John Fred Meekins

X-ray Pulsar in the Crab Nebula

X-ray pulsations have been observed in the Crab Nebula at a frequency closely matching the radio and optical pulsations. About 5 percent of the total x-ray power of the nebula appears in the pulsed component. The x-ray pulsations have the form of a main pulse and an interpulse separated by about 12 milliseconds.

Observations of outbursts from the recurrent X-ray transient A0538-66 and LMC X-4

Nine X-ray outbursts from the LMC have been observed with the HEAO 1 Large-Area Sky Survey Instrument. Some are shown to originate in the recurrent transient A0538-66, confirming the proposed 16 day periodicity and showing that the duration of the events can be as long as 14 days or as short as a few hours. Deviations from precise periodicity can be attributed to phase jitter or to a change in period occurring around the time of an exceptionally long outburst. Other outbursts which are irregular and consistently shorter originate in LMC X-4. A long-term light curve indicates that the LMC X-4 outbursts occur only when the source is in a high state, but are not strongly correlated with the binary phase.

Optimization of layered synthetic microstructures for broadband reflectivity at soft x-ray and EUV wavelengths.

A technique is described which allows the thickness of each layer in a layered synthetic microstructure to yield a useful constant efficiency over a broad band of wavelengths, several hundred angstroms wide, in the soft x-ray and EUV wave bands.

Observations of the Soft X-Ray Background,

Abstract : Observations of the diffuse X-ray background over a hemisphere of the sky in the galactic anticenter direction provide clear evidence for an excess intensity below 1 keV in all directions. The correlation of this low energy flux with galactic latitude and with hydrogen column density implies that the radiation originates partially within and partially outside the absorbing layers of the Galaxy. (Author)

X-ray line and continuum spectra of solar flares from 0.5 to 8.5 angstroms.

Two crystal spectrometers aboard the orbiting solar observatory OSO-4 cover the wavelength ranges 0.5 to 3.9 angstroms and 1.0 to 8.5 angstroms. Within this range, there appear emission lines from hydrogen-like and helium-like states of calcium, sulfur, silicon, magnesium, and aluminum. The Mg XII Lyman-α is present strongly in all x-ray flares. The most intense flares (such as class 3) produce strong Si XIV Lyman-α and often S XVI Lyman-α. Emission, in the form of Ka lines of highly ionized states of calcium, iron, aluminum, and silicon is usually present. The continuum from 1 to 10 angstroms always dominates the line emission by more than an order of magnitude. Electron temperatures derived from the slope of the continuum spectrum are in the range of 107 to 108 �K, considerably higher than theoretical ionization equilibrium temperatures.

Millisecond variability of Cygnus X-1

The May 7, 1978 HEAO 1 spacecraft observations of Cygnus X-1 with a 10 microsec time resolution have revealed 3 ms variability, as well as a 300 ms component and features which extend to 6 s. Emission on time scales shorter than 1 s can be approximately modeled as a superposition of uncorrelated 3 ms and 300 ms shot contributions, both with peak luminosities near 10 to the 37th ergs/s, and with shot rates of about 10/s and 0.2/s, respectively. The 3 ms variability is consistent with the time scales expected for variability near the inner edge of a viscous accretion disk that surrounds a 10-solar mass black hole.

X-ray spectra of several discrete cosmic sources.

Abstract : Spectra of Scorpius XR-1, Cygnus XR-1, and Cygnus XR-2 are derived for the 1.5-13 keV photon energy range from proportional counter measurements made on September 8, 1967. (Author)

The X-ray spectra of the Crab Nebula and NP 0532

Crab Nebula and pulsar NP 0532 X ray spectra discussing pulse profile, emission and interstellar absorption

Evidence for coherent emission with a 12 millisecond period during a burst from MXB 1728--34

Four bursts of MXB 1728--34 have been observed with the HEAO A-1 instrument using 5 ms timing resolution. The rapid initial rise has been resolved in all four bursts. Fourier analysis indicates the presence of a periodic component with a 12.2 ms period during one of the bursts. Epoch-folding analysis confirms this period and further indicates that the period decreases with time, with dP/dt = 10/sup -6/. The signal has a probability of 2.5 x 10/sup -9/ to occur at random, and an expectation of 3 x 10/sup -3/ to occur in the number of epoch folding performed.

Identification of a faint X-ray source with the W Ursae Majoris star VW Cephei

The NRL instrument aboard the HEAO 1 satellite has detected a faint X-ray source, which has been identified tentatively with the contact binary star (W UMa variable) VW Cephei. Its luminosity is between 3 x 10/sup 30/ and 4 x 10/sup 31/ ergs s/sup -1/ (0.1--10 keV), and the results suggest some variation of the X-ray flux with phase.