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We report two binary systems, LAMOST J035540 + 381550 (hereafter J035540) and LAMOST J035916 + 400732 (hereafter J035916), identified through the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) low-resolution survey (LRS). Each of these two systems contains an M-type star orbiting with a invisible compact object candidate. Follow-up spectroscopic observations of Palomar 200-in. telescope (P200) enhance radial velocity measurements. We use radial velocities from LAMOST and P200, as well as light curves from Zwicky Transient Facility (ZTF) to constrain orbital parameters. The masses of the visible M-type stars are estimated by fitting the MIST isochrones and spectral energy distributions. The mass functions for the unseen companions are: |$0.22\pm 0.01\,{\rm M}_{\odot }$| for J035540 and |$0.16\pm 0.01\, {\rm M}_{\odot }$| for J035916. With the orbital and stellar parameters derived above and assuming the orbital inclination is 90° (edge-on), we find that the minimum masses of the invisible companions exceeds that of the visible stars. The single-lined feature and the dynamical evidence suggest the presence of compact objects. J035540's ZTF light curve, modelled with phoebe , yields a compact object mass of |$0.70^{+0.12}_{-0.05}\, {\rm M}_{\odot }$|⁠. For J035916, ellipsoidal modulation analysis constrains the light-curve amplitude, yielding a compact object mass range of |$0.57-0.90\, {\rm M}_{\odot }$|⁠. The mass estimates indicate that both are likely white dwarfs. These findings underscore the efficiency of optical time-domain surveys and dynamical methods in identifying faint, massive white dwarfs, along with other compact objects in binaries. [ABSTRACT FROM AUTHOR]

The variability of active galactic nuclei (AGNs) has long been servicing as an essential avenue of exploring the accretion physics of a black hole (BH). There are two commonly used methods for analyzing AGN variability. First, the AGN variability, characterized by the structure function (SF) of a single band, can be well described by a damped random walk (DRW) process on timescales longer than ∼weeks, shorter than which departures have been reported. Second, the color variation (CV) between two bands behaves timescale dependent, raising challenges to the widely accepted reprocessing scenario. However, both the departure from the DRW process and the timescale-dependent CV are hitherto limited to AGNs, mainly quasars, at the supermassive scale. Here, utilizing the high-cadence multiwavelength monitoring on NGC 4395 harboring an intermediate-mass BH, we unveil at the intermediate-mass scale for the first time, prominent departures from the DRW process at timescales shorter than ∼hours in all three nights and bands, and plausible timescale-dependent CVs in the two longest nights of observation. Furthermore, comparing SFs of NGC 4395 to four AGNs at the supermassive scale, we suggest a new scaling relation between the timescale (τ ; across nearly 3 orders of magnitude) and the BH mass (M BH): τ ∝ M BH γ where the exponent γ is likely ≃0.6–0.8. This exponent differs from most previous measurements, but confirms a few, and is consistent with a recent theoretical prediction, suggesting a similar accretion process in AGNs across different mass scales. [ABSTRACT FROM AUTHOR]

In situ cyclized polyacrylonitrile (CPAN) is developed to replace n‐type metal oxide semiconductors (TiO2 or SnO2) as an electron selective layer (ESL) for highly efficient and stable n‐i‐p perovskite solar cells (PSCs). The CPAN layer is fabricated via facile in situ cyclization reaction of polyacrylonitrile (PAN) coated on a conducting glass substrate. The CPAN layer is robust and insoluble in common solvents, and possesses n‐type semiconductor properties with a high electron mobility of 4.13×10−3 cm2 V−1 s−1. With the CPAN as an ESL, the PSC affords a power conversion efficiency (PCE) of 23.12 %, which is the highest for the n‐i‐p PSCs with organic ESLs. Moreover, the device with the CPAN layer holds superior operational stability, maintaining over 90 % of their initial efficiency after 500 h continuous light soaking. These results confirm that the CPAN layer would be a desirable low‐cost and efficient ESL for n‐i‐p PSCs and other photoelectronic devices with high performance and stability. [ABSTRACT FROM AUTHOR]

This article, published in the British Journal of Surgery, examines the importance of nodular number in predicting the prognosis of patients with intermediate-stage hepatocellular carcinoma (HCC) who undergo hepatectomy. The study, conducted at multiple hepatobiliary centers in China, Italy, and the USA, analyzed data from HCC patients who had undergone curative-intent hepatic resection between 2008 and 2018. The findings indicate that patients with three or more tumor nodules had lower overall survival and recurrence-free survival rates compared to those with two nodules. The study suggests that nodular number should be considered when predicting long-term prognosis after hepatic resection for intermediate-stage HCC. However, further research is needed to validate these findings. The study was supported by various funding sources and the authors have no conflicts of interest. [Extracted from the article]

We present a deep optical imaging campaign on the starburst galaxy NGC 4631 with CFHT/MegaCam. By supplementing the HST/ACS and Chandra/ACIS archival data, we search for the optical counterpart candidates of the five brightest X-ray sources in this galaxy, four of which are identified as ultraluminous X-ray sources (ULXs). The stellar environments of the X-ray sources are analyzed using the extinction-corrected color–magnitude diagrams and the isochrone models. We discover a highly asymmetric bubble nebula around X4 that exhibits different morphology in the H α and [O iii ] images. The [O iii ]/H α ratio map shows that the H α -bright bubble may be formed mainly via the shock ionization by the one-sided jet/outflow, while the more compact [O iii ] structure is photoionized by the ULX. We constrain the bubble expansion velocity and interstellar medium density with the MAPPINGS V code and hence estimate the mechanical power injected into the bubble as P w ∼ 5 × 1040 erg s−1 and the corresponding bubble age as ∼7 × 105 yr. Relativistic jets are needed to provide such a level of mechanical power with a mass-loss rate of ∼10−7 M ⊙ yr−1. Besides the accretion, the black hole spin is likely an additional energy source for the super-Eddington jet power. [ABSTRACT FROM AUTHOR]

The formation of relativistic jets by an accreting compact object is one of the fundamental mysteries of astrophysics. Although the theory is poorly understood, observations of relativistic jets from systems known as microquasars (compact binary stars) (1, 2) have led to a well established phenomenology (3, 4). Relativistic jets are not expected to be produced by sources with soft or supersoft X-ray spectra, although two such systems are known to produce relatively low-velocity bipolar outflows (5, 6). Here we report the optical spectra of an ultraluminous supersoft X-ray source (ULS (7, 8)) in the nearby galaxy M81 (M81 ULS-1; refs 9, 10). Unexpectedly, the spectra show blueshifted, broad Ha emission lines, characteristic of baryonic jets with relativistic speeds. These time-variable emission lines have projected velocities of about 17 per cent of the speed of light, and seem to be similar to those from the prototype microquasar SS 433 (refs 11, 12). Such relativistic jets are not expected to be launched from white dwarfs (13), and an origin from a black hole or a neutron star is hard to reconcile with the persistence of M81 ULS-1's soft X-rays (10). Thus the unexpected presence of relativistic jets in a ULS challenges canonical theories of jet formation (3, 4), but might be explained by a long-speculated, supercritically accreting black hole with optically thick outflows (14-20)., Initial spectroscopic observations (21) of M81 ULS-1, made at the W M. Keck Observatory in 2010, found broad Balmer hydrogen emission lines (as wide as 400 km [s.sup.-1]) on top [...]

Ultraluminous X-ray bursts (ULXBs) are ultraluminous X-ray flares with a fast rise (∼1 minute) and a slow decay (∼1 hour), which are commonly observed in extragalactic globular clusters. Most ULXBs are observational one-off bursts, whereas five flares from the same source in NGC 5128 were discovered by Irwin et al. In this article, we propose a neutron star (NS)â€"white dwarf (WD) binary model with super-Eddington accretion rates to explain the repeating behavior of the ULXB source in NGC 5128. With an eccentric orbit, the mass transfer occurs at the periastron where the WD fills its Roche lobe. The ultraluminous X-ray flares can be produced by the accretion column around the NS magnetic poles. On the other hand, some repeating fast radio bursts (FRBs) were also found in extragalactic globular clusters. Repeating ULXBs and repeating FRBs are the most violent bursts in the X-ray and radio bands, respectively. We propose a possible association between the repeating ULXBs and the repeating FRBs. Such an association is worth further investigation by follow-up observations on nearby extragalactic globular clusters. [ABSTRACT FROM AUTHOR]

Outflows are inevitably driven from the disk if the vertical component of the black hole (BH) gravity cannot resist the radiation force. We derive the mass-loss rate in the outflows by solving a dynamical equation for the vertical gas motion in the disk. The structure of a supercritical accretion disk is calculated with the radial energy advection included. We find that most inflowing gas is driven into outflows if the disk is accreting at a moderate Eddington-scaled rate (up to ∼100) at its outer edge, i.e., only a small fraction of gas is accreted by the BH, which is radiating at several Eddington luminosities, while it reaches around ten for extremely high accretion rate cases ( m ̇ ≡ M ̇ / M ̇ Edd ∼ 1000). Compared with a normal slim disk, the disk luminosity is substantially suppressed due to the mass loss in the outflows. We apply the model to the light curves of the tidal disruption events (TDEs) and find that the disk luminosity declines very slowly with time even if a typical accretion rate m ̇ ∝ t âˆ' 5 / 3 is assumed at the outer edge of the disk, which is qualitatively consistent with the observed light curves in some TDEs and helps us to understand the energy deficient phenomenon observed in the TDEs. Strong outflows from supercritical accretion disks surrounding supermassive BHs may play crucial roles in their host galaxies, which can be taken as an ingredient in the mechanical feedback models. The implications of the results on the growth of supermassive BHs are also discussed. [ABSTRACT FROM AUTHOR]

We report a single-lined white dwarfâ€"main-sequence binary system, LAMOST J172900.17+652952.8, which is discovered by the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST)’s medium-resolution time-domain surveys. The radial-velocity semi-amplitude and orbital period of the optical visible star are measured by using follow-up observations with the Palomar 200 inch telescope and light curves from the Transiting Exoplanet Survey Satellite (TESS). Thus the mass function of the invisible candidate white dwarf is derived, f (M 2) = 0.120 ± 0.003 M ⊙. The mass of the visible star is measured based on a spectral energy distribution fitting, M 1 = 0.81 âˆ' 0.06 + 0.07 M ⊙ . Hence, the mass of its invisible companion is M 2 ≳ 0.63 M ⊙. The companion ought to be a compact object rather than a main-sequence star owing to the mass ratio q = M 2/ M 1 ≳ 0.78 and the single-lined spectra. The compact object is likely to be a white dwarf if the inclination angle is not small, i ≳ 40°. By using the Galaxy Evolution Explorer (GALEX) near-UV flux, the effective temperature of the white dwarf candidate is constrained as T eff WD ≲ 12,000â€"13,500 K. It is difficult to detect white dwarfs which are outshone by their bright companions via single-epoch optical spectroscopic surveys. Therefore, optical time-domain surveys can play an important role in unveiling invisible white dwarfs and other compact objects in binaries. [ABSTRACT FROM AUTHOR]

We present LAMOST J041920.07+072545.4 (hereafter J0419), a close binary consisting of a bloated, extremely low mass pre-white dwarf (pre-ELM WD) and a compact object with an orbital period of 0.607189 days. The large-amplitude ellipsoidal variations and the evident Balmer and He i emission lines suggest a filled Roche lobe and ongoing mass transfer. No outburst events were detected in the 15 years of monitoring of J0419, indicating a very low mass transfer rate. The temperature of the pre-ELM, T eff = 5793 âˆ' 133 + 124 K , makes it cooler than the known ELMs, but hotter than most cataclysmic variable donors. Combining the mean density within the Roche lobe and the radius constrained from our spectral energy distribution fitting, we obtain the mass of the pre-ELM, M 1 = 0.176 ± 0.014 M ⊙. The joint fitting of light and radial velocity curves yields an inclination angle of i = 66.5 âˆ' 1.7 + 1.4 degrees, corresponding to a mass of the compact object of M 2 = 1.09 ± 0.05 M ⊙. The very bloated pre-ELM has a smaller surface gravity ( log g = 3.9 ± 0.01 , R 1 = 0.78 ± 0.02 R ⊙) than the known ELMs or pre-ELMs. The temperature and the luminosity ( L bol = 0.62 âˆ' 0.10 + 0.11 L ⊙ ) of J0419 are close to those of the main sequence, which makes the selection of such systems through the H-R diagram inefficient. Based on the evolutionary model, the relatively long period and small log g indicate that J0419 could be close to the “bifurcation period” in the orbital evolution, which makes J0419 a unique source to connect ELM/pre-ELM WD systems, wide binaries, and cataclysmic variables. [ABSTRACT FROM AUTHOR]

Inorganic cesium lead iodide perovskite CsPbI3 is attracting great attention as a light absorber for single or multi‐junction photovoltaics due to its outstanding thermal stability and proper band gap. However, the device performance of CsPbI3‐based perovskite solar cells (PSCs) is limited by the unsatisfactory crystal quality and thus severe non‐radiative recombination. Here, vacuum‐assisted thermal annealing (VATA) is demonstrated as an effective approach for controlling the morphology and crystallinity of the CsPbI3 perovskite films formed from the precursors of PbI2, CsI, and dimethylammonium iodide (DMAI). By this method, a large‐area and high‐quality CsPbI3 film is obtained, exhibiting a much reduced trap‐state density with prolonged charge lifetime. Consequently, the solar cell efficiency is raised from 17.26 to 20.06 %, along with enhanced stability. The VATA would be an effective approach for fabricating high‐performance thin‐film CsPbI3 perovskite optoelectronics. [ABSTRACT FROM AUTHOR]