Related papers: Correlated X-ray and optical variability in KV UMa

We present a study of the persistent X-ray emission from the low-mass X-ray binary 4U 1636-53 based ont he entire archival EXOSAT ME data set. We per- formed a homogeneous analysis of all five EXOSAT observations in terms of the correlated…

We observe strong correlations between the temporal properties of gamma ray bursts (GRBs) and their apparent peak brightness. The strongest effect (with a significance level of 10^{-6}) is the difference between the brightness distributions…

Blazars are known to show flux variations over a range of energies from low energy radio to high energy gamma-rays. Cross-correlation analysis of the optical and $\gamma$-ray light curves in blazars shows that flux variations are generally…

The serendipitous observation of GRB 780506 by co-aligned gamma-ray (HEAO 1 A-4 0.02 - 6 MeV) and X-ray (HEAO 1 A-2 2-60 keV) instruments during a six hour pointing at a blank section of the sky gave us unprecedented high signal-to-noise…

We present a statistical analysis of simultaneous optical and X-ray light curves, spanning 600 ks, for 814 pre-main-sequence (PMS) stars in the Orion Nebula Cluster. The aim of this study is to establish the relationship, if any, between…

We present three observations (four exposures) of Mkn 421 performed by XMM--Newton in the Autumn of 2002, concentrating on the EPIC--PN camera data. The X-ray spectra were soft and steepening toward high energies. The source was highly…

We present a multi-epoch study of the extreme X-ray variability of the type~1 quasar SDSS~J000532.84+200717.4 using archival observations from \textit{XMM-Newton}, \textit{Swift}/XRT, \textit{EP-FXT}, and \textit{ROSAT}, together with new…

We propose that the UV/X-ray correlation observed in NGC 4151 by EXOSAT and IUE is due to reemission of the X-ray flux absorbed by cold clouds in the line of sight. This transmission model satisfies the energy balance, provides a good fit…

We observed the low mass X-ray binary Cyg X-2 for a total of 18 nights over two observing runs in July and September of 2006, using the Otto Struve Telescope at McDonald Observatory and the Rossi X-ray Timing Explorer. Using discrete cross…

The results of a series of five \sax observations of the TeV BL Lac object 1ES2344+514 are briefly presented. Large amplitude luminosity variability, associated to impressive spectral changes in the hard X-rays, have been found. The shape…

Short-term variability of X-ray continuum spectra has been reported for several Active Galactic Nuclei. Significant X-ray flux variations are observed within time scales down to 10^3-10^5 seconds. We discuss short variability time scales in…

We present optical spectra and images of the X-ray binary Circinus X-1. The optical light curve of Cir X-1 is strongly variable, changing in brightness by 1.2 magnitudes in the space of four days. The shape of the light curve is consistent…

Recent supernovae (SNe) observations have motivated renewed interest in SN shock breakouts from stars surrounded by thick winds. In such events the interaction with the wind powers the observed luminosity, and predictions include observable…

For a long time XMMU J010331.7-730144 was proposed as a high-mass X-ray binary candidate based on its X-ray properties, however, its optical behaviour was unclear - in particular previous observations did not reveal key Balmer emission…

We present the results of the first long-term (2.2 years) spectroscopic monitoring of a gravitationally lensed quasar, namely the Einstein Cross Q2237+0305. The goal of this paper is to present the observational facts to be compared in…

Mkn 421 was observed for about two days with BeppoSAX, prior to and partly overlapping the start of a 1 week continuous exposure with ASCA in April 1998, as part of a world-wide multiwavelength campaign. A pronounced, well defined, flare…

We report the results of long-term simultaneous X-ray and UV monitoring of the nearby (z=0.03145) Seyfert 1.5 galaxy Mrk 817 using the Neil Gehrels Swift Observatory XRT and UVOT. Prior work has revealed that the X-ray flux from Mrk 817 has…

We study the binary corrected X-ray light curve of Cygnus X-3 using the RXTE-ASM data and RXTE-PCA data. We find that the X-ray template derived from the EXOSAT observations adequately explains the binary variations. Using the recently…

After 25 years of quiescence, the microquasar V404 Cyg entered a new period of activity in June 2015. This X-ray source is known to undergo extremely bright and variable outbursts seen at all wavelengths. It is therefore an object of prime…

We present a detailed X-ray study of the 2003 XMM-Newton observation of the High Mass X-ray Binary XTE J0421+560/CI Cam. The continuum of the X-ray spectrum is well described by a flat power law (Gamma=1.0+/-0.2) with a large intrinsic…