Variations in the spectra and pulse period of GX 301-2
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Swank, J. H.↗
Engineering topics
Becker, R. H.
Publications and source records attributed to Becker, R. H..
X-ray emission from the supernova remnant G287.8-0.5
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Becker, R. H.↗
Spectra of Her X-1 near a turn-on in the 35-day cycle
X-ray spectra for Her X-l are presented for times before, during, and after a turn-on in the 35 day on-off cycle, as well as during an anomalous dip in the X-ray intensity. All four spectra are well represented by a power law of number index approximately .9 with a high energy cutoff near 20 keV. However, the column density of cold matter along the line of sight as estimated by the low energy cutoff varies substantially among the four intervals. The low level flux present prior to turn-on does not pulse and shows very little low energy absorption, in contrast to the X-rays observed during the turn-on and the anomalous dip. It seems likely that the pre-turn-on flux is composed of X-rays scattered into the line of sight by material away from the accretion disk.
Becker, R. H.↗
Spectral evolution of a long X-ray burst
An X-ray burst-like event with a peak intensity 1 1/2 times that of the Crab and a decay time of approximately 100s was observed. Significant spectral changes occurred during the burst. The spectra were best fit by the black form with kT ranging from .87 keV to 2.3 keV. They suggest a source with smaller dimensions than a massive black hole. A weak source was observed after the burst with a 10 keV thermal spectrum and an indication of iron line emission.
Swank, J. H.↗
X-ray observations of the Vela pulsar - Statistics and spectrum
The Vela pulsar (3U 0833-45) was observed in the range 2-60 keV by a proportional-counter experiment on board OSO-8 with temporal resolution sufficient to make possible a sensitive search for pulsed X-rays at the radio pulsar period. A statistical analysis yielded 8 percent as the 3-sigma upper limit on the pulsed fraction. The energy spectrum is fitted well by a structureless power law with number index 2.2 (+ or - 0.2) and absorption by a hydrogen column density of 2.9(+ or - 2.0) by 10 to the 22nd power per sq cm.
Pravdo, S. H.↗
Spectral variability in the X-ray pulsar GX 1 + 4
Observations of the galactic-center-region hard X-ray source GX 1 + 4 by the GSFC X-ray spectroscopy experiment on OSO-8 confirm that GX 1 + 4 is a slow X-ray pulsar. The amount of absorption by cold matter in the spectrum of GX 1 + 4 varies significantly within a 24-hour period, which is typical of many X-ray binary systems. The light curve for the pulsations from GX 1 + 4 appears to be energy-dependent.
Becker, R. H.↗
Observations of intensity and linear polarization of CTB 80 at 6 and 2.8 cm
The paper presents observations of the distribution of intensity and linear polarization over the radio source CTB 80 at 6 and 2.8 cm. The physical nature of the source is examined, particularly the relation between the strong central component and a ridgelike structure that extends across the northern half in the E-W direction. The structure, nonthermal spectrum, and polarization of the central component are found to be very similar to those of a supernova remnant, but the ridge is shown to be unlike any feature of any other SNR. It is suggested that the ridge may have resulted from expansion of the remnant shell into a dense interstellar cloud or, alternatively, that CTB 80 might be a nearby extragalactic radio source similar to Centaurus A.
Velusamy, T.↗
3.7 and 11.1 centimeter observations of the radio galaxy 3C 386
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Becker, R. H.↗
X-ray emission from the supernova remnant G287.8-0.5
The GSFC Cosmic X-ray spectroscopy experiment on OSO-8 observed a weak galactic X-ray source near theta 2 at 288 deg, b2 at -1 deg. The spectrum for this source between 2-20 keV is well represented by a thermal spectrum of kT = 7.34(+3.6), sub -2.6 keV with an intense iron emission line centered at 6.5 + or - .2 keV. The error box of the Uhuru source 4U1043-59, the only known X-ray source in our field of view, contains the radio supernova remnant G287.8-0.5. The possible association of the X-ray source with this supernova remnant is discussed.
Becker, R. H.↗
Variations in the spectra and pulse period of GX301-2
Spectra from observations of GX301-2 (3U1223-62) by the Goddard X-ray spectroscopy experiment on OSO-8 show an absorption edge due to cool iron with column densities of a few x 10 to the 19th power/cm squared. A decrease in intensity was associated with increased absorption and a spectrum similar to those of binary X-ray sources in absorption dips. Observed variations of the pulse period are consistent with Doppler shifts for reasonable orbit parameters.
Swank, J. H.↗
Iron line emission from a high-temperature plasma in Cassiopeia A
The letter reports a measurement of the X-ray spectrum of Cas A with a proportional counter on board OSO-8. The high-energy data (greater than 7 keV) are found to agree equally well with a power law having a number index of about 4.5 and with a thermal spectrum having kT of about 3.9 keV. A narrow iron line predicted by the thermal model is also observed; this line is centered at about 6.67 keV and has an equivalent width of approximately 1270 eV. The low-energy data (below 6 keV) are not fully accounted for by the above thermal spectrum, but are fitted well by an additional low-temperature thermal component with kT not exceeding 0.7 keV and an atomic hydrogen column density of approximately 10 to the 22nd power per sq cm. The iron abundance in the plasma at an electron temperature of 40 keV is estimated from the observed line-to-continuum ratio, and it is shown that a normal cosmic iron abundance is adequate to explain the observation.
Pravdo, S. H.↗
X-ray observations of the Vela pulsar: Statistics and spectrum
The Vela pulsar was observed in the range 2-60 keV by the GSFC proportional counter experiment onboard OSO-8 with temporal resolution sufficient to make possible a sensitive search for pulsed X-rays at the radio pulsar period. A statistical analysis yielded 8 per cent as the 3 sigma upper limit on the pulsed fraction. The energy spectrum is fit well by a structureless power law with number index 2.21 + or - 0.2 and absorption by a hydrogen column density of N sub H equals 2.9 + or - 2.0 times ten to the twenty-second power per sq.cm.
Pravdo, S. H.↗
Spectral variability in the X-ray pulsar GX 1+4
Observations of the galactic center region, hard X-ray source GX 1+4 by the GSFC X-ray spectroscopy experiment on OSO-8 confirm that GX 1+4 is a slow X-ray pulsar. The amount of absorption by cold matter in the spectrum of GX 1+4 varies significantly within a 24 hour period, behavior typical of many X-ray binary systems. The light curve for the pulsations from GX 1+4 appears to be energy dependent.
Becker, R. H.↗
High-resolution radio observations of three supernova remnants
The paper presents and discusses radio observations of three supernova remnants (G21.5-0.9, G29.7-0.3, and 3C 391) made at 3.7 and 11.1 centimeters. The supernova remnant G21.5-0.9 has an elliptical brightness distribution and is similar to the Crab Nebula as well as 3C 58 in appearance and spectrum. The two remnants G29.7-0.3 and 3C 391 both show a broken shell structure typical of most galactic supernova remnants.
Becker, R. H.↗
Iron line emission from a high temperature plasma in Cas A
The X-ray spectrum of Cassiopeia A was observed for several days by the proportional counter experiment on board OSO-8. The high energy ( 5 keV) data are fit well by a thermal spectrum. A narrow iron line which is predicted by the thermal model is also observed. The low energy (2-5 keV) data show an excess over the high temperature component which is consistent with the presence of an additional low temperature thermal component. Iron abundance in the source relative to normal cosmic abundance is discussed, as in the relation of this observation to shock wave and multi-component thermal models for supernova remnants.
Pravdo, S. H.↗
Cosmic X-ray observations with OSO-8
The GSFC Cosmic X-ray Spectroscopy experiment aboard OSO-8 has operated successfully since launch providing spectral and temporal data on X-ray sources in tha energy range 2-60 keV. Analysis of quick look data shows a variety of spectral features, some stable, others variable, which will increase understanding of the nature of individual sources. In particular, observed emission and absorption features that can be attributed to iron will result in abundance measures of this important element in sources such as some X-ray binaries, the supernova remnant Cas A, and the nucleus of the galaxy Cen A.
Serlemitsos, P. J.↗
OSO-8 observations of Hercules X-1
The X-ray binary Her X-1 was observed by the GSFC cosmic X-ray detectors aboard OSO-8 between August 26 and September 3, 1975. The results reported are based on quick look tapes which contain less than 10% of the total time spent on source. Spectra were observed during different phases of the binary period including the anomalous low state (dip) in X-ray intensity. The normal high spectra is well represented by a power law with a short cutoff above approximately 25 keV. A significant and varying enhancement in the intensity around 6.7 keV was observed, suggesting the presence of an iron line. Absorption was seen in the spectrum immediately following eclipse. The dip spectrum is found to be considerably flattened. Also spectra are presented for different phases of the pulse period.
Pravdo, S. H.↗
OSO-8 GSFC results on Cen X-3
Spectra of Cen X-3 during eclipse, in transition out of eclipse, and during several later phases of the binary orbit were obtained from quick look data of the July 16-25, 1975 observation by the Goddard X-ray spectroscopy experiment on OSO-8. In the high state there was no absorption turn over. Pulsations were present at least to 23 keV. The spectrum at the pulse minimum was flatter above 7 keV than that of the pulse peak. In transition out of eclipse Cen X-3 emerged above a small low energy flux seen during eclipse. The observations appear to indicate absorption by cold and ionized matter and the presence of iron in the companion's atmosphere. Decreased intensities were observed at late phases of some binary orbits in some cases corresponding to dips. Absorption appears although the low energy component remains. Variable features may be interpretable as absorption and emission by iron and possibly other trace elements.
Swank, J. H.↗