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

We present three XMM-Newton observations of the ultra-luminous compact X-ray source Holmberg II X-1 in its historical brightest and faintest states. The source was in its brightest state in April 2002 with an isotropic X-ray luminosity of ∼ 2 × 10 40 erg s −1 but changed to a peculiar low/soft state in September 2002 in which the X-ray flux dropped by a factor of ∼ 4 and the spectrum softened. In all cases, a soft excess component, which can be described by a simple or multicolor disk blackbody (MCD; kT ∼ 120 − 170 eV), is statistically required in addition to a power-law continuum (Γ ∼ 2.4 − 2.9). Both the spectral components became weaker and softer in the low/soft state, however, the dramatic variability is seen in the power-law component. This spectral transition is opposite to the 'canonical' high/softlow/hard transitions seen in many Galactic black hole binaries. There is possible contribution from an optically thin thermal plasma. When this component is taken into account, the spectral transition appears to be normal -a drop of the power-law flux and slightly softer blackbody component in the low state.

We investigate the origin of the soft X-ray excess emission from narrow-line Seyfert 1 galaxies Akn 564 and Mrk 1044 using XMM-Newton observations. We find clear evidence for time delays between the soft and hard X-ray emission from Akn 564 based on a ∼ 100 ks long observation. The variations in the 4 − 10 keV band lag behind that in the 0.2 − 0.5 keV band by 1768 ± 122 s. The full band power density spectrum (PDS) of Akn 564 has a break at ∼ 1.2 × 10 −3 Hz with power-law indices of ∼ 1 and ∼ 3 below and above the break. The hard (3 − 10 keV) band PDS is stronger and flatter than that in the soft (0.2 − 0.5 keV) band. Based on a short observation of Mrk 1044, we find no correlation between the 0.2 − 0.3 keV and 5 − 10 keV bands at zero lag. These observations imply that the soft excess is not the reprocessed hard X-ray emission. The high resolution spectrum of Akn 564 obtained with the reflection grating spectrometer (RGS) shows evidence for a highly ionized and another weakly ionized warm absorber medium. The smeared wind and blurred ionized reflection models do not describe the EPIC-pn data adequately. The spectrum is consistent with a complex model consisting of optically thick Comptonization in a cool plasma for the soft excess and a steep power-law, modified by two warm absorber media as inferred from the RGS data and the foreground Galactic absorption. The smeared wind and optically thick Comptonization models both describe the spectrum of Mrk 1044 satisfactorily, but the ionized reflection model requires extreme parameters. The data suggest two component corona -a cool, optically thick corona for the soft excess and a hot corona for the power-law component. The existence of a break in the soft band PDS suggests a compact cool corona that can either be an ionized surface of the inner disk or an inner optically thick region coupled to a truncated disk. The steep power-law component is likely arising from an extended region.

The optical spectra of the recurrent nova U Sco obtained in Ðve epochs 0.45È42.35 days after the 1999 outburst maximum are presented here. For the Ðrst time, an outburst spectrum of U Sco has been obtained as early as 0.45 days after maximum. The spectral evolution is broadly similar to the 1979 and 1987 outbursts. The mass of the ejected shell is estimated to be D10~7 Based on the Mg I b M _. 5174 A and the Fe I ] Ca I absorption indices in the late-decline phase spectrum of day 42.35, we esti-5270 A mate the secondary to be a K2 subgiant star.