky survey, and the second was an observation in which the instrument was pointed at A401 during a lunar occultation. The emission is shown to be unusually extended and to be centered on a point lying between A401 and A399. The best fit of a uniform disk model to the data yielded a radius of 25.5 + or -4.4 arcmin for the lunar occultation and 42 + or - 17 arcmin for the scans. A possible explanation of the results is that A401 and A399 are both diffuse cluster X-ray sources. Alternatively, the emission may come from a large gas cloud of at least 10 to the 15th solar masses enveloping both clusters.

Ulmer, M. P.↗
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.↗
NASA NTRS1977

Observations of NGC 4151 from Uhuru

Uhuru X-ray observations of NGC 4151 over the energy range from 2 to 10 keV are reported. A best-fit exponential power-law spectrum with a constant of 0.0096 and a spectral index of -0.1 is determined for the cited energy range. A comparison with Ariel 5 results indicates that a previously reported intensity variation was accompanied by a change in spectral shape. It is suggested that the X-ray source might have two components.

Ulmer, M. P.↗
NASA NTRS1977

Some further information on the rapid burster MXB 1730-335

Further analysis of SAS-3 data on the rapid burster MXB 1730-335 show the existence of anomalous bursts. They have approximately 3-s rise times and low peak intensities; they also violate the energy vs. interburst-interval relationship for normal bursts. The short normal bursts of about 4-s duration do not show a long tail such as observed in the long normal bursts. Evidence for time structure in normal bursts down to a time scale of 50 ms is presented. No periodic variations in the total X-ray flux were found in the 1-500-Hz range.

Ulmer, M. P.↗
NASA NTRS1976

Observations of high-latitude X-ray sources with the Uhuru satellite

Uhuru observations of 22 unidentified high-galactic-latitude X-ray sources over the period from December 1970 to April 1973 are analyzed. The results confirm the existence of at least 19 sources, improve the positions for several of them, and yield evidence that some are variable. Two sources, 3U 0042+32 and 3U 1809-50, are found to be variable at the 3-sigma level. The improved positions for 3U 1555+27 and 3U 0405+10 confirm that these sources are, respectively, the Abell galaxies A2142 and A478.

Murray, S. S.↗
NASA NTRS1975

Observations of the Circinus X-1 region

The X-ray telescope on board the OSO-7 satellite has provided observations of the Cir X-1 region for over 110 days between December 1971 and March 1973. Although statistically significant fluctuations in the 7- to 11-keV flux were measured, no periodicities in the range between 5 hours and 100 days were found to an upper limit of about 40 percent amplitude. Intensities in the 7- to 57-keV range show variability by a factor of approximately 25 and changes in the spectral shape reflected by a number spectral index varying from about 1.1 to about 3.0. There is a positive correlation between intensity and spectral shape, with a steeper spectrum at times of peak intensity. Although power-law, exponential, and blackbody spectral shapes are equally good fits to these data alone, examination of all the available data appears to rule out a simple blackbody spectrum, at least at times of maximum intensity.

Baity, W. A.↗