BeppoSAX observations of GRS 1915+105.

Results from a BeppoSAX observational campaign on GRS 1915+105, performed in October/November 1996, are presented. The source was observed 10 times (nine 10 ksec snapshots, one 100 ksec long observation). The broad band spectral analysis reveals a complex spectrum, including Compton reflection and an iron emission line, probably originating from a relativistic disc.     

ASCA observations of two steep soft X-ray quasars

Steep soft X-ray (0.1–2 keV) quasars share several unusual properties: narrow Balmer lines, strong Fe  II emission, large and fast X-ray variability, and a rather steep 2–10 keV spectrum. These intriguing objects have been suggested to be the analogues of Galactic black hole candidates in the high, soft state. We present here results from ASCA observations for two of these quasars: NAB 0205 + 024 and PG 1244 + 026.   Both objects show similar variations (factor of ∼ 2 in 10 ks), despite a factor of ∼ 10 difference in the 0.5–10 keV luminosity (7.3 × 10⁴³ erg s⁻¹ for PG 1244 + 026 and 6.4 × 10⁴⁴ erg s⁻¹ for NAB 0205 + 024, assuming isotropic emission, H ₀ = 50.0 and q ₀ = 0.0).   The X-ray continuum of the two quasars flattens by 0.5–1 going from the 0.1–2 keV band towards higher energies, strengthening recent results on another half-dozen steep soft X-ray active galactic nuclei.   PG 1244 + 026 shows a significant feature in the '1-keV' region, which can be described either as a broad emission line centred at 0.95 keV (quasar frame) or as edge or line absorption at 1.17 (1.22) keV. The line emission could be a result of reflection from a highly ionized accretion disc, in line with the view that steep soft X-ray quasars are emitting close to the Eddington luminosity. Photoelectric edge absorption or resonant line absorption could be produced by gas outflowing at a large velocity (0.3–0.6 c ).     

Infrared instruments for the Gemini 8-M telescopes

The Gemini Telescopes are being built to exploit the splendid infrared sites of Mauna Kea in Hawaii and Cerro Pachon in Chile. Both telescopes are being designed to deliver 0.1 arcsecond images at 2.2 m to the focal plane. This image size includes all tracking and enclosure effects. To exploit the superb infrared characteristics of the sites and telescopes we will require a new generation of IR instruments which will challenge both instrument designers and infrared array technologies.     

LAGUNA GUATAVITA: NOT METEORITIC,PROBABLE SALT COLLAPSE CRATER

Laguna Guatavita (Colombia), a crater 700 m across and 125 m deep containing a central lake, appears not to be a meteorite crater as widely supposed. The tectonic style is not that of an impact site and there is no raised rim or ejected debris. We could find no impactite, shock metamorphic effects or shock fractures (shatter cones). Most likely it is a collapsed crater caused by the solution and withdrawal of salt from an underlying anticline     

Hard X-Ray Emission from the Galaxy Cluster A2256

After the positive detection by BeppoSAX of hard X-ray radiation up to approximately 80 keV in the Coma Cluster spectrum, we present evidence for nonthermal emission from A2256 in excess of thermal emission at a 4.6 sigma confidence level. In addition to this power-law component, a second nonthermal component already detected by ASCA could be present in the X-ray spectrum of the cluster, which is not surprising given the complex radio morphology of the cluster central region. The spectral index of the hard tail detected by the Phoswich Detection System on board BeppoSAX is marginally consistent with that expected for the inverse Compton model. A value of approximately 0.05 μG is derived for the intracluster magnetic field of the extended radio emission in the northern regions of the cluster, while a higher value of approximately 0.5 μG could be present in the central radio halo, which is likely related to the hard tail detected by ASCA.