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Strongly magnetized, accreting neutron stars show periodic and aperiodic variability over a wide range of time scales. By obtaining spectral and timing information on these different time scales, we can have a closer look into the physics…

[Abbreviated] Upcoming large area sky surveys like EUCLID and eROSITA crucially depend on accurate photometric redshifts (photo-z). The identification of variable sources, such as AGNs, and the achievable redshift accuracy for varying…

A new measurement of the cosmic ray positron fraction in the energy range of 1-50 GeV is presented. The measurement is based on data taken by the AMS-01 experiment during its 10 day space shuttle flight in June 1998. A proton background…

Studying the cross-correlation function between the soft and hard X-ray emission in Neutron Star Low Mass X-ray Binaries provides crucial insight into the structure and dynamics of the innermost accretion regions. In this work, we…

One of the main results of the ATIC (Advanced Thin Ionization Calorimeter) experiment is a collection of energy spectra of abundant cosmic-ray nuclei: protons, He, C, O, Ne, Mg, Si, Fe measured in terms of energy per particle in the energy…

Variability of active galactic nuclei (AGNs) has long been servicing as an essential avenue of exploring the accretion physics of black hole (BH). There are two commonly used methods for analyzing AGN variability. First, the AGN…

Variable continuum emission from AGN can be used to probe the structure of their accretion disks via reverberation mapping. Assuming a variable, hot inner light source irradiates the surrounding accretion disk, time delays between different…

We report monitoring of the 0.3-10 keV spectrum of NGC4258 with XMM over 1.5 years.We als o report reprocessing of an overlapping series of archival Chandra observations. By including earlier ASCA and SAX observations, we present a new,…

We investigate the properties of a variability-selected complete sample of AGN in order to identify the mechanisms which cause large amplitude X-ray variability on time scales of years. A complete sample of 24 sources was constructed, from…

High-energy neutrinos and photons are complementary messengers, probing violent astrophysical processes and structural evolution of the Universe. X-ray and neutrino observations jointly constrain conditions in active galactic nuclei (AGN)…

We discuss the methods used to compile a high signal-to-noise dataset representative of both the instrumental and cosmic background signal measured at high galactic latitude by the XMM-Newton EPIC cameras. The characteristics of the EPIC…

Information about the X-ray luminosity of the supermassive black hole located at the Galactic center (GC), Sgr A*, and its temporal variations in the past is imprinted in the scattered emission observed today in the direction towards giant…

Galactic cosmic rays (GCRs) entering the heliosphere are disturbed by the magnetic field of the Sun, which varies the shape and intensity of their local interstellar spectrum. The force-field approximation is a popular way of dealing with…

We present an X-ray stacking analysis of $\sim$75,000 star-forming galaxies between $0.1<z<5.0$ using the Chandra COSMOS Legacy survey to study the X-ray emission of low-luminosity active galactic nuclei (AGN) and its connection to host…

This study investigates the X-ray characteristics of jet-associated radio-quiet AGNs across distinct optical/UV to X-ray correlation phases. Quasi-simultaneous optical/UV/X-ray observations of NGC 4051 from May-June 2009, obtained through…

We tested how the AGN contribution (5% - 75% of the total flux) may affect different morphological parameters commonly used in galaxy classification. We carried out all analysis at $z$,$sim$,0 and at higher redshifts that correspond to the…

We present analysis of the light curve from the ROSAT HRI monitoring observations of the broad-line radio galaxy 3C 390.3. Observed every three days for about 9 months, this is the first well sampled X-ray light curve on these time scales.…

A recently released XMM-Newton technical note has revealed a significant calibration issue between NuSTAR and XMM-Newton EPIC, and provided an empirical correction to EPIC effective area. To quantify the bias caused by the calibration issue…

Using archival RXTE data, we show that the ultracompact X-ray binary in NGC 1851 exhibits large amplitude X-ray flux varations of more than a factor of 10 on timescales of days to weeks and undergoes sustained periods of months where the…

PAPER WITHDRAWN. The recent detection of Sgr A* in the X-ray band, together with the radio polarization measurements conducted over the past few years, offer the best constraints yet for understanding the nature of the emitting gas within…