On 17 August 2017, Swope Supernova Survey 2017a (SSS17a) was discovered as the optical counterpart of the binary neutron star gravitational wave event GW170817. We report time-series spectroscopy of ...SSS17a from 11.75 hours until 8.5 days after the merger. Over the first hour of observations, the ejecta rapidly expanded and cooled. Applying blackbody fits to the spectra, we measured the photosphere cooling from
11,000
−
900
+
3400
to
9300
−
300
+
300
kelvin, and determined a photospheric velocity of roughly 30% of the speed of light. The spectra of SSS17a began displaying broad features after 1.46 days and evolved qualitatively over each subsequent day, with distinct blue (early-time) and red (late-time) components. The late-time component is consistent with theoretical models of r-process–enriched neutron star ejecta, whereas the blue component requires high-velocity, lanthanide-free material.
We present the discovery of ASASSN-18ey (MAXI J1820+070), a new black hole low-mass X-ray binary (LMXB) discovered by the All-Sky Automated Survey for SuperNovae (ASAS-SN). A week after ASAS-SN ...discovered ASASSN-18ey as an optical transient, it was detected as an X-ray transient by MAXI/GCS. Here, we analyze ASAS-SN and Asteroid Terrestrial-impact Last Alert System pre-outburst optical light curves, finding evidence of intrinsic variability for several years prior to the outburst. While there was no long-term rise leading to the outburst, as has been seen in several other systems, the start of the outburst in the optical preceded that in the X-rays by 7.20 0.97 days. We analyze the spectroscopic evolution of ASASSN-18ey from pre-maximum to >100 days post-maximum. The spectra of ASASSN-18ey exhibit broad, asymmetric, double-peaked H emission. The Bowen blend (λ 4650 ) in the post-maximum spectra shows highly variable double-peaked profiles, likely arising from irradiation of the companion by the accretion disk, typical of low-mass X-ray binaries. The optical and X-ray luminosities of ASASSN-18ey are consistent with black hole low-mass X-ray binaries, both in outburst and quiescence.
Coral bleaching is the single largest global threat to coral reefs worldwide. Integrating the diverse body of work on coral bleaching is critical to understanding and combating this global problem. ...Yet investigating the drivers, patterns, and processes of coral bleaching poses a major challenge. A recent review of published experiments revealed a wide range of experimental variables used across studies. Such a wide range of approaches enhances discovery, but without full transparency in the experimental and analytical methods used, can also make comparisons among studies challenging. To increase comparability but not stifle innovation, we propose a common framework for coral bleaching experiments that includes consideration of coral provenance, experimental conditions, and husbandry. For example, reporting the number of genets used, collection site conditions, the experimental temperature offset(s) from the maximum monthly mean (MMM) of the collection site, experimental light conditions, flow, and the feeding regime will greatly facilitate comparability across studies. Similarly, quantifying common response variables of endosymbiont (Symbiodiniaceae) and holobiont phenotypes (i.e., color, chlorophyll, endosymbiont cell density, mortality, and skeletal growth) could further facilitate cross-study comparisons. While no single bleaching experiment can provide the data necessary to determine global coral responses of all corals to current and future ocean warming, linking studies through a common framework as outlined here, would help increase comparability among experiments, facilitate synthetic insights into the causes and underlying mechanisms of coral bleaching, and reveal unique bleaching responses among genets, species, and regions. Such a collaborative framework that fosters transparency in methods used would strengthen comparisons among studies that can help inform coral reef management and facilitate conservation strategies to mitigate coral bleaching worldwide.
On 17 August 2017, gravitational waves (GWs) were detected from a binary neutron star merger, GW170817, along with a coincident short gamma-ray burst, GRB 170817A. An optical transient source, Swope ...Supernova Survey 17a (SSS17a),was subsequently identified as the counterpart of this event. We present ultraviolet, optical, and infrared light curves of SSS17a extending from 10.9 hours to 18 days postmerger. We constrain the radioactively powered transient resulting from the ejection of neutron-rich material. The fast rise of the light curves, subsequent decay, and rapid color evolution are consistent with multiple ejecta components of differing lanthanide abundance. The late-time light curve indicates that SSS17a produced at least ~0.05 solar masses of heavy elements, demonstrating that neutron star mergers play a role in rapid neutron capture (r-process) nucleosynthesis in the universe.
In recent years, spin-orbit effects have been widely used to produce and detect spin currents in spintronic devices. The peculiar symmetry of the spin Hall effect allows creation of a spin ...accumulation at the interface between a metal with strong spin-orbit interaction and a magnetic insulator, which can lead to a net pure spin current flowing from the metal into the insulator. This spin current applies a torque on the magnetization, which can eventually be driven into steady motion. Tailoring this experiment on extended films has proven to be elusive, probably due to mode competition. This requires the reduction of both the thickness and lateral size to reach full damping compensation. Here we show clear evidence of coherent spin-orbit torque-induced auto-oscillation in micron-sized yttrium iron garnet discs of thickness 20 nm. Our results emphasize the key role of quasi-degenerate spin-wave modes, which increase the threshold current.
We present ground-based and Swift photometric and spectroscopic observations of the candidate tidal disruption event (TDE) ASASSN-14li, found at the centre of PGC 043234 (d ... 90 Mpc) by the All-Sky ...Automated Survey for SuperNovae (ASAS-SN). The source had a peak bolometric luminosity of ... and a total integrated energy of ... erg radiated over the ~6 months of observations presented. The UV/optical emission of the source is well fitted by a blackbody with roughly constant temperature of T ... 35,000 K, while the luminosity declines by roughly a factor of 16 over this time. The optical/UV luminosity decline is broadly consistent with an exponential decline, ..., with t0 ... 60 d. ASASSN-14li also exhibits soft X-ray emission comparable in luminosity to the optical and UV emission but declining at a slower rate, and the X-ray emission now dominates. Spectra of the source show broad Balmer and helium lines in emission as well as strong blue continuum emission at all epochs. We use the discoveries of ASASSN-14li and ASASSN-14ae to estimate the TDE rate implied by ASAS-SN, finding an average rate of ... per galaxy with a 90 per cent confidence interval of ... per galaxy. ASAS-SN found roughly 1 TDE for every 70 Type Ia supernovae in 2014, a rate that is much higher than that of other surveys. (ProQuest: ... denotes formulae/symbols omitted.)
We present the ATLAS discovery and initial analysis of the first 18 days of the unusual transient event, ATLAS18qqn/AT2018cow. It is characterized by a high peak luminosity (∼1.7 × 1044 erg s−1), ...rapidly evolving light curves (>5 mag rise to peak in ∼3.5 days), and hot blackbody spectra, peaking at ∼27,000 K that are relatively featureless and unchanging over the first two weeks. The bolometric light curve cannot be powered by radioactive decay under realistic assumptions. The detection of high-energy emission may suggest a central engine as the powering source. Using a magnetar model, we estimated an ejected mass of 0.1-0.4 M , which lies between that of low-energy core-collapse events and the kilonova, AT2017gfo. The spectra cooled rapidly from 27,000 to 15,000 K in just over two weeks but remained smooth and featureless. Broad and shallow emission lines appear after about 20 days, and we tentatively identify them as He i although they would be redshifted from their rest wavelengths. We rule out that there are any features in the spectra due to intermediate mass elements up to and including the Fe group. The presence of r-process elements cannot be ruled out. If these lines are due to He, then we suggest a low-mass star with residual He as a potential progenitor. Alternatively, models of magnetars formed in neutron star mergers, or accretion onto a central compact object, give plausible matches to the data.
ASASSN-14ae: a tidal disruption event at 200 Mpc Holoien, T. W.-S; Prieto, J. L; Bersier, D ...
Monthly notices of the Royal Astronomical Society,
12/2014, Letnik:
445, Številka:
3
Journal Article
Recenzirano
Odprti dostop
ASASSN-14ae is a candidate tidal disruption event (TDE) found at the centre of SDSS J110840.11+340552.2 (d ≃ 200 Mpc) by the All-Sky Automated Survey for Supernovae (ASAS-SN). We present ground-based ...and Swift follow-up photometric and spectroscopic observations of the source, finding that the transient had a peak luminosity of L ≃ 8 × 1043 erg s−1 and a total integrated energy of E ≃ 1.7 × 1050 erg radiated over the ∼5 months of observations presented. The blackbody temperature of the transient remains roughly constant at T ∼ 20 000 K while the luminosity declines by nearly 1.5 orders of magnitude during this time, a drop that is most consistent with an exponential, L ∝ e-t/t
0
with t
0 ≃ 39 d. The source has broad Balmer lines in emission at all epochs as well as a broad He ii feature emerging in later epochs. We compare the colour and spectral evolution to both supernovae and normal AGN to show that ASASSN-14ae does not resemble either type of object and conclude that a TDE is the most likely explanation for our observations. At z = 0.0436, ASASSN-14ae is the lowest-redshift TDE candidate discovered at optical/UV wavelengths to date, and we estimate that ASAS-SN may discover 0.1–3 of these events every year in the future.
Enterococci are Gram-positive bacteria that are found in plants, soil and as commensals of the gastrointestinal tract of humans, mammals, and insects. Despite their commensal nature, they have also ...become globally important nosocomial pathogens. Within the genus Enterococcus, Enterococcus faecium, and Enterococcus faecalis are clinically most relevant. In this review, we will discuss how E. faecium and E. faecalis have evolved to become a globally disseminated nosocomial pathogen. E. faecium has a defined sub-population that is associated with hospitalized patients and is rarely encountered in community settings. These hospital-associated clones are characterized by the acquisition of adaptive genetic elements, including genes involved in metabolism, biofilm formation, and antibiotic resistance. In contrast to E. faecium, clones of E. faecalis isolated from hospitalized patients, including strains causing clinical infections, are not exclusively found in hospitals but are also present in healthy individuals and animals. This observation suggests that the division between commensals and hospital-adapted lineages is less clear for E. faecalis than for E. faecium. In addition, genes that are reported to be associated with virulence of E. faecalis are often not unique to clinical isolates, but are also found in strains that originate from commensal niches. As a reflection of more ancient association of E. faecalis with different hosts, these determinants Thus, they may not represent genuine virulence genes but may act as host-adaptive functions that are useful in a variety of intestinal environments. The scope of the review is to summarize recent trends in the emergence of antibiotic resistance and explore recent developments in the molecular epidemiology, population structure and mechanisms of adaptation of E. faecium and E. faecalis.
Magnetoelectric coupling between magnetic and electrical properties presents valuable degrees of freedom for applications. The two most promising scenarios are magnetic-field sensors that could ...replace low-temperature superconducting quantum interference devices, and electric-write magnetic-read memory devices that combine the best of ferroelectric and magnetic random-access memory. The former scenario requires magnetically induced continuous and reversible changes in electrical polarization. These are commonly observed, but the coupling constants thus obtained are invalid for data-storage applications, where the more difficult to achieve and rarely studied magnetic response to an electric field is required. Here, we demonstrate electrically induced giant, sharp and persistent magnetic changes (up to 2.3×10−7 s m−1) at a single epitaxial interface in ferromagnetic 40 nm La0.67Sr0.33MnO3 films on 0.5 mm ferroelectric BaTiO3 substrates. X-ray diffraction confirms strain coupling via ferroelastic non-180 BaTiO3 domains. Our findings are valid over a wide range of temperatures including room temperature, and should inspire further study with single epitaxial interfaces.
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