Lags measured from correlated X-ray/UV/optical monitoring of AGN allow us to determine whether UV/optical variability is driven by reprocessing of X-rays or Xray variability is driven by UV/optical seed photon variations. We present the results of the largest study to date of the relationship between the X-ray, UV and optical variability in an AGN with 554 observations, over a 750d period, of the Seyfert 1 galaxy NGC5548 with Swift. There is a good overall correlation between the X-ray and UV/optical bands, particularly on short timescales (tens of days). These bands lag the X-ray band with lags which are proportional to wavelength to the power 1.23±0.31. This power is very close to the power (4/3) expected if short timescale UV/optical variability is driven by reprocessing of X-rays by a surrounding accretion disc.The observed lags, however, are longer than expected from a standard Shakura-Sunyaev accretion disc with X-ray heating, given the currently accepted black hole mass and accretion rate values, but can be explained with a slightly larger mass and accretion rate, and a generally hotter disc.Some long term UV/optical variations are not paralleled exactly in the X-rays, suggesting an additional component to the UV/optical variability arising perhaps from accretion rate perturbations propagating inwards through the disc.

Swift monitoring of NGC 4151 with an∼6hr sampling over a total of 69 days in early 2016 is used to construct light curves covering five bands in the X-rays (0.3-50keV) and six in the ultraviolet (UV)/optical (1900-5500Å). The three hardest X-ray bands (>2.5keV) are all strongly correlated with no measurable interband lag,while the two softer bands show lower variability and weaker correlations. The UV/optical bands are significantly correlated with the X-rays, lagging ∼3-4days behind the hard X-rays. The variability within the UV/optical bands is also strongly correlated, with the UV appearing to lead the optical by ∼0.5-1days. This combination of 3day lags between the X-rays and UV and 1day lags within the UV/optical appears to rule out the "lamp-post" reprocessing model in which a hot, X-ray emitting corona directly illuminates the accretion disk, which then reprocesses the energy in the UV/optical. Instead, these results appear consistent with the Gardner & Done picture in which two separate reprocessings occur: first, emission from the corona illuminates an extreme-UV-emitting toroidal component that shields the disk from the corona; this then heats the extreme-UV component,which illuminates the disk and drives its variability.

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 X-ray spectral variability of 24 local active galactic nuclei (AGN) from the Palomar sample of nearby galaxies, as observed mainly by Swift. From hardness ratio measurements, we find that 18 AGN with low accretion rates show hardening with increasing count rate, converse to the softer-when-brighter behaviour normally observed in AGN with higher accretion rates. Two AGN show softening with increasing count rate, two show more complex behaviour, and two do not show any simple relationship.Sufficient data were available for the spectra of 13 AGN to be summed in fluxbins. In 9 of these sources, correlated luminosity-dependent changes in the photon index (Γ) of a power-law component are found to be the main cause of hardness variability. For 6 objects, with a low accretion rate as a fraction of the Eddington rate (ṁ Edd ), Γ is anticorrelated withṁ Edd , i.e. 'harder-when-brighter' behaviour is observed. The 3 higher-ṁ Edd -rate objects show a positive correlation between Γ anḋ m Edd . This transition from harder-when-brighter at lowṁ Edd to softer-when-brighter at highṁ Edd can be explained by a change in the dominant source of seed-photons for X-ray emission from cyclo-synchrotron emission from the Comptonising corona itself to thermal seed-photons from the accretion disc. This transition is also seen in the 'hard state' of black hole X-ray binaries (BHXRBs). The results support the idea that LINERs are analogues of BHXRBs in the hard state and that Seyferts are analogues of BHXRBs in either the high-accretion-rate end of the hard state or in the hard-intermediate state.

We present long-term (months-years) X-ray spectral variability of the Seyfert 1.8 galaxy NGC 1365 as observed by Swift, which provides well sampled observations over a much longer timescale (6 years) and a much larger flux range than is afforded by other observatories. At very low luminosities the spectrum is very soft, becoming rapidly harder as the luminosity increases and then, above a particular luminosity, softening again. At a given flux level, the scatter in hardness ratio is not very large, meaning that the spectral shape is largely determined by the luminosity. The spectra were therefore summed in luminosity bins and fitted with a variety of models. The best fitting model consists of two power laws, one unabsorbed and another, more luminous, which is absorbed. In this model, we find a range of intrinsic 0.5-10.0 keV luminosities of approximately 1.1 − 3.5 ergs s −1 , and a very large range of absorbing columns, of approximately 10 22 − 10 24 cm −2 . Interestingly, we find that the absorbing column decreases with increasing luminosity, but that this result is not due to changes in ionisation. We suggest that these observations might be interpreted in terms of a wind model in which the launch radius varies as a function of ionising flux and disc temperature and therefore moves out with increasing accretion rate, i.e. increasing X-ray luminosity. Thus, depending on the inclination angle of the disc relative to the observer, the absorbing column may decrease as the accretion rate goes up. The weaker, unabsorbed, component may be a scattered component from the wind.

The origin of short timescale (weeks/months) variability of AGN, whether due to intrinsic disc variations or reprocessing of X-ray emission by a surrounding accretion disc, has been a puzzle for many years. However recently a number of observational programmes, particularly of NGC5548 with Swift, have shown that the UV/optical variations lag behind the X-ray variations in a manner strongly supportive of X-ray reprocessing. Somewhat surprisingly the implied size of the accretion disc is ∼ 3× greater than expected from a standard, smooth, Shakura-Sunyaev thin disc model. Although the difference may be explained by a clumpy accretion disc, it is not clear whether the difference will occur in all AGN or whether it may change as, eg, a function of black hole mass, accretion rate or disc temperature. Measurements of interband lags for most AGN require long timescale monitoring, which is hard to arrange. However for low mass (< 10 6 M⊙) AGN, the combination of XMM-Newton EPIC (X-rays) with the optical monitor in fast readout mode allows an X-ray/UVoptical lag to be measured within a single long observation. Here we summarise previous related observations and report on XMM-Newton observations of NGC4395 (mass 100× lower, accretion rate ∼ 20× lower than for NGC5548). We find that the UVW1 lags the X-rays by ∼ 470s. Simultaneous observations at 6 different ground based observatories also allowed the g-band lag (∼ 800s) to be measured. These observations are in agreement with X-ray reprocessing but initial analysis suggests that, for NGC4395, they do not differ markedly from the predictions of the standard thin disc model. Models for UV/Optical Variability and relationship to X-ray VariabilityThe origin of UV/optical variability in AGN and its relationship to X-ray variability has been a puzzle for some time and there are two main possibilities for the origin of the UV/optical variability. The UV/optical variability could result from reprocessing of X-ray emission by the accretion disc or it could simply be the result of intrinsic variability of the thermal emission from the disc. These two models can, in principle, be distinguished simply by measuring the lag between the X-ray and UV/optical wavebands. In the reprocessing model, the UV/optical variations will lag behind the X-ray variations by the light travel time between the two emission regions. For a typical AGN this time will be a few hours. If the UV/optical variations are produced by intrinsic ⋆ Corresponding author: e-mail: imh@soton.ac.uk disc variations there are two possible lag timescales. If the UV/optical photons are the seed photons for the X-ray emission, being Compton up-scattered in the central corona, then if the X-ray variations are driven by seed photon variations, the X-ray emission will lag behind the UV/optical variations by the light travel time between the two emission regions, ie a few hours. Alternatively, if the UV/optical variations are caused by inwardly propagating accretion rate variations (Arévalo & Uttley 2006), these variations will ev...

The core of the nearby galaxy NGC 660 has recently undergone a spectacular radio outburst; using a combination of archival radio and Chandra X-ray data, together with new observations, the nature of this event is investigated. Radio observations made using e-MERLIN in mid-2013 show a new compact and extremely bright continuum source at the centre of the galaxy. High angular resolution observations carried out with the European VLBI Network show an obvious jet-like feature to the north east and evidence of a weak extension to the west, possibly a counter-jet. We also examine high angular resolution Hi spectra of these new sources, and the radio spectral energy distribution using the new wide-band capabilities of e-MERLIN. We compare the properties of the new object with possible explanations, concluding that we are seeing a period of new AGN activity in the core of this polar ring galaxy.

We study multi-wavelength variability of a bare Seyfert 1 galaxy Fairall 9 using Swift monitoring observations consisting of 165 usable pointings spanning nearly two years and covering six UV/optical bands and X-rays. Fairall 9 is highly variable in all bands though the variability amplitude decreases from X-ray to optical bands.The variations in the X-ray and UV/optical bands are strongly correlated. Our reverberation mapping analysis using the JAVALIN tool shows that the variation in the UV/optical bands lag behind the variations in the X-ray band by ∼ 2 − 10 days.These lag measurements strongly suggest that the optical/UV variations are mainly caused by variations in the X-rays, and the origin of most of the optical/UV emission is X-ray reprocessing. The observed lags are found to vary as τ ∝ λ 1.36±0.13 , consistent with the prediction, τ ∝ λ 4/3 , for X-ray reprocessing in a standard accretion disc. However, the predicted lags for an standard accretion disc with X-ray reprocessing using black hole mass (M BH ∼ 2.6 × 10 8 M ⊙ ) estimated from the reverberation mapping of broad emission lines and accretion rate relative to the Eddington rate (ṁ E = 0.02) are shorter than the observed lags. These observations suggest that accretion disc in Fairall 9 is larger than that predicted by the standard disc model, and confirm similar findings in a few other Seyfert 1 galaxies such as NGC 5548.