We report on the discovery of compact, narrow OH line emission from the hydroxyl molecule at 1720 MHz toward the extended TeV source J1834-087. The origin of this high energy emission is unknown; it ...could be powered by one or more candidate neutron stars (leptonic) or by cosmic rays interacting with dense gas (hadronic). The OH emission is detected near the center of J1834-087, coincident with the radio continuum of the supernova remnant W41, and the radial velocity of the line is the same velocity as a giant molecular cloud along the line of sight. We argue that the OH is maser emission stimulated by the interaction of the W41 shock with the molecular cloud. The known correlation between gamma -ray bright supernova remnants and OH masers favors a hadronic interpretation for this high energy emission.
The inner 10 pc of our Galaxy contains many counterpart candidates of the very high energy (VHE; >100 GeV) γ-ray point source HESS J1745-290. Within the point spread function of the H.E.S.S. ...measurement, at least three objects are capable of accelerating particles to VHE and beyond and of providing the observed γ-ray flux. Previous attempts to address this source confusion were hampered by the fact that the projected distances between these objects were of the order of the error circle radius of the emission centroid (34 arcsec, dominated by the pointing uncertainty of the H.E.S.S. instrument). Here we present H.E.S.S. data of the Galactic Centre region, recorded with an improved control of the instrument pointing compared to H.E.S.S. standard pointing procedures. Stars observed during γ-ray observations by optical guiding cameras mounted on each H.E.S.S. telescope are used for off-line pointing calibration, thereby decreasing the systematic pointing uncertainties from 20 to 6 arcsec per axis. The position of HESS J1745-290 is obtained by fitting a multi-Gaussian profile to the background-subtracted γ-ray count map. A spatial comparison of the best-fitting position of HESS J1745-290 with the position and morphology of candidate counterparts is performed. The position is, within a total error circle radius of 13 arcsec, coincident with the position of the supermassive black hole Sgr A* and the recently discovered pulsar wind nebula candidate G359.95-0.04. It is significantly displaced from the centroid of the supernova remnant Sgr A East, excluding this object with high probability as the dominant source of the VHE γ-ray emission. PUBLICATION ABSTRACT
In July 2012, as the four ground-based gamma-ray telescopes of the H.E.S.S. (High Energy Stereoscopic System) array reached their tenth year of operation in Khomas Highlands, Namibia, a fifth ...telescope took its first data as part of the system. This new Cherenkov detector, comprising a 614.5m2 reflector with a highly pixelized camera in its focal plane, improves the sensitivity of the current array by a factor two and extends its energy domain down to a few tens of GeV.
The present part I of the paper gives a detailed description of the fifth H.E.S.S. telescope׳s camera, presenting the details of both the hardware and the software, emphasizing the main improvements as compared to previous H.E.S.S. camera technology.
Context. The detection of gamma-rays in the very-high-energy (VHE) range (100 GeV−100 TeV) offers the possibility of studying the parent population of ultrarelativistic particles found in ...astrophysical sources, so it is useful for understanding the underlying astrophysical processes in nonthermal sources. Aims. The discovery of the VHE gamma-ray source HESS J1507-622 is reported and possibilities regarding its nature are investigated. Methods. The H.E.S.S. array of imaging atmospheric Cherenkov telescopes (IACTs) has a high sensitivity compared with previous instruments (~1% of the Crab flux in 25 h observation time for a 5σ point-source detection) and has a large field of view (~5° in diameter). HESS J1507-622 was discovered within the ongoing H.E.S.S. survey of the inner Galaxy, and the source was also studied by means of dedicated multiwavelength observations. Results. A Galactic gamma-ray source, HESS J1507-622, located ~3.5° from the Galactic plane was detected with a statistical significance >9σ. Its energy spectrum is well fitted by a power law with spectral index Γ = 2.24 ± 0.16stat ± 0.20sys and a flux above 1 TeV of (1.5 ± 0.4stat ± 0.3sys) × 10-12 cm-2 s-1. Possible interpretations (considering both hadronic and leptonic models) of the VHE gamma-ray emission are discussed in the absence of an obvious counterpart.
In the published version of the paper, errors were made in calculating the exposure time due to an analysis mistake. While they do not affect gas emissivities of the R CrA and Cepheus & Polaris flare ...regions significantly (the differences are within the systematic uncertainty), that of the Chamaeleon region is increased by approx.20%. Although we claimed a difference of ∼50% in gas emissivity among these molecular cloud regions in the original paper, it is decreased to ∼30% (comparable to the sum of the statistical and systematic uncertainties) in the revised analysis. Therefore, our conclusion of the original paper, that a small variation (approx. 20%) of the CR density in the solar neighborhood exists, is not supported by the data if we take these uncertainties into account. On the other hand, the obtained XCO and XAv values, and the masses of gas calculated from them are not changed significantly (the differences are within the statistical errors). Errors and corrections in the original paper are summarized below. 1. In the Abstract (lines 5-6) and Section 3 (lines 4-5 in the 3rd paragraph) in the original paper, the gamma -ray emissivity above 250 MeV for the Chamaeleon region should be (7.2 +/- 0.1stat +/- 1.0sys) × 10(exp −27) photons/s/sr/H-atom, not (5.9 +/-0.1stat +0.9−1.0sys) × 10(exp −27) photons/s/sr/H-atom. 2. In the Abstract (lines 8-10), "Whereas the energy dependences of the emissivities agree well with that predicted from direct CR observations at the Earth, the measured emissivities from 250 MeV to 10 GeV indicate a variation of the CR density by approx.20% in the neighborhood of the solar system, even if we consider the systematic uncertainties." should be changed to "The energy dependences of the emissivities agree well with that predicted from direct CR observations at the Earth. Although the measured emissivities from 250 MeV to 10 GeV differ by approx.30% among these molecular cloud regions, the difference is not significant if we take the systematic uncertainty into account." 3. Table 1 and Figure 13, which show gas emissivities and spectra for the Chamaeleon region in the original paper, should be changed to the Table 1 and Figure 1 as shown below. 4. Figure 16, which compares Hi gas emissivities among several regions in the original paper, should be changed to Figure 2 as shown below. 5. The text from the line 13 to the last one in the first paragraph of Section 4.1, "The spectral shapes for the three regions..., indicating a difference of the CR density between the Chamaeleon and the others as shown in Figure 16." should be changed to the paragraph that follows. "The shaded area of each spectrum indicates the systematic uncertainty as described in Section 3. We note that the systematic uncertainty of the LAT effective area (5% at 100 MeV and 20% at 10 GeV; Rando et al. 2009) does not affect the relative value of emissivities. The effect of unresolved point sources is small; we have verified that the obtained emissivities are almost unaffected by decreasing the threshold for point sources from TS = 100 to TS = 50. We also confirmed that the residual excess of photons around (l = 280deg to 288deg, b = −20deg to −12deg; see the bottom panel of Figure 8) in the Chamaeleon region does not affect the local Hi emissivity very much. Thus the total systematic uncertainty is reasonably expressed by the shaded area shown in Fig. 1.
The previously unidentified very high-energy (VHE) gamma -ray source HESS J1303-631 is re-examined including new data from the HESS Cherenkov telescope array in order to identify this object. ...Detailed morphological and spectral studies of VHE gamma -ray emission as well as of the XMM-Newton X-ray data are performed. Significant energy-dependent morphology of this source, as well as the identification of an associated X-ray PWN from XMM-Newton observations enable identification of the VHE source as an evolved PWN associated to the pulsar PSR J1301-6305. This identification is supported by the one zone leptonic model, which suggests that the energetics of the gamma -ray and X-ray radiation are such that they may have a similar origin in the pulsar nebula. This would explain the low level of synchrotron radiation and the difficulty in detecting counterparts at lower energies, the reason this source was originally classified as a "dark' VHE gamma -ray source.
Vela X is a region of extended radio emission in the western part of the Vela constellation: one of the nearest pulsar wind nebulae, and associated with the energetic Vela pulsar. A deeper ...observation of the entire Vela X nebula region, also including larger offsets from the cocoon, has been performed with HESS. This re-observation was carried out in order to probe the extent of the non-thermal emission from the Vela X region at TeV energies and to investigate its spectral properties. To increase the sensitivity to the faint gamma -ray emission from the very extended Vela X region, a multivariate analysis method combining three complementary reconstruction techniques of Cherenkov-shower images is applied for the selection of gamma -ray events. The Vela X region exhibits almost uniform gamma -ray spectra over its full extent: the differential energy spectrum can be described by a power-law function with a hard spectral index ... and an exponential cutoff at an energy of TeV.(ProQuest: ... denotes formulae/symbols omitted.)
In some galaxy clusters, powerful active galactic nuclei (AGN) have blown bubbles with cluster scale extent into the ambient medium. The main pressure support of these bubbles is not known to date, ...but cosmic rays are a viable possibility. Hydra A, the closest galaxy cluster hosting a cluster scale AGN outburst, located at a redshift of 0.0538, is investigated for being a gamma-ray emitter with the High Energy Stereoscopic System (H.E.S.S.) array and the Fermi Large Area Telescope (Fermi-LAT). Data obtained in 20.2 h of dedicated H.E.S.S. observations and 38 months of Fermi-LAT data, gathered by its usual all-sky scanning mode, have been analyzed to search for a gamma-ray signal. No signal has been found in either data set. Upper limits on the gamma-ray flux are derived and are compared to models. The non-detection of Hydra A in gamma-rays has important implications on the particle populations and physical conditions inside the bubbles in this system.
1RXS J101015.9-311909 is a galaxy located at a redshift of z = 0.14 hosting an active nucleus belonging to the class of bright BL Lac objects. The authors report on results from VHE observations ...performed between 2006 and 2010 with the H.E.S.S. instrument, an array of four imaging atmospheric Cherenkov telescopes. H.E.S.S. data have been analysed with enhanced analysis methods, making the detection of faint sources more significant. VHE emission at a position coincident with 1RXS J101015.9-311909 is detected with H.E.S.S. for the first time. In a total good-quality livetime of about 49 h, the authors measure 263 excess counts, corresponding to a significance of 7.1 standard deviations. The photon spectrum above 0.2 TeV can be described by a power-law with a photon index of ... . The integral flux above 0.2 TeV is about 0.8% of the flux of the Crab nebula and shows no significant variability over the time reported. (ProQuest: ... denotes formulae/symbols omitted.)
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![Localizing the VHE [gamma]-...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0035-8711/small "Localizing the VHE [gamma]-ray source at the Galactic Centre")
