832 research outputs found
Exploring the dark accelerator HESS J1745-303 with Fermi Large Area Telescope
We present a detailed analysis of the gamma-ray emission from HESS J1745-303
with the data obtained by the Fermi Gamma-ray Space Telescope in the first ~29
months observation.The source can be clearly detected at the level of ~18-sigma
and ~6-sigma in 1-20 GeV and 10-20 GeV respectively. Different from the results
obtained by the Compton Gamma-ray Observatory, we do not find any evidence of
variability. Most of emission in 10-20 GeV is found to coincide with the region
C of HESS J1745-303. A simple power-law is sufficient to describe the GeV
spectrum with a photon index of ~2.6. The power-law spectrum inferred in the
GeV regime can be connected to that of a particular spatial component of HESS
J1745-303 in 1-10 TeV without any spectral break. These properties impose
independent constraints for understanding the nature of this "dark particle
accelerator".Comment: 8 pages, 3 figures, 1 table, accepted for publication in Ap
A Note on Tsallis Holographic Dark Energy
We explore the effects of considering various infrared (IR) cutoffs,
including the particle horizon, Ricci horizon and Granda-Oliveros (GO) cutoffs,
on the properties of Tsallis holographic dark energy (THDE) model, proposed
inspired by Tsallis generalized entropy formalism \cite{THDE}. Interestingly
enough, we find that for the particle horizon as IR cutoff, the obtained THDE
model can describe the accelerated universe. This is in contrast to the usual
HDE model which cannot lead to an accelerated universe, if one consider the
particle horizon as IR cutoff. We also investigate the cosmological
consequences of THDE under the assumption of a mutual interaction between the
dark sectors of the Universe. It is shown that the evolution history of the
Universe can be described by these IR cutoffs and thus the current cosmic
acceleration can also been realized. The sound instability of THDE models for
each cutoff are also explored, separately.Comment: 12 pages, 31 figure
Dissipation and detection of polaritons in ultrastrong coupling regime
We have investigated theoretically a dissipative polariton system in the
ultrastrong light-matter coupling regime without using the rotating-wave
approximation on system-reservoir coupling. Photons in a cavity and excitations
in matter respectively couple two large ensembles of harmonic oscillators
(photonic and excitonic reservoirs). Inheriting the quantum statistics of
polaritons in the ultrastrong coupling regime, in the ground state of the whole
system, the two reservoirs are not in the vacuum states but they are squeezed
and correlated. We suppose this non-vacuum reservoir state in the master
equation and in the input-output formalism with Langevin equations. Both two
approaches consistently guarantee the decay of polariton system to its ground
state, and no photon detection is also obtained when the polariton system is in
the ground state.Comment: 18 pages, 3 figure
Chandra deep X-ray observation on the Galactic plane
Using the Chandra ACIS-I instruments, we have carried out the deepest X-ray
observation on a typical Galactic plane region at l 28.5 deg, where no discrete
X-ray sources have been known previously. We have detected, as well as strong
diffuse emission, 275 new point X-ray sources (4 sigma confidence) within two
partially overlapping fields (~250 arcmin^2 in total) down to ~3 x 10^{-15} erg
s^{-1} cm^{-2} (2 -- 10 keV) or ~ 7 x 10^{-16} erg s^{-1} cm^{-2} (0.5 -- 2
keV). We have studied spectral distribution of these point sources, and found
that very soft sources detected only below ~ 3 keV are more numerous than hard
sources detected only above ~ 3 keV. Only small number of sources are detected
both in the soft and hard bands. Surface density of the hard sources is almost
consistent with that at high Galactic regions, thus most of the hard sources
are considered to be Active Galactic Nuclei seen through the milky way. On the
other hand, some of the bright hard X-ray sources which show extremely flat
spectra and iron line or edge features are considered to be Galactic,
presumably quiescent dwarf novae. The soft sources show thermal spectra and
small interstellar hydrogen column densities, and some of them exhibit X-ray
flares. Therefore, most of the soft sources are probably X-ray active nearby
late type stars.Comment: Contribution to the proceedings of the "New Visions of the X-Ray
Universe in the XMM-Newton and Chandra Era" symposium at ESTEC, The
Netherlands. 26-30 Nov. 200
Tsallis Holographic Dark Energy
Employing the modified entropy-area relation suggested by Tsallis and Cirto
\cite{non3}, and the holographic hypothesis, a new holographic dark energy
(HDE) model is proposed. Considering a flat Friedmann-Robertson-Walker (FRW)
universe in which there is no interaction between the cosmos sectors, the
cosmic implications of the proposed HDE are investigated. Interestingly enough,
we find that the identification of IR-cutoff with the Hubble radius, can lead
to the late time accelerated Universe even in the absence of interaction
between two dark sectors of the Universe. This is in contrast to the standard
HDE model with Hubble cutoff, which does not imply the accelerated expansion,
unless the interaction is taken into account.Comment: 6 pages, 4 figures, accepted version by PL
Multiwavelength studies of G298.60.0: An old GeV supernova remnant interacting with molecular clouds
Hadronic -ray sources associated with supernova remnants (SNRs) can
serve as stopwatches for the escape of cosmic rays from SNRs, which gradually
develops from highest-energy particles to lowest-energy particles with time. In
this work, we analyze the 13.7~yr \emph{Fermi}-LAT data to investigate the
-ray feature in/around the SNR G298.60.0 region. With -ray
spatial analyses, we detect three point-like components. Among them, Src-NE is
at the eastern SNR shell, and Src-NW is adjacent to the western edge of this
SNR. Src-NE and Src-NW demonstrate spectral breaks at energies around/below
1.8~GeV, suggesting an old SNR age of 10~kyr. We also look into the X-ray
emission from the G298.60.0 region, with the Chandra-ACIS data. We detected
an extended keV source having a centrally filled structure inside the radio
shell. The X-ray spectra are well fit by a model which assumes a collisional
ionisation equilibrium of the thermal plasma, further supporting an old SNR
age. Based on our analyses of the NANTEN CO- and ATCA-Parkes HI-line data, we
determined a kinematic distance of 10.1~kpc from us to G298.60.0. This
distance entails a large physical radius of the SNR of 15.5~pc, which is
an additional evidence for an old age of 10~kyr. Besides, the CO data cube
enables us to three-dimensionally locate the molecular clouds (MCs) which are
potentially interacting with SNR G298.60.0 and could account for the
hadronic -rays detected at Src-NE or Src-NW. Furthermore, the
multiwavelength observational properties unanimously imply that the SNR--MC
interaction occurs mainly in the northeast direction.Comment: Accepted by Publications of the Astronomical Society of Japan (PASJ)
on 16-Jan-202
On the influence of shock-cloud interactions on the nonthermal X-ray emission from the supernova remnant RCW 86
The effect of the surrounding environment of supernova remnant shocks on nonthermal X-rays from accelerated electrons, with or without interacting dense material, is an open issue. We conduct spatially resolved X-ray spectroscopy of the shock–cloud interacting region of RCW 86 with XMM–Newton. It is found that bright soft X-ray filaments surround the dense cloud, observed with 12CO and H I emission lines. These filaments are brighter in thermal X-ray emission, and fainter and possibly softer in synchrotron X-rays, compared to those without interaction. Our results show that the shock decelerates due to the interaction with clouds, which results in an enhancement of thermal X-ray emission. This could possibly also explain the softer X-ray synchrotron component, because it implies that those shocks that move through a low-density environment, and therefore decelerate much less, can be more efficient accelerators. This is similar to SN 1006 and Tycho, and is in contrast to RX J1713.7−3946. This difference among remnants may be due to the clumpiness of dense material interacting with the shock, which should be examined in future observations
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