On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ∼ 1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40 − 8 + 8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 M ⊙ . An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ∼ 40 Mpc ) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ∼10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ∼ 9 and ∼ 16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta.

We present results from a homogeneous analysis of the broadband 0.3 − 10 keV CCD resolution as well as of soft X-ray high-resolution grating spectra of a hard X-ray flux-limited sample of 26 Seyfert galaxies observed with XMM-Newton. Our goal is to characterise warm absorbers (WAs) along the line-of-sight to the active nucleus. We significantly detect WAs in 65% of the sample sources. Our results are consistent with WAs being present in at least half of the Seyfert galaxies in the nearby Universe, in agreement with previous estimates . We find a gap in the distribution of the ionisation parameter in the range 0.5 < log ξ < 1.5 which we interpret as a thermally unstable region for WA clouds. This may indicate that the warm absorber flow is probably constituted by a clumpy distribution of discrete clouds rather than a continuous medium. The distribution of the WA column densities for the sources with broad Fe Kα lines are similar to those sources which do not have broadened emission lines. Therefore the detected broad Fe Kα emission lines are bonafide and not artifacts of ionised absorption in the soft X-rays. The WA parameters show no correlation among themselves, with the exception of the ionisation parameter versus column density. The shallow slope of the log ξ versus log v out linear regression (0.12 ± 0.03) is inconsistent with the scaling laws predicted by radiation or magneto-hydrodynamic-driven winds. Our results suggest also that WA and Ultra Fast Outflows (UFOs) do not represent extreme manifestation of the same astrophysical system.

We report the results of intensive X-ray, UV and optical monitoring of the Seyfert 1 galaxy NGC 4593 with Swift. There is no intrinsic flux-related spectral change in the the variable components in any band with small apparent variations due only to contamination by a second constant component, possibly a (hard) reflection component in the X-rays and the (red) host galaxy in the UV/optical bands. Relative to the shortest wavelength band, UVW2, the lags of the other UV and optical bands are mostly in agreement with the predictions of reprocessing of high energy emission from an accretion disc. The U-band lag is, however, far larger than expected, almost certainly because of reprocessed Balmer continuum emission from the more distant broad line region gas. The UVW2 band is well correlated with the X-rays but lags by ∼ 6× more than expected if the UVW2 results from reprocessing of X-rays on the accretion disc. However, if the lightcurves are filtered to remove variations on timescales > 5d, the lag approaches the expectation from disc reprocessing. MEMEcho analysis shows that direct X-rays can be the driver of most of the variations in the UV/optical bands as long as the response functions for those bands all have long tails (up to 10d) in addition to a strong peak (from disc reprocessing) at short lag (< 1 d). We interpret the tails as due to reprocessing from the surrounding gas. Comparison of X-ray to UVW2 and UVW2 to V-band lags for 4 AGN, including NGC 4593, shows that all have UVW2 to V-band lags which exceed the expectations from disc resprocessing by ∼ < 2. However the X-ray to UVW2 lags are, mostly, in greater excess from the expectations from disc reprocessing and differ between AGN. The largest excess is in NGC 4151. Absorption and scattering may be affecting X-ray to UV lags.

We present the results of the simultaneous deep XMM-Newton and Chandra observations of the bright Seyfert 1.9 galaxy MCG À5-23-16, which is thought to have one of the best known examples of a relativistically broadened iron K line. The time-averaged spectral analysis shows that the iron K-shell complex is best modeled with an unresolved narrow emission component (FWHM < 5000 km s À1 , EW $ 60 eV ) plus a broad component. This latter component has FWHM $ 44;000 km s À1 and EW $ 50 eV. Its profile is well described by an emission line originating from an accretion disk viewed with an inclination angle $40 , with the emission arising from within a few tens of gravitational radii of the central black hole. The time-resolved spectral analysis of the XMM-Newton EPIC pn spectrum shows that both the narrow and broad components of the Fe K emission line appear to be constant in time within the errors. We detected a narrow sporadic absorption line at 7.7 keV, which appears to be variable on a timescale of 20 ks. If associated with Fe xxvi Ly, this absorption is indicative of a possibly variable, high-ionization, high-velocity outflow. The variability of this absorption feature appears to rule out a local (z ¼ 0) origin. The analysis of the XMM-Newton RGS spectrum reveals that the soft X-ray emission of MCG À5-23-16 is likely dominated by several emission lines superimposed on an unabsorbed scattered power-law continuum. The lack of strong Fe L-shell emission, together with the detection of a strong forbidden line in the O vii triplet, is consistent with a scenario in which the soft X-ray emission lines are produced in a plasma photoionized by the nuclear emission.

We report the first clear evidence for the simultaneous presence of a low-frequency break and a QPO in the fluctuation power spectrum of a well-known ultraluminous X-ray source (ULX) in M82 using long XMM-Newton observations. The break occurs at a frequency of 34.2+6-3 mHz. The QPO has a centroid at νQPO=114.3+/-1.5 mHz, a coherence Q≡ν_QPO/ΔνFWHM~=3.5, and an amplitude (rms) of 19% in the 2-10 keV band. The power spectrum is approximately flat below the break frequency and then falls off above the break frequency as a power law with the QPO superposed. This form of the power spectrum is characteristic of the Galactic X-ray binaries (XRBs) in their high or intermediate states. M82 X-1 was likely in an intermediate state during the observation. The EPIC pn spectrum is well described by a model comprising an absorbed power law (Γ~2) and an iron line at ~6.6 keV with a width σ~0.2 keV and an equivalent width of ~180 eV. Using the well-established correlations between the power and energy spectral parameters for XRBs, we estimate a black hole mass for M82 X-1 in the range of ~25-520 M_solar, including systematic errors that arise due to the uncertainty in the calibration of the photon spectral index versus QPO frequency relation