117 research outputs found
More on difference between angular momentum and pseudo-angular momentum
We extend the discussion on the difference between angular momentum and
pseudo-angular momentum in field theory. We show that the often quoted
expressions in [Phys.Rev.B 103, L100409 (2021)] only apply to a non-linear
system, and derive the correct rotation symmetry and the corresponding angular
momentum for a linear elastic system governed by Navier-Cauchy equation. By
mapping the concepts and methods for the elastic wave into electromagnetic
theory, we argue that the renowned canonical and Benlinfante angular momentum
of light are actually pseudo-angular momentum. Then, we derive the ``Newtonian"
momentum and angular momentum for a free electromagnetic
wave, which are conserved quantities during propagation in vacuum.Comment: 8 pages, no figure
The Very Early Soft X-ray Plateau of GRB 230307A: Signature of an Evolving Radiative Efficiency in Magnetar Wind Dissipation?
Very recently, a particularly long gamma-ray burst (GRB) 230307A was reported
and proposed to originate from a compact binary merger based on its host galaxy
property, kilonova, and heavy elements. More intriguingly, a very early plateau
followed by a rapid decline in soft X-ray band was detected in its light curve
by the Lobster Eye Imager for Astronomy, indicating strong evidence of the
existence of a magnetar as the merger product. This work explores that the
Magnetar Wind Internal Gradual MAgnetic Dissipation (MIGMAD) model, in which
the radiative efficiency evolves over time, successfully fits it to the
observed data. Our results reinforce the notion that the X-ray plateau serves
as a powerful indicator of a magnetar and imply that an evolving efficiency is
likely to be a common feature in X-ray plateaus of GRB afterglows. In addition,
we also discuss the explanations for the prompt emission, GRB afterglows, as
well as kilonova, and predict possible kilonova afterglows in a magnetar
central engine.Comment: 10 pages, 4 figures, 2 tables. Accepted for publication in The
Astrophysical Journal Letter
Target of Opportunity Observations Detectability of Kilonovae with WFST
Kilonovae are approximately thermal transients, produced by mergers of binary
neutron stars (BNSs) and NS-black hole binaries. As the optical counterpart of
the gravitational wave event GW170817, AT2017gfo is the first kilonova detected
with smoking-gun evidence. Its observation offers vital information for
constraining the Hubble constant, the source of cosmic -process enrichment,
and the equation of state of neutron stars. The 2.5-meter Wide-Field Survey
Telescope (WFST) operates at six bands (u, g, r, i, z, w), spanning from 320 to
925 nm. It will be completed in the first half of 2023, and with a
field-of-view diameter of 3 degrees, aims to detect kilonovae in the near
future. In this article, considering the influence of the host galaxies and sky
brightness, we generate simulated images to investigate WFST's ability to
detect AT2017gfo-like kilonovae. Due to their spectra, host galaxies can
significantly impact kilonova detection at a longer wavelength. When kilonovae
are at peak luminosity, we find that WFST performs better in the g and r bands
and can detect 90\% (50\%) kilonovae at a luminosity distance of 248 Mpc (338
Mpc) with 30 s exposures. Furthermore, to reflect actual efficiency under
target-of-opportunity observations, we calculate the total time of follow-up
under various localization areas and distances. We find that if the
localization areas of most BNS events detected during the fourth observing (O4)
run of LIGO and Virgo are hundreds of deg, WFST is expected to find
30\% kilonovae in the first two nights during O4 period.Comment: 18 pages, 11 figure
FAST observations of an extremely active episode of FRB 20201124A: IV. Spin Period Search
We report the properties of more than 800 bursts detected from the repeating
fast radio burst (FRB) source FRB 20201124A with the Five-hundred-meter
Aperture Spherical radio telescope (FAST) during an extremely active episode on
UTC September 25th-28th, 2021 in a series of four papers. In this fourth paper
of the series, we present a systematic search of the spin period and linear
acceleration of the source object from both 996 individual pulse peaks and the
dedispersed time series. No credible spin period was found from this data set.
We rule out the presence of significant periodicity in the range between 1 ms
to 100 s with a pulse duty cycle (when the profile is defined
by a von-Mises function, not a boxcar function) and linear acceleration up to
m s in each of the four one-hour observing sessions, and up to
m s in all 4 days. These searches contest theoretical scenarios
involving a 1 ms to 100 s isolated magnetar/pulsar with surface magnetic field
G and a small duty cycle (such as in a polar-cap emission mode) or a
pulsar with a companion star or black hole up to 100 M and
hours. We also perform a periodicity search of the fine structures and
identify 53 unrelated millisecond-timescale "periods" in multi-components with
the highest significance of 3.9 . The "periods" recovered from the fine
structures are neither consistent nor harmonically related. Thus they are not
likely to come from a spin period. We caution against claiming spin periodicity
with significance below 4 with multi-components from one-off
FRBs. We discuss the implications of our results and the possible connections
between FRB multi-components and pulsar micro-structures.Comment: Accepted by Research in Astronomy and Astrophysics (RAA
FAST observations of an extremely active episode of FRB 20201124A: III. Polarimetry
As the third paper in the multiple-part series, we report the statistical
properties of radio bursts detected from the repeating fast radio burst (FRB)
source FRB 20201124A with the Five-hundred-meter Aperture Spherical radio
telescope (FAST) during an extremely active episode between the 25th and the
28th of September 2021 (UT). We focus on the polarisation properties of 536
bright bursts with . We found that the Faraday rotation
measures (RMs) monotonically dropped from to in the 4-day window. The RM values were compatible with
the values ( to ) reported 4 month ago (Xu et
al. 2022). However, the RM evolution rate in the current observation window was
at least an order of magnitude smaller than the one ($\sim 500\ {\rm rad \
m^{-2}\, day^{-1}}\le 1\ {\rm rad \ m^{-2} day^{-1}}L/IV/I\sigma$) were observed in 33% of
all bursts. The polarisation of single pulses seems to follow certain complex
trajectories on the Poincar\'e sphere, which may shed light on the radiation
mechanism at the source or the plasma properties along the path of FRB
propagation.Comment: 25 pages, 16 figures. Accepted by Research in Astronomy and
Astrophysics (RAA
Magnetic activities and parameters of 43 flare stars in the GWAC archive
In the archive of the Ground Wide Angle Camera (GWAC), we found 43 white
light flares from 43 stars, among which, three are sympathetic or homologous
flares, and one of them also has a quasi-periodic pulsation with a period of
minutes. Among these 43 flare stars, there are 19 new active stars
and 41 stars that have available TESS and/or K2 light curves, from which we
found 931 stellar flares. We also obtained rotational or orbital periods of 34
GWAC flare stars, of which 33 are less than 5.4 days, and ephemerides of three
eclipsing binaries from these light curves. Combining with low resolution
spectra from LAMOST and the Xinglong 2.16m telescope, we found that are in the saturation region in the rotation-activity
diagram. From the LAMOST medium-resolution spectrum, we found that Star \#3
(HAT 178-02667) has double H emissions which imply it is a binary, and
two components are both active stars. Thirteen stars have flare frequency
distributions (FFDs) from TESS and/or K2 light curves. These FFDs show that the
flares detected by GWAC can occur at a frequency of 0.5 to 9.5 yr. The
impact of flares on habitable planets was also studied based on these FFDs, and
flares from some GWAC flare stars may produce enough energetic flares to
destroy ozone layers, but none can trigger prebiotic chemistry on their
habitable planets.Comment: 20 pages, 9 figures, 3 table
Functional building blocks for scalable multipartite entanglement in optical lattices
Featuring excellent coherence and operated parallelly, ultracold atoms in
optical lattices form a competitive candidate for quantum computation. For
this, a massive number of parallel entangled atom pairs have been realized in
superlattices. However, the more formidable challenge is to scale-up and detect
multipartite entanglement due to the lack of manipulations over local atomic
spins in retro-reflected bichromatic superlattices. Here we developed a new
architecture based on a cross-angle spin-dependent superlattice for
implementing layers of quantum gates over moderately-separated atoms
incorporated with a quantum gas microscope for single-atom manipulation. We
created and verified functional building blocks for scalable multipartite
entanglement by connecting Bell pairs to one-dimensional 10-atom chains and
two-dimensional plaquettes of atoms. This offers a new platform
towards scalable quantum computation and simulation
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