Related papers: Oscillation Phenomena in the disk around the massi…
We report on the submillimeter properties of Sagittarius A* derived from observations with the Submillimeter Array and its polarimeter. We find that the spectrum of Sgr A* between 230 and 690 GHz is slightly decreasing when measured…
High-frequency quasi-periodic oscillations (QPOs) appear in general-relativistic magnetohydrodynamic simulations of magnetically choked accretion flows around rapidly rotating black holes (BHs). We perform polarized radiative transfer…
We have detected substructure within the smooth scattering disk of the celebrated Galactic Center radio source Sagittarius A* (SgrA*). We observed this structure at 1.3 cm wavelength with the Very Long Baseline Array together with the Green…
Quasi-periodic oscillation (QPO) detected in the X-ray radiation of black hole X-ray binaries (BHXBs) is thought to originate from dynamical processes in the close vicinity of the black holes (BHs), and thus carries important physical…
We summarize the current state of polarization observations of Sagittarius A*, the compact radio source and supermassive black hole candidate in the Galactic Center. These observations are providing new tools for understanding accretion…
We analyzed 77 epochs of Atacama Large Millimeter/submillimeter Array (ALMA) archival data to investigate flux variability in Sagittarius A$^*$ (Sgr A$^*$), the supermassive black hole at the Galactic Center. Among these, we identified a…
We determine the spin of a supermassive black hole in the context of discseismology by comparing newly detected quasi-periodic oscillations (QPOs) of radio emission in the Galactic centre, Sagittarius A* (Sgr A*), as well as infrared and…
The near-infrared emission from the black hole at the Galactic center (Sgr A*) has unique properties. The most striking feature is a suggestive periodic sub-structure that has been observed in a couple of flares so far. Using near-infrared…
We report on 85-101 GHz light curves of the Galactic Center supermassive black hole, Sagittarius A* (Sgr A*), observed in April 2017 with the Atacama Large Millimeter/submillimeter Array (ALMA). This study of high-cadence full-Stokes data…
In all four microquasars which show double peak kHz QPOs, the ratio of the two frequencies is 3:2. This strongly supports the suggestion that twin peak kHz QPOs are due to a resonance between some modes of accretion disk oscillations. Here,…
The compact radio source at the center of our Galaxy, Sagittarius A* (Sgr A*), is the subject of intensive study as it provides a close-up view of an accreting supermassive black hole. Sgr A* provides us with a prototype of a low-luminosity…
PKS 1155+251 is a radio-loud quasar source at z=0.203. Observations using very long baseline interferometry (VLBI) at ~2, 5, 8 and 15 GHz show that the structure of the radio source is quite complicated on parsec scales and that the outer…
Sagittarius A* (Sgr A*) is a compact radio source at the Galactic center. Observations have confirmed that its mass is approximately (4.1)*10$^{6}$ M$_{\odot}$, and Sgr A* is generally believed to be powered by gas accretion onto a…
3:2 and/or 3:1 twin high frequency quasi-periodic oscillations (HFQPOs) have been measured for the three microquasars GRO J1655-40, XTE J1550-564 and GRS 1915+105. For a test particle orbiting a rotating black on a stable circular orbit…
Context. The compact radio and near-infrared (NIR) source Sagittarius A* (Sgr A*) associated with the supermassive black hole in the Galactic center was observed at 7 mm in the context of a NIR triggered global Very Long Baseline Array…
We report the discovery of a $\sim 1.5 \times 10^{-4}$ Hz ($\sim 2$ hr) X-ray quasi-periodic oscillation (QPO) in the active galaxy MS 2254.9-3712, using a $\sim 70$ ks XMM-Newton observation. The QPO is significantly detected ($\sim 3.3…
We report the discovery of variability in the linear polarization from the Galactic Center black hole source, Sagittarius A*. New polarimetry obtained with the Berkeley-Illinois-Maryland Association array at a wavelength of 1.3 mm shows a…
The shocked wave created on the accretion disk after different physical phenomena (accretion flows with pressure gradients, star-disk interaction etc.) may be responsible observed Quasi Periodic Oscillations (QPOs) in $X-$ray binaries. We…
We present the first fully relativistic study of gravitational radiation from bodies in circular equatorial orbits around the massive black hole at the Galactic Center, Sgr A* and we assess the detectability of various kinds of objects by…
There is some evidence, though yet unconfirmed, that Sagittarius A*--the supermassive black hole at the Galactic center--emits its radio waves modulated with a ~100-day period. What is intriguing about this apparent quasi-periodicity is…