Abstract
Following shock breakout, the emission from an astrophysical explosion is dominated by the radiation of shock-heated material as it expands and cools, known as shock cooling emission (SCE). ...The luminosity of SCE is proportional to the initial radius of the emitting material, which makes its measurement useful for investigating the progenitors of these explosions. Recent observations have shown some transient events have especially prominent SCE, indicating a large radius that is potentially due to low-mass extended material. Motivated by this, we present an updated analytic model for SCE that can be utilized to fit these observations and learn more about the origin of these events. This model is compared with numerical simulations to assess its validity and limitations. We also discuss SN 2016gkg and SN 2019dge, two transients with large early luminosity peaks that have previously been attributed to SCE of extended material. We show that their early power-law evolution and photometry are well matched by our model, strengthening support for this interpretation.
Applications of optical switches, such as signal routing and data-intensive computing, are critical in optical interconnects and optical computing. Integrated optical switches enabled by ...two-dimensional (2D) materials and beyond, such as graphene and black phosphorus, have demonstrated many advantages in terms of speed and energy consumption compared to their conventional silicon-based counterparts. Here we review the state-of-the-art of optical switches enabled by 2D materials and beyond and organize them into several tables. The performance tables and future projections show the frontiers of optical switches fabricated from 2D materials and beyond, providing researchers with an overview of this field and enabling them to identify existing challenges and predict promising research directions.
Conventional all‐dielectric metasurfaces made from high‐index and low‐loss materials (such as Si or GaAs) can achieve high optical efficiencies as well as broadband characteristics, mostly for the ...infrared (IR) light. However, maintaining the bandwidth and efficiency for conventional all‐dielectric metasurfaces for visible or near‐IR light becomes challenging, due to the limitations from material selection as well as fabrication techniques. In this paper, the idea of heterogeneous all‐dielectric metasurfaces is proposed for a better metasurface design in shorter‐wavelength ranges. An ultra‐broadband reflector, as a proof‐of‐principle demonstration, is presented in this paper, both numerically and experimentally. The broadband reflector demonstrates a good optical efficiency, a broadband reflectance, as well as a great manufacturability. Nanoimprint lithography patterning process and advanced etching recipes are developed for the large‐area and low‐cost heterogeneous metasurface fabrication.
Heterogeneous all‐dielectric metasurfaces are introduced to overcome the limitation of conventional all‐dielectric metasurface designs that maintaining both broad bandwidth and good efficiency in visible or near‐IR wavelengths is challenging. Following the design paradigm, an ultra‐broadband reflector is demonstrated for applications in shorter‐wavelength ranges.
Supercritical accretion onto compact objects powers a massive wind that is optically thick and Eddington-limited. If most of the hard X-rays from the central disk are obscured by the wind, the source ...will display a blackbody-like spectrum with a luminosity scaled with the mass of the compact object. From the Chandra archive of nearby galaxies, we selected a sample of luminous and very soft sources and excluded contamination from foreground objects and supernova remnants. They are found to be preferentially associated with late-type galaxies. The majority of sources in our sample are either too hot or too luminous to be explained by nuclear burning on the surface of white dwarfs, and are argued to be powered by accretion. The most likely explanation is that they are due to emission from the photosphere of a wind driven by supercritical accretion onto compact objects. Their blackbody luminosity ranges from ∼1037 to nearly 1040 erg s−1, indicative of the presence of both neutron stars and stellar-mass black holes. The blackbody luminosity also shows a possible bimodal distribution, albeit at low significance, peaked around the Eddington limit for neutron stars and stellar-mass black holes, respectively. If this can be confirmed, it will be smoking gun evidence that supercritical accretion powers thick winds. Based on a wind model, the inferred mass accretion rate of these objects is around a few hundred times the Eddington rate, suggesting that they may be intermediate between the canonical ultraluminous X-ray sources and SS 433 in terms of the accretion rate.
Abstract
We present AT2020mrf (SRGe J154754.2+443907), an extra-galactic (
z
= 0.1353) fast blue optical transient (FBOT) with a rise time of
t
g
,rise
= 3.7 days and a peak luminosity of
M
g
,peak
= ...−20.0. Its optical spectrum around peak shows a broad (
v
∼ 0.1
c
) emission feature on a blue continuum (
T
∼ 2 × 10
4
K), which bears a striking resemblance to AT2018cow. Its bright radio emission (
ν
L
ν
= 1.2 × 10
39
erg s
−1
;
ν
rest
= 7.4 GHz; 261 days) is similar to four other AT2018cow-like events, and can be explained by synchrotron radiation from the interaction between a sub-relativistic (≳0.07–0.08c) forward shock and a dense environment (
M
̇
≲
10
−
3
M
⊙
yr
−
1
for
v
w
= 10
3
km s
−1
). AT2020mrf occurs in a galaxy with
M
*
∼ 10
8
M
⊙
and specific star formation rate ∼10
−10
yr
−1
, supporting the idea that AT2018cow-like events are preferentially hosted by dwarf galaxies. The X-ray luminosity of AT2020mrf is the highest among FBOTs. At 35–37 days, SRG/eROSITA detected luminous (
L
X
∼ 2 × 10
43
erg s
−1
; 0.3–10 keV) X-ray emission. The X-ray spectral shape (
f
ν
∝
ν
−0.8
) and erratic intraday variability are reminiscent of AT2018cow, but the luminosity is a factor of ∼20 greater than AT2018cow. At 328 days, Chandra detected it at
L
X
∼ 10
42
erg s
−1
, which is >200 times more luminous than AT2018cow and CSS161010. At the same time, the X-ray emission remains variable on the timescale of ∼1 day. We show that a central engine, probably a millisecond magnetar or an accreting black hole, is required to power the explosion. We predict the rates at which events like AT2018cow and AT2020mrf will be detected by SRG and Einstein Probe.
Microwave photonic filters have been regarded as an alternative to traditional radio‐frequency filters because of their wide bandwidth and large tunability. Integrated microwave photonic filters can ...integrate all necessary components into a single chip and are highly demanded for future radio‐frequency applications. Here, a highly integrated frequency‐tunable microwave photonic bandpass filter based on a silicon platform is proposed and demonstrated. The integrated filter consists of a phase modulator, four cascaded microring resonators and a photodetector. The frequency‐tunable range of the integrated filter is from 6.1 to 35.9 GHz, and the reconfigurable bandwidth is from 0.22 to 0.54 GHz. A large spurious free dynamic range of 102.1 dB Hz2/3 is obtained. This highly integrated approach holds great promise for miniaturised, flexible, and high‐performance microwave signal processing in modern radar and communication systems.
We report a highly integrated microwave photonic bandpass filter with wide‐frequency tunable range and reconfigurable bandwidth. Both active and passive components are monolithically integrated on silicon‐on‐insulator platform. This work is a solid step towards the implementation of an on‐chip miniaturised microwave signal processing system.
Abstract We present a systematic analysis of the X-ray emission of a sample of 17 optically selected, X-ray-detected tidal disruption events (TDEs) discovered between 2014 and 2021. The X-ray light ...curves show a diverse range of temporal behaviors, with most sources not following the expected power-law decline. The X-ray spectra are mostly extremely soft and consistent with thermal emission from the innermost region of an accretion disk, which cools as the accretion rate decreases. Three sources show formation of a hard X-ray corona at late times. The spectral energy distribution shape, probed by the ratio ( L BB / L X ) between the UV/optical and X-ray, shows a wide range of L BB / L X ∈ (0.5, 3000) at early times and converges to disklike values of L BB / L X ∈ (0.5, 10) at late times. We estimate the fraction of optically discovered TDEs with L X ≥ 10 42 erg s −1 to be at least 40% and show that X-ray loudness is independent of black hole mass. We argue that distinct disk formation timescales are unlikely to be able to explain the diverse range of X-ray evolution. We combine our sample with X-ray-discovered ones to construct an X-ray luminosity function, best fit by a broken power law, with a break at L X ≈ 10 44 erg s −1 . We show that there is no dichotomy between optically and X-ray-selected TDEs; instead, there is a continuum of early-time L BB / L X , at least as wide as L BB / L X ∈ (0.1, 3000), with optical/X-ray surveys selecting preferentially, but not exclusively, from the higher/lower end of the distribution. Our findings are consistent with unification models for the overall TDE population.
This study aimed to investigate the preventive effects of the total polyphenols from
(NCTP) on LPS-induced septic acute lung injury (ALI) in mice and its mechanisms. NCTP could significantly ...ameliorate LPS-induced lung tissue pathological injury in mice as well as lung wet/dry ratio and MPO activities (
< 0.05). NCTP could significantly decrease the blood leukocyte, neutrophil, monocyte, basophil, and eosinophil amounts and LPS contents in ALI mice compared with the model group (
< 0.05), improving lymphocyte amounts (
< 0.05). Moreover, compared with the model group, NCTP could decrease lung tissue TNF-α, IL-6, and IL-1β levels (
< 0.05) and downregulate the protein expression of TLR4, MyD88, TRAF6, IKKβ, IκB-α, p-IκB-α, NF-κB p65, p-NF-κB p65, NLRP3, ASC, and Caspase1 in lung tissues (
< 0.05). Furthermore, NCTP could inhibit ileum histopathological injuries, restoring the ileum tight junctions by increasing the expression of ZO-1 and occludin. Simultaneously, NCTP could reverse the gut microbiota disorder, restore the diversity of gut microbiota, increase the relative abundance of Clostridiales and Lachnospiraceae, and enhance the content of SCFAs (acetic acid, propionic acid, and butyric acid) in feces. These results suggested that NCTP has preventive effects on septic ALI, and its mechanism is related to the regulation of gut microbiota, SCFA metabolism, and the TLR-4/NF-κB and NLRP3 pathways.
2D materials, such as graphene, black phosphorous and transition metal dichalcogenides, have gained persistent attention in the past few years thanks to their unique properties for optoelectronics. ...More importantly, introducing 2D materials into silicon photonic devices will greatly promote the performance of optoelectronic devices, including improvement of response speed, reduction of energy consumption, and simplification of fabrication process. Moreover, 2D materials meet the requirements of complementary metal‐oxide‐semiconductor compatible silicon photonic manufacturing. A comprehensive overview and evaluation of state‐of‐the‐art 2D photonic integrated devices for telecommunication applications is provided, including light sources, optical modulators, and photodetectors. Optimized by unique structures such as photonic crystal waveguide, slot waveguide, and microring resonator, these 2D material‐based photonic devices can be further improved in light‐matter interactions, providing a powerful design for silicon photonic integrated circuits.
2D materials have gained persistent attention in the past few years and they meet the requirements of complementary metal‐oxide‐semiconductor compatible silicon photonic manufacturing. A comprehensive overview of fabrication and evaluation of state‐of‐the‐art 2D photonic integrated devices for telecommunication applications is provided, including light sources, optical modulators, and photodetectors in on‐chip devices.
Abstract
We conduct a systematic tidal disruption event (TDE) demographics analysis using the largest sample of optically selected TDEs. A flux-limited, spectroscopically complete sample of 33 TDEs ...is constructed using the Zwicky Transient Facility over 3 yr (from 2018 October to 2021 September). We infer the black hole (BH) mass (
M
BH
) with host galaxy scaling relations, showing that the sample
M
BH
ranges from 10
5.1
M
⊙
to 10
8.2
M
⊙
. We developed a survey efficiency corrected maximum volume method to infer the rates. The rest-frame
g
-band luminosity function can be well described by a broken power law of
ϕ
(
L
g
)
∝
L
g
/
L
bk
0.3
+
L
g
/
L
bk
2.6
−
1
, with
L
bk
= 10
43.1
erg s
−1
. In the BH mass regime of 10
5.3
≲ (
M
BH
/
M
⊙
) ≲ 10
7.3
, the TDE mass function follows
ϕ
(
M
BH
)
∝
M
BH
−
0.25
, which favors a flat local BH mass function (
dn
BH
/
d
log
M
BH
≈
constant
). We confirm the significant rate suppression at the high-mass end (
M
BH
≳ 10
7.5
M
⊙
), which is consistent with theoretical predictions considering direct capture of hydrogen-burning stars by the event horizon. At a host galaxy mass of
M
gal
∼ 10
10
M
⊙
, the average optical TDE rate is ≈3.2 × 10
−5
galaxy
−1
yr
−1
. We constrain the optical TDE rate to be 3.7, 7.4, and 1.6 × 10
−5
galaxy
−1
yr
−1
in galaxies with red, green, and blue colors.
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