Search

Black hole accretion discs can produce powerful outflowing plasma (disc winds), seen as blue-shifted absorption lines in stellar and supermassive systems. These winds in Quasars have an essential role in controlling galaxy formation across cosmic time, but there is no consensus on how these are physically launched. A single unique observation of a stellar-mass black hole GRO J1655-40 was used to argue that magnetic driving was the only viable mechanism and motivated unified models of magnetic winds in both binaries and Quasars. The alternative, X-ray heating (thermal-radiative wind), was ruled out for the low observed luminosity by the high wind density estimated from an absorption line of a metastable level of Fe xxii. Here we reanalyse these data using a photoionisation code that includes cascades from radiative excitation as well as collisions in populating the metastable level. The cascade reduces the inferred wind density by more than an order of magnitude. The derived column is also optically thick, so the source is intrinsically more luminous than observed. We show that a thermal-radiative wind model calculated from a radiation hydrodynamic simulation matches well with the data. We revisit the previous magnetic wind solution and show that this is also optically thick, leading to a larger source luminosity. However, unlike the thermal-radiative wind, it struggles to reproduce the overall ion population at the required density. These results remove the requirement for a magnetic wind in these data and remove the basis of the self-similar unified magnetic wind models extrapolated to Quasar outflows, 14 pages, 15 figures, accepted by MNRAS

We explore the accretion geometry in Arakelian 120 using intensive UV and X-ray monitoring from \textit{Swift}. The hard X-rays ($1-10$ keV) show large amplitude, fast (few-day) variability, so we expect reverberation from the disc to produce UV variability from the varying hard X-ray illumination. We model the spectral energy distribution including an outer standard disc (optical), an intermediate warm Comptonisation region (UV and soft X-ray) and a hot corona (hard X-rays). Unlike the lower Eddington fraction AGN (NGC 4151 and NGC 5548 at $L/L_{Edd}\sim 0.02$ and $0.03$ respectively), the SED of Akn 120 ($L\sim 0.05L_{Edd}$) is dominated by the UV, restricting the impact of reverberating hard X-rays by energetics alone. Illumination from a hard X-ray corona with height $\sim10 R_g$ produces minimal UV variability. Increasing the coronal scale height to $\sim 100 R_g$ improves the match to the observed amplitude of UV variability as the disc subtends a larger solid angle, but results in too much fast variability to match the UV data. The soft X-rays (connected to the UV in the warm Comptonisation model) are more variable than the hard, but again contain too much fast variability to match the observed smoother variability seen in the UV. Results on lower Eddington fraction AGN have emphasised the contribution from reverberation from larger scales (the broad line region), but reverberation induces lags on similar timescales to the smoothing, producing a larger delay than is compatible with the data. We conclude that the majority of the UV variability is therefore intrinsic, connected to mass accretion rate fluctuations in the warm Comptonisation region., Accepted in MNRAS

NGC 1313 X-2 is one of the few known pulsating ultraluminous X-ray sources (PULXs), and so is thought to contain a neutron star that accretes at highly super-Eddington rates. However, the physics of this accretion remains to be determined. Here, we report the results of two simultaneous XMM-Newton and HST observations of this PULX taken to observe two distinct X-ray behaviours as defined from its Swift light curve. We find that the X-ray spectrum of the PULX is best described by the hard ultraluminous regime during the observation taken in the lower flux, lower variability amplitude behaviour; its spectrum changes to a broadened disc during the higher flux, higher variability amplitude epoch. However, we see no accompanying changes in the optical/UV fluxes, with the only difference being a reduction in flux in the near-infrared (NIR) as the X-ray flux increased. We attempt to fit irradiation models to explain the UV/optical/IR fluxes but they fail to provide meaningful constraints. Instead, a physical model for the system leads us to conclude that the optical light is dominated by a companion O/B star, albeit with an IR excess that may be indicative of a jet. We discuss how these results may be consistent with the precession of the inner regions of the accretion disc leading to changes in the observed X-ray properties, but not the optical, and whether we should expect to observe reprocessed emission from ULXs., RS gratefully acknowledges the receipt of a studentship grant from the STFC ST/N50404X/1. TPR was funded as part of the STFC consolidated grant ST/K000861/1. RS is extremely grateful for the guidance provided by Andrew Dolphin on HST data analysis. [...] EA acknowledges funding from the Italian Space Agency, contract ASI/INAF n. I/004/11/4. LZ acknowledges financial support from the Italian Space Agency (ASI) and National Institute for Astrophysics (INAF) under agreements ASI-INAF I/037/12/0 and ASI-INAF n.2017-14-H.0 and from INAF ’Sostegno alla ricerca scientifica main streams dell’INAF’ Presidential Decree 43/2018. RS acknowledges grant number 12073029 from the National Science Foundation of China.

The nature and geometry of the accretion flow in the low/hard state of black hole binaries is currently controversial. While most properties are generally explained in the truncated disc/hot inner flow model, the detection of a broad residual around the iron line argues for strong relativistic effects from an untruncated disc. Since spectral fitting alone is somewhat degenerate, we combine it with the additional information in the fast X-ray variability and perform a full spectral-timing analysis for NICER and NuSTAR data on a bright low/hard state of MAXI J1820+070. We model the variability with propagating mass accretion rate fluctuations by combining two separate current insights: that the hot flow is spectrally inhomogeneous, and that there is a discontinuous jump in viscous time-scale between the hot flow and variable disc. Our model naturally gives the double-humped shape of the power spectra, and the increasing high-frequency variability with energy in the second hump. Including reflection and reprocessing from a disc truncated at a few tens of gravitational radii quantitatively reproduces the switch in the lag-frequency spectra, from hard lagging soft at low frequencies (propagation through the variable flow) to the soft lagging hard at the high frequencies (reverberation from the hard X-ray continuum illuminating the disc). The viscous time-scale of the hot flow is derived from the model, and we show how this can be used to observationally test ideas about the origin of the jet., 17 pages, 11 figures, 3 tables. Accepted for publication in MNRAS

UltraFast Outflows (UFO) are observed in some active galactic nuclei (AGN), with blueshifted and highly ionised Fe-K absorption features. AGN typically have a UV bright accretion flow, so UV line driving is an obvious candidate for launching these winds. However this mechanism requires material with UV opacity, in apparent conflict with the observed high ionisation state of the wind. In this paper we synthesise the X-ray energy spectra resulting from different lines of sight through a state of the art radiation hydrodynamics UV line driven disc wind simulation. We demonstrate that there are some lines of sight which only intercept highly ionised and fast outflowing material. The cooler material required for the UV line driving acceleration is out of the line of sight, close to the disc, shielded from the X-rays by a failed wind. We fit these simulated wind spectra to data from the archetypal UFO source PG 1211+143 and show that they broadly reproduce the depth and velocity of the iron absorption lines seen. This directly demonstrates that UV line driving is a viable mechanism to launch even the fastest UFOs. We simulate microcalorimeter observations of this wind and show that their high energy resolution can resolve the detailed structure in the wind and recover the wind energetics when combined with models which correctly estimate the line formation radius of the wind. New data from microcalorimeters will pave the way for physical predictions of AGN wind feedback in cosmological simulations., Comment: 17 pages, 19 figures, accepted for publication in MNRAS. Please ignore the figure in the last page (I tried to remove it but cannot. Please let me know how if you know...)

RE J1034+396 is a narrow-line Seyfert 1 galaxy (NLS1) in which the first significant X-ray quasi-periodic oscillation (QPO) in an active galactic nuclei (AGN) was observed in 2007. We report the detection of this QPO in a recent XMM-Newton observation in 2018 with an even higher significance. The quality factor of this QPO is 20, and its period is 3550 $\pm$ 80 s, which is 250 $\pm$ 100 s shorter than in 2007. While the QPO's period has no significant energy dependence, its fractional root-mean-square (rms) variability increases from 4% in 0.3-1 keV to 12% in 1-4 keV bands. An interesting phenomenon is that the QPO in 0.3-1 keV leads that in the 1-4 keV bands by 430 $\pm$ 50 s with a high coherence, opposite to the soft X-ray lag reported for the observation in 2007. We speculate that the QPO has an intrinsic hard lag, while the previous reported soft lag is caused by the interference of stochastic variability. This soft X-ray lead in the new data supports the idea that the QPO of RE J1034+396 is a possible AGN counterpart of the 67 Hz high-frequency QPO seen in the black hole binary (BHB) GRS 1915+105. We also search for QPO harmonics, but do not find any significant signals. Our new data reinforce previous results that the QPO is seen in a specific spectral state, as the only 2 observations showing no significant QPO signal exhibit an even stronger soft X-ray excess than the other 6 observations which display the QPO. Therefore, our results imply that the QPO in RE J1034+396 is physically linked to a soft X-ray component., 13 pages, 9 figures, accepted for publication in MNRAS

Based on recent X-ray observations, ultra-fast outflows from supermassive black holes are expected to have enough energy to dramatically affect their host galaxy but their launch and acceleration mechanisms are not well understood. We perform two-dimensional radiation hydrodynamics simulations of UV line-driven disc winds in order to calculate the mass loss rates and kinetic power in these models. We develop a new iterative technique which reduces the mass accretion rate through the inner disc in response to the wind mass loss. This makes the inner disc is less UV bright, reducing the wind power compared to previous simulations which assumed a constant accretion rate with radius. The line-driven winds in our simulations are still extremely powerful, with around half the supplied mass accretion rate being ejected in the wind for black holes with mass $10^8-$$10^{10}\, M_\odot$ accreting at $L/L_{\rm Edd}=0.5-$$0.9$. Our results open up the way for estimating the growth rate of supermassive black hole and evaluating the kinetic energy ejected into the inter stellar medium (active galactic nuclei feedback) based on a physical model of line-driven disc winds., Comment: 12 pages, 7 figures, accepted for publication in MNRAS

BackgroundThe Ontario Breast Screening Program expanded in July 2011 to screen high-risk women age 30–69 years with annual magnetic resonance imaging (MRI) and digital mammography. This study examined the benefits of screening with mammography and MRI by age and risk criteria.MethodsThis prospective cohort study included 8782 women age 30–69 years referred to the High Risk Ontario Breast Screening Program from July 2011 to June 2015, with final results to December 2016. Cancer detection rates, sensitivity, and specificity of MRI and mammography combined were compared with each modality individually within risk groups stratified by age using generalized estimating equation models. Prognostic features of screen-detected breast cancers were compared by modality using Fisher exact test. All P values are two-sided.ResultsAmong 20 053 screening episodes, there were 280 screen-detected breast cancers (cancer detection rate = 14.0 per 1000, 95% confidence interval [CI] = 12.4 to 15.7). The sensitivity of mammography was statistically significantly lower than that of MRI plus mammography (40.8%, 95% CI = 29.3% to 53.5% vs 96.0%, 95% CI = 92.2% to 98.0%, P ConclusionsScreening high risk women age 30–39 years with annual MRI only may be sufficient for cancer detection and should be evaluated further, particularly for mutation carriers. Among women age 50–69 years, detection is most effective when mammography is included with annual MRI.

X-ray irradiation in X-ray binaries is thought to control the behaviour at the outer disc, which is observable mainly at optical wavelengths. It is generally parametrized phenomenologically, but it can also be predicted from theoretical models of irradiated discs and their coronae/winds. We test these models using five multiwavelength Hubble Space Telescopeand quasi simultaneous Rossi X-Ray Timing Explorer (RXTE) data sets from the black hole binary XTE J1859 + 226. These show how the reprocessed optical emission changes during outburst as the source fades from the very high/intermediate state at ∼0.4LEdd down through the high/soft state towards the transition to the hard state at ∼0.02LEdd. The models are able to reproduce the small change in reprocessing efficiency as the source flux decreases by a factor of two, and the spectrum softens from the very high/intermediate state to the bright high/soft state. However, the low luminosity high/soft state as well as the transition spectrum show more complex behaviour that is not well described by current models. We suggest the disc geometry has changed drastically during the outburst, probably due to tidal forces, and that the disc is no longer in steady state at the late stage of the outburst.

We model the broadband (optical/UV and X-ray) continuum spectrum of the "changing-look" active galactic nucleus (AGN) Mrk 1018 as it fades from Seyfert 1 to 1.9 in $\sim 8$ years. The brightest spectrum, with Eddington ratio $L/L_{\rm Edd}\sim 0.08$, has a typical type 1 AGN continuum, with a strong "soft X-ray excess" spanning between the UV and soft X-rays. The dimmest spectrum, at $L/L_{\rm Edd} \sim 0.006$, is very different in shape as well as luminosity, with the soft excess dropping by much more than the hard X-rays. The soft X-ray excess produces most of the ionizing photons, so its dramatic drop leads to the disappearance of the broad line region, driving the "changing-look" phenomena. This spectral hardening appears similar to the soft-to-hard state transition in black hole binaries at $L/L_{\rm Edd} \sim 0.02$, where the inner disc evaporates into an advection dominated accretion flow, while the overall drop in luminosity appears consistent with the Hydrogen ionization disc instability. Nonetheless, both processes happen much faster in Mrk 1018 than predicted by disc theory. We critically examine scaling from galactic binary systems, and show that a major difference is that radiation pressure should be much more important in AGNs, so that the sound speed is much faster than expected from the gas temperature. Including magnetic pressure to stabilize the disc shortens the timescales even further. We suggest that all changing-look AGNs are similarly associated with the state transition at $L/L_{\rm Edd} \sim$ a few percent., Comment: 10 pages, 3 figures, 1 table, accepted for publication in MNRAS

The spectra of black hole binaries in the low/hard state are complex, with evidence for multiple different Comptonization regions contributing to the hard X-rays in addition to a cool disc component. We show this explicitly for some of the best RXTE data from Cyg X-1, where the spectrum strongly requires (at least) two different Comptonization components in order to fit the continuum above 3 keV, where the disc does not contribute. However, it is difficult to constrain the physical properties of these Comptonization components uniquely using spectral data alone. Instead, we show that additional information from fast variability can break this degeneracy. Specifically, we use the observed variability power spectra in each energy channel to reconstruct the energy spectra of the variability on time-scales of ∼10, 1, and 0.1 s. The two longer time-scale spectra have similar shapes, but the fastest component is dramatically harder, and has strong curvature indicating that its seed photons are not from the cool disc. We interpret this in the context of propagating fluctuations through a hot flow, where the outer regions are cooler and optically thick, so that they shield the inner region from the disc. The seed photons for the hot inner region are then from the cooler Comptonization region rather than the disc itself.

We present an optical to X-ray spectral analysis of four 'hypervariable' AGN (HVAs) discovered by comparing Pan-STARRS data to that from SDSS over a 10 year baseline (Lawrence et al 2016). There is some evidence that these objects are X-ray loud for their corresponding UV luminosities, but given that we measured them in a historic high state, it is not clear whether to take the high-state or low-state as typical of the properties of these HVAs. We estimate black hole masses based on MgII and H$\alpha$ emission line profiles, and either the high and low state luminosities, finding mass ranges $\log(M_{\rm BH}/M_{\odot}) = 8.2-8.8$ and $\log(M_{\rm BH}/M_{\odot}) = 7.9-8.3$ respectively. We then fit energy conserving models to the SEDs, obtaining strong constraints on the bolometric luminosity and $\alpha_{\rm OX}$. We compare the SED properties with a larger, X-ray selected AGN sample for both of these scenarios, and observe distinct groupings in spectral shape versus luminosity parameter space. In general, the SED properties are closer to normal if we assume that the low-state is representative. This supports the idea that the large slow outbursts may be due to extrinsic effects (for example microlensing) as opposed to accretion rate changes, but a larger sample of HVAs is needed to be confident of this conclusion., Comment: 11 pages, 7 figures, 5 tables; accepted for publication in MNRAS

Recent monitoring campaigns designed to map the accretion regime in AGN show major discrepancies with models where the optical/ultraviolet (UV) is produced by X-ray-illuminated, optically thick disc material within a few hundred gravitational radii. However, these campaigns only monitored X-rays below $10$ keV, whereas the bolometric luminosity for most of these AGN peaks above $50$ keV. We use data from the recent multiwavelength campaign by \cite{E17} on NGC 4151 - the only AGN bright enough to be monitored at higher energies with \textit{Swift} BAT. We develop a spectral-timing model with a hot corona, warm Comptonisation, and outer standard disc. This fits the time-averaged spectrum well, but completely fails to match the UV variability predicted from the X-ray lightcurve. However, it reveals that NGC 4151 had a bolometric luminosity around $1.4\%$ of the Eddington luminosity during this campaign, close to the luminosity at which AGN show a `changing-state' transition, where the broad optical lines disappear. Stellar mass black holes show a state transition at a similarly low Eddington fraction, which is broadly interpreted as the inner disc being replaced by an optically thin flow. We find that the UV lightcurve can instead be matched by reprocessing of the X-ray flux on size scales of the broad line region (BLR; $1.5-20$ light-days) and rule out there being optically thick material inwards of this, as expected if the thin disc is replaced by the flow below the inner radius of the BLR. These results emphasise the need for even longer-timescale, multiwavelength monitoring campaigns on variable AGN.