The successful joint observation of the gravitational wave (GW) event GW170817 and its multiwavelength electromagnetic counterparts enabled us to witness a definite merger event of two neutron stars ...(NSs) for the first time. This historical event confirms the origin of short-duration gamma-ray bursts (GRBs) and, in particular, identifies the theoretically predicted kilonova phenomenon that is powered by radioactive decays of r-process heavy elements. However, whether or not a long-lived remnant NS could be formed during this merger event remains unknown; though, such a central engine has been suggested by afterglow observations of some short-duration GRBs. By invoking this long-lived remnant NS, we propose a model of hybrid energy sources for the kilonova AT 2017gfo associated with GW170817. While the early emission of AT 2017gfo is still powered radioactively, as is usually suggested, its late emission is primarily caused by delayed energy injection from the remnant NS. In our model, only one single opacity is required and an intermediate value of κ 0.97 cm2 g−1 is revealed, which could be naturally provided by lanthanide-rich ejecta that are deeply ionized by the emission from a wind of the NS. These self-consistent results indicate that a long-lived remnant NS, which must have a very stiff equation of state, was formed during the merger event of GW170817. This provides a very stringent constraint on the strong interaction in nuclear-quark matter. It is further implied that such GW events could provide a probe of the early spin and magnetic evolutions of NSs, e.g., the burying of surface magnetic fields.
The joint detection of GW170817 and GRB 170817A indicated that at least a fraction of short gamma-ray bursts (SGRBs) originate from binary neutron star (BNS) mergers. One possible remnant of a BNS ...merger is a rapidly rotating, strongly magnetized neutron star, which has been discussed as one possible central engine for gamma-ray bursts. For a rapidly rotating magnetar central engine, the deposition of the rotation energy into the ejecta launched from the merger could lead to bright radio emission. The brightness of radio emission years after an SGRB would provide an estimate of the kinetic energy of ejecta and, hence, a possible constraint on the BNS merger product. We perform a more detailed calculation on the brightness of radio emission from the interaction between the merger ejecta and circumburst medium in the magnetar scenario, invoking several important physical processes such as generic hydrodynamics, relativistic effects, and the deep Newtonian phase. We use the model to constrain the allowed parameter space for 15 SGRBs that have late radio observations. Our results show that an injection energy of Einj ∼ 1052 erg is allowed for all the cases, which suggests that the possibility of a supramassive or hypermassive neutron star remnant is not disfavored by the available radio data.
Due to their sessile state, plants are inevitably affected by and respond to the external environment. So far, plants have developed multiple adaptation and regulation strategies to abiotic stresses. ...One such system is epigenetic regulation, among which DNA methylation is one of the earliest and most studied regulatory mechanisms, which can regulate genome functioning and induce plant resistance and adaption to abiotic stresses. In this review, we outline the most recent findings on plant DNA methylation responses to drought, high temperature, cold, salt, and heavy metal stresses. In addition, we discuss stress memory regulated by DNA methylation, both in a transient way and the long-term memory that could pass to next generations. To sum up, the present review furnishes an updated account of DNA methylation in plant responses and adaptations to abiotic stresses.
Abstract
The regioselectivity of C−H functionalization is commonly achieved by directing groups, electronic factors, or steric hindrance, which facilitate the identification of reaction sites. ...However, such strategies are less effective for reactants such as simple monofluoroarenes due to their relatively low reactivity and the modest steric demands of the fluorine atom. Herein, we present an undirected gold‐catalyzed
para
‐C−H arylation of a wide array of monofluoroarenes using air‐stable aryl silanes and germanes at room temperature. A high
para
‐regioselectivity (up to 98 : 2) can be realized by utilizing a dinuclear dppm(AuOTs)
2
(dppm=bis(diphenylphosphino)methane) as the catalyst and hexafluorobenzene as the solvent. This provides a general and practical protocol for the concise construction of structurally diverse
para
‐arylated monofluoroarenes through C−H activation manner. It features excellent functional group tolerance and a broad substrate scope (>80 examples). Besides, this strategy is also robust for other simple monosubstituted arenes and heteroarenes. Our mechanistic studies and theoretical calculations suggest that
para
‐C−H selectivity arises from highly electrophilic and structurally flexible dinuclear Ar−Au(III)−Au(I) species, coupled with noncovalent interaction induced by hexafluorobenzene.
In this paper, we explore the viewing angle effect on black hole-neutron star (BH-NS) merger kilonova lightcurves. We extrapolate the fitting formulae for the mass and velocity of dynamical ejecta ...across a wide mass ratio range validated with 66 simulations and use them in kilonova lightcurve calculations. The calculated peak luminosity of a BH-NS merger kilonova is typically about a few times 1041 erg s−1, which is always 4.5 × 1041 erg s−1. This corresponds to AB absolute magnitudes fainter than ∼−15 mag in the optical and ∼−16 mag in the infrared. The dynamical ejecta usually contribute to the majority of the kilonova emission, as its projected photosphere area is much larger than that of the disk wind outflows. The fitted blackbody temperature and the observed multiband lightcurve shape are insensitive to the line of sight. The peak time of the observed multiband lightcurves, affected by the light-propagation effect, is related to the relative motion direction between the dynamical ejecta and the observer. The predicted peak luminosity, which changes with the projected photosphere area, only varies by a factor of ∼(2-3) (or by ∼1 mag) for different viewing angles. When taking the short-duration gamma-ray burst afterglow into account, for an on-axis geometry, the kilonova emission is usually outshone by the afterglow emission and can only be observed in the redder bands, especially in the K band at late times. Compared with GW 170817/AT 2017gfo, BH-NS merger kilonovae are optically dim but possibly infrared bright, and have lower fitting temperature at the same epoch after the merger.
Abstract
Despite the fact that the progenitor of fast blue optical transients (FBOTs) is still a subject of debate, FBOTs are sometimes suggested to originate from the core collapse of ultra-stripped ...stars and be powered by a spinning-down neutron star. Following this consideration, it is expected that the late-time evolution of the progenitor stars can leave important imprints in the circumstellar material (CSM) of FBOTs, due to the strong mass loss of the stars. The interaction of the FBOT ejecta with the CSM can drive a long-lasting shock to generate radio emission, which thus enables us to probe the CSM properties through radio observation although such observations are still rare. Within the framework of the magnetar-powered model, Liu et al. fitted the multi-band optical light curves of 40 FBOTs, and hence, the statistical distributions of the FBOT magnetar and ejecta parameters were obtained. Based on these FBOT population results, we investigate the dependence of the radio emission on the mass-loss rate of the progenitors and evaluate the detectability of radio emission from FBOTs with current and future telescopes. It is found that the distribution of the peak time and peak luminosity of the emission at 8.4 GHz are primarily in the regions of
t
peak,
ν
= 10
2.12±0.63
days and
L
peak,
ν
= 10
28.73±0.83
erg s
−1
Hz
−1
, respectively. A joint detection of the Zwicky Transient Facility and Very Large Array could achieve success in about 8.7% FBOTs of
z
≤ 1. Furthermore, if considering a joint detection of the Chinese Space Station Telescope and the Square Kilometer Array, this rate of success could be increased to about 23.9%.
Abstract
Recent observations indicate that hydrogen-poor superluminous supernovae (SLSNe-I) often display bumpy declining light curves. However, the cause of these undulations remains unclear. In ...this paper, we have improved the magnetar model, which includes flare activities. We present a systematic analysis of a well-observed SLSN-I sample with bumpy light curves in their late phase. These SLSNe-I were identified from multiple transient surveys, such as the Pan-STARRS1 Medium Deep Survey and the Zwicky Transient Facility. Our study provides a set of magnetar-powered model light curve fits for five SLSNe-I, which accurately reproduce the observed light curves using reasonable physical parameters. By extracting the essential characteristics of both the explosions and central engines, these fits provide valuable insights into investigating their potential association with gamma-ray burst engines. We found that the SLSN flares tend to be the dim and long extension of GRB flares in the peak luminosity versus peak time plane. Conducting large-scale, high-cadence surveys in the near future could enhance our comprehension of both SLSN undulating light curve properties and their potential relationship with GRBs by modeling their light curve characteristics.
Abstract
White dwarfs (WDs) embedded in the gaseous disks of active galactic nuclei (AGNs) can rapidly accrete materials from these disks and grow in mass to reach, or even exceed, the Chandrasekhar ...limit. Binary WD (BWD) mergers are also believed to occur in AGN accretion disks. We study observational signatures from these events. We suggest that mass-accreting WDs and BWD mergers in AGN disks can lead to thermonuclear explosions that drive an ejecta shock breakout from the disk surface and power a slow-rising, relatively dim Type Ia supernova (SN). It is possible that such SNe Ia may be outshone by the emission of the AGN disk around a supermassive black hole (BH) with a mass of
M
SMBH
≳ 10
8
M
⊙
. In addition, accretion-induced collapses (AICs) of WDs in AGN disks may sometimes occur, which may form highly magnetized millisecond neutron stars (NSs). The subsequent spindown process of this nascent magnetar can deposit its rotational energy into the disk materials, resulting in a magnetar-driven shock breakout and a luminous magnetar-powered transient. We show that such an AIC event could power a rapidly evolving and luminous transient for a magnetic field of
B
∼ 10
15
G. The rising time and peak luminosity of the transient, powered by a magnetar with
B
∼ 10
14
G, are predicted to have similar properties to those of superluminous SNe. AIC events taking place in the inner parts of disks around relatively less massive supermassive BHs (
M
SMBH
≲ 10
8
M
⊙
) are more likely to power transients that are much brighter than the AGN disk emission, and hence easily identified.
The groundbreaking discovery of the optical transient AT2017gfo associated with GW170817 opens a unique opportunity to study the physics of double neutron star (NS) mergers. We argue that the ...standard interpretation of AT2017gfo as being powered by radioactive decay of r-process elements faces the challenge of simultaneously accounting for the peak luminosity and peak time of the event, as it is not easy to achieve the required high mass, and especially the low opacity of the ejecta required to fit the data. A plausible solution would be to invoke an additional energy source, which is probably provided by the merger product. We consider energy injection from two types of the merger products: (1) a post-merger black hole powered by fallback accretion; and (2) a long-lived NS remnant. The former case can only account for the early emission of AT2017gfo, with the late emission still powered by radioactive decay. In the latter case, both early- and late-emission components can be well interpreted as due to energy injection from a spinning-down NS, with the required mass and opacity of the ejecta components well consistent with known numerical simulation results. We suggest that there is a strong indication that the merger product of GW170817 is a long-lived (supramassive or even permanently stable), low magnetic field NS. The result provides a stringent constraint on the equations of state of NSs.
The aryl hydrocarbon receptor (AHR) is a nuclear receptor that modulates the response to environmental stimuli. It was recognized historically for its role in toxicology but, in recent decades, it ...has been increasingly recognized as an important modulator of disease-especially for its role in modulating immune and inflammatory responses. AHR has been implicated in many diseases that are driven by immune/inflammatory processes, including major depressive disorder, multiple sclerosis, rheumatoid arthritis, asthma, and allergic responses, among others. The mechanisms by which AHR has been suggested to impact immune/inflammatory diseases include targeted gene expression and altered immune differentiation. It has been suggested that single nucleotide polymorphisms (SNPs) that are near AHR-regulated genes may contribute to AHR-dependent disease mechanisms/pathways. Further, we have found that SNPs that are outside of nuclear receptor binding sites (i.e., outside of AHR response elements (AHREs)) may contribute to AHR-dependent gene regulation in a SNP- and ligand-dependent manner. This review will discuss the evidence and mechanisms of AHR contributions to immune/inflammatory diseases and will consider the possibility that SNPs that are outside of AHR binding sites might contribute to AHR ligand-dependent inter-individual variation in disease pathophysiology and response to pharmacotherapeutics.
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