X-ray continuum and line emission of the Seyfert galaxy MCG - 5-23-16

We report observations of X-ray continum and line emission from the highly absorbed and variable Seyfert galaxy MCG-5-23-16, using the low-energy and the medium-energy detectors of the Exosat Observatory.The galaxy was observed in 1983 December and 1984 May. The X-ray intensity of the source is observed to vary by ~25% in the hard (2-10 keV) and by ~40 percent in the soft (0.1-2.0 keV) energy bands over a period of 6 months. The 0.1-10 keV X-ray spectrum is adequately explained by a simple power law. The measured energy index lies in the range 0.42-0.89 and shows a dependence on the intensity. Line emission at 6.4 keV is detected in the 1984 observations when the X-ray spectrum is relatively harder. The equivalent width of the line is measured to be 346 ± 146 eV. The presence of line emission is also indicated in the 1983 data. The line-of-sight absorption is much higher than the 21-cm value, suggesting a very high obscuration of the nuclear source. The present observations are well explained by the reflection of X-rays by cold material in an accretion disk around the nuclear source. It is suggested that as the absorption(due to the disk) of the direct component increases with time, so does the amount of the reflected component, thus hardening the spectrum and also producing more line emission

X-ray observations of the bright Seyfert galaxy IC 4329A

We have performed a detailed analysis of the broad-band (0.1-25 keV) EXOSAT observations of. the high luminosity, nearby Seyfert type I galaxy IC 4329A. The observations were carried out on two occasions, 1984 July and 1985 July. The X-ray luminosity decreased by ~35% over one year. A significant short-term variability where the intensity decreased by ~12% on a time scale of ~2 x 104s was detected in the 1985 data. The observed X-ray spectra are all well fitted by simple power-law models with nearly 10 times larger absorption than the Galactic value, indicating significant absorbing matter local to the source, consistent with the reddening observed in the optical spectrum. We do not find any evidence for low-energy excess in the spectra. The photon index Γ is measured to be 1.85 ± 0.06 (90% confidence) in 1984 and 1.77+0.06-0.05 (90% confidence) in 1985. We find a Fe line emission at 6.4 keV with an equivalent width of 169+124-113 eV in the 1984 data when the source was bright. The results are used to constrain the mass of the putative supermassive black hole in the nucleus of IC 4329A. The implications of the results on the matter surrounding the active galactic nucleus in IC 4329A are discussed

On the possible source of GRB 930131

A series of recent papers (Kouveliotou et al., 1994; Sommer et al., 1994; Ryan et al., 1994) have discussed the localization and properties of GRB930131, the brightest gamma ray burst (GRB) observed by the Compton Gamma Ray Observatory (CGRO). Schaefer et al. (1994) have looked for objects in the neighborhood of this GRB. They have shown that there are to X-ray sources near the CGRO localization, which were identified with the stars HD 106225 and HR 4657. In the present Letter we discuss these two sources in detail. HR 4657 is a visual binary of spectral type F at a distance of 34 pc and it is unlikely to be the source of GRB930131. The object HD 106225 is one of the most active RS CVn type of binaries at a distance of 220 pc and it exhibits surface magnetic activity in all wavelengths from radio to X-rays (Strassmeier et al., 1993). Vahia and Rao (1988) have suggested that the GRBs arise from flares on Magnetically Active Stellar Systems (MASS) consisting of flare stars, RS CVn binaries and cataclysmic variables of which about 300 sources are known. The probability of finding a magnetically active system in the CGRO error box is about 3 x 10-3. Other properties of the GRB also agree well with our expectations of flares on such a binary

IONS (ANURADHA): Ionization states of low energy cosmic rays

IONS (ANURADHA), the experimental payload designed specifically to determine the ionization states, flux, composition, energy spectra and arrival directions of low energy (10 to 100 MeV/amu) anomalous cosmic ray ions of helium to iron in near-Earth space, had a highly successful flight and operation Spacelab-3 mission. The experiment combines the accuracy of a highly sensitive CR-39 nuclear track detector with active components included in the payload to achieve the experimental objectives. Post-flight analysis of detector calibration pieces placed within the payload indicated no measurable changes in detector response due to its exposure in spacelab environment. Nuclear tracks produced by alpha-particles, oxygen group and Fe ions in low energy anomalous cosmic rays were identified. It is calculated that the main detector has recorded high quality events of about 10,000 alpha-particles and similar number of oxygen group and heavier ions of low energy cosmic rays

Observations of enhanced sub-iron (Sc-Cr) to iron abundance ratios in the low energy galactic cosmic rays in Spacelab-3 and their implications

The Anuradha cosmic ray experiment in Spacelab-3, flown in the orbit at 350 km with an inclination of 57° for about six days, was used to measure the low energy galactic cosmic ray (GCR) heavy ions using a specially designed CR-39 detector module incorporating the arrival time information of the particles. The abundances of sub-iron (Sc-Cr) and iron particles in the low energy interval of 30-300 MeV/N were determined from the measurements made in four different depths of the CR-39 detector module of 150 layers. From these studies we obtained sub-iron (Sc-Cr) to iron abundance ratios of 0.8 to 1.2 in 30-300 MeV/N energy range. It is found that these ratios are enhanced by a factor of two as compared to interplanetary ratios of about 0.5. It is shown that the enhancement of the ratio inside the earth's magnetosphere is probably due to the degree of ionization of low energy Sc to Cr and Fe ions in the galactic cosmic rays and to the rigidity filtering effects of the geomagnetic field. Further studies are needed to understand fully the phenomena and their implications