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Register a new userSuzaku Observations of HESS J1616-508: Evidence for a Dark Particle Accelerator
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Hironori Matsumoto
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We observed the bright unidentified TeV gamma-ray source HESS J1616-508 with the X-ray Imaging Spectrometers onboard the Suzaku satellite. No X-ray counterpart was found to a limiting flux of 3.1e-13 erg/s/cm^2 in the 2--10 keV band, which is some 60 times below the gamma-ray flux in the 1--10 TeV band. This object is bright in TeV gamma-rays but very dim in the X-ray band, and thus is one of the best examples in the Galaxy of a dark particle accelerator. We also detected soft thermal emission with kT=0.3--0.6 keV near the location of HESSJ1616. This may be due to the dust grain scattering halo from the nearby bright supernova remnant RCW103.
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HESS J1614$-$518 and HESS J1616$-$508 are two tera-electron volt (TeV) $gamma$-ray sources that are not firmly associated with any known counterparts at other wavelengths. We investigate the distribution of interstellar medium towards the TeV $gamma$-ray sources using results from a 7 mm-wavelength Mopra study, the Mopra Southern Galactic Plane CO Survey, the Millimetre Astronomers Legacy Team - 45 GHz survey and [CI] data from the HEAT telescope. Data in the CO(1$-$0) transition lines reveal diffuse gas overlapping the two TeV sources at several velocities along the line of sight, while observations in the CS(1$-$0) transition line reveal several interesting dense gas features. To account for the diffuse atomic gas, archival HI data was taken from the Southern Galactic Plane Survey. The observations reveal gas components with masses $sim10^3$ to $10^5$ M$_odot$ and with densities $sim10^2$ to $10^3$ cm$^{-3}$ overlapping the two TeV sources. Several origin scenarios potentially associated with the TeV $gamma$-ray sources are discussed in light of the distribution of the local interstellar medium. We find no strong convincing evidence linking any counterpart with HESS J1614$-$518 or HESS J1616$-$508.
The unidentified very-high-energy (VHE; E $>$ 0.1 TeV) $gamma$-ray source, HESS J1826$-$130, was discovered with the High Energy Stereoscopic System (HESS) in the Galactic plane. The analysis of 215 h of HESS data has revealed a steady $gamma$-ray flux from HESS J1826$-$130, which appears extended with a half-width of 0.21$^{circ}$ $pm$ 0.02$^{circ}_{text{stat}}$ $pm$ 0.05$^{circ}_{text{sys}}$. The source spectrum is best fit with either a power-law function with a spectral index $Gamma$ = 1.78 $pm$ 0.10$_{text{stat}}$ $pm$ 0.20$_{text{sys}}$ and an exponential cut-off at 15.2$^{+5.5}_{-3.2}$ TeV, or a broken power-law with $Gamma_{1}$ = 1.96 $pm$ 0.06$_{text{stat}}$ $pm$ 0.20$_{text{sys}}$, $Gamma_{2}$ = 3.59 $pm$ 0.69$_{text{stat}}$ $pm$ 0.20$_{text{sys}}$ for energies below and above $E_{rm{br}}$ = 11.2 $pm$ 2.7 TeV, respectively. The VHE flux from HESS J1826$-$130 is contaminated by the extended emission of the bright, nearby pulsar wind nebula (PWN), HESS J1825$-$137, particularly at the low end of the energy spectrum. Leptonic scenarios for the origin of HESS J1826$-$130 VHE emission related to PSR J1826$-$1256 are confronted by our spectral and morphological analysis. In a hadronic framework, taking into account the properties of dense gas regions surrounding HESS J1826$-$130, the source spectrum would imply an astrophysical object capable of accelerating the parent particle population up to $gtrsim$200 TeV. Our results are also discussed in a multiwavelength context, accounting for both the presence of nearby supernova remnants (SNRs), molecular clouds, and counterparts detected in radio, X-rays, and TeV energies.
A detailed analysis of the nonthermal X-ray emission from the North-Western and Southern parts of the supernova remnant (SNR) HESS J1731$ - $347 with {it Suzaku} is presented. The shell portions covered by the observations emit hard and line-less X-rays. The spectrum can be reproduced by a simple absorbed power-law model with a photon index $Gamma$ of 1.8-2.7 and an absorption column density $N_{rm H}$ of (1.0-2.1)$times 10^{22}$ cm$^{-2}$. These quantities change significantly from region to region; the North-Western part of the SNR has the hardest and most absorbed spectrum. The Western part of the X-ray shell has a smaller curvature than North-Western and Southern shell segments. A comparison of the X-ray morphology to the Very High Energy (VHE) gamma-ray and radio images was performed. The efficiency of electron acceleration and emission mechanism in each portion of the shell are discussed. Thermal X-ray emission from the SNR was searched for but could not be detected at a significant level.
HESS J1507-622 is one of the bright unidentified TeV objects. HESS J1507-622 is unique, since the location of the object is off the Galactic disk. We observed the HESS J1507-622 region with the Suzaku XIS, and found no obvious counterpart although there is no severe interstellar extinction. However, there are two interesting X-ray objects; SRC1 is a bright extended source, and SRC2 is a faint diffuse object. If either of them is a counterpart, the flux ratio between TeV and X-ray is large, and HESS J1507-622 is a real dark particle accelerator.
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.
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