Related papers: X-raying the zeta Tau binary system
We present photometric observations of the field around the optical counterparts of high-mass X-ray binaries. Our aim is to study the long-term photometric variability in correlation with their X-ray activity and derive a set of secondary…
Differences have been reported between the X-ray emission of accreting and non-accreting stars. Some observations have suggested that accretion shocks could be responsible for part of the X-ray emission in Classical T Tauri stars (CTTS). We…
LSI +61 303 is one of the few X-ray binaries with a Be star companion from which radio, X-rays and high-energy gamma-ray (GeV and TeV) emission have been observed. The nature of the high energy activity of the system is not yet fully…
Observations of high energy gamma rays recently revealed a persistent source in spatial coincidence with the binary system Eta Carinae. Since modulation of the observed gamma-ray flux on orbital time scales has not been reported so far, an…
We report on new X-ray observations of the classical T Tauri star DG Tau. DG Tau drives a collimated bi-polar jet known to be a source of X-ray emission perhaps driven by internal shocks. The rather modest extinction permits study of the…
The star CQ Tau belongs to the family of UX Ori type stars. It has very complex photometric behavior and complex structure of the circumstellar environment. In our paper we constructed the historical 125 years light curve of this star…
Gamma Cas analog sources are a subset of Be stars that emit intense and hard X-ray emission. Two competing ideas for their X-ray production mechanism are (a) the magnetic activities of the Be star and its disk and (b) the accretion from the…
Some T Tauri stars show a peculiar X-ray spectrum that can be modelled by two components with different absorbing column densities. We seek to explain the soft X-ray component in DG Tau, the best studied of these sources, with an outflow…
The X-ray emission from active galactic nuclei (AGN) is believed to come from a combination of inverse Compton scattering of photons from the accretion disk and reprocessing of the direct X-ray emission by reflection. We present hard (10-80…
The spectral analysis of two XMM-Newton observations of the high-mass X-ray binary system Cen X-3 is presented. In particular, it is focused on the eclipse and out-of-eclipse spectra in order to compare the properties of the environment…
Several aspects concerning the origin of the very strong X-ray activity of T Tauri Stars (TTS) are still not well understood. Important new insight came recently from the Chandra Orion Ultradeep Project (COUP), a unique 10-day long Chandra…
We present optical and X-ray data for a sample of serendipitous XMM-Newton sources that are selected to have 0.5-2 keV vs 2-4.5 keV X-ray hardness ratios which are harder than the X-ray background. The sources have 2-4.5 keV X-ray flux >=…
We present data from simultaneous Chandra, XMM-Newton and BeppoSAX observations of the Seyfert 1 galaxy NGC 3516, taken during 2001 April and Nov. We have investigated the nature of the very flat observed X-ray spectrum. Chandra grating…
We summarize new X-ray detections of four nitrogen-type Wolf-Rayet (WR) stars obtained in a limited survey aimed at establishing the X-ray properties of WN stars across their full range of spectral subtypes. None of the detected stars is so…
The origin of the hard, bright X-ray emission that defines the gamma Cas analog class of Be stars remains an outstanding question in Be star literature. This work explores the possibility that the X-ray flux is produced by accretion onto a…
Classical Be stars, regardless of spectral subtype, display multiperiodic light modulations in the frequency range 0.1-12 d$^{-1}$, when observed with high-cadence and long duration. This behaviour is attributed to non-radial pulsations…
We present a study of the X-ray properties of a sample of six nearby late-type spiral galaxies based on XMM-Newton observations. Since our primary focus is on the linkage between X-ray emission and star formation in extended, extranuclear…
We present the results of a 17 ks Chandra ACIS-S observation of the nearby dwarf spiral galaxy NGC 4395. Chandra affords the first high-quality, broadband X-ray detection of the active nucleus of this object that is uncontaminated by nearby…
This work is devoted to the study of the broadband 0.8-79 keV spectral and timing properties of the poorly studied X-ray pulsar XTE J1859+083 during its 2015 outburst based on the data from the NuSTAR and Swift observatories. We show that…
We report spatially resolved spectroscopy of both components of the low-mass pre-main-sequence binary GV Tau. High resolution spectroscopy in the K- and L-bands is used to characterize the stellar properties of the binary and to explore the…