Related papers: Delayed emission from luminous blue optical transi…
Low mass white dwarfs are the remnants of disrupted red giant stars in binary millisecond pulsars and other exotic binary star systems. Some low mass white dwarfs cool rapidly, while others stay bright for millions of years due to stable…
We present the first deep X-ray observations of a luminous FBOT AT2018cow, at $\sim3.7\,\rm{yr}$ since discovery, together with the re-analysis of the observation at $\delta t\sim 220$ d. X-ray emission is significantly detected at a…
Accreting black-hole binaries change their properties during evolution, passing through two main luminous states, dominated by either hard or soft X-rays. In the hard state, steady compact jets emitting multiwavelength radiation are…
Fast X-ray transients (FXRTs) are short-lived X-ray outbursts with diverse progenitor scenarios, including compact object mergers, stellar core-collapses and tidal disruption events. The Einstein Probe (EP) has enabled the rapid discovery…
Context. Accreting ultracompact binaries contain a white dwarf that is accreting from a degenerate object and have orbital periods shorter than 65 minutes. Aims. The aims of this letter are to report the discovery and the orbital period of…
Optical Transients from gamma-ray burst sources, in addition to offering a distance determination, convey important information on the physics of the emission mechanism, and perhaps also about the underlying energy source. As the gamma-ray…
Supergiant Fast X-ray Transients (SFXTs) are a new class of High Mass X-ray Binaries, discovered by the INTEGRAL satellite, which display flares lasting from minutes to hours, with peak luminosity of 1E36-1E37 erg/s. Outside the bright…
The discovery of SN 2018gep (ZTF18abukavn) challenged our understanding of the late-phase evolution of massive stars and their supernovae (SNe). The fast rise in luminosity of this SN (spectroscopically classified as a broad-lined Type Ic…
A new effect is presented, which changes the emittance during colliding-beam operation in circular colliders. If the initial transverse distribution is Gaussian, the collision probability is much higher for particles in the core of the beam…
Recoiling supermassive black holes (SMBHs) are considered one plausible physical mechanism to explain high velocity shifts between narrow and broad emission lines sometimes observed in quasar spectra. If the sphere of influence of the…
Radio monitoring unveiled late (hundreds to a thousand days) radio flares in a significant fraction of tidal disruption events. We propose that these late-time radio flares are a natural outcome if the surrounding density profile flattens…
Two X-ray sources were recently discovered by Irwin et al. in compact companions to elliptical galaxies to show ultra-luminous flares with fast rise (~ minute) and decay (~ hour), and with a peak luminosity ~10^{40-41} erg/s. Together with…
We present radio observations of 23 optically discovered tidal disruption events (TDEs) on timescales of 500-3200 days post discovery. We detect nine new TDEs that did not have detectable radio emission at earlier times, indicating a…
Short gamma-ray bursts (sGRBs) are thought to be produced by binary NS mergers. While a sGRB requires a relativistic jet to break out of ejecta, the jet may be choked and fails to produce a successful sGRB. We propose a "delayed breakout"…
Black hole impacts on accretion disks in galactic nuclei can power luminous transients, but predicting their observable signatures is challenging because the post-collision flow is highly time-dependent and inhomogeneous. We present a…
We discuss the implications of rapid (few-minute) variability in the TeV flux of blazars, which has been observed recently with the HESS and MAGIC telescopes. The variability timescales seen in PKS 2155-304 and Mrk 501 are much shorter than…
The RossiXTE mission provided us with an unprecedentedly large database of X-ray observations of transient black-hole candidates. These systems are crucial for the understanding of the physical properties of mass accretion onto black holes.…
In classical P-Cygni profiles, theory predicts emission to peak at zero rest velocity. However, supernova spectra exhibit emission that is generally blue shifted. While this characteristic has been reported in many supernovae, it is rarely…
Many RR Lyrae stars show long-term variations of their pulsation period, some of them in a cyclic way. Such behaviour can be attributed to the light-travel time effect (LTTE) caused by an unseen companion. Solutions of the LTTE often…
The exact nature of the luminous fast blue optical transient AT 2018cow is still debated. In this first of a two-paper series, we present a detailed analysis of three Hubble Space Telescope (HST) observations of AT 2018cow covering…