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  • ASTROPHYSICS  (11)
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  • 1
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    On the nature of soft gamma repeaters (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The nature of soft gamma repeaters (SGRs) is discussed on the basis of data available for the March 5, 1979 superburst described by Cline et al. (1982) and for the less intense bursts detected by instruments on board Venera 11/12 and 13/14. It is argued that the three known SGR bursters can be explained most economically and consistently as belonging to a single class, with source distances of tens of kiloparsecs. The viability of several proposed models developed for the SGR energy release mechanism is examined.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 366; 240-252
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  • 2
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    Intense X-ray flares from active stellar systems - EV Lacertae and HD 8357 (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The HEAO A-1 Sky Survey Experiment included X-ray data used to define light curves for the flare star EV Lac and for X-ray flares observed in the binary system HD 8357. The data were taken during flare events and were detailed enough to calculate the flare rates and flaring luminosities. The peak luminosities during flares were several times the luminosities in normal X-ray flares emitted by the objects. Peak luminosities reached 30-50 times the normal variations and were associated with an order of magnitude increase in energy output. EV Lac was sufficiently active to be recommended for inclusion in future X-ray monitoring programs.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 284; 270-277
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  • 3
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    H0547-14 - X-ray flux from a weak gamma-ray burst? (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Data concerning a fast X ray transient observed by the HEAO 1 on March 17, 1978 are discussed. The object, labeled H0547-14, was located in Lepus, with galactic coordinates 219.37 deg longitude, b = -20.12 deg in the anticenter direction. A 10 sec scan of the transient was obtained with proportional counter detectors. An X ray luminosity of more than 5.1 x 10 to the 31st ergs/sec was measured as a lower limit, with the decay taking 17 min. A lower limit to the flare was set at 30 sec. The flux intensity resided in the range 4.4/1 billion-4/100 million erg/sq cm per sec, with a rise time of a factor of 10 in about 5 sec. Possible characterizations of the object, as either a gamma ray burst or as an M dwarf star, are discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 269; June 15
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  • 4
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    Millisecond variability of Cygnus X-1 (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: 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.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 278; 288-297
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  • 5
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    An X-ray survey of clusters of galaxies. IV - A survey of southern clusters and a compilation of upper limits for both Abell and southern clusters (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The results of the HEAO 1 A-1 X-ray survey of galaxy clusters are reported. X-ray error boxes and intensities are presented for all clusters in the Abell catalog and for the catalog of southern clusters and groups compiled by Duus and Newell (1977). A correlation is derived on the basis of the X-ray luminosity function for 2-6 keV which may be used to calculate the contribution of clusters to the diffuse X-ray background at different energies. The cluster X-ray is estimated to be 9.3 percent (+ 1.9 or - 1.5 percent). Correlations between X-ray luminosity and other cluster properties are exmained, and it is found that the distribution of upper limits may be applied to obtaining a more precise estimate of the average X-ray luminosity of clusters. The Abell richness class and southern cluster concentrations were strongly correlated with X-ray luminosity. Correlations between optical x-ray luminosity and optical radius velocity dispersion, spiral fraction, and radio power are analyzed. The evidence for all these correlations was considered to be weak because of poor scatter in the data.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 56; 403-506
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  • 6
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    Discovery of a 7.1 hour period and eclipses from MXB 1659-29 (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A 7.1 hr period has been discovered in the X-ray emission from the 'transient' X-ray burst source MXB 1659-29. Erratic variations in X-ray flux are seen during approximately 25 percent of the 7.1 hr cycle; at the end of this period, a stable dip in the flux occurs. Further analysis indicates that this dip is, in all probability, an eclipse by the companion star in the low-mass binary system. The short (about 15 minute) eclipse duration is used to refine the period determination (7.114104 + or - 0.000168 hr) and to constrain the companion star mass and binary system parameters. The companion star is found to be in the range 0.25-0.9 solar mass; probabilistic arguments and observations of cataclysmic variables with comparable periods indicate that the companion star is most likely less massive than the standard theories would indicate.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 283; 765-773
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  • 7
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    New evidence on the nature of the neutron star and accretion flow in Vela X-1 from pulse timing observations (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: It is believed that variations in the intrinsic pulse frequencies of neutron star X-ray sources reflect changes in the rotation rate of the stellar crust produced by torque originating outside and inside the star. The external torque depends on the flow pattern of the accreting plasma, while the internal torque depends on the state of the interior and its coupling to the crust. Information about the accretion flow and the star itself can, therefore, be obtained on the basis of a study of intrinsic frequency variations. The present investigation is concerned with the results of a detailed study of the 283 s pulsing X-ray star Vela X-1 using pulse timing techniques. It is found that the frequency variations in this source are consistent with the occurrence of a succession of temporally unresolved events which can be characterized mathematically as second-order red noise in the pulse phase.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 283; L53-L56
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  • 8
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    An 80 day X-ray light curve of 3C 371 (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The Large Area Sky Survey (LASS) experiment on HEAO 1 that monitored the N galaxy/BL Lacertae object 3C 371 from August 19 to November 7, 1977 is discussed, noting that statistically significant threefold or larger intensity variations were observed in the flux range 0.5-20 keV. It is found that the degree of variability depends on the time of observation, with the source sometimes appearing constant and sometimes changing on time scales of 1 to 2 weeks. Also observed was an X-ray flare that lasted approximately 25 days. The total 80-day X-ray light curve is seen as suggesting either a superposition of X-ray flares or a variable injection rate that changes on weekly time scales. The observed X-ray flux is found to be consistent with that expected by extrapolating the nonthermal optical spectrum, suggesting that the optical to X-ray flux could be synchrotron radiation, provided that it is possible to account for the patterns of variability seen at optical and X-ray wavelengths and to dispose of inverse Compton difficulties.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 259
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  • 9
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    X-ray variability of Scorpius X-1 during a multiwavelength campaign (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: Consideration is given to the X-ray variability of Scorpius X-1, which was observed with Ginga on March 9-11, 1989 as part of a multiwavelength campaign. The temporal characteristics observed, including quasi-periodic oscillations, HF noise, and VLF noise, are consistent with previous observations of Sco X-1. Quasi-periodic oscillations are observed on both the normal branch and the lower flaring branch, but not on the upper flaring branch. Limits are placed on the fractional rms variation of quasi-period oscillations on the upper flaring branch of less than or approximately equal to 2 percent of the total intensity. The characteristics of the observed red noise components are found to vary along the flaring branch. The fractional rms variation of VLF noise increases from less than 2 to greater than 6 percent as Sco X-1 moves from the flaring branch-normal branch vertex to the upper end of the flaring branch.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 396; 1 Se; 201-218
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  • 10
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    Searches for millisecond pulsations in low-mass X-ray binaries (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: High-sensitivity search techniques for millisecond periods are presented and applied to data from the Japanese satellite Ginga and HEAO 1. The search is optimized for pulsed signals whose period, drift rate, and amplitude conform with what is expected for low-class X-ray binary (LMXB) sources. Consideration is given to how the current understanding of LMXBs guides the search strategy and sets these parameter limits. An optimized one-parameter coherence recovery technique (CRT) developed for recovery of phase coherence is presented. This technique provides a large increase in sensitivity over the method of incoherent summation of Fourier power spectra. The range of spin periods expected from LMXB phenomenology is discussed, the necessary constraints on the application of CRT are described in terms of integration time and orbital parameters, and the residual power unrecovered by the quadratic approximation for realistic cases is estimated.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 379; 295-309
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