Search Publications
INTEGRAL and XMM-Newton observations of LSI +61° 303
Walter, R.; Chernyakova, M.; Neronov, A.
LSI +61° 303 is one of the few X-ray binaries with Be star companion from which both radio and high-energy γ-ray emission have been observed. We present XMM-Newton and INTEGRAL observations which reveal variability of the X-ray spectral index of the system. The X-ray spectrum is hard (photon index Γ ~= 1.5) during the orbital phases of both high a…
Absolute magnitudes of OB and Be stars based on Hipparcos parallaxes - II
Wegner, W.
A new method of determining absolute visual magnitudes of early-type stars, based on averaging Hipparcos parallaxes (ESA 1997) inside samples of the same spectrum and luminosity (Sp/L) classes, is proposed. The used sample consists of 6262 unreddened and reddened OB stars as well as 430 Be stars of luminosity classes Ia, Iab, Ib, II, III, IV and V…
Luminosity function of contact binaries based on the All Sky Automated Survey (ASAS)
Rucinski, Slavek M.
The luminosity function for contact binary stars of the W UMa type is evaluated on the basis of the All Sky Automated Survey (ASAS) photometric project covering all stars south of δ=+ 28° within a magnitude range 8 < V < 13. Lack of colour indices enforced a limitation to 3374 systems with P < 0.562 d (i.e. 73 per cent of all systems with…
The spectral energy distribution of PKS 2004-447: a compact steep-spectrum source and possible radio-loud narrow-line Seyfert 1 galaxy
Kataoka, J.; Boller, Th.; Welsh, W. F. +10 more
An investigation of the spectral energy distribution (SED) of the compact steep-spectrum (CSS) source and possible radio-loud narrow-line Seyfert 1 galaxy (NLS1), PKS 2004-447, is presented. Five out of six well-studied radio-loud NLS1 share this dual classification [optically defined as an NLS1 with radio definition of a CSS or gigahertz-peaked s…
A deep XMM-Newton observation of the ultraluminous X-ray source Holmberg II X-1: the case against a 1000-Msolar black hole
Uttley, P.; Reeves, J. N.; Roberts, T. P. +1 more
We present results from a 112-ks long look by XMM-Newton at the ultraluminous X-ray source (ULX) Holmberg II X-1 (Ho II X-1), long thought to be the one of best candidates for the missing class of intermediate-mass black holes (IMBHs). Our data comprises the first high-quality XMM-Newton/RGS (reflection grating spectrometer) spectrum of an ULX, an…
Spectral-timing evidence for a very high state in the narrow-line Seyfert 1 Ark 564
Papadakis, I. E.; Uttley, P.; Arévalo, P. +2 more
We use a 100ks long XMM-Newton observation of the narrow-line Seyfert 1 galaxy Ark 564 and combine it with the month-long monitoring of the same source produced by ASCA, to calculate the phase lags and coherence between different energy bands, over frequencies from ~10-6 to 10-3Hz. This is the widest frequency range for which…
On the weakness of disc models in bright ULXs
Soria, R.; Gonçalves, A. C.
It is sometimes suggested that phenomenological power law plus cool disc-blackbody models represent the simplest, most robust interpretation of the X-ray spectra of bright ultraluminous X-ray sources (ULXs); this has been taken as evidence for the presence of intermediate-mass black holes (BHs) (M ~ 103Msolar) in those source…
Unveiling the thermal and magnetic map of neutron star surfaces though their X-ray emission: method and light-curve analysis
Turolla, Roberto; Zane, Silvia
Recent Chandra and XMM-Newton observations of a number of X-ray `dim' pulsating neutron stars have revealed quite unexpected features in the emission from these sources. Their soft thermal spectrum, believed to originate directly from the star surface, shows evidence for a phase-varying absorption line at some hundred eVs. The pulse modulation is …
A weak lensing estimate from GEMS of the virial to stellar mass ratio in massive galaxies to z ~ 0.8
Bell, Eric F.; Wisotzki, Lutz; Wolf, Christian +14 more
We present constraints on the evolution of the virial to stellar mass ratio of galaxies with high stellar masses in the redshift range 0.2 < z < 0.8, by comparing weak lensing measurements of virial mass Mvir with estimates of stellar mass Mstar. For a complete sample of galaxies with log(Mstar/Msolar
Constraints on Type Ia supernova progenitor time delays from high-z supernovae and the star formation history
Wolf, C.; Förster, F.; Podsiadlowski, Ph. +1 more
We re-assess the question of a systematic time delay between the formation of the progenitor and its explosion in a Type Ia supernova (SN Ia) using the Hubble Higher-z Supernova Search sample. While a previous analysis indicated a significant time delay, with a most likely value of 3.4 Gyr, effectively ruling out all previously proposed progenitor…