H. Friedman

Discovery of X-ray pulsations in SMC X-1

Observations of SMC X-1 from an Aerobee rocket and an Apollo spacecraft have detected X-ray pulsations with a period of 0.716 s. The pulsed fraction in the 1.6--10 keV energy range is 25--35 percent. Evidence for significant pulse shape and pulsed fraction changes in the 0.6--1.6 keV range is also presented. The spectrum during both observations is fitted by a photon power law, 0.040 E/sup -0/./sup 8/. (AIP)

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

Soft X-ray emission in Eridanus: An old supernova remnant

Data are presented on the soft X-ray intensity and spectrum of a region of extended emission in the constellation Eridanus. This region also includes optical filaments, the hard X-ray source 3U 0431--10, the radio pulsar MP 0450, a neutral hydrogen shell structure, and an O VI absorption feature. It is suggested that these features are all part of an old supernova remnant with an age in the range 10/sup 5/--10/sup 6/ yrs. (AIP)

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.

High-resolution observations of X-ray sources at the galactic center

A region about 1 deg of arc in radius and centered on the galactic nucleus has been surveyed during a rocket flight, using X-ray detectors equipped with 10-arcmin by 4-deg (FWHM) collimators. The extended source 4U 1743-29 has been resolved into at least four discrete sources having luminosities (2-10 KeV) between 4 by 10 to the 36th power and 3.5 by 10 to the 37th power erg/s.

On X-ray line emission from Scorpius XR-1.

Scorpius XR-1 X ray emission spectra, discussing Fe emission line near 7 kev plasma models, supernova mass and cosmic abundance

Soft X-ray sources and supernova remnants in Cygnus - Rocket and Apollo-Soyuz results

Soft X-ray observations of the Cygnus region obtained from proportional counters aboard a rocket and also on the Apollo-Soyuz mission are reported. It is found that Cyg X-6, a source whose flux in confined to the 0.5-2.0-keV band, is a long narrow filament oriented nearly perpendicular to the galactic plane. This feature has a linear dimension greater than or of the order of 150 parsecs, and its spectrum is adequately described by an exponential. Another intense soft source whose flux is also confined to the 0.5-2.0-keV band has been discovered near Gamma Cygni. This source, designed Cyg X-7, has a spectrum characterized by a temperature of 1.5 to 5 million K and a hydrogen column density of at least 10 to the 21st power per sq cm. The possible association of Cyg X-7 with the supernova remnant DR 4 is discussed. An interpretation of this object in terms of the standard adiabatic spherical-shock-wave model yields plausible values for the free paramenters. HB 21, another old supernova remnant, has not been detected as a soft X-ray source.