Abstract
We report on analysis of observations of the bright transient X-ray pulsar Swift J0243.6+6124 obtained during its 2017-2018 giant outburst with Insight-HXMT, NuSTAR, and Swift observatories. ...We focus on the discovery of a sharp state transition of the timing and spectral properties of the source at super-Eddington accretion rates, which we associate with the transition of the accretion disk to a radiation pressure dominated (RPD) state, the first ever directly observed for magnetized neutron star. This transition occurs at slightly higher luminosity compared to already reported transition of the source from sub- to super-critical accretion regime associate with onset of an accretion column. We argue that this scenario can only be realized for comparatively weakly magnetized neutron star, not dissimilar to other ultra-luminous X-ray pulsars (ULPs), which accrete at similar rates. Further evidence for this conclusion is provided by the non-detection of the transition to the propeller state in quiescence which strongly implies compact magnetosphere and thus rules out magnetar-like fields.
With the aim of gathering temporal trends on bacterial epidemiology and resistance from multiple laboratories in China, the CHINET surveillance system was organized in 2005. Antimicrobial ...susceptibility testing was carried out according to a unified protocol using the Kirby-Bauer method or automated systems. Results were analyzed according to Clinical and Laboratory Standards Institute (CLSI) 2014 definitions. Between 2005 and 2014, the number of bacterial isolates ranged between 22 774 and 84 572 annually. Rates of extended-spectrum β-lactamase production among Escherichia coli isolates were stable, between 51.7 and 55.8%. Resistance of E. coli and Klebsiella pneumoniae to amikacin, ciprofloxacin, piperacillin/tazobactam and cefoperazone/sulbactam decreased with time. Carbapenem resistance among K. pneumoniae isolates increased from 2.4 to 13.4%. Resistance of Pseudomonas aeruginosa strains against all of antimicrobial agents tested including imipenem and meropenem decreased with time. On the contrary, resistance of Acinetobacter baumannii strains to carbapenems increased from 31 to 66.7%. A marked decrease of methicillin resistance from 69% in 2005 to 44.6% in 2014 was observed for Staphylococcus aureus. Carbapenem resistance rates in K. pneumoniae and A. baumannii in China are high. Our results indicate the importance of bacterial surveillance studies.
Fast radio bursts (FRBs) are millisecond-duration radio transients
of unknown origin. Two possible mechanisms that could generate extremely coherent emission from FRBs invoke neutron star ...magnetospheres
or relativistic shocks far from the central energy source
. Detailed polarization observations may help us to understand the emission mechanism. However, the available FRB polarization data have been perplexing, because they show a host of polarimetric properties, including either a constant polarization angle during each burst for some repeaters
or variable polarization angles in some other apparently one-off events
. Here we report observations of 15 bursts from FRB 180301 and find various polarization angle swings in seven of them. The diversity of the polarization angle features of these bursts is consistent with a magnetospheric origin of the radio emission, and disfavours the radiation models invoking relativistic shocks.
Abstract
We present the second release of value-added catalogues of the LAMOST Spectroscopic Survey of the Galactic Anticentre (LSS-GAC DR2). The catalogues present values of radial velocity Vr, ...atmospheric parameters – effective temperature Teff, surface gravity log g, metallicity Fe/H, α-element to iron (metal) abundance ratio α/Fe (α/M), elemental abundances C/H and N/H and absolute magnitudes MV and $M_{K_{\rm s}}$ deduced from 1.8 million spectra of 1.4 million unique stars targeted by the LSS-GAC since 2011 September until 2014 June. The catalogues also give values of interstellar reddening, distance and orbital parameters determined with a variety of techniques, as well as proper motions and multiband photometry from the far-UV to the mid-IR collected from the literature and various surveys. Accuracies of radial velocities reach 5 km s−1 for the late-type stars, and those of distance estimates range between 10 and 30 per cent, depending on the spectral signal-to-noise ratios. Precisions of Fe/H, C/H and N/H estimates reach 0.1 dex, and those of α/Fe and α/M reach 0.05 dex. The large number of stars, the contiguous sky coverage, the simple yet non-trivial target selection function and the robust estimates of stellar radial velocities and atmospheric parameters, distances and elemental abundances make the catalogues a valuable data set to study the structure and evolution of the Galaxy, especially the solar-neighbourhood and the outer disc.
High-energy cosmic-ray electrons and positrons (CREs), which lose energy quickly during their propagation, provide a probe of Galactic high-energy processes and may enable the observation of ...phenomena such as dark-matter particle annihilation or decay. The CRE spectrum has been measured directly up to approximately 2 teraelectronvolts in previous balloon- or space-borne experiments, and indirectly up to approximately 5 teraelectronvolts using ground-based Cherenkov γ-ray telescope arrays. Evidence for a spectral break in the teraelectronvolt energy range has been provided by indirect measurements, although the results were qualified by sizeable systematic uncertainties. Here we report a direct measurement of CREs in the energy range 25 gigaelectronvolts to 4.6 teraelectronvolts by the Dark Matter Particle Explorer (DAMPE) with unprecedentedly high energy resolution and low background. The largest part of the spectrum can be well fitted by a 'smoothly broken power-law' model rather than a single power-law model. The direct detection of a spectral break at about 0.9 teraelectronvolts confirms the evidence found by previous indirect measurements, clarifies the behaviour of the CRE spectrum at energies above 1 teraelectronvolt and sheds light on the physical origin of the sub-teraelectronvolt CREs.
Context.
No robust detection of prompt electromagnetic counterparts to fast radio bursts (FRBs) has yet been obtained, in spite of several multi-wavelength searches having been carried out so far. ...Specifically, X/
γ
-rays counterparts are predicted by some models.
Aims.
We aim to search for prompt
γ
-ray counterparts in the Insight-Hard X-ray Modulation Telescope (Insight-HXMT) data, taking advantage of the unique combination of the large effective area in the keV–MeV energy range, and of sub-ms time resolution.
Methods.
We selected 39 FRBs that were promptly visible from the High-Energy (HE) instrument aboard Insight-HXMT. After calculating the expected arrival times at the location of the spacecraft, we searched for a significant excess in both individual and cumulative time profiles over a wide range of time resolutions, from several seconds down to sub-ms scales. Using the dispersion measures in excess of the Galactic terms, we estimated the upper limits on the redshifts.
Results.
No convincing signal was found, and for each FRB we constrained the
γ
-ray isotropic-equivalent luminosity and the released energy as a function of emission timescale. For the nearest FRB source, the periodic repeater FRB 180916.J0158+65, we find
L
γ
, iso
< 5.5 × 10
47
erg s
−1
over 1 s, whereas
L
γ
, iso
< 10
49
− 10
51
erg s
−1
for the bulk of FRBs. The same values scale up by a factor of ∼100 for a ms-long emission.
Conclusions.
Even on a timescale comparable with that of the radio pulse itself, no keV–MeV emission is observed. A systematic association with either long or short GRBs is ruled out with high confidence, except for sub-luminous events, as is the case for the core-collapse of massive stars (long) or binary neutron star mergers (short) viewed off axis. Only giant flares from extragalactic magnetars at least ten times more energetic than Galactic siblings are ruled out for the nearest FRB.
From 2006 to 2007, the daily concentrations of major inorganic water-soluble constituents, mineral aerosol, organic carbon (OC) and elemental carbon (EC) in ambient PM10 samples were investigated ...from 16 urban, rural and remote sites in various regions of China, and were compared with global aerosol measurements. A large difference between urban and rural chemical species was found, normally with 1.5 to 2.5 factors higher in urban than in rural sites. Optically-scattering aerosols, such as sulfate (~16%), OC (~15%), nitrate (~7%), ammonium (~5%) and mineral aerosol (~35%) in most circumstance, are majorities of the total aerosols, indicating a dominant scattering feature of aerosols in China. Of the total OC, ~55%–60% can be attributed to the formation of the secondary organic carbon (SOC). The absorbing aerosol EC only accounts for ~3.5% of the total PM10. Seasonally, maximum concentrations of most aerosol species were found in winter while mineral aerosol peaks in spring. In addition to the regular seasonal maximum, secondary peaks were found for sulfate and ammonium in summer and for OC and EC in May and June. This can be considered as a typical seasonal pattern in various aerosol components in China. Aerosol acidity was normally neutral in most of urban areas, but becomes some acidic in rural areas. Based on the surface visibility observations from 681 meteorological stations in China between 1957 and 2005, four major haze areas are identified with similar visibility changes, namely, (1) Hua Bei Plain in N. China, and the Guanzhong Plain; (2) E. China with the main body in the Yangtze River Delta area; (3) S. China with most areas of Guangdong and the Pearl River Delta area; (4) The Si Chuan Basin in S.W. China. The degradation of visibility in these areas is linked with the emission changes and high PM concentrations. Such quantitative chemical characterization of aerosols is essential in assessing their role in atmospheric chemistry and weather-climate effects, and in validating atmospheric models.
Scattering of solar radiation by aerosol particles is highly dependent on relative humidity (RH) as hygroscopic particles take up water with increasing RH. To achieve a better understanding of the ...effect of aerosol hygroscopic growth on light scattering properties and radiative forcing, the aerosol scattering coefficients at RH in the range of 40 to ~ 90 % were measured using a humidified nephelometer system in the Yangtze River Delta of China in March 2013. In addition, the aerosol size distribution and chemical composition were measured. During the observation period, the mean and standard deviation (SD) of enhancement factors at RH = 85 % for the scattering coefficient (f(85 %)), backscattering coefficient (fb(85 %)), and hemispheric backscatter fraction (f beta (85 %)) were 1.58 plus or minus 0.12, 1.25 plus or minus 0.07, and 0.79 plus or minus 0.04, respectively, i.e., aerosol scattering coefficient and backscattering coefficient increased by 58 and 25 % as the RH increased from 40 to 85 %. Concurrently, the aerosol hemispheric backscatter fraction decreased by 21 %. The relative amount of organic matter (OM) or inorganics in PM1 was found to be a main factor determining the magnitude of f(RH). The highest values of f(RH) corresponded to the aerosols with a small fraction of OM, and vice versa. The relative amount of NO3- in fine particles was strongly correlated with f(85 %), which suggests that NO3- played a vital role in aerosol hygroscopic growth during this study. The mass fraction of nitrate also had a close relationship to the curvature of the humidograms; higher mass fractions of nitrate were associated with humidograms that had the least curvature. Aerosol hygroscopic growth caused a 47 % increase in the calculated aerosol direct radiative forcing at 85 % RH, compared to the forcing at 40 % RH.
We performed the broadband (1-100 keV) spectral analysis of the first Galactic Be ultraluminous X-ray pulsar (BeULX) Swift J0243.6+6124 observed by Insight-HXMT during the 2017−2018 outburst. The ...results show spectral transitions at two typical luminosities, roughly consistently with those reported previously via pure timing analysis. We find that the spectrum evolves and becomes softer and has higher cutoff energies until the luminosity reaches L1 (∼1.5 × 1038 erg s−1). Afterwards the spectrum becomes harder with lower cutoff energies until the luminosity increases to L2 (∼4.4 × 1038 erg s−1), around which the second spectral transition occurs. Beyond L2, the spectrum softens again and has larger cutoff energies. Similar behaviors were observed previously in other high-mass X-ray binary systems (HMXBs), especially for the second transition at higher luminosities, which is believed to have a correlation with the magnetic field of the harbored neutron star. Accordingly, we speculate that Swift J0243.6+6124 owns a neutron star with magnetic field strength >1013 G. The spectral transition at around L1 of Swift J0243.6+6124 is first observed thoroughly for any HMXB outburst characterized by strong evolution of the thermal component: the temperature of the blackbody drops sharply accompanied by a sudden increase of the blackbody radius. These spectral transitions can in principle be understood in a general scenario of balancing the emission patterns between the pencil and the fan beams at the magnetic pole, for which the extreme brightness of Swift J0243.6+6124 may provide an almost unique lab to probe the details.
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