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Singh, K. P.

Publications and source records attributed to Singh, K. P..

25 records · Page 2
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NASA NTRS1985

Soft X-ray maps of the Large Magellanic Cloud (LMC)

Soft X-ray maps of the Large Magellanic Cloud (LMC) were obtained from scanning-observations with the HEAO-1 low energy detectors. Comparison of the 1/4 keV X-ray observations with the neutral hydrogen column densities in the LMC obtained from a 21 cm line survey, shows no evidence for absorption effects in the 1/4 keV X-ray flux from the LMC due to the neutral matter in the LMC. Instead, faint X-ray emission is detected from the LMC. The extent of this emission is smaller than the size of the halo or the disk of the LMC. Assuming this 1/4 keV emission to be diffuse, it is identified with a supergiant shell of optical nebulosity known as Shapley III, and the bar of the LMC. The X-ray luminosities of the regions are estimated to be 9 times 10 to the 38th power ergs/sec and 1.8 times 10 to the 39th power ergs/sec for the Shapley III region and the bar of the LMC respectively. Shapley III could be an X-ray superbubble.

Singh, K. P.↗
NASA NTRS1984

An X-ray survey of beta Cephei stars

Results of an X-ray survey of beta Cephei stars carried out with the Imaging Proportional Counter are reported. Three of six surveyed beta Cephei stars observed was detected with an X-ray luminosity (LX) lying in the range (0.8 - 4.2 x 10 to the 31st erg/s. The mean value of the ratio of X-ray luminosity to bolometric luminosity for nine beta Cephei stars is found to be 8.6 x 10 to the -8th. No dependence of LX or bolometric luminosity is found on the binary or short pulsation periods of the stars, and no correlation was found between LX and the rotation velocity of the stars. It is concluded that the X-ray characteristics of the beta Cephei stars are indistinguishable from other B stars of similar luminosity. An indication was found of X-ray variations by a factor of about 2 on a time scale of about 10 min from Beta CMa.

Agrawal, P. C.↗
NASA NTRS1984

Binary modulation and transient periodic variations in X-ray emission from the AM Her binary H 0139 - 68

A detailed timing analysis of HEAO-1 and Einstein satellite soft X-ray data on the AM Her-type binary H 0139 - 68 indicates that the X-ray flux is modulated at the 113.6363-min period of its optical counterpart, and that the X-ray source shows high and low states. Transient X-ray pulsations with a period of about 275 sec are noted in the Imaging Proportional Counter (IPC) data during the high state, and the rapid X-ray flickering observed in the IPC light curve is characterized by an average e-folding autocorrelation time of about 10-20 sec. The present optical and X-ray data preclude the presence of an accretion disk in the primary system.

Singh, K. P.↗
NASA NTRS1983

Detection of an extended soft X-ray source H 2326-79 in the southern sky

A new extended soft X-ray source H 2326-79 has been detected with the low energy detectors of the HEAO1 A-2 experiment. The source is found to have a size of approximately 2.5 arcsec and is centered at RA(1950)=23 h 26 m, Decl.(1950)= -79 deg 24 min. The observed energy flux, seen mainly in the 0.18-0.4 keV band, corrected for finite source size, is found to be about 2.6 x 10 to the -11th erg/sq cm-sec. It is determined that the source spectrum fits well with either an exponential model (gaunt factor included) or with a Raymond Smith plasma model. The observed characteristics of the source are studied for two physical models: a very old low surface brightness supernova remnant undetected in the radio and optical regions, and an enhanced X-ray emission region surrounding an H I cloud embedded in the hot cavity of Loop I. The observed source is also interpreted as a group of two or more unresolved stellar X-ray sources.

Agrawal, P. C.↗
NASA NTRS1983

X-ray emission from the Pleiades cluster

The detection and identification of H0344+24, a new X-ray source located in the Pleiades cluster, is reported, based on observations made with HEAO A-2 low-energy detector 1 in the 0.15-3.0-keV energy band in August, 1977. The 90-percent-confidence error box for the new source is centered at 03 h 44.1 min right ascension (1950), near the center star of the 500-star Pleiades cluster, 25-eta-Tau. Since no likely galactic or extragalactic source of X-rays was found in a catalog search of the error-box region, identification of the source with the Pleiades cluster is considered secure. X-ray luminosity of the source is calculated to be about 10 to the 32nd ergs/sec, based on a distance of 125 pc. The X-ray characteristics of the Pleiades stars are discussed, and it is concluded that H0344+24 can best be explained as the integrated X-ray emission of all the B and F stars in the cluster.

Agrawal, P. C.↗
NASA NTRS1983

X-ray variability of BL Lac objects - H2155-304 and PKS 0548-322

X-ray emission from two BL Lacertae objects (H2155-304 and PKS 0548-322) has been studied with the High-Resolution Imager and Monitor Proportional Counter (MPC) on the Einstein Observatory. The high-spatial-resolution observations confirm the identification of these X-ray sources with the BL Lac objects and give a source size less than about 2 arcsec. Variations in the X-ray intensity and spectrum of these sources were detected over time scales of a few hours from analysis of the MPC observations.

Agrawal, P. C.↗