Fast radio bursts (FRBs) are highly dispersed radio bursts prevailing in the universe [1][2][3] . The recent detection of FRB 200428 from a Galactic magnetar [4][5][6][7][8] suggested that at least some FRBs originate from magnetars, but it is unclear whether the majority of cosmological FRBs, especially the actively repeating ones, are produced from the magnetar channel. Here we report the detection of 1863 polarised bursts from the repeating source FRB 20201124A 9 during a dedicated radio observational campaign of Five-hundred-meter Aperture Spherical radio Telescope (FAST). The large sample of radio bursts detected in 88 hr over 54 days indicate a significant, irregular, short-time variation of the Faraday rotation measure (RM) of the source during the first 36 days, followed by a constant RM during the later 18 days. Significant circular polarisation up to 75% was observed in a good fraction of bursts. Evidence suggests that some low-level circular polarisation originates from the conversion from linear polarisation during the propagation of the radio waves, but an intrinsic radiation mechanism is required to produce the higher degree of circular polarisation. All of these features provide evidence for a more complicated, dynamically evolving, magnetised immediate environment around this FRB source. Its host galaxy was previously known 10-12 . Our optical observations reveal that it is a Milky-Way-sized, metal-rich, barred-spiral galaxy at redshift z = 0.09795 ± 0.00003, with the FRB source residing in a low stellar density, interarm region

THESEUS is a space mission concept aimed at exploiting Gamma-Ray Bursts for investigating the early Universe and at providing a substantial advancement of multi-messenger and time-domain astrophysics. These goals will be achieved through a unique combination of instruments allowing GRB and X-ray transient detection over a broad field of view (more than 1sr) with 0.5-1 arcmin localization, an energy band extending from several MeV down to 0.3 keV and high sensitivity to transient sources in the soft X-ray domain, as well as on-board prompt (few minutes) followup with a 0.7 m class IR telescope with both imaging and spectroscopic capabilities. THESEUS will be perfectly suited for addressing the main open issues in cosmology such as, e.g., star formation rate and metallicity evolution of the inter-stellar and intra-galactic medium up to redshift ∼10, signatures of Pop III stars, sources and physics of reionization, and the faint end of the galaxy luminosity function. In addition, it will provide unprecedented capability to monitor the X-ray variable sky, thus detecting, localizing, and identifying the electromagnetic counterparts to sources of gravitational radiation, which may be routinely detected in the late '20s / early '30s by next generation facilities like aLIGO/ aVirgo, eLISA, KAGRA, and Einstein Telescope. THESEUS will also provide powerful synergies with the next generation of multi-wavelength observatories (e.g., LSST, ELT, SKA, CTA, ATHENA).

We present a Chandra Advanced CCD Imaging Spectrometer observation of supernova remnant G54.1ϩ0.3. This supernova remnant is resolved into several distinct X-ray-emitting components: a central bright pointlike source (CXOU J193030.13ϩ185214.1), a surrounding ring, bipolar elongations, plus low surface brightness diffuse emission. The spectra of these components are all well described by power-law models; the spectral index steepens with increasing distance from the pointlike source. We find no evidence for any thermal plasma emission that would correspond to shocked interstellar medium or ejecta. The observed morphological and spectral characteristics suggest that G54.1ϩ0.3 is the closest "cousin" of the Crab Nebula-a pulsar wind nebula driven by a combination of equatorial and polar outflows from the putative pulsar represented by the pointlike X-ray source. Subject headings: ISM: individual (G54.1ϩ0.3) -ISM: jets and outflows -stars: neutronsupernova remnants -X-rays: ISM On-line material: color figure

We study the statistics of 61 measured masses of neutron stars (NSs) in binary pulsar systems, including 18 double NS (DNS) systems, 26 radio pulsars (10 in our Galaxy) with white dwarf (WD) companions, 3 NSs with main-sequence companions, 13 NSs in X-ray binaries, and one undetermined system. We derive a mean value of M = 1.46 ± 0.30 M . When the 46 NSs with measured spin periods are divided into two groups at 20 milliseconds, i.e., the millisecond pulsar (MSP) group and others, we find that their mass averages are, respectively, M = 1.57 ± 0.35 M and M = 1.37 ± 0.23 M . In the framework of the pulsar recycling hypothesis, this suggests that an accretion of approximately ∼0.2 M is sufficient to spin up a neutron star and place it in the millisecond pulsar group. Based on these estimates, an approximate empirical relation between the accreting mass (ΔM) of recycled pulsar and its spin period is proposed as ΔM = 0.43 (M )(P/1 ms) −2/3 . If we focus only on the DNS, the mass average of all 18 DNSs is 1.32 ± 0.14 M , and the mass averages of the recycled DNSs and the non-recycled NS companions are, respectively, 1.38 ± 0.12 M and 1.25 ± 0.13 M . This is consistent with the hypothesis that the masses of both NSs in DNS system have been affected by accretion. The mass average of MSPs is higher than the Chandrasekhar limit 1.44 M , which may imply that most of binary MSPs form via the standard scenario by accretion recycling. If we were to assume that the mass of a MSP formed by the accretion induced collapse (AIC) of a white dwarf must be less than 1.35 M , then the portion of the binary MSPs involved in the AICs would not be higher than 20%, which imposes a constraint on the AIC origin of MSPs. With accreting mass from the companion, the nuclear matter composition of MSP may experience a transition from the "soft" equation of state (EOS) to a "stiff" EOS or even neutron to quark matter.

We report here direct contact membrane distillation results from modules having 0.28 m2 of membrane surface area employing porous hydrophobic polypropylene hollow fibers of internal diameter (330 μm) and wall thickness (150 μm) with a porous fluorosilicone coating on the outside surface. The brine salt concentration and temperature and the distillate temperature and velocity were varied. Water vapor fluxes approach values obtained earlier in much smaller modules. As the brine temperature was increased from 40 to 92 °C, water vapor flux increased almost exponentially. Increasing the distillate temperature to 60 from 32 °C yielded reasonable fluxes. Salt concentration increases to 10% led to a small flux reduction. An extended 5-day run did not show any pore wetting. A model using the mass transfer coefficient k m as an adjustable parameter predicted the brine temperature drop, distillate temperature rise, and water vapor flux well for the large module and the smaller module of 119-cm2 surface area.

The milestone of GW 170817-GRB 170817A-AT 2017gfo 1 has shown that gravitational wave (GW) is produced during the merger of neutron star-neutron star/black hole and that in electromagnetic (EM) wave a gamma-ray burst (GRB) and a kilonovae (KN) are generated in sequence after the merger. Observationally, however, EM property during a merger is still unclear. Here we report a peculiar precursor in a KN-associated long GRB 211211A. The duration of the precursor is ∼ 0.2 s, and the waiting time between the precursor and the main emission (ME) of the burst is ∼ 1 s, which is about the same as the time interval between GW 170817 and GRB 170817A. Quasi-Periodic Oscillations (QPO) with frequency ∼22 Hz (at > 5σ significance) are found throughout the precursor, the first detection of periodic signals from any bona fide GRBs. This indicates most likely that a magnetar participated in the merger, and the precursor might be produced due to a catastrophic flare accompanying with torsional or crustal oscillations of the magnetar. The strong seed magnetic field of ∼ 10 14−15 G at the surface of the magnetar may also account for the prolonged duration of GRB 211211A. However, it is a challenge to reconcile the rather short lifetime of a magnetar

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We present a study of the centroid frequencies and phase lags of the quasiperiodic oscillations (QPOs) as functions of photon energy for GRS 1915+105.It is found that the centroid frequencies of the 0.5-10 Hz QPOs and their phase lags are both energy dependent, and there exists an anti-correlation between the QPO frequency and phase lag. These new results challenge the popular QPO models, because none of them can fully explain the observed properties. We suggest that the observed QPO phase lags are partially due to the variation of the QPO frequency with energy, especially for those with frequency higher than 3.5 Hz.