Since the discovery of the first broad iron-K line in 1995 from the Seyfert Galaxy MCG-6-30-15 1 , broad iron-K lines have been found in several other Seyfert galaxies 2 , from accreting stellar mass black holes 3 and even from accreting neutron stars 4 . The iron-K line is prominent in the reflection spectrum 5,6 created by the hard X-ray continuum irradiating dense accreting matter. Relativistic distortion 7 of the line makes it sensitive to the strong gravity and spin of the black hole 8 . The accompanying iron-L line emission should be detectable when the iron abundance is high. Here we report the first discovery of both iron-K and L emission, using XMM-Newton observations of the Narrow-1

GRB 160821B is a short duration gamma-ray burst (GRB) detected and localized by the Neil Gehrels Swift Observatory in the outskirts of a spiral galaxy at z=0.1613, at a projected physical offset of ≈16 kpc from the galaxy's center. We present Xray, optical/nIR and radio observations of its counterpart and model them with two distinct components of emission: a standard afterglow, arising from the interaction of the relativistic jet with the surrounding medium, and a kilonova, powered by the radioactive decay of the sub-relativistic ejecta. Broadband modeling of the afterglow data reveals a weak reverse shock propagating backward into the jet, and a likely jet-break at ≈3.5 d. This is consistent with a structured jet seen slightly off-axis (θ view ∼ θ core ) while expanding into a low-density medium (n ≈10 −3 cm −3 ). Analysis of the kilonova properties suggests a rapid evolution toward red colors, similar to AT2017gfo, and a low nIR luminosity, possibly due to the presence of a long-lived neutron star. The global properties of the environment, the inferred low mass (M ej 0.006 M ⊙ ) and velocities (v ej 0.05c) of lanthanide-rich ejecta are consistent with a binary neutron star merger progenitor.

X-ray reverberation echoes are assumed to be produced in the strongly distorted spacetime around accreting supermassive black holes. This signal allows us to spatially map the geometry of the inner accretion flow 1,2 -a region which cannot yet be spatially resolved by any telescopeand provides a direct measure of the black hole mass and spin. The reverberation timescale is set by the light travel path between the direct emission from a hot X-ray corona and the reprocessed emission from the inner edge of the accretion disc 3-6 . However, there is an inherent degeneracy in the reverberation signal between black hole mass, inner disc radius and height of the illuminating corona above the disc. Here, we use a long X-ray observation of the highlyvariable active galaxy, IRAS 13224-3809, to track the reverberation signal as the system evolves on timescales of a day 7,8 . With the inclusion of all the relativistic effects, modelling reveals that the height of the X-ray corona increases with increasing luminosity, providing a dynamic view of the inner accretion region. This simultaneous modelling allows us to break the inherent degeneracies and obtain an independent timing-based estimate for the mass and spin of the black hole. The uncertainty on black hole mass is comparable to the leading optical reverberation method 9 , making X-ray reverberation a powerful technique, particularly for sources with low optical variability 10 .IRAS 13224-3809 is a nearby and bright active galactic nucleus (AGN). As a Narrow Line Seyfert 1 (NLS1) type AGN, it is characterised by a high rate of accretion 11,12 onto a relatively low mass, supermassive black hole ( "#~1 0 ' ⊙ , where ⊙ is the solar mass). In accordance with such extreme rates of accretion, highly ionised winds driven from the accretion flow at near relativistic speeds have been detected from this source 13,14 . IRAS 13224-3809 has been observed for 16 full orbits (~130 ks per orbit) with the European Space Agency's X-ray Multi-Mirror Mission (XMM-Newton 15 ), totalling 2 Mega-seconds of observations. The source is one of the most variable X-ray objects in the sky, undergoing rapid and large amplitude variations on timescales of minutes 7,8 . It is unique in that the shape of the variability (visualised as power spectral density -PSD) is also time-dependent, varying on days timescales 7,8 . This short-timescale variability is observed in most AGN, which -along with gravitational microlensing observations of quasars 16 -indicates that the X-rays are emerging from a region within the central ~15 + (where + = "# / 0 is the gravitational radius, G is the gravitational constant and c is the speed of light). At a distance of nearly a billion light years, such regions have an angular size on the sky too small to be resolved using present or planned instruments.Observations of AGN tell us there must be a hot 'corona' of electrons close to the black hole, which constitutes a significant fraction of their total luminosity 11,12 . The origin and geometry of this corona is unknown, but i...

We present observations of rapid (sub-second) optical flux variability in V404 Cyg during its 2015 June outburst. Simultaneous three-band observations with the ULTRACAM fast imager on four nights show steep power spectra dominated by slow variations on ∼ 100-1000 s timescales. Near the peak of the outburst on June 26, a dramatic change occurs and additional, persistent sub-second optical flaring appears close in time to giant radio and X-ray flaring. The flares reach peak optical luminosities of ∼ few × 10 36 erg s −1 . Some are unresolved down to a time resolution of 24 milliseconds. Whereas the fast flares are stronger in the red, the slow variations are bluer when brighter. The redder slopes, emitted power, and characteristic timescales of the fast flares can be explained as optically-thin synchrotron emission from a compact jet arising on size scales ∼140-500 Gravitational radii (with a possible additional contribution by a thermal particle distribution). The origin of the slower variations is unclear. The optical continuum spectral slopes are strongly affected by dereddening uncertainties and contamination by strong Hα emission, but the variations of these slopes follow relatively stable loci as a function of flux. Cross-correlating the slow variations between the different bands shows asymmetries on all nights consistent with a small red skew (i.e., red lag). X-ray reprocessing and non-thermal emission could both contribute to these. These data reveal a complex mix of components over five decades in timescale during the outburst.