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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Determining iconometric parameters of imaging devices using a wide-angle collimator

The problem of determining the iconometric parameters of the imaging device can be solved if the camera being calibrated is used to obtain the image of a group of reference points, the directions to which are known. In order to specify the imaging device coordinate system, it is sufficient in principle to obtain on the picture the images of three reference points which do not lie on a single straight line. Many more such points are required in order to determine the distortion corrections, and they must be distributed uniformly over the entire field of view of the camera being calibrated. Experimental studies were made using this technique to calibrate photographic and phototelevision systems. Evaluation of the results of these experiments permits recommending collimators for calibrating television and phototelevision imaging systems, and also short-focus small-format photographic cameras.

Ziman, Y. L.↗
NASA NTRS1976

Improved collimator for imaging system

System's collimator, consisting of metal plate with many small-diameter holes and fiber optics scintillator, can increase system resolution to 1 mm and reduce scintillation loss to 25 percent.

Holladay, A. M.↗
NASA NTRS1975

Scatter-free collimated convection and cosmic-ray transport at 1 AU

Observations of solar cosmic rays between 0.1 MeV and 1 GeV are more consistent with scatter-free than diffusive propagation near 1 AU. Since these particles also are constrained to interplanetary magnetic field lines, the parallel and transverse flow are decoupled by collimated convection. Local propagation is therefore more appropriately described by Liouville's equation, and transport properties can be examined from the exact zeroeth and first moments of the equation averaged over all directions in momentum space. Observational results which may be explained directly without invoking local scattering include the decay of solar flare events as well as the radial gradient, diurnal and semidiurnal variation of galactic cosmic rays.

Roelof, E. C.↗
NASA NTRS1976

Collimators for soft X-ray measurements

The development of X-ray grid collimators at the Los Alamos Scientific Laboratory is considered with attention given to grid design (patterns and artwork for masters, materials, layout of grid patterns), mounting techniques (index housings, L-bar and T-bar housings, U-housings, rectangular housings). Alignment techniques (adjustable frames and alignment telescope, adjustable frames and on-axis and off-axis telescopes) are considered along with test procedures (plane parallel X-ray beam, convolved response).

Blake, R. L.↗
NASA NTRS1978

Measurements of X-ray source positions by the scanning modulation collimator on HEAO 1

This paper reports preliminary results on the positions of X-ray sources obtained with the modulation collimator on the first NASA High Energy Astronomy Observatory, HEAO 1. Calibration on Sco X-1 establishes the experiment capabilities to be within 7 sec as limited by aspect errors. For the reported X-ray sources certain ambiguities in their positions are resolved and the previous optical identifications of four sources are confirmed, two of which are X-ray bursters and one of which is the black hole candidate Cir X-1. An accurate position for a new transient source is also presented.

Gursky, H.↗
NASA NTRS1978

Location of unidentified weak X-ray sources by the HEAO-1 scanning modulation collimator

Four weak sources for which precise positions have been obtained from the HEAO-1 Scanning Modulation Collimator (MC) experiment are discussed. One source (4U 0446+44) with the center of the cluster of galaxies containing 3C129 and 3C129.1 has been identified, and its angular size has been measured. One source with a galactic star is identified, although it is at galactic latitude b = 51 deg. The other two sources, 2A 0526-328 and 2A 0922-317, remain unidentified.

Schwartz, D. A.↗
NASA NTRS1978

The scanning modulation collimator experiment on the HEAO-1

The purpose of this experiment is to localize celestial sources of X-rays to a precision of 5 to 20 arcsec, so that they may be identified with optical or radio counterparts. We also study their angular size and structure, to elucidate the X-ray emission mechanism. Four grids, wound with nickel alloy wires, are aligned to produce a modulated X-ray signal when the spacecraft rotation carries the collimator field of view across an X-ray source. An image dissector star camera and rate integrating gyroscopes are used to deduce the celestial position from which a peak X-ray signal arises. On-orbit performance and thermal stability have been very good. Based on the first six weeks of quick look data, we have the following results: the location of an X-ray burst source within a globular cluster; the location of 4U1608-52, a unique object which shows bursting, transient, and steady X-ray behavior and is also an optical source; the location of the X-ray transient H1705-25, which provided Anglo-Australian astronomers the basis for an optical identification with a nova-like object; the location of the X-ray transient H1743-32 in the galactic center; and a precise measurement of the angular extent of the Crab Nebula.

Schwartz, D. A.↗
NASA NTRS1978

LMC X-1, X-2, and X-3 - Precise positions from the HEAO 1 modulation collimator

Precise (to about 20 arcsec) positions are reported for the Large Magellanic Cloud X-ray sources LMC X-1, X-2, and X-3, determined with the HEAO 1 scanning modulation collimator. The error regions for LMC X-1 and X-3 contain, respectively, the B5 supergiant R148 and a possibly variable B III-IV star. Spectra taken of the latter confirm the spectral type and show that it is a member of the LMC. A search for a previously reported extended component of LMC X-1 yields upper limits which exclude it.

Johnston, M. D.↗
NASA NTRS1978

SS Cygni as a hard X-ray source identified with the scanning modulation collimator on HEAO 1

Hard X-ray emission from a 15 min by 1.5 deg area containing SS Cygni had previously been reported and identified with SS Cygni. This paper reports a 0.4 sq arc min measurement of the position of the X-ray source with the HEAO 1 modulation collimator experiment which leads to an unequivocal identification of SS Cygni as an X-ray emitter in the 2-10 keV energy range. The historical light curve in hard X-rays was also investigated by analyzing relevant Uhuru data, and two instances of possible source detection in the 2-6 keV band were noted. From Ariel 5 observations it is calculated that the X-ray luminosity of SS Cygni in the 2-10 keV energy range is of the order of 10 to the 33rd erg/sec in the optical low state and probably at least an order of magnitude less in the high state. By contrast, the soft X-ray luminosity increases by an order of magnitude between the optical low and high states. A coronal model or accretion onto the white dwarf can account for the inverse correlation of the soft and hard X-rays.

Fabbiano, G.↗
NASA NTRS1979

Location of the recurrent /LMC/ X-ray transient A0538-66 with the HEAO 1 scanning modulation collimator

Two brief (about 12 hr) X-ray flares from the direction of the Large Magellanic Cloud have been observed with the HEAO 1 scanning modulation collimator. It is argued that both originated from the recurrent fast transient A0538-66, first observed with the Ariel 5 satellite. A precise position for the source is obtained, and a B2 Iab star in the Large Magellanic Cloud is suggested as the optical counterpart. Evidence for a 16.66-day periodicity in the outburst times is presented and discussed.

Johnston, M. D.↗
NASA NTRS1979

X-ray observations of high-excitation emission-line galaxies with the HEAO 1 scanning modulation collimator

Data from the scanning modulation collimator on HEAO 1 are presented which firmly establish high-excitation emission-line galaxies as a class of X-ray source. For NGC 5506 and M82, the X-ray emission (1-13 keV) is shown to originate in the nuclear region of the galaxy; NGC 2992 and NGC 526a are also identified as X-ray emitters, but are not resolved. The latter is a new identification for 2A 0120-353, previously associated with the NGC 526/527 group. In these four particular cases, the observed X-ray-emitting galaxies have a close companion, and the X-ray emission may have been triggered by a close encounter

Griffiths, R. E.↗
NASA NTRS1979

HEAO 1 scanning modulation collimator discovery of an extended X-ray source at Cygnus A

The HEAO 1 modulation-collimator data associate the X-ray emission from the Cygnus A region (4U 1957 + 40) with a small area including the radio galaxy. The source appears to be extended, with a size of about 2 arcmin; it may have a complex geometry. Any point-source component must have a flux no greater than 1.3 UFU. A lower limit of 1 microgauss is placed on the magnetic field in the radio lobes, based on the upper limit on the X-ray flux due to inverse Compton scattering of radio electrons on the 2.7-K microwave background radiation. The X-ray emission is more likely due to driven accretion of the intercluster gas onto the giant cD radio galaxy. Therefore this source appears to be similar to the Virgo and Perseus clusters. The density derived for the X-ray-emitting gas is too small for its thermal pressure to confine the radio source.

Fabbiano, G.↗
NASA NTRS1979

X-ray locations and sizes of clusters of galaxies observed with the HEAO 1 scanning modulation collimator

Observations with the HEAO 1 scanning modulation collimator (MC) have yielded improved locations for the centroids of X-ray sources in clusters of galaxies dominated by a giant central galaxy. For A85, A478, A1795, A2029, A2199, A2319 A, and SC 0316-444, these positions are consistent with those of the clusters' dominant cD galaxies. By comparing the HEAO 1 MC flux with that obtained with the HEAO 1 A-2 experiment, estimates of the X-ray sizes for these clusters have been obtained. The correlation of these sizes with other cluster properties is discussed.

Schwarz, J.↗
NASA NTRS1979

Observations of Type 1 Seyfert galaxies with the HEAO-1 scanning modulation collimator

Precise positions of four X-ray sources associated with Type 1 Seyfert galaxies are reported which were measured with the HEAO 1 scanning modulation collimator. The Seyferts are confirmed as the X-ray emitters in each case. The sources (and corresponding galaxies) studied include 2A 0551+466 (NGC 4151), 2A 1207+397 (MCG 8-11-11), 2A 1914-589 (ESO 141-G55), and A 1021+198 (NGC 3227). It is found that the X-ray source is located in the nucleus or the nuclear region for NGC 4151 and that the galaxy is unresolved by the present instrument in the other cases.

Griffiths, R. E.↗
NASA NTRS1980

Seyfert Type 1 galaxies observed with the HEAO 1 scanning modulation collimator

The paper deals with the detection of 16 X-ray sources (1.5 to 13.5 keV) during pointed observations with the HEAO 1 satellite of 19 Seyfert Type 1 (Sy 1) galaxies. For 15 sources, the Sy 1 galaxy nucleus, previously proposed as the X-ray source counterpart, lies within one of the 1 to 5 square arcmin uncertainty regions determined with the HEAO 1 modulation collimator experiment.

Dower, R. G.↗
NASA NTRS1980

Optical identification of 4U1907 + 09 using the HEAO-1 scanning modulation collimator position

The paper reports an optical identification of 4U1907 + 09 with a m(v) = 16.4 stellar object in the location determined by the scanning modulation collimator experiment on the first High Energy Astronomy Observatory (HEAO-1). The identification is based on the presence of very strong and broad H-alpha emission. The optical data constrain the distance to be 2-13 kpc, and this gives a range of uncertainty to the typical 2-10 keV luminosity of (1 x 10 to the 35th to 3 x 10 to the 36th) erg/s. The X-ray spectrum and variability is reported, and consideration is given to the hypothesis that the object is an OB supergiant, although its faintness in the blue makes precise spectral classification impossible. It is suggested that this system is an example of a luminous, massive primary emitting a stellar wind which is accreted on the compact object.

Schwartz, D. A.↗