118 research outputs found
First detection of GeV emission from an ultraluminous infrared galaxy: Arp 220 as seen with the Fermi Large Area Telescope
Cosmic rays (CRs) in starburst galaxies produce high energy gamma-rays by
colliding with the dense interstellar medium (ISM). Arp 220 is the nearest
ultra luminous infrared galaxy (ULIRG) that has star-formation at extreme
levels, so it has long been predicted to emit high-energy gamma-rays. However,
no evidence of gamma-ray emission was found despite intense efforts of search.
Here we report the discovery of high-energy gamma-ray emission above 200 MeV
from Arp 220 at a confidence level of using 7.5 years of
\textsl {Fermi} Large Area Telescope observations. The gamma-ray emission shows
no significant variability over the observation period and it is consistent
with the quasi-linear scaling relation between the gamma-ray luminosity and
total infrared luminosity for star-forming galaxies, suggesting that these
gamma-rays arise from CR interactions. As the high density medium of Arp 220
makes it an ideal CR calorimeter, the gamma-ray luminosity can be used to
measure the efficiency of powering CRs by supernova (SN) remnants given a known
supernova rate in Arp 220. We find that this efficiency is about
for CRs above 1 GeV.Comment: Accepted by ApJL, 6 pages, 3 figure
Evidence of a spectral break in the gamma-ray emission of the disk component of Large Magellanic Cloud: a hadronic origin?
It has been suggested that high-energy gamma-ray emission ()
of nearby star-forming galaxies may be produced predominantly by cosmic rays
colliding with the interstellar medium through neutral pion decay. The
pion-decay mechanism predicts a unique spectral signature in the gamma-ray
spectrum, characterized by a fast rising spectrum and a spectral break below a
few hundreds of MeV. We here report the evidence of a spectral break around 500
MeV in the disk emission of Large Magellanic Cloud (LMC), which is found in the
analysis of the gamma-ray data extending down to 60 MeV observed by {\it
Fermi}-Large Area Telescope. The break is well consistent with the pion-decay
model for the gamma-ray emission, although leptonic models, such as the
electron bremsstrahlung emission, cannot be ruled out completely.Comment: 11 pages, 4 figures, Accepted by Ap
Detection of gamma-ray emission from the Coma cluster with Fermi Large Area Telescope and tentative evidence for an extended spatial structure
Many galaxy clusters have giant halos of non-thermal radio emission,
indicating the presence of relativistic electrons in the clusters. Relativistic
protons may also be accelerated by merger and/or accretion shocks in galaxy
clusters. These cosmic-ray (CR) electrons and/or protons are expected to
produce gamma-rays through inverse-Compton scatterings or inelastic
collisions respectively. Despite of intense efforts in searching for
high-energy gamma-ray emission from galaxy clusters, conclusive evidence is
still missing so far. Here we report the discovery of MeV gamma-ray
emission from the Coma cluster direction with an unbinned likelihood analysis
of the 9 years of {\it Fermi}-LAT Pass 8 data. The gamma-ray emission shows a
spatial morphology roughly coincident with the giant radio halo, with an
apparent excess at the southwest of the cluster. Using the test statistic
analysis, we further find tentative evidence that the gamma-ray emission at the
Coma center is spatially extended. The extended component has an integral
energy flux of in the
energy range of 0.2 - 300 GeV and the spectrum is soft with a photon index of
. Interpreting the gamma-ray emission as arising from CR proton
interaction, we find that the volume-averaged value of the CR to thermal
pressure ratio in the Coma cluster is about . Our results show that
galaxy clusters are likely a new type of GeV gamma-ray sources, and they are
probably also giant reservoirs of CR protons.Comment: 10 pages, 10 figures, Accepted by Physical Review D, more spatial
models for the gamma-ray emission are used, systematic checks on the results
are adde
Implication of GRB 221009A: Can TeV Emission Come from the GRB Prompt Phase?
Recently, the B.O.A.T. ("brightest of all time") gamma-ray burst, dubbed GRB
221009A, was detected by various instruments. Unprecedentedly, the GRB
presented very-high-energy (VHE, energy above 0.1 TeV) gamma-ray emission with
energy extending above 10 TeV, as reported by the Large High Altitude Air
Shower Observatory (LHAASO). We here demonstrate that the VHE and especially
>10 TeV emission may originate from the internal hadronic dissipation of the
GRB, without the need of invoking any exotic processes as suggested by some
previous studies. We also discuss the constraints on the properties of the GRB
ejecta from multiwavelength and multi-messenger observations, which favors a
magnetically dominated GRB ejecta. The suggested Poynting-flux-dominated GRB
ejecta in this work supports the Blandford & Znajek (BZ) mechanism as the
possible central engine model of GRB.Comment: 13 pages, 7 figures, 3 tables, accepted versio
Modeling the broadband emission of Fermi/LAT GRB 090902B
GRB 090902B, detected by Fermi Large Array Telescope (Fermi/LAT), shows
extend high-energy emission (>100 MeV) up to 10^3 s after the burst, which
decays with time in a power-law as t^{-1.5}. It has been also observed by
several follow-up low-energy instruments, including an early optical detection
around 5000 s after the burst. The optical emission at early time decays faster
than t^{-1.6}, which has been suspected to originate from the reverse shock. We
here explore the models that can possibly explain the the broadband afterglow
emission of GRB 090902B. We find that the reverse shock model for the early
optical emission would overpredict the radio afterglow flux that is
inconsistent with observations. A partially radiative blast wave model, which
though is able to produce a sufficiently steep decay slope, can not explain the
broadband data of GRB 090902B. The two-component jet model, which consists of a
narrow and bright jet component in the core and a surrounding wider and less
energetic jet component, is shown to be able to explain the broadband afterglow
data, including the LAT high-energy data after ~50 s and low-energy (radio,
optical and X-ray) afterglow data. The early-time high-energy emission detected
by LAT before ~50 s is likely due to internal origin as that of the sub-MeV
emission. The highest energy (33 GeV) photon of GRB090902B detected at 80 s can
be marginally accommodated within the forward shock emission under the
optimistic condition that electrons are accelerated by the Bohm diffusive
shock.Comment: Accepted for publication in ApJ (minor changes, references updated),
11 pages (emulateapj style), 4 figure
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Rhein targets macrophage SIRT2 to promote adipose tissue thermogenesis in obesity in mice.
Rhein, a component derived from rhubarb, has been proven to possess anti-inflammatory properties. Here, we show that rhein mitigates obesity by promoting adipose tissue thermogenesis in diet-induced obese mice. We construct a macrophage-adipocyte co-culture system and demonstrate that rhein promotes adipocyte thermogenesis through inhibiting NLRP3 inflammasome activation in macrophages. Moreover, clues from acetylome analysis identify SIRT2 as a potential drug target of rhein. We further verify that rhein directly interacts with SIRT2 and inhibits NLRP3 inflammasome activation in a SIRT2-dependent way. Myeloid knockdown of SIRT2 abrogates adipose tissue thermogenesis and metabolic benefits in obese mice induced by rhein. Together, our findings elucidate that rhein inhibits NLRP3 inflammasome activation in macrophages by regulating SIRT2, and thus promotes white adipose tissue thermogenesis during obesity. These findings uncover the molecular mechanism underlying the anti-inflammatory and anti-obesity effects of rhein, and suggest that rhein may become a potential drug for treating obesity
Experimental evidence for Berry curvature multipoles in antiferromagnets
Berry curvature multipoles appearing in topological quantum materials have
recently attracted much attention. Their presence can manifest in novel
phenomena, such as nonlinear anomalous Hall effects (NLAHE). The notion of
Berry curvature multipoles extends our understanding of Berry curvature effects
on the material properties. Hence, research on this subject is of fundamental
importance and may also enable future applications in energy harvesting and
high-frequency technology. It was shown that a Berry curvature dipole can give
rise to a 2nd order NLAHE in materials of low crystalline symmetry. Here, we
demonstrate a fundamentally new mechanism for Berry curvature multipoles in
antiferromagnets that are supported by the underlying magnetic symmetries.
Carrying out electric transport measurements on the kagome antiferromagnet
FeSn, we observe a 3rd order NLAHE, which appears as a transverse voltage
response at the 3rd harmonic frequency when a longitudinal a.c. current drive
is applied. Interestingly, this NLAHE is strongest at and above room
temperature. We combine these measurements with a scaling law analysis, a
symmetry analysis, model calculations, first-principle calculations, and
magnetic Monte-Carlo simulations to show that the observed NLAHE is induced by
a Berry curvature quadrupole appearing in the spin-canted state of FeSn. At a
practical level, our study establishes NLAHE as a sensitive probe of
antiferromagnetic phase transitions in other materials, such as moir\'e
superlattices, two-dimensional van der Waal magnets, and quantum spin liquid
candidates, that remain poorly understood to date. More broadly, Berry
curvature multipole effects are predicted to exist for 90 magnetic point
groups. Hence, our work opens a new research area to study a variety of
topological magnetic materials through nonlinear measurement protocols
Destabilization of Fatty Acid Synthase by Acetylation Inhibits De Novo Lipogenesis and Tumor Cell Growth
Fatty acid synthase (FASN) is the terminal enzyme in de novo lipogenesis and plays a key role in cell proliferation. Pharmacological inhibitors of FASN are being evaluated in clinical trials for treatment of cancer, obesity and other diseases. Here we report a previously unknown mechanism of FASN regulation involving its acetylation by KAT8 and its deacetylation by HDAC3. FASN acetylation promoted its degradation via the ubiquitin-proteasome pathway. FASN acetylation enhanced its association with the E3 ubiquitin-ligase TRIM21. Acetylation destabilized FASN and resulted in decreased de novo lipogenesis and tumor cell growth. FASN acetylation was frequently reduced in human hepatocellular carcinoma samples, which correlated with increased HDAC3 expression and FASN protein levels. Our results suggest opportunities to target FASN acetylation as an anticancer strategy
Dual-comb spectroscopy over 100km open-air path
Satellite-based greenhouse gases (GHG) sensing technologies play a critical
role in the study of global carbon emissions and climate change. However, none
of the existing satellite-based GHG sensing technologies can achieve the
measurement of broad bandwidth, high temporal-spatial resolution, and high
sensitivity at the same time. Recently, dual-comb spectroscopy (DCS) has been
proposed as a superior candidate technology for GHG sensing because it can
measure broadband spectra with high temporal-spatial resolution and high
sensitivity. The main barrier to DCS's display on satellites is its short
measurement distance in open air achieved thus far. Prior research has not been
able to implement DCS over 20 km of open-air path. Here, by developing a
bistatic setup using time-frequency dissemination and high-power optical
frequency combs, we have implemented DCS over a 113 km turbulent horizontal
open-air path. Our experiment successfully measured GHG with 7 nm spectral
bandwidth and a 10 kHz frequency and achieved a CO2 sensing precision of <2 ppm
in 5 minutes and <0.6 ppm in 36 minutes. Our results represent a significant
step towards advancing the implementation of DCS as a satellite-based
technology and improving technologies for GHG monitoringComment: 24 pages, 6 figure
Mesaconine alleviates doxorubicin-triggered cardiotoxicity and heart failure by activating PINK1-dependent cardiac mitophagy
Aberrant mitophagy has been identified as a driver for energy metabolism disorder in most cardiac pathological processes. However, finding effective targeted agents and uncovering their precise modulatory mechanisms remain unconquered. Fuzi, the lateral roots of Aconitum carmichaelii, shows unique efficacy in reviving Yang for resuscitation, which has been widely used in clinics. As a main cardiotonic component of Fuzi, mesaconine has been proven effective in various cardiomyopathy models. Here, we aimed to define a previously unrevealed cardioprotective mechanism of mesaconine-mediated restoration of obstructive mitophagy. The functional implications of mesaconine were evaluated in doxorubicin (DOX)-induced heart failure models. DOX-treated mice showed characteristic cardiac dysfunction, ectopic myocardial energy disorder, and impaired mitophagy in cardiomyocytes, which could be remarkably reversed by mesaconine. The cardioprotective effect of mesaconine was primarily attributed to its ability to promote the restoration of mitophagy in cardiomyocytes, as evidenced by elevated expression of PINK1, a key mediator of mitophagy induction. Silencing PINK1 or deactivating mitophagy could completely abolish the protective effects of mesaconine. Together, our findings suggest that the cardioprotective effects of mesaconine appear to be dependent on the activation of PINK1-induced mitophagy and that mesaconine may constitute a promising therapeutic agent for the treatment of heart failure
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