3,132 research outputs found
High-Energy Gamma-Rays from GRB X-ray Flares
The recent detection of X-ray flares during the afterglow phase of gamma-ray
bursts (GRBs) suggests an inner-engine origin, at radii inside the forward
shock. There must be inverse Compton (IC) emission arising from such flare
photons scattered by forward shock afterglow electrons when they are passing
through the forward shock. We find that this IC emission produces high energy
gamma-ray flares, which may be detected by AGILE, GLAST and ground-based TeV
telescopes. The anisotropic IC scattering between flare photons and forward
shock electrons does not affect the total IC component intensity, but cause a
time delay of the IC component peak relative to the flare peak. The anisotropic
scattering effect may also weaken, to some extent, the suppression effect of
the afterglow intensity induced by the enhanced electron cooling due to flare
photons. We speculate that this IC component may already have been detected by
EGRET from a very strong burst--GRB940217. Future observations by GLAST may
help to distinguish whether X-ray flares originate from late central engine
activity or from external shocks.Comment: 4 pages, Contributed talk presented at "The First GLAST Symposium",
Feb.5-8 2007, Stanford Universit
On the magnetization of gamma-ray burst blast waves
The origin of magnetic fields that permeate the blast waves of gamma-ray
bursts (GRBs) is a long-standing problem. The present paper argues that in four
GRBs revealing extended emission at >100 MeV, with follow-up in the radio,
optical and X-ray domains at later times, this magnetization can be described
as the partial decay of the micro-turbulence that is generated in the shock
precursor. Assuming that the bulk of the extended emission >100 MeV can be
interpreted as synchrotron emission of shock accelerated electrons, we model
the multi-wavelength light curves of GRB 090902B, GRB 090323, GRB 090328 and
GRB 110731A, using a simplified then a full synchrotron calculation with
power-law-decaying microturbulence \epsilon_B \propto t^{\alpha_t} (t denotes
the time since injection through the shock, in the comoving blast frame). We
find that these models point to a consistent value of the decay exponent -0.5 <
\alpha_t < -0.4.Comment: 8 pages, 4 figures - discussion added, conclusions unchanged -
version to appear in MNRA
Jet-cloud/star interaction as an interpretation of neutrino outburst from the blazar TXS 0506+056
Recently, a high-energy neutrino event IceCube-170922A in the spatial and
temporal coincidence with the flaring gamma-ray blazar TXS 0506+056 was
reported. A neutrino outburst between September 2014 and March 2015 was
discovered in the same direction by a further investigation of years of
IceCube data, while the blazar is in a quiescent state during the outburst with
a gamma-ray flux only about one-fifth of the neutrino flux. In this letter, we
propose the neutrino outburst originates from the interaction between a
relativistic jet and a dense gas cloud which may be formed via the tidally
disrupted envelope of a red giant being blown by the impact of the jet.
Gamma-ray photons and electron/positron pairs that are produced correspondingly
will induce electromagnetic cascades. Comptonization of the cascade emission
inside the cloud forms an X-ray photon field with Wien distribution. GeV flux
is suppressed due to the absorption by the Comptonized photon field and, as a
result, a hard spectrum above 10 GeV is formed. The gamma-ray spectrum
predicted in our model is consistent with the Fermi-LAT data of TXS 0506+056.Comment: 6 pages, 3 figure
Observation of recoil-induced resonances and electromagnetically induced absorption of cold atoms in diffuse light
In this paper we report an experiment on the observation of the
recoil-induced resonances (RIR) and electromagnetically induced absorption
(EIA) of cold Rb87 atoms in diffuse light. The pump light of the RIR and the
EIA comes from the diffuse light in an integrating sphere, which also serves
the cooling light. The probe light beam is a weak laser split from the cooling
laser in order to keep the cooling and probe lasers correlated. We measured the
RIR and the EIA signal varying with the detuning of the diffuse laser light,
and also measured the temperature of the cold atoms at the different detunings.
The mechanism of RIR and EIA in the configuration with diffuse-light pumping
and laser probing is discussed, and the difference of nonlinear spectra of cold
atoms between in diffuse-light cooling system and in optical molasses as well
as in a magneto-optical trap (MOT) are studied.Comment: 9 pages, 6 figure
GeV-TeV and X-ray flares from gamma-ray bursts
The recent detection of delayed X-ray flares during the afterglow phase of
gamma-ray bursts (GRBs) suggests an inner-engine origin, at radii inside the
deceleration radius characterizing the beginning of the forward shock afterglow
emission. Given the observed temporal overlapping between the flares and
afterglows, there must be inverse Compton (IC) emission arising from such flare
photons scattered by forward shock afterglow electrons. We find that this IC
emission produces GeV-TeV flares, which may be detected by GLAST and
ground-based TeV telescopes. We speculate that this kind of emission may
already have been detected by EGRET from a very strong burst--GRB940217. The
enhanced cooling of the forward shock electrons by the X-ray flare photons may
suppress the synchrotron emission of the afterglows during the flare period.
The detection of GeV-TeV flares combined with low energy observations may help
to constrain the poorly known magnetic field in afterglow shocks. We also
consider the self-IC emission in the context of internal-shock and
external-shock models for X-ray flares. The emission above GeV from internal
shocks is low, while the external shock model can also produce GeV-TeV flares,
but with a different temporal behavior from that caused by IC scattering of
flare photons by afterglow electrons. This suggests a useful approach for
distinguishing whether X-ray flares originate from late central engine activity
or from external shocks.Comment: slightly shortened version, accepted for publication in ApJ Letters,
4 emulateapj pages, no figure
Identification of a Potentially Functional microRNA-mRNA Regulatory Network in Lung Adenocarcinoma Using a Bioinformatics Analysis
Background Lung adenocarcinoma (LUAD) is a common lung cancer with a high mortality, for which microRNAs (miRNAs) play a vital role in its regulation. Multiple messenger RNAs (mRNAs) may be regulated by miRNAs, involved in LUAD tumorigenesis and progression. However, the miRNA-mRNA regulatory network involved in LUAD has not been fully elucidated. Methods Differentially expressed miRNAs and mRNA were derived from the Cancer Genome Atlas (TCGA) dataset in tissue samples and from our microarray data in plasma (GSE151963). Then, common differentially expressed (Co-DE) miRNAs were obtained through intersected analyses between the above two datasets. An overlap was applied to confirm the Co-DEmRNAs identified both in targeted mRNAs and DEmRNAs in TCGA. A miRNA-mRNA regulatory network was constructed using Cytoscape. The top five miRNA were identified as hub miRNA by degrees in the network. The functions and signaling pathways associated with the hub miRNA-targeted genes were revealed through Gene Ontology (GO) analysis and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway. The key mRNAs in the protein-protein interaction (PPI) network were identified using the STRING database and CytoHubba. Survival analyses were performed using Gene Expression Profiling Interactive Analysis (GEPIA). Results The miRNA-mRNA regulatory network consists of 19 Co-DEmiRNAs and 760 Co-DEmRNAs. The five miRNAs (miR-539-5p, miR-656-3p, miR-2110, let-7b-5p, and miR-92b-3p) in the network were identified as hub miRNAs by degrees (>100). The 677 Co-DEmRNAs were targeted mRNAs from the five hub miRNAs, showing the roles in the functional analyses of the GO analysis and KEGG pathways (inclusion criteria: 836 and 48, respectively). The PPI network and Cytoscape analyses revealed that the top ten key mRNAs were NOTCH1, MMP2, IGF1, KDR, SPP1, FLT1, HGF, TEK, ANGPT1, and PDGFB. SPP1 and HGF emerged as hub genes through survival analysis. A high SPP1 expression indicated a poor survival, whereas HGF positively associated with survival outcomes in LUAD. Conclusion This study investigated a miRNA-mRNA regulatory network associated with LUAD, exploring the hub miRNAs and potential functions of mRNA in the network. These findings contribute to identify new prognostic markers and therapeutic targets for LUAD patients in clinical settings.Peer reviewe
- …