A spectral study of gamma-ray emitting AGN

In this paper we present a statistical analysis of the gamma-ray spectra of flat-spectrum radio quasars (FSRQ) compared to those of BL Lacs. The average spectra and possible systematic deviations from power-law behaviour are investigated by summing up the intensity and the power-law fit statistic for both classes of objects. We also compare the time-averaged spectrum to that at the time of gamma-ray outbursts. The spectrum of the average AGN is softer than that of the extragalactic gamma-ray background. It may be that BL Lacs, which on average have a harder spectrum than FSRQs, make up the bulk of the extragalactic background. We also find apparent cut-offs at both low and high energies in the spectra of FSRQs at the time of gamma-ray outbursts. While the cut-off at high energies may have something to do with opacity, the cut-off at low energies may be taken as indication that the gamma-ray emission of FSRQs is not a one component spectrum.Comment: 8 pages, accepted for publication in A&

The energy-dependent temporal variation of the ROSAT PSPC gain

The existence of systematic spectral-fit residuals in ROSAT PSPC spectra, and their dependence on time, is by now a well established fact. This paper describes how those residuals may be related to second order variations of the gain of the PSPC as a function of energy and time. As a result, the energy scale used for the interpretation of PSPC spectra can be incorrect producing significant systematic effects, in particular at energies where the effective area of the instrument changes rapidly. A monotonic gain decay of #approx# 1% per year is measured at 1 keV. A quantitative description of the PSPC gain-time variation as a function of energy is provided. The functional dependence of this variation is found to be well represented by a second order polynomial. (orig.)Available from TIB Hannover: RN 9303(355) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

ROSAT survey diffuse X-ray background maps. Paper 2

This paper presents new maps of the soft X-ray background from the ROSAT all-sky survey. These maps represent a significant improvement over the previous version in that(1) the position resolution of the PSPC has been used to improve the angular resolution from #propor to#2 to 12', (2) there are six energy bands that divide each of the previous three into two parts, and(3) the contributions of point sources have been removed to a uniform source flux level over most of the sky. These new maps will be available in electronic format in 1997. In this paper we also consider the bright emission in the general direction of the Galactic center in the 0.5-2.9 keV band, and the apparent absorption trough that runs through it along the Galactic plane. We find that while the northern hemisphere data are confused by emission from Loop I, the emission seen south of the plane is consistent with a bulge of hot gas surrounding the Galactic center (in our simple model, a cylinder with an exponential fall-off density with height above the plane). The cylinder has a radial extent of #propor to#5.6 kpc. The X-ray emitting gas has a scale height of 1.9 kpc, an in-plane electron density of #propor to#0.0035 cm"-"3, a temperature of #propor to#10"6"."6 K, a thermal pressure of #propor to#28,000 cm"-"3 K, and a total luminosity of #propor to#2 x 10"3"9 ergs s"-"1 using a collisional ionization equilibrium (CIE) plasma emission model. (orig.)SIGLEAvailable from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman