Very high energy (VHE; >100 GeV) gamma-ray observations of PG 1553+113 were made with the High Energy Stereoscopic System (HESS) in 2005 and 2006. A strong signal, ~10 standard deviations, is detected by HESS during the 2 years of observations (24.8 hours live time). The time-averaged energy spectrum, measured between 225 GeV to ~1.3 TeV, is characterized by a very steep power law (photon index of Gamma = (4.5 +- 0.3 {stat} +- 0.1 {syst}). The integral flux above 300 GeV is ~3.4% of the Crab Nebula flux and shows no evidence for any variations, on any time scale. H+K (1.45-2.45 micron) spectroscopy of PG 1553+113 was performed in March 2006 with SINFONI, an integral field spectrometer of the ESO Very Large Telescope (VLT) in Chile. The redshift of PG 1553+113 is still unknown, as no absorption or emission lines were found.
We present the international collaboration MINE (Multi-lambda Integral NEtwork) aimed at conducting multi-wavelength observations of X-ray binaries and microquasars simultaneously with INTEGRAL. The first results on GRS 1915+105 are encouraging and those to come should help us to understand the physics of the accretion and ejection phenomena around a compact object. A collaboration such as MINE could be very useful for observing quasars and microquasars simultaneously with HESS and later with ANTARES.
The field of the extended TeV source HESS J1804-216 was serendipitously observed with the Chandra ACIS detector. The data reveal several X-ray sources within the bright part of HESS J1804-216. The brightest of these objects, CXOU J180432.4-214009, which has been also detected with Swift and Suzaku, is consistent with being a point-like source, with the 0.3-7 keV flux of (1.7\pm0.2)\times10^{-13} ergs s^{-1} cm^{-2}. Its hard and strongly absorbed spectrum can be fitted by the absorbed power-law model with the best-fit photon index of 0.45 and hydrogen column density of 4\times10^{22} cm^{-2}, …
The detection of gamma rays in the very-high-energy (VHE) energy range (100 GeV--100 TeV) provides a direct view of the parent population of ultra-relativistic particles found in astrophysical sources. For this reason, VHE gamma rays are useful for understanding the underlying astrophysical processes in non-thermal sources. We investigate unidentified VHE gamma-ray sources that have been discovered with HESS in the most sensitive blind survey of the Galactic plane at VHE energies conducted so far. The HESS array of imaging atmospheric Cherenkov telescopes (IACTs) has a high sensitivity compare…
Recently, the HESS collaboration has reported the detection of gamma-ray emission above a few hundred GeV from eight new sources located close to the Galactic Plane. The source HESS J1813-178 has sparked particular interest, as subsequent radio observations imply an association with SNR G12.82-0.02. Triggered by the detection in VHE gamma-rays, a positionally coincident source has also been found in INTEGRAL and ASCA data. In this Letter we present MAGIC observations of HESS J1813-178, resulting in the detection of a differential gamma-ray flux consistent with a hard-slope power law, described…
HESS J1745-303 is an extended, unidentified VHE (very high energy) gamma-ray source discovered using HESS in the Galactic Plane Survey. Since no obvious counterpart has previously been found in longer-wavelength data, the processes that power the VHE emission are not well understood. Combining the latest VHE data with recent XMM-Newton observations and a variety of source catalogs and lower-energy survey data, we attempt to match (from an energetic and positional standpoint) the various parts of the emission of HESS J1745-303 with possible candidates. Though no single counterpart is found to f…
Very high energy (VHE; >100 GeV) observations of a sample of selected active galactic nuclei (AGN) were performed between January 2005 and April 2007 with the High Energy Stereoscopic System (HESS), an array of imaging atmospheric-Cherenkov telescopes. Significant detections are reported elsewhere for many of these objects. Here, integral flux upper limits for twelve candidate very high energy (VHE; >100 GeV) gamma-ray emitters are presented. In addition, results from HESS observations of four known VHE-bright AGN are given although no significant signal is measured. For three of these AGN (1E…
Stochastic acceleration of electrons interacting resonantly with a turbulent magnetic field in a small accretion torus appears to be the likely mechanism responsible for much of Sagittarius A*'s millimeter and shorter wavelength spectrum. The longer wavelength radiation is produced at larger radii by electrons either diffusing from smaller scales or accelerated in situ. An important prediction of this model is the ejection of a significant flux of relativistic protons from a magnetic-field-dominated acceleration site into the wind-shocked medium surrounding the black hole. Recently, several ai…
Motivated by recent detections of pulsar wind nebulae in very-high-energy (VHE) gamma rays, a systematic search for VHE gamma-ray sources associated with energetic pulsars was performed, using data obtained with the H.E.S.S. (High Energy Stereoscopic System) instrument. The search for VHE gamma-ray sources near the pulsar PSR J1718-3825 revealed the new VHE gamma-ray source HESS J1718-385. We report on the results from the HESS data analysis of this source and on possible associations with the pulsar and at other wavelengths. We investigate the energy spectrum of HESS J1718-385 that shows a cl…
Recently, the HESS array has reported the detection of gamma-ray emission above a few hundred GeV from eight new sources located close to the Galactic Plane. The source HESS J1834-087 is spatially coincident with SNR G23.3-0.3 (W41). Here we present MAGIC observations of this source, resulting in the detection of a differential gamma-ray flux consistent with a power law, described as dN/(dA dt dE) = (3.7 +/- 0.6)*10^(-12) (E/TeV)^(-2.5 +/- 0.2) \ cm^(-2)s^(-1)TeV^(-1). We confirm the extended character of this flux. We briefly discuss the observational technique used, the procedure implemented…
We observed the unidentified TeV gamma-ray source HESS J1804-216 with the CANGAROO-III atmospheric Cerenkov telescopes from May to July in 2006. We detected very high energy gamma rays above 600 GeV at the 10 sigma level in an effective exposure of 76 hr. We obtained a differential flux of (5.0+/-1.5_{stat}+/-1.6_{sys})\times 10^{-12}(E/1 TeV)^{-α} cm^{-2}s^{-1}TeV^{-1} with a photon index αof 2.69 +/- 0.30_{stat} +/- 0.34_{sys}, which is consistent with that of the H.E.S.S. observation in 2004. We also confirm the extended morphology of the source. By combining our result with multi-wavelengt…
We present X-ray observations of the as of yet unidentified very high-energy (VHE) gamma-ray source HESSJ1640-465 with the aim of establishing a counterpart of this source in the keV energy range, and identifying the mechanism responsible for the VHE emission. The 21.8 ksec XMM-Newton observation of HESSJ1640-465 in September 2005 represents a significant improvement in sensitivity and angular resolution over previous ASCA studies in this region. These new data show a hard-spectrum X-ray emitting object at the centroid of the H.E.S.S. source, within the shell of the radio Supernova Remnant (SN…
The high resolution capabilities of the High Energy Stereoscopic System (HESS) introduced a new era in Gamma-Ray Astronomy, and opens a new window on pulsar wind nebula (PWN) research. A rotationally induced jet (associated with PSR B1509-58) is resolved for the first time in gamma-rays, allowing us to trace the particle transport directly, without having the complicating effect of spatially varying field distributions on the synchrotron emissivity. For PWN older or more extended than Crab (i.e. those with lower field strengths), HESS also reveals the properties of electrons contributing to th…
The unidentified TeV gamma-ray source MGRO J1908+06/HESS J1908+063 was observed with the VERITAS Imaging Atmospheric Cherenkov Array during October 2007 and May-June 2008. This extended source is located on the galactic plane at a galactic longitude of 40.45 degrees and has a hard TeV spectrum with an index of approximately 2.08. The Very High Energy (VHE) gamma-ray flux was measured by H.E.S.S. out to energies greater than 30 TeV which along with its unidentified nature makes it an interesting hard-spectrum extended source for study. We confirm the detection of VHE gamma-ray emission from thi…
The H.E.S.S. survey of the inner Galaxy in the very-high-energy gamma-ray domain has led to the discovery of many extended sources, some of which do not appear to be associated with any obvious counterpart at traditional wavelengths (radio, infrared and X-ray). In this contribution, preliminary H.E.S.S. results on one of these so-called "dark" sources, namely HESS J1503-582, are presented. After introducing the properties of this source candidate, results of the search for counterparts in several astronomical windows are shown. Finally, its possible association with a "Forbidden-Velocity-Wing"…
AIMS: The properties of the very high energy (VHE; E>100 GeV) gamma-ray emission from the high-frequency peaked BL Lac PG 1553+113 are investigated. An attempt is made to measure the currently unknown redshift of this object. METHODS: VHE Observations of PG 1553+113 were made with the High Energy Stereoscopic System (HESS) in 2005 and 2006. H+K (1.45-2.45 micron) spectroscopy of PG 1553+113 was performed in March 2006 with SINFONI, an integral field spectrometer of the ESO Very Large Telescope (VLT) in Chile. RESULTS: A VHE signal, ~10 standard deviations, is detected by HESS during the 2 year…
In order to provide a firm identification of the newly discovered Galactic TeV sources, a search for counterparts in a broad band from soft X-ray to soft gamma-rays is crucial as data in these wavebands allow us to distinguish between different types of suggested models (for example leptonic versus hadronic) and, in turn, to disentangle their nature. In this paper, we report the results of a set of follow-up observations performed by the Swift/X-Ray Telescope (XRT) on seven sources recently discovered by HESS, in the range from few hundred GeV to about 10 TeV, during the inner Galaxy survey (A…
AIMS: Very high energy (VHE; E>100 GeV) gamma-ray studies were performed for 18 active galactic nuclei (AGN) from a variety of AGN classes. METHODS: VHE observations of a sample of 14 AGN, considered candidate VHE emitters, were made with the High Energy Stereoscopic System (HESS) between January 2005 and July 2007. Large-zenith-angle observations of three northern AGN (Mkn 421, Mkn 501, 1ES 1218+304), known to emit VHE gamma rays, were also performed in order to sample their spectral energy distributions (SEDs) above 1 TeV. In addition, the VHE flux from 1ES 1101-232, previously detected by H…
Suzaku observations of a TeV unidentified (unID) source, HESS J1745-303, are presented. A possible excess of neutral iron line emission is discovered, and is likely associated with the main part of HESS J1745-303, named "region A". It may be an X-ray reflection nebula where the X-rays from previous Galactic Center (GC) activity are reflected by a molecular cloud. This result further strengthens the assumption that the molecular cloud which is spatially coincident with region A of HESS J1745-303 is located in the GC region. The TeV emission from molecular clouds is reminiscent of the diffuse Te…
The serendipitous discovery of an unidentified extended TeVgamma-ray source close to the galactic plane named HESS J1303-631 at a significance of 21 standard deviations is reported. The observations were performed between February and June 2004 with the H.E.S.S. stereoscopic system of Cherenkov telescopes in Namibia. HESS J1303-631 was discovered roughly 0.6 deg north of the binary system PSR B1259-63/SS 2883, the target object of the initial observation campaign which was also detected at TeV energies in the same field of view. HESS J1303-631 is extended with a width of an assumed intrinsic G…
H.E.S.S. (High Energy Stereoscopic System), which is designed to detect TeV gamma-rays, is a system of four Imaging Atmospheric Cherenkov Telescopes situated in Namibia. The system has been shown to be very successful in detecting and observing galactic and extra-galactic TeV sources. In order to explore the highest energy end of GRB spectra, a GRB observing program has been established in the H.E.S.S. collaboration. Here we introduce our GRB observing program and report on its current status.
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 h…
The imaging atmospheric Cherenkov array H.E.S.S. recently discovered an extended source in the 0.4$-$10 TeV energy range, HESS J1303-631. We obtained a 5 ks observation with the ACIS-I array on the Chandra X-ray observatory that does not reveal an obvious compact or diffuse X-ray counterpart. Archival ROSAT images are also blank in this region. Although there are several radio pulsars within the field of HESS J1303-631, none is detected in X-rays to a flux limit of $<5 \times 10^{-14}$ ergs cm$^{-2}$ s$^{-1}$, and none is a likely counterpart on energetic grounds. Over the entire $17^{\prime} …
The recently discovered extended TeV source HESS J1834-087 is associated with both a diffuse X-ray enhancement and a molecular cloud, projected at the center of an old radio supernova remnant G23.3-0.3 (SNR W41). New HI observations from the VLA Galactic Plane Survey (VGPS) show unambiguous structures associated with W41 in the radial velocity range of 53 to 63 km/s, so we obtain for W41 a distance of 4+-0.2 kpc. A new higher sensitivity VGPS continuum image of W41 at 1420 MHz shows faint emission in its eastern part not detected by previous observations, so we give a new angular size of 36'x3…
In recent years, apparent anisotropies in the ~EeV cosmic ray (CR) flux arriving at Earth from the general direction of the galactic center have been reported from the analysis of AGASA and SUGAR data. The more recently commissioned Auger Observatory has not confirmed these results. HESS has now detected an unusually soft TeV source roughly coincident with the location of the previously claimed CR anisotropy. In this paper, we develop a model for the TeV emission from this object, consistent with observations at other wavelengths, and examine the circumstances under which it might have contrib…
We observed the brightest part of HESS J1825-137 with the Suzaku XIS, and found diffuse X-rays extending at least up to 15' (~ 17 pc) from the pulsar PSR J1826-1334. The spectra have no emission line, and are fitted with an absorbed power-law model. The X-rays, therefore, are likely due to synchrotron emission from a pulsar wind nebula. The photon index near at the pulsar (r<1.5') is 1.7 while those in r=1.5-16 are nearly constant at Gamma=2.0. The spectral energy distribution of the Suzaku and H.E.S.S. results are naturally explained by a combined process; synchrotron X-rays and gamma-rays by…
Combined X-ray synchrotron and inverse-Compton gamma-ray observations of pulsar wind nebulae (PWN) may help to elucidate the processes of acceleration and energy loss in these systems. In particular, such observations provide constraints on the particle injection history and the magnetic field strength in these objects. The newly discovered TeV gamma-ray source HESS J1718-385 has been proposed as the likely PWN of the high spin-down luminosity pulsar PSR J1718-3825. The absence of previous sensitive X-ray measurements of this pulsar, and the unusual energy spectrum of the TeV source, motivated…
We present X-ray and 12CO(J=1-0) observations of the very-high-energy (VHE) gamma-ray source HESS J1813-178 with the aim of understanding the origin of the gamma-ray emission. Using this dataset we are able to undertake spectral and morphological studies of the X-ray emission from this object with greater precision than previous studies. NANTEN 12CO(J=1-0) data are used to search for correlations of the gamma-ray emission with molecular clouds which could act as target material for gamma-ray production in a hadronic scenario. The NANTEN 12CO(J=1-0) observations show a giant molecular cloud of …
Context: We investigate the possible theoretical properties of the putative pulsar associated with the pulsar wind nebula IGR J18135-1751/HESS J1813-178 based upon recent gamma-ray observations and archival multi-wavelength observations. Aims: We show that when using the standard equations for magnetic dipole radiation with recent soft gamma-ray observations leads to deriving an extreme set of parameters (magnetic field, period and spin down rate) for the putative pulsar. Alternative scenarios that generate more typical parameter values are explored. Methods: The properties of the putative pul…
The High Energy Stereoscopic System (HESS) survey of the Galactic plane has established the existence of a substantial number (~40) of Galactic TeV gamma-ray sources, a large fraction of which remain unidentified. HESS J0632+057 is one of a small fraction of these objects which is point-like in nature(<2' rms), and is one of only two point-like sources that remain unidentified. Follow-up observations of this object with XMM-Newton have revealed an X-ray source coincident with the TeV source and with the massive star MWC 148, of the spectral type B0pe. This source exhibits a hard spectrum, cons…
During its first cycle of observations, the MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov) telescope has observed very high energy gamma-rays from five galactic objects: the Crab Nebula, the SNRs HESS J1813-178 and HESS J1834-087, the Galactic Center and the gamma-ray binary LS I +61 303. After a short introduction to the MAGIC telescope and the data analysis procedure, the results of these five sources are reviewed.
Observations with H.E.S.S. revealed a new source of very high-energy (VHE) gamma-rays above 100 GeV - HESS J1825-137 - extending mainly to the south of the energetic pulsar PSR B1823-13. A detailed spectral and morphological analysis of HESS J1825-137 reveals for the first time in VHE gamma-ray astronomy a steepening of the energy spectrum with increasing distance from the pulsar. This behaviour can be understood by invoking radiative cooling of the IC-Compton gamma-ray emitting electrons during their propagation. In this scenario the vastly different sizes between the VHE gamma-ray emitting r…
AIMS: To investigate the very high energy (VHE: >100 GeV) gamma-ray emission from the high-frequency peaked BL Lac 1ES 0229+200. METHODS: Observations of 1ES 0229+200 at energies above 580 GeV were performed with the High Energy Stereoscopic System (HESS) in 2005 and 2006. RESULTS: 1ES 0229+200 is discovered by HESS to be an emitter of VHE photons. A signal is detected at the 6.6 sigma level in the HESS observations (41.8 h live time). The integral flux above 580 GeV is (9.4 +- 1.5 {stat} +- 1.9 {syst}) x 10^{-13} cm^{-2} s^{-1}, corresponding to ~1.8% of the flux observed from the Crab Nebula…
In this review paper on pulsar wind nebulae (PWN) we discuss the properties of such nebulae within the context of containment against cross-field diffusion (versus normal advection), the effect of reverse shocks on the evolution of offset ``Vela-like'' PWN, constraints on maximum particle energetics, magnetic field strength estimates based on spectral and spatial properties, and the implication of such field estimates on the composition of the wind. A significant part of the discussion is based on the High Energy Stereoscopic System ({\it H.E.S.S.} or {\it HESS}) detection of the two evolved p…
We present recent X-ray and radio observations of pulsar wind nebulae discovered in EGRET error boxes. Two XMM-Newton observations show the X-ray extent of the rapidly moving PWN associated with the variable gamma-ray source 3EG J1809-2328, and a trail coming from the new millisecond pulsar PSR J1614-2230 at high Galactic z. We also briefly discuss three PWN that are HESS TeV sources including a new HESS source we argue is associated with the Eel nebula in 3EG J1826-1302.
The source HESS J1809-193 was discovered in 2006 in data of the Galactic Plane survey, followed by several re-observations. It shows a hard gamma-ray spectrum and the emission is clearly extended. Its vicinity to PSR J1809-1917, a high spin-down luminosity pulsar powerful enough to drive the observed gamma-ray emission, makes it a plausible candidate for a TeV Pulsar Wind Nebula (PWN). On the other hand, in this region of the sky a number of faint, radio-emitting supernova remnants can be found, making a firm conclusion on the source type difficult. Here we present a detailed morphological stu…
The soft X-ray and soft gamma observations of the new discovered TeV sources by HESS and MAGIC are crucial to discriminate between various emitting scenarios and to fully understand their nature. The INTEGRAL Observatory has regularly observed the entire galactic plane during the first 1000 day in orbit providing a survey in the 20-100 keV range resulted in a soft gamma-ray sky populated with more than 200 sources. In the case of HESS J1813-178 INTEGRAL found the hard X-ray counterpart IGR J18135-1751 and Swift/XRT Telescope performed follow-up observations on this source. Here we present the …
HESS J1616-508 is one of the brightest emitters in the TeV sky. Recent observations with the IBIS/ISGRI telescope on board the INTEGRAL spacecraft have revealed that a young, nearby and energetic pulsar, PSR J1617-5055, is a powerful emitter of soft gamma-rays in the 20-100 keV domain. In this paper we present an analysis of all available data from the INTEGRAL, Swift, BeppoSAX and XMM-Newton telescopes with a view to assessing the most likely counterpart to the HESS source. We find that the energy source that fuels the X/gamma-ray emissions is derived from the pulsar, both on the basis of the…
The results from H.E.S.S. observations towards Westerlund 2 are presented. The detection of very-high-energy gamma-ray emission towards the young stellar cluster Westerlund 2 in the HII complex RCW49 by H.E.S.S. provides ample evidence that particle acceleration to extreme energies is associated with this region. A variety of possible emission scenarios is mentioned, ranging from high-energy gamma-ray production in the colliding wind zone of the massive Wolf-Rayet binary WR20a, collective wind scenarios, diffusive shock acceleration at the boundaries of wind-blown bubbles in the stellar cluste…
