Iron line emission from X-ray sources

Iron line emission from X ray source

Millisecond temporal structure in Cyg X-1

Evidence is presented for the X-ray variability of Cyg X-1 on time scales down to a millisecond. Several bursts of millisecond duration are observed. The duty cycle for bursting is estimated to be approximately greater than. 0002 averaged over the entire 49. second exposure, although the maximum burst activity is associated with a region of enhanced emission lasting about 1/3 second. Such bursts may be associated with turbulence in disk accretion at the innermost orbits for a black hole

What is special about Cygnus X-1?

The X-ray evidence from several experiments is reviewed, with special emphasis on those characteristics which appear to distinguish Cygnus X-1 from other compact X-ray emitting objects. Data are examined within the context of a model in which millisecond bursts are superposed upon shot-noise fluctuations arising from events of durations on the order of a second. Possible spectral-temporal correlations are investigated which provide additional evidence that Cygnus X-1 is very likely a black hole

A new measurement of the Her X-1 X-ray pulse profile

A triple peaked 1.24 sec. pulse profile in a 1-minute rocket borne exposure to Her X-1 was measured, in contrast to the doublepeaked profiles expected from models which maximize the X ray emission at the magnetic equator of an accreting neutron star. The profile exhibits statistically significant energy dependence, with the emission approximately greater than 12 keV having narrower peaks which lag (by approximately 5% of the pulse period) the corresponding peaks at lower energies. Approximately one third of the total emission from the source is nonpulsed

Long-term studies with the Ariel 5 ASM. 2: The strong Cygnus sources

The three bright 3-6 keV X-ray sources in Cygnus are examined for regular temporal variability with a 1300-day record from the Ariel 5 All Sky Monitor. The only periods consistently observed are 5.6 days for Cyg X-1, 11.23 days for Cyg X-2, and 4.8 hours for Cyg X-3

A change in the X-ray spectrum of MK 421

HEAO-1 experiment A-2 observations of the BL Lac object MK421 in May 1978 show a marked spectral change from the OSO-8 observations of May 1977. The source was not detected above 10 keV in May 1978. The 2-10 keV spectrum could be well fit by a power law of energy slope 2.2 is less than or minus 4.2; thermal bremsstrahlung models with T less than 2 X 10 to the 7th power deg K are also acceptable. There was no indication of any low energy turnover, so that the inferred column density N sub H is less than 7 X 10 to the 21st power at/sq cm. The total flux is consistent with an extrapolation of the UV data from IUE, but the slope is not consistent with the UV slope. Possible models for the origin of the spectral transition are discussed

X-ray spectra of Hercules X-1. 2: Intrinsic beam

The X-ray spectrum of Hercules X-1 was observed in the energy range 2-24 keV with sufficient temporal resolution to allow detailed study of spectral correlations with the 1.24 sec pulse phase. A region of spectral hardening which extends over approximately the 1/10 pulse phase may be associated with the underlying beam. The pulse shape stability and its asymmetry relative to this intrinsic beam are discussed

Long-term X-ray studies of Sco X-1

No modulation of the 3-6 keV X-ray intensity of Sco X-1 at a level of excess of 1% was observed at the optical period of .787313d. Evidence is found for shot-noise character in a large fraction of the X-ray emission. Almost all of the Sco X-1 emission can be synthesized in terms of approximately 200 shots per day, each with a duration of approximately 1/3 day. A pinhole camera was used to obtain data and the data were statistically analyzed

Recurrent X-ray outbursts from Aquila X-1

Aquila X-1 observations by the All Sky Monitor on Ariel 5 are presented. Data is compared with that obtained by rocket survey, and by the Uhuru, OSO 7, and OAO 3 satellites. The variability of brightness is discussed as a connection between dwarf novae and long term transient X ray sources

Evidence for a 16d.6 period from Circinus X-1

Analysis of All-Sky Monitor observations of Cir X-1 (3U1516-56) over the period October 1975 - April 1976 revealed a well-defined modulation of the 3-6 keV flux at a period of 16.585 + or - 0.01. The light-curve is characterized by an abrupt drop in emission occurring on a timescale of 0.07, with epoch JD 2,442,877.181 + or - 0.07. No clear correspondingly sharp increase in emission is observed during the cycle, so that a noneclipse origin for this effect cannot be ruled out