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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.

Nova explosions are caused by global thermonuclear runaways triggered in the surface layers of accreting white dwarfs. It has been predicted that localised thermonuclear bursts on white dwarfs can also take place, similar to Type I X-ray bursts observed in accreting neutron stars. Unexplained rapid bursts from the binary system TV Columbae, in which mass is accreted onto a moderately-strong magnetised white dwarf from a low-mass companion, have been observed on several occasions in the past $\approx40$ years. During these bursts the optical/UV luminosity increases by a factor of $>3$ in less than an hour and fades over $\approx10$ hours. Fast outflows have been observed in UV spectral lines, with velocities $>3500$ km s$^{-1}$, comparable to the escape velocity from the white dwarf surface. Here we report on optical bursts observed in TV Columbae as well as in two additional accreting systems, EI Ursae Majoris and ASASSN-19bh. The bursts have a total energy $\approx~10^{-6}$ those of classical nova explosions ("micronovae"), and bear a strong resemblance to Type I X-ray bursts. We exclude accretion or stellar magnetic reconnection events as their origin and suggest thermonuclear runaway events in magnetically-confined accretion columns as a viable explanation., 11 pages, 7 figures. Submitted on 4 October 2021. Accepted for publication in Nature on 1 February 2022

Nova explosions are caused by global thermonuclear runaways triggered in the surface layers of accreting white dwarfs

In this paper, we investigate the existence and uniqueness results for summation–difference type equations in cone metric spaces. The results are obtained by using some extensions of Banach’s contraction principle in a complete cone metric space.

Novel methylpalladium(II) complexes of the general composition [PdCl(CH3){N∧D∧N}] ({N∧D∧N} = (mim)3COCH3 (1a), (mim)2CHCH2C(O)Bu-t (3a)) were synthesized from [PdCl(CH3)(COD)] and the respective N-methylimidazole (mim) ligands. The cationic derivatives [Pd2(CH3)2{N∧D∧N}2](BF4)2 (1b; {N∧D∧N} = (mim)3COCH3) and [Pd(CH3){N∧D∧N)(CH3CN)](BF4) (3b; {N∧D∧N} = (mim)2CHCH2C(O)Bu-t) were obtained by halide abstraction with AgBF4. The effect of varying the third donor moiety (D = “O”, “N”, “P”) in the structurally very similar ligands on the coordination chemistry and reactivity of 1 and 3 and the previously reported [PdCl(CH3){N∧D∧N}] (2a; {N∧D∧N} = (mim)2CHCH2PPh2) was investigated in detail. Thus, a neutral monomeric and an ionic dimeric isomer were identified for 1a, with the ligand adopting a σ2-N∧N coordination mode in the former and a σ3-N∧N∧N coordination mode in the latter. Exclusive formation of the ionic dimer occurs in methanol. Crystal structures are recorded for 1b and [Pd2Cl(CH3){N∧N∧N}2]Cl2 (1c). Eac...

A variety of neutral and cationic methyl palladium(II) complexes [Pd(CH 3 )(Cl)(L–L)] ( 3 ) and [Pd(CH 3 )(CH 3 CN)(L–L)]BF 4 ( 4 ), containing known and new N -methylimidazole-2-yl (mim) and N -methylbenzimidazole-2-yl (bmim) based chelate ligands (L–L) have been synthesised. The dichloro complexes [Pd(Cl) 2 {(mim) 2 CO}] ( 2b ) and [Pd(Cl) 2 (mim)PPh 2 ] ( 2e ) have also been synthesised. The crystal structures of [Pd(Cl) 2 {(mim) 2 CNPh}] ( 2d ) and [Pd(CH 3 )(Cl){(bmim) 2 CO}] ( 3c ) have been determined and show a square planar geometry at palladium(II) with an appreciable diminished bite angle (85.6°) in 3c compared to 2d (88.5°). The molecular structure of 2d and 3c show both bisimidazole ligands coordinated via the ring nitrogen donors and inclination of the chelate ring bridge to the coordination plane (boat conformation). Low temperature NMR spectra indicate boat-to-boat inversion of the chelate ring in [Pd(CH 3 )(CH 3 CN){(mim) 2 CO}] + ( 4b ). Examples of the neutral and cationic complexes were tested in the Heck reaction and CO/ethylene copolimerisation respectively. The CO bridged bisimidazole complex ( 3b ) exhibited high activity (TON of 100 000) in the Heck reaction whereas the closely related benzimidazole complex 3c was about half as active (TON of 53 000). Low activities were found for the cationic complex 4b in the CO/ethylene copolymerisation (TON 449).

Reflection of the X-ray emission from the surface of the white dwarf should be present in all hard X-ray emitting CV systems. It is clearly identified in the Ginga 2… 20 keV spectra of the polars AM Her and EF Eri, and also in the quiescent spectra of the dwarf novae SS Cyg. The inclusion of the hard reflection spectrum lowers the derived continuum temperature, so resolving a long standing problem of the mismatch of the iron line and continuum properties, and, with more realistic multi-temperature continuua, the derived shock temperatures are close to those expected from theoretical models of a strong shock.

The reaction of PdMe2(bpy) (bpy = 2,2-bipyridine) with diaroyl peroxides is a complex process in which initial oxidation of Pd(II) is followed by methyl group exchange between an undetected Pd(IV) intermediate and PdMe2(bpy) to give PdMe(O2CAr)(bpy) and PdMe3(O2CAr)(bpy); the latter Pd(IV) complex decomposes by elimination of Me–Me to give additional PdMe(O2CAr)(bpy) which reacts with (ArCO2)2 to give Me–O2CAr and Pd(O2CAr)2(bpy). The complexes Pd(O2CPh)2(L2) (L2=bpy, N,N,N′,N′-tetramethylethylyenediamine) have been characterised by X-ray diffraction.

Although a great deal of progress has been made towards understanding the nature of ultraluminous X‐ray sources (ULXs) over the past decade, many basic issues remain to be settled. Chief amongst these is the mass of the accretor in these systems: what proportion of ULXs are powered by accretion onto an intermediate‐mass black hole (IMBH), and how big are these objects? Or can we explain their extraordinary X‐ray luminosities by exotic, extreme accretion rate processes onto more prosaic stellar‐mass black holes? Here we report the results of two new studies using the best available XMM‐Newton observations to probe the astrophysics of ULXs. A systematic study of ULX power spectra shows a significant proportion of luminous objects with unusually suppressed variability compared to standard black hole binaries and AGN. Furthermore, detailed spectral studies confirm that ULX spectra appear unlike any standard accretion state in the XMM‐Newton band pass. Hence we infer that many ULXs contain small black holes operating in a new, super‐Eddington “ultraluminous” accretion state. We show that ULX spectra appear to vary with accretion rate, being closest to standard states at around Eddington, with an optically thick corona becoming the characteristic feature as we reach super‐Eddington rates. At the highest rates we see evidence for the emergence of a cool photosphere, likely related to a massive outflowing wind.

Suzaku has enabled us to study wide‐band spectral and timing properties of black‐hole binaries and AGNs more accurately than ever, and revealed how the continuum definition can affect Fe‐Kline profiles. We have reproduced 0.5–300 keV spectra of Cyg X‐1 and GRO J1655‐40 in terms of thermal Comptonization in highly inhomogeneous coronae. In both objects, Rin was constrained by the Fe‐K line profile and soft excess as ∼10 Rg, as opposed to the relativistic Fe‐K line reported in the literature. We also re‐analyzed the 0.7–300 keV Suzaku spectra of GX 339‐4, and found that a careful modeling of the continuum leads to Rin>Rg(Yamada et al. 2009), again in disagreement with Miller et al. (2008). Furthermore, through a systematic analysis of AGNs, we discovered a hard spectral component in the HXD‐PIN band, which varies independently of the powerlaw. Taking this into account, the time‐averaged spectra of MCG‐6‐30‐15 have been explained by invoking neither a large refection fraction, nor an extreme broad Fe‐K line....

The Narrow Line Seyfert 1 galaxy REJ1034+396 is so far unique amongst AGN in showing a Quasi-periodic oscillation (QPO) in its variability power spectrum. There are multiple types of QPO seen in black hole binary (BHB) systems, so we need to identify which BHB QPO corresponds to the one seen in the AGN. A key hint is the `hot disc dominated' energy spectrum of REJ1034+396 which is sufficiently unusual that it suggests a mildly super-Eddington flow, also favoured by the most recent mass estimates for the AGN. This suggests the 67Hz QPO seen occasionally in the mildly super-Eddington BHB GRS 1915+105 as the most likely counterpart, assuming mass scaling of the QPO frequency. This is supported by the fact that these data from GRS 1915+105 have an energy spectrum which is also dominated by a `hot disc' component. Here we show that the underlying broad band power spectral shape and normalisation are also similar, providing further consistency checks for this identification. Thus the AGN QPO adds to the growing evidence for a simple mass scaling of the accretion flow properties between stellar and supermassive black holes., 9 pages, 12 figures, to be published in MNRAS

Nephrin, a major component of the glomerular slit diaphragm (SD), is both a structural protein as well as a signaling molecule influencing foot process (FP) formation and maintenance of podocyte integrity. Analyses of near-term embryonic kidneys showed normal cellular viability and no apoptosis in glomeruli from nephrin knockout mice. Moreover, expression and location of other SD or glomerular basement membrane components were similar in wild-type and mutant mice as was the location and levels of most podocyte-specific proteins. Transcriptional profiling showed that the lack of nephrin had minor impact on the expression of genes for FPs and SD proteins. Claudin 3, a tight-junction protein normally absent in glomeruli, was upregulated threefold in the knockout mice, suggesting a role of nephrin in claudin 3 gene expression within the glomeruli. Our results suggest that nephrin is expressed late in the process of podocyte differentiation and is a locus for the formation of SD and FP maintenance and physical integrity in vivo. Nephrin does not seem to have a primary role in cell survival but has a small impact on gene regulation during glomerular development.

We model the reflected spectrum expected from localized magnetic flares above an ionised accretion disk. We concentrate on the case of very luminous magnetic flares above a standard accretion disk extending down to the last stable orbit, and use a simple parameterisation to allow for an X-ray driven wind. Full disk spectra including relativistic smearing are calculated. When fit with the constant density reflection models, these spectra give both a low reflected fraction and a small line width as seen in the hard spectra from Galactic Black Hole Binaries and Active Galactic Nuclei. We fit our calculated spectra to real data from the low/hard state of Nova Muscae and Cyg X-1 and show that these models give comparable $\chi^2$ to those obtained from the constant density reflection models which implied a truncated disk. This explicitally demonstrates that the data are consistent with either magnetic flares above an ionized disk extending down to the last stable orbit around a black hole, or with non-ionized, truncated disks., Comment: 8 pages, accepted for publication in MNRAS

We re-analyse the ASCA and GINGA X-ray data from BY Cam, a slightly asynchronous magnetic accreting white dwarf. The spectra are strongly affected by complex absorption, which we model as a continuous (power law) distribution of covering fraction and column of neutral material. This absorption causes a smooth hardening of the spectrum below 3 keV, and is probably produced by material in the preshock column which overlies the X-ray emission region. The ASCA data show that the intrinsic emission from the shock is not consistent with a single temperature plasma. Significant iron L emission co-existing with iron K shell lines from H and He-like iron clearly shows that there is a wide range of temperatures present, as expected from a cooling shock structure. The GINGA data give the best constraints on the maximum temperature emission in the shocked plasma, with kT(max)=21(+18,-4) keV. Cyclotron cooling should also be important, which supresses the highest temperature bremsstrahlung components, so the X-ray data only give a lower limit on the mass of the white dwarf of M> 0.5 solar masses. Reflection of the multi-temperature bremsstrahlung emission from the white dwarf surface is also significantly detected. We stress the importance of modelling ALL these effects in order to gain a physically self-consistent picture of the X-ray spectra from polars in general and BY Cam in particular., 9 pages, 4 figures, MNRAS, accepted

Summary We investigate the effects of a re-acceleration mechanism in compact sources where electron-positron pair production is important. The pairs increase the number of particles to be accelerated and decrease the mean particle energy if the source luminosity remains constant. The acceleration mechanism is loaded. Models in which this effect is included reproduce the γ-ray break seen in active galactic nuclei. It is mainly due to the reduced particle energy and not to photon-photon absorption. The X-ray spectra are generally flatter than those observed if the electrons are accelerated to a single energy. Pair reradiation no longer steepens the spectrum, since loading enhances the importance of the primary emission spectrum. Spectra in agreement with observations can be obtained if the electrons are re-accelerated with a power-law energy distribution. Our investigation highlights the accumulation of cooled particles within the source. It is a severe constraint on continuous injection models. The lack of any obvious spectral break attributable to Compton downscattering in the high-energy spectra of active galactic nuclei conflicts with the predictions of most models. Highly compact sources produce large amounts of pairs and so have a high optical depth of cooled electrons. We consider this ‘dead electron’ problem for a wide range of models. Reacceleration of the electrons, which is often invoked as a means of overcoming the problem, is not an adequate solution in most cases.

The choice of male parents for an F1-hybrid barley variety depends upon a number of characteristics, among which will be the combining ability for yield, the transference of disease resistance and the ability to release large quantities of viable pollen to ensure a high set of F1 -hybrid seed on the male-sterile Une. A number of cultivars were assessed as potential pollen parents using a common male-sterile variety. Various experimental methods to assess the potential of male parents were used at locations in the United Kingdom and elsewhere in Western Europe over a period of three years. Significant differences were demonstrated between the cross-pollinating ability of varieties; ‘good’ pollinators gave consistent results. A marked effect of crossing-block size was found and there was also some evidence of environmental interactions.

SUMMARY Small and large scale trials of F1 barley hybrids were done in a glasshouse in the United Kingdom and in the field in the United Kingdom and Europe in 1970, 1971 and 1972. The results showed that there were few instances of significant positive heterosis in yield with either the small or field scale experiments. The hybrids studied were all derived from American varieties as male-sterile parents and therefore the hybrids were not adapted to European countries, thus the case for or against F1-hybrids cannot be assessed solely on this material.

The X-ray luminosity and variability of many AGN are sufficiently extreme that any hard γ-rays produced in the source will collide with the X-rays and create electron-positron pairs, rather than escape. A small region where vast amounts of energy are produced, such as an AGN, is an ideal place to accelerate particles to relativistic energies and so produce γ-rays by Compton scattering. The observed X-ray spectra of AGN are hard and indicate that most of the luminosity is at the highest energies so that absorption of the γ-rays represents a large fraction of the energy flux, which can then be re-radiated at lower energies. Pairs can thus effectively reprocess much of the radiant power in an AGN.

High-time-resolution X-ray observations of compact objects provide direct access to strong-field gravity, to the equation of state of ultra-dense matter and to black hole masses and spins. A 10 m^2-class instrument in combination with good spectral resolution is required to exploit the relevant diagnostics and answer two of the fundamental questions of the European Space Agency (ESA) Cosmic Vision Theme "Matter under extreme conditions", namely: does matter orbiting close to the event horizon follow the predictions of general relativity? What is the equation of state of matter in neutron stars? The Large Observatory For X-ray Timing (LOFT), selected by ESA as one of the four Cosmic Vision M3 candidate missions to undergo an assessment phase, will revolutionise the study of collapsed objects in our galaxy and of the brightest supermassive black holes in active galactic nuclei. Thanks to an innovative design and the development of large-area monolithic Silicon Drift Detectors, the Large Area Detector (LAD) on board LOFT will achieve an effective area of ~12 m^2 (more than an order of magnitude larger than any spaceborne predecessor) in the 2-30 keV range (up to 50 keV in expanded mode), yet still fits a conventional platform and small/medium-class launcher. With this large area and a spectral resolution of, 29 pages, 10 figures. Accepted for publication in Experimental Astronomy