R. J. Thompson

ROSAT High Resolution Imager observations of PSR 0656 + 14

We have used the High Resolution Imager (HRI) on ROSAT to image PSR 0656 + 14 at soft X-ray energies. With a net observing time of 10,326 s, we obtained a source event rate of 0.382 +/- 0.007 counts/s. Comparing the radial distribution of these counts between 15 and 100 arcsec to an empirically derived point spread function for HRI soft sources, we find no evidence of a spatially extended X-ray nebula to a limiting surface brightness of 1.67 x 10 exp -6 counts/s/sq arcsec, corresponding to a limit of 14 percent of the observed flux out to a radius of 100 arcsec. The X-ray emission of the pulsar is pulsed at the 0.385 s period of the radio pulsar, with a pulse fraction of 7 +/- 2.2 percent and a FWHM of 0.10 s. We discuss some models of the X-ray radiation of PSR 0656 + 14 compatible with both the HRI and PSPC results.

Revised proper-motion results for the soft X-ray-emitting radio pulsar PSR 0656+14

A third set of astrometric observations of the soft X-ray-emitting radio pulsar PSR 0656+14 has been carried out with the NRAO Very Large Array. Our result for the magnitude of the proper motion, 0.070 sec +/- 0.010 sec yr(sup -1), is in agreement with our previously reported result based on the first two observations. The direction of motion, however, has been found to be 180 deg from that previously reported. This casts doubt on a proposed connection between this pulsar and the Gemini-Monoceros X-Ray Enhancement.

Active galactic nuclei with ultrasoft X-ray emission

The discovery of a class of AGN with clearly distinguishable soft X-ray components below 0.5 keV is reported. These AGN were detected through equivalent hydrogen column densities that are less than a few times 10 exp 20/sq cm. At least three kinds of AGN comprise this sample: low-redshift quasars and Seyfert galaxies that have only ultrasoft emission (these objects lack detectable hard X-ray emission); AGN that have both ultrasoft as well as hard X-ray components; and high-redshift quasars whose soft emission may originate, as proposed for the lensed quasar 0957 + 561, in an extended source or, alternately, in a source that is luminosity-enhanced due to relativistic beaming.

The proper motion of the soft X-ray-emitting radio pulsar PSR 0656+14

The VLA has been used to measure the motion of the soft X-ray-emitting radio pulsar PSR 0656+14 relative to background radio sources. From observations at epochs 1989.07 and 1990.38, its proper motion has been determined to be 0.078″ ± 0.012″ at position angle 294°. PSR 0656+14, as noted by Nousek and coworkers, is very close to the geometric center of a 20° diameter ring of soft X-ray emission. The present measurement, which shows that the direction of the pulsars motion is away from the center of the ring, strengthens the contention that the ring of soft X-ray emission is the 100000 year old supernova remnant of the pulsars progenitor.

The development of the quartz crystal oscillator industry of World War II

This paper offers a history of a critical episode in military and electronics history-the difficult creation of quartz crystal frequency control units for radio communications during World War II. As a means of controlling the frequencies of radio transmitters and receivers, amateur radio hobbyists quickly accepted the quartz crystal oscillator after its initial development in the late 1920s. The military, however, declined to adopt this technology until just prior to World War II. Due to the small market for crystal oscillators, no mass production industry had ever developed to produce this extremely high precision electronic component. As war engulfed the nation, the U.S. Army Signal Corps found itself in the dangerous position of having gambled the integrity of its communications equipment on a component that could not possibly be produced in the quantities immediately needed. This paper looks at the challenges the United States faced in building a crystal manufacturing capability and in supplying this industry with sufficient supplies of raw quartz. A fairly specialized component of communications technology emerged from spare beginnings in prewar amateur radio to become the very foundation of a wide range of electronic devices today.

A statistical analysis of the broadband 0.1 to 3.5 keV spectral properties of X-ray-selected active galactic nuclei

We survey the broadband spectral properties of approximately 500 X-ray-selected active galactic nuclei (AGNs) observed with the Einstein Observatory. Included in this survey are the approximately 450 AGNs in the Extended Medium Sensitivity Survey (EMSS) of Gioia et al. (1990) and the approximately 50 AGNs in the Ultrasoft Survey of Cordova et al. (1992). We present a revised version of the latter sample, based on the post publication discovery of a software error in the Einstein Rev-1b processing. We find that the mean spectral index of the AGNs between 0.1 and 0.6 keV is softer, and the distribution of indices wider, than previous estimates based on analyses of the X-ray spectra of optically selected AGNs. A subset of these AGNs exhibit flux variabiulity, some on timescales as short as 0.05 days. A correlation between radio and hard X-ray luminosity is confirmed, but the data do not support a correlation between the radio and soft X-ray luminosities, or between radio loudness and soft X-ray spectral slope. Evidence for physically distinct soft and hard X-ray components is found, along with the possibility of a bias in previous optically selected samples toward selection of AGNs with flatter X-ray spectra.

ROSAT observations of X-ray-selected active galactic nuclei

We have observed sample of six optically faint, X-ray-selected active galactic nuclei with the Roentgen Satellite (ROSAT) Position Sensitive Proportional Counter (PSPC). These objects represents a sample of soft and hard spectrum sources; all were observed previously with the Einstein X-Ray Observatory. Included in this sample is EO132.8-4111, whose soft X-ray and ultraviolet flux distributions bear a striking resemblance to that of Mrk 841, but whose relative hard X-ray emission is much less than that of Mrk 841. The spectra are all fitted satisfactorily with single power-law models and their spectral indices (with one exception) agree with those estimated from the Einstein Image Propotional Counter (IPC) observations. Tests of short-term variability are carried out, with all sources showing constant count rates over the period of their ROSAT observations. Some sources do, however, show significant changes in count rate when compared to previous Einstein data taken a decade earlier.

Towards a complete sample of ultrasoft X‐ray emitting AGN

In the course of selecting ultrasoft X‐ray‐emitting objects from the data base of the Einstein Observatory, we have found a class of active galactic nuclei with clearly distinguishable soft X‐ray components below 0.5 keV. The spectrum or the soft emission corresponds to that of a ∼10 eV blackbody. These AGN have necessarily been detected through equivalent hydrogen columns densities that are less than a few times 1020 cm−2. At least three kinds of AGN comprise this sample: (1) low redshift quasars and Seyfert galaxies that have only ultrasoft emission: these AGN lack detectable hard X‐ray emission; (2) AGN that have both ultrasoft as well as hard X‐ray components; for some of these objects multiple observations exist which show that the components may be independently variable; and (3) high redshift quasars whose soft X‐ray emission may originate, as in the case of the lensed quasar 0957+561, in an extended source, or in a source that is luminosity‐enhanced due to relativistic beaming. This report represe...

Building an industry from scratch: the quartz oscillator industry of World War II

Prior to World War II, the use of quartz crystal oscillators for frequency control took place primarily within the domains of the amateur (or ham) and the commercial radio broadcasters. The oscillator manufacturing industry, such as it was, was able to accommodate this small market through an artisan (i.e., making oscillators one at a time by hand) rather than a mass production approach. With the U.S. militarys switch to crystal control just prior to the war, the reality of crystal oscillator production changed dramatically. With the coming of war, the military suddenly needed millions of oscillators, a task far beyond the current industry which had never produced more than 100,000 units in a single year. Within a year, a truly mass-production industry was up and running, producing almost 6 million units in 1942 alone (and over two million units per month by the end of the war). This paper gives an overview of the war-time development of this most important industry.

SOFT X-RAY ANALYSIS AND MULTIWAVELENGTH MODELING OF X-RAY SELECTED ACTIVE GALACTIC NUCLEI

We survey the broadband spectral properties of ~500 X-ray-selected Active Galactic Nuclei (AGN) observed with the Einstein X-ray Observatory in order to better understand the X-ray emission characteristics of this population as compared to previously studied optically- and radio-selected populations. We further select a subsample of X-ray-selected AGN which possess strong components of soft X-ray emission below ~0.5 keV. This sample is used to investigate in greater detail this ultrasoft emission and to search for possible correlations between it and emission at other wavelengths. These ultrasoft sources are used for multiwavelength accretion disk modeling in a test of the current black hole plus accretion disk paradigm of AGN energy generation. We find the mean spectral index of the AGN between 0.1 and 0.6 keV to be softer, and the distributions of indices wider, than previous estimates based on analyses of the X-ray spectra of optically-selected AGN. We confirm a correlation between radio and hard X-ray luminosity, but find that the data do not support a correlation between radio and soft X-ray spectral slope. We report evidence for physically distinct soft and hard X-ray components. Imaging photometry in the J, H, and K infrared bands is carried out for a sample of eight AGN. The infrared images show the AGN to be primarily point sources, with little extended emission from the host galaxy. The photometric measurements represent part of a multiwavelength database to be used for accretion disk modeling. We report observations of six AGN in the ultraviolet region with the International Ultraviolet Explorer satellite. The ultraviolet spectra from these observations are used for measurement of the strengths of the emission lines present (e.g., Ly-alpha, CIV, and CIII]). The data also allow a measurement of the shape of the ultraviolet continua of these AGN to be used further in multiwavelength accretion disk modeling. Observations of a sample of six optically faint, X-ray-selected AGN with the ROSAT Position Sensitive Proportional Counter are reported. The spectra of the AGN are all fit satisfactorily with single power-law models and their spectral indices (with one exception) agree with those estimated from their Einstein IPC observations. Tests of short term variability are carried out, with all sources showing constant count rates over the period of their ROSAT observations. Some sources do show significant changes in count rate when compared to previous Einstein data taken a decade earlier. The measurements of the soft X-ray spectra of these objects are combined with the infrared and ultraviolet data discussed above to carry out multiwavelength accretion disk modeling. Accretion disk modeling is carried out on a sample of five Seyfert I galaxies possessing strong optical-ultraviolet-soft X-ray emission components. It is found that while bare accretion disk models cannot account for the soft X-ray emission observed in these objects, the addition of a hot (kTe~120 keV), Comptonizing component enables the soft X-ray emission to be accounted for within the black hole plus accretion disk paradigm.