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Helmken, H.

Publications and source records attributed to Helmken, H..

10 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Gamma-ray burst observations from Helios 2

Observations of five gamma-ray bursts made with the solar orbiter Helios 2 are reported. Wavefront timing from Helios 2, at distances of up to 1.98 AU, to Vela 5A and 6A, in earth orbit, provides source location bands as narrow as 2 arcmin, although several degrees in length. The burst intensities and time profiles measured in interplanetary space by Helios 2 are the same as those observed near the earth, ruling out a narrow-beam interplanetary origin model. Also, the source direction bands for these events are inconsistent with the directions of all known celestial X-ray objects, X-ray bursters, and high-energy gamma-ray source regions. The gamma-ray burst source objects therefore appear to form a class distinct from all lower-energy X-ray or higher energy gamma-ray emitters.

Cline, T. L.↗
NASA NTRS1979

Helios 2-Vela-Ariel 5 gamma-ray burst source position

The gamma-ray burst of January 28, 1976, one of 18 events thus far detected in interplanetary space with Helios 2, was also observed with the Vela 5A and 6A and the Ariel 5 satellites. A small source field is obtained from the intersection of the region derived from the observed time delays between Helios 2 and Vela 5A and 6A, with the source region independently found with the Ariel 5 X-ray detector. This area contains neither any steady X-ray source as scanned by HEAO 1 nor any previously cataloged X-ray, radio, or infrared sources, X-ray transients, quasars, Seyferts, globular clusters, flare stars, pulsars, white dwarfs, or high enery gamma-ray sources. The region is, however, within the source field of a gamma-ray transient observed in 1974 by Jacobson et al. (1978) which exhibited nuclear gamma-ray line structure.

Cline, T. L.↗
NASA NTRS1978

4U0241+61 - A luminous low-redshift QSO

The faint (1.8 micro Jy, 2-11 keV) X-ray QSO 4U0241+61 is considered in terms of its celestial position (galactic latitude = +2.4 plus or minus 30 sec), luminosity (M sub v = -25.8 plus or minus 1.8), redshift (z = 0.0438), and radio emission (0.2-0.5 Jy). Counting rates in two energy channels are presented, and found comparable to the Type 1 Seyfert 3C120. Spectrophotometric calibration to an approximately 8 A resolution was also achieved. Attention is given to the close relation between X-ray emitting QSOs and Seyferts.

Apparao, K. M. V.↗
NASA NTRS1978

Possible X-ray counterparts of gamma-ray sources

The results are presented of a survey regarding the X-ray source positions which fall within the error boxes of 10 unidentified gamma-ray sources observed with the aid of the COS-B satellite. In three cases, including CG 135-1, CG 312-1, and CG 327-0, an X-ray source was found within the gamma-ray error box. However, because of the large uncertainty regarding the gamma-ray source positions, the positional coincidence is not necessarily conclusive. It is, therefore, necessary to take into account additional information on the spectral or temporal characteristics of the X-ray sources. It is found that the X-ray source 4U 02416 plus 1 is a possible candidate as the X-ray-counterpart of CG 135 plus 1 in connection with both spectral hardness characteristics and positional coincidence.

Maraschi, L.↗
NASA NTRS1978

Compact and diffuse X-ray sources in the core of the Perseus cluster /Abell 426/

Data on the X-ray structure of the Perseus cluster of galaxies in the energy range from 2 to 10 keV are analyzed which were obtained during a 12-day observation with the rotating modulation collimator aboard SAS 3. In particular, the nature of the compact X-ray source coincident with NGC 1275 is examined. The data are shown to confirm the presence of a diffuse region of X-ray emission surrounding the nucleus of NGC 1275; it is found that a model which also includes a point source at the nucleus is consistent with the data if the point contribution is no larger than 20% of the X-ray flux detected within 3 to 5 arcmin of the galaxy. The results suggest that NGC 1275 may have accreted a large amount of gas from the intracluster medium and that the flux from the possible point source is consistent with a synchro/Compton model.

Helmken, H.↗
NASA NTRS1977

X-ray and radio observations of the structure of Abell 478

The complex X-ray and radio structures of the cluster of galaxies Abell 478 have been observed in the 2-11-keV energy band by the rotating modulation collimators on the SAS-3 X-ray observatory and at 1415 MHz by the Westerbork synthesis radio telescope. The X-ray data imply an extended source (X-ray luminosity of the order of 10 to the 45th power erg/s) and are consistent with the presence of a coincident pointlike source X-ray luminosity of the order of 10 to the 45th power erg/s. The X-ray source position is also coincident with a cD radio galaxy at the core of the cluster.

Schnopper, H. W.↗
NASA NTRS1977

Variability of LMC X-4

X-rays in the 2-11-keV band were detected from LMC X-4 using the rotating modulation collimator system on SAS-3. The derived X-ray luminosity of LMC X-4 is of the order of 10 to the 38th power ergs/s. A transition to a high-intensity state which lasted about 40 minutes was detected during which short-time-scale flares (about 20 s) were observed. The temporal and spectral behavior of LMC X-4 is found to be similar to that of several X-ray binaries. A derived 90% error circle with a radius of 1 arcmin is also presented.

Epstein, A.↗
NASA NTRS1976

Detection of X-rays from Algol /beta Persei/

X-rays in the 2-6 keV band were detected from the Algol system using the rotating modulation collimator system on SAS-3 during an observation in October 1975. The measured X-ray flux is 3.8 x 10 to the -11th ergs/sq cm/s/keV. No positive detection was made in the 6-11 keV band. The data are consistent with either a power-law spectrum with photon spectral index not less than 2.5 or a thermal bremsstrahlung spectrum with a temperature not greater than 3 x 10 to the 7th K.

Schnopper, H. W.↗