A plausible energy source and structure for quasi-stellar objects

If a collision of two large, massive, fast gas clouds occurs, their kinetic energy is converted to radiation in a pair of shock fronts at their interface. The resulting structure is described, and the relevance of this as a radiation source for quasi-stellar objects is considered

On the He(plus) triplet line intensities

The theoretical calculations of helium triplet line strengths, including collisional enhancement, are compared to astronomical observations. Both are plotted on an I(10830)/I(5876) vs I(5876)/I(4471) plane. It appears that the theory of helium triplet line strengths agrees with present observations, and that the question of an additional depopulation mechanism for the 2 3S population is probably predicted correctly within 30%

The high-excitation planetary nebulae: NGC 3918 and IC 2448

International Ultraviolet Exploration observations of NGC 3918 and IC 2448 are presented. Combining these observations with data in the optical range and computed model structure, the chemical composition for these objects is derived. For NGC 3918 log C = -3.02, log N = -3.61 and log 0 = -3.22; while for IC 2448 log C = -3.44, log N = -81 and log 0 = 3.54

Decaying Sterile Neutrinos as a Heating Source in the Milky Way Center

Recent Chandra and Newton observations indicate that there are two-temperature components ($T \sim$ 8 keV, 0.8 keV) of the diffuse x-rays emitted from deep inside the center of Milky Way. We show that this can be explained by the existence of sterile neutrinos, which decay to emit photons that can be bound-free absorbed by the isothermal hot gas particles in the center of Milky Way. This model can account for the two-temperature components naturally as well as the energy needed to maintain the $\sim$ 8 keV temperature in the hot gas. The predicted sterile neutrino mass is between 16-18 keV.Comment: Accepted by MNRAS with minor correction

The warm interstellar medium around the Cygnus Loop

Observations of the oxygen lines [OII]3729 and [OIII]5007 in the medium immediately beyond the Cygnus Loop supernova remnant were carried out with the scanning Fabry-P\'erot spectrophotometer ESOP. Both lines were detected in three different directions - east, northeast and southwest - and up to a distance of 15 pc from the shock front. The ionized medium is in the immediate vicinity of the remnant, as evinced by the smooth brightening of both lines as the adiabatic shock transition (defined by the X-ray perimeter) is crossed. These lines are usually brighter around the Cygnus Loop than in the general background in directions where the galactic latitude is above 5 degrees. There is also marginal (but significant) evidence that the degree of ionization is somewhat larger around the Cygnus Loop. We conclude that the energy necessary to ionize this large bubble of gas could have been supplied by an O8 or O9 type progenitor or the particles heated by the expanding shock front. The second possibility, though highly atractive, would have to be assessed by extensive modelling.Comment: 18 pages, 8 figures, ApJ 512 in pres

Analysing the Suzaku Spectra of the Broad-Line Seyfert 1 Galaxy CBS 126

We analysed new simultaneous \emph{Suzaku} and \emph{Swift} data of the Broad Line Seyfert 1 (BLS1) galaxy CBS 126. A clear Fe emission line and a strong soft excess are present in the source spectra. We fit the spectra with a relativistic reflection model and find the model tends to fit the data with a high iron abundance possibly due to the large soft excess present. By checking the difference and the RMS spectra, we find there is likely an absorption edge at $\sim$ 0.89 keV, which might be caused by oxygen or neon. We also produced an analysis of the time-resolved spectra in order to examine the existence of the edge. Although high iron abundance is required more in the time-resolved spectra, a model of solar iron abundance together with an absorption edge gives a more physical explanation. Variation of the ionisation parameter is an alternative, plausible explanation for the excess seen in the difference spectra. It is difficult to know if there are warm absorbers in this source from the current data. To further investigate the presence of possible warm absorbers, higher signal-to-noise low-energy data are needed. The work presented here tentatively suggests that the spectra of a BLS1 can be explained by a relativistic reflection model similar to that often seen in their narrow-line cousins.Comment: 10 pages, 12 figures, accepted for publication in MNRA

XMM-Newton observations of the nitrogen-rich Wolf-Rayet star WR 1

We present XMM-Newton results for the X-ray spectrum from the N-richWolf-Rayet (WR) star WR1. The EPIC instrument was used to obtain a medium-resolution spectrum. The following features characterize this spectrum: ( a) significant emission "bumps" appear that are coincident with the wavelengths of typical strong lines, such as MgXI, SiXIII, and SXV; (b) little emission is detected above 4 keV, in contrast to recent reports of a hard component in the stars WR 6 and WR 110 which are of similar subtype; and ( c) evidence for sulfur K-edge absorption at about 2.6 keV, which could only arise from absorption of X- rays by the ambient stellar wind. The lack of hard emission in our dataset is suggestive that WR 1 may truly be a single star, thus representing the first detailed X-ray spectrum that isolates the WR wind alone ( in contrast to colliding wind zones). Although the properties of the S-edge are not well- constrained by our data, it does appear to be real, and its detection indicates that at least some of the hot gas in WR 1 must reside interior to the radius of optical depth unity for the total absorptive opacity at the energy of the edge

On the broadening of emission lines in active galactic nuclei

Recent works, both theoretical and observational, have suggested that turbulence could play a non-negligible role in the broadening of emission lines in active galactic nuclei. The purpose of this note is to show how shock wave-turbulence interaction, under unsteady regime, can affect the broadening of emission lines.Comment: 5 pages, 2 figures. General revision of the paper, title changed, but the basic idea is the same. Accepted by Astronomy and Astrophysic

Recombination spectrum and reddening in NGC 1068

Measurements of the emission-line intensities of NGC 1068 have been made over the wavelength range extending from λ_(rest) = 1216 Å to 1.875 μm. The data, plus other available emission-line data, can be explained in terms of a simple model where the emission lines are formed in an H II region, and the line ratios are consistent with those predicted by standard radiative recombination theory and reddening corresponding to E_(B-v) = 0.4 mag. The continuum flux is seen to consist of a galaxy component plus a nonstellar component which dominates the observed flux in the ultraviolet. The observed ultraviolet continuum does not show an absorption dip caused by the interstellar 2200 A feature nor does it contain enough energy to power the observed infrared flux

Spatially extended absorption around the z=2.63 radio galaxy MRC 2025-218: outflow or infall?

We present an investigation into the absorber in front of the z=2.63 radio galaxy MRC 2025-218, using integral field spectroscopy obtained at the Very Large Telescope, and long slit spectroscopy obtained at the Keck II telescope. The properties of MRC 2025-218 are particularly conducive to study the nature of the absorbing gas, i.e., this galaxy shows bright and spatially extended Ly-alpha emission, along with bright continuum emission from the active nucleus. Ly-alpha absorption is detected across ~40x30 kpc^2, has a covering factor of ~1, and shows remarkably little variation in its properties across its entire spatial extent. This absorber is kinematically detached from the extended emission line region (EELR). Its properties suggest that the absorber is outside of the EELR. We derive lower limits to the HI, HII and H column densities for this absorber of 3x10^16, 7x10^17 and 2x10^18 cm^-2, respectively. Moreover, the relatively bright emission from the active nucleus has allowed us to measure a number of metal absorption lines: CI, CII, CIV, NV, OI, SiII, SiIV, AlII and AlIII. The column density ratios are most naturally explained using photoionization by a hard continuum, with an ionization parameter U~0.0005-0.005. Shocks or photoionization by young stars cannot reproduce satisfactorily the measured column ratios. Using the ratio between the SiII* and SiII column densities, we derive a lower limit of >10 cm^-3 for the electron density of the absorber. The data do not allow useful constraints to be placed on the metallicity of the absorber. We consider two possibilities for the nature of this absorber: the cosmological infall of gas, and an outflow driven by supernovae or the radio-jets.Comment: Accepted for publication in MNRA