Engineering topics

Chanan, G. A.

Publications and source records attributed to Chanan, G. A..

30 records · Page 2

NASA NTRS1982

Infrared properties of serendipitous X-ray quasars

Near infrared measurements were obtained of 30 quasars originally found serendipitously as X-ray sources in fields of other objects. The observations show that the infrared characteristics of these quasars do not differ significantly from those of quasars selected by other criteria. Because this X-ray selected sample is subject to different selection biases than previous radio and optical surveys, this conclusion is useful in validating previous inferences regarding the infrared colors of 'typical' quasars.

Neugebauer, G.↗

NASA NTRS1981

Spectroscopy from 2 to 200 keV

The astrophysical processes responsible for line and continuum emission in the spectra range 2 keV to 200 keV are examined from the viewpoint of designing a spectrometer which would operate in this regime. Phenomena considered include fluorescent line radiation in X-ray binaries, magnetically shifted iron lines and cyclotron emission from neutron star surfaces, line emission from cosmically abundant elements in thermal plasmas, and nuclear deexcitation lines in fresh nucleosynthetically produced matter. An instrument consisting of a approximately 10 sq cm array of planar germanium detectors surrounded by a large sodium-iodide anticoincidence shield is described and projected background rates and sensitivities are considered. A sample observing program for a two-day shuttle-based mission is included as an example of the wide range of scientific questions which could be addressed by such an instrument.

Helfand, D. J.↗

NASA NTRS1981

On the equilibrium distribution of the elements in the gas in the Coma cluster

The equilibrium distribution of the elements for the case of an isothermal plasma in a gravitational potential well is given governing equations and a rapidly converging iterative procedure for their solution. Results are applied to the intracluster gas in clusters of galaxies, and implications are identified for the controversy as to whether iron nuclei settle out in the cluster core, and with respect to the interpretation of distribution size and shape for continuum X-ray emission from clusters. A model for the Coma cluster is considered in which the intracluster gas is in equilibrium and partially processed. It is found that this model can account for the angular dependence of the continuum X-ray emission from Coma, as determined by Einstein Observatory observations, at least as well as the uniform composition model.

Abramopoulos, F.↗

NASA NTRS1981

A companion quasar to 3C345

The discovery of a new quasistellar object (QSO) which presents the strongest evidence to date for the membership of quasars in rich clusters is reported. During X-ray observations of quasar 3C345, a serendipitous X-ray source located 8 arcmin northeast of the quasar was discovered. The observed flux of the new source is 3.2 x 10 to the -13th erg/sq cm/sec in the 0.5-4.5 keV band. Three separate observations over a six-month period failed to show intensity variability in excess of the statistical uncertainty in the count rate. The spectrum shows a modest signal-to-noise ratio but four strong emission lines. It is suggested that the redshift agreement between the two QSOs indicates a common membership in a cluster of galaxies which may well be a rich cluster.

Margon, B.↗

NASA NTRS1981

Optical identification of serendipitous Einstein sources - 19 X-ray-selected active galactic nuclei

The identification of counterparts to 19 serendipitous Einstein Observatory X-ray sources at high galactic latitude is reported. The counterparts are identified as previously uncataloged active galactic nuclei (AGNs) - quasars or Seyfert galaxies - with redshifts varying from z = 0.036 through z = 1.40. The success rate, that is, the fraction of X-ray sources that are identified as AGNs, is approximately 50%, an order of magnitude larger than for traditional ultraviolet surveys. It is expected that this method will produce a large number of X-ray-selected AGNs for statistical studies. For the 19 AGNs in this sample, which is free from the radio selection effects that have complicated previous studies, the X-ray-to-optical-flux slope is found to be 1.30 + or - 0.05.

Chanan, G. A.↗

NASA NTRS1980

The X-ray polarization of the Cygnus sources

Multiple observations of Cygnus X-1, Cygnus X-2, and Cygnus X-3 were carried out with the Bragg crystal polarimeters aboard OSO 8. Of these sources, an unambiguous detection of the time-averaged polarization was obtained only for Cygnus X-1, which has a polarization of 2.4% plus or minus 1.1% at 2.6 keV and 5.3% plus or minus 2.5% at 5.2 keV. While statistically significant evidence for polarization of Cygnus X-2 of 4.9% at 2.6 keV was obtained in a 1975 observation, this result was not confirmed in later observations. For Cygnus X-3, modulation of the observed flux at twice the rotation frequency of the satellite, the signature of polarization, was also detected, but spurious modulation due to the presence of additional sources in the field of view cannot be ruled out.

Long, K. S.↗

NASA NTRS1980

Thermal X-ray emission from neutron stars

In the present paper, the status of theories concerning the thermal properties of neutron stars are reviewed, and means by which observational astronomy may contribute to future studies are examined. Particular attention is given to program of the Einstein Observatory (HEAO 2) which calls for observations of over 50 SNR and 35 radio pulsars. The present paper includes a survey of all objects within 350 pc of the earth.

Helfand, D. J.↗

NASA NTRS1979

Einstein observations of the Orion Nebula

A single 3.5 hour observation on 1979 March 6 with the imaging proportional counter aboard the Einstein Observatory has revealed the presence of numerous low-luminosity (10 to the 31st ergs/s) X-ray sources in a region centered near the Trapezium in the Orion Nebula. In addition to the Trapezium, 22 discrete sources have been detected in a 1 x 1 deg field at or above the 4 sigma level. These sources are clearly associated with star formation, as indicated by the similarity of their spatial distribution with that of the nebular variables, a class of pre-main-sequence stars. Because the field is quite crowded, however, individual identifications of these sources are difficult. In addition to the discrete sources, there is evidence for diffuse or unresolved emission from two ridges extending 16 deg to the north and 15 deg to the west of the Trapezium. The nature of the discrete sources and of the diffuse emission is discussed.

Ku, W. H.-M.↗

NASA NTRS1979

The linear X-ray polarization of Scorpius X-1

Scorpius X-1 was observed with the Bragg crystal polarimeters aboard OSO 8 in August 1977 and again in August 1978. An analysis of these observations reveals a time-averaged polarization of 0.39% plus or minus 0.20% at 2.6 keV and 1.31% plus or minus 0.40% at 5.2 keV. The corresponding position angles are 29 deg plus or minus 10 deg and 57 deg plus or minus 6 deg, respectively. Binary phase-dependent polarization was searched for but not observed.

Long, K. S.↗

NASA NTRS1979

Further comments on the effects of vacuum birefringence on the polarization of X-rays emitted from magnetic neutron stars

The birefringence of the vacuum in the presence of strong (of the order of 1 teragauss) magnetic fields will in general affect the polarization of X-rays propagating through these fields. Two of the four Stokes parameters will vary so rapidly with wavelength as to be 'washed out' and unobservable, but the remaining two parameters will be unaffected. These results show that one conclusion of an earlier work is incorrect: Polarized X-ray emission from the surface of a magnetic neutron star will not in general be completely depolarized by the effects of vacuum birefringence. In particular, this birefringence has no effect on the linear polarization of cyclotron emission from the poles of magnetic neutron stars, and a similar result holds for synchrotron emission. More general cases of the propagation of polarized X-rays in magnetic fields are also discussed.

Chanan, G. A.↗

NASA NTRS1979

X-ray polarimetry

The method by which the Bragg-crystal X-ray polarimeters aboard Ariel 5 and OSO 8 operate is briefly described, and some results obtained with these instruments for six Galactic X-ray sources are summarized. A precision measurement of the linear polarization in the Crab Nebula at energies of 2.6 and 5.2 keV is presented. Evidence is given for polarization in Sco X-1, Cyg X-2, Cen X-3, and the X-ray transient A0620-00. The determined or estimated polarizations are approximately 19.2% at 2.6 keV and 19.5% at 5.2 keV for the Crab Nebula, 1.1% at 2.6 keV and 2.4% at 5.2 keV for Sco X-1, 2.5% at 2.6 keV and 9.8% at 5.2 keV for Cyg X-1, an upper limit of 13.5% for A0620-00, an upper limit of 13.5% to the time-averaged polarization of Cen X-3, and an apparent value of about 5% for Cyg X-2.

Long, K. S.↗

NASA NTRS1979

Bragg crystal spectroscopy on the OSO 8 satellite

Results are reported for high-resolution OSO 8 Bragg-crystal spectroscopy of a variety of cosmic X-ray sources in the energy range from 2 to 10 keV. A continuous spectrum of Sco X-1 is examined, and results of a search for narrow line emission due to iron near 6.7 keV are presented for 32 galactic X-ray sources, including Sco X-1, Cyg X-3, and Cen X-3. It is noted that the strongest evidence for iron line emission has been obtained for Cyg X-3 and that evidence for an iron line feature has also been found in the spectrum of Cen X-3.

Long, K. S.↗