The TeV gamma-ray point source HESS J1832−093 remains unidentified despite extensive multiwavelength studies. The gamma-ray emission could originate in a very compact pulsar wind nebula or an X-ray ...binary system composed of the X-ray source XMMU J183245−0921539, and a companion star (2MASS J18324516−0921545). To unveil the nature of XMMU J183245−0921539 and its relation to HESS J1832−093, we performed deeper follow-up observations in X-rays with Chandra and Swift to improve source localization and to investigate time variability. We observed an increase of the X-ray flux by a factor of ∼6 in the Chandra data compared to previous observations. The source is point-like for Chandra and its updated position is only 0.3 arcsec offset from 2MASS J18324516−0921545, confirming the association with this infrared source. Subsequent Swift target of opportunity observations resulted in a lower flux, again compatible with the one previously measured with XMM–Newton, indicating a variability time-scale of the order of two months or shorter. The now-established association of XMMU J183245−0921539 and 2MASS J18324516−0921545, and the observed variability in X-rays are strong evidence for binary nature of HESS J1832−093. Furthermore, observations to characterize the optical counterpart as well as to search for orbital periodicity are needed to confirm this scenario.
Context. Millisecond pulsars (MSPs) represent nearly half of the more than 160 currently known x-ray pulsars detected by the Large Area Telescope on the Fermi satellite, and a third of all known MSPs ...are seen in x-rays. Because of the Shklovskii effect, precise proper motion and distance measurements are key ingredients for determining the spin-down luminosities of MSPs accurately. Our aim is to obtain new measurements of these parameters for x-ray MSPs when possible, and clarify the relationship between the x-ray luminosity of pulsars and their spin-down luminosity. We made use of the high-quality pulsar timing data recorded at the Nancay Radio Telescope over several years to characterize the properties of a selection of MSPs. For one of the pulsars, the dataset was complemented with Westerbork Synthesis Radio Telescope observations. For the MSPs considered in this study, we obtained new transverse proper motion measurements or updated the existing ones, and placed new distance constraints for some of them, with four new timing parallax measurements.
We report on gamma-ray analysis of the region containing the bright TeV source HESS J1640-465 and the close-by TeV source HESS J1641 -463 using 64 months of observations with the Fermi Large Area ...Telescope (LAT). Previously only one GeV source was reported in this region and was associated with HESS J1640-465. With an increased data set and the improved sensitivity afforded by the reprocessed data (P7REP) of the LAT, we now report the detection, morphological study, and spectral analysis of two distinct sources above 100 MeV. The softest emission in this region comes from the TeV source HESS J1641-463 which is well fitted with a power law of index Gamma = 2.47 0.05 0.06 and presents no significant gamma-ray signal above 10 GeV, which contrasts with its hard spectrum at TeV energies. The Fermi-LAT spectrum of the second TeV source, HESS J1640-465 is well described by a power-law shape of index Gamma = 1.99 0.04 0.07 that links up naturally with the spectral data points obtained by the High Energy Stereoscopic System (H.E.S.S.). These new results provide new constraints concerning the identification of these two puzzling y-ray sources
Context. Millisecond pulsars (MSPs) represent nearly half of the more than 160 currently known γ-ray pulsars detected by the Large Area Telescope on the Fermi satellite, and a third of all known MSPs ...are seen in γ rays. The least energetic γ-ray MSPs enable us to probe the so-called deathline for high-energy emission, i.e., the spin-down luminosity limit under which pulsars (PSRs) cease to produce detectable high-energy radiation. Characterizing the MSP luminosity distribution helps to determine their contribution to the Galactic diffuse γ-ray emission. Aims. Because of the Shklovskii effect, precise proper motion and distance measurements are key ingredients for determining the spin-down luminosities of MSPs accurately. Our aim is to obtain new measurements of these parameters for γ-ray MSPs when possible, and clarify the relationship between the γ-ray luminosity of pulsars and their spin-down luminosity. Detecting low spin-down luminosity pulsars in γ rays and characterizing their spin properties is also particularly interesting for constraining the deathline for high-energy emission. Methods. We made use of the high-quality pulsar timing data recorded at the Nançay Radio Telescope over several years to characterize the properties of a selection of MSPs. For one of the pulsars, the dataset was complemented with Westerbork Synthesis Radio Telescope observations. The rotation ephemerides derived from this analysis were also used to search the LAT data for new γ-ray MSPs. Results. For the MSPs considered in this study, we obtained new transverse proper motion measurements or updated the existing ones, and placed new distance constraints for some of them, with four new timing parallax measurements. We discovered significant GeV γ-ray signals from four MSPs, i.e., PSRs J0740+6620, J0931−1902, J1455−3330, and J1730−2304. The latter is now the least energetic γ-ray pulsar found to date. Despite the improved Ė and Lγ estimates, the relationship between these two quantities remains unclear, especially at low Ė values.
We report on γ-ray analysis of the region containing the bright TeV source HESS J1640–465 and the close-by TeV source HESS J1641–463 using 64 months of observations with the Fermi Large Area ...Telescope (LAT). Previously only one GeV source was reported in this region and was associated with HESS J1640–465. With an increased data set and the improved sensitivity afforded by the reprocessed data (P7REP) of the LAT, we now report the detection, morphological study, and spectral analysis of two distinct sources above 100 MeV. The softest emission in this region comes from the TeV source HESS J1641–463 which is well fitted with a power law of index Γ = 2.47 ± 0.05 ± 0.06 and presents no significant γ-ray signal above 10 GeV, which contrasts with its hard spectrum at TeV energies. The Fermi-LAT spectrum of the second TeV source, HESS J1640–465 is well described by a power-law shape of index Γ = 1.99 ± 0.04 ± 0.07 that links up naturally with the spectral data points obtained by the High Energy Stereoscopic System (H.E.S.S.). These new results provide new constraints concerning the identification of these two puzzling γ-ray sources.
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.)
Multiwavelength (MWL) observations of the blazar PKS 2155-304 during two weeks in July 2006 and August 2006, the period when two exceptional flares at very high energies occurred, provide a detailed ...picture of the evolution of its emission. The data set offers a close view of the evolution of the source on different time scales and yields new insights into the properties of the emission process. The predictions of synchrotron self-Compton (SSC) scenarios are compared to the MWL data, with the aim of describing the dominant features in the data down to the hour time scale. SSC modelling is used to interpret the general trends of the varying spectral energy distribution. The X-ray and VHE gamma -ray emission are correlated during the observed high state of the source, but show no direct connection with longer wavelengths. The long-term flux evolution in the optical and radio bands is found to be correlated and shows that the source reaches a high state at long wavelengths after the occurrence of the VHE flares.
The 1ES 0414++009 is a distant high-frequency-peaked BL Lac object, and has long been considered a likely emitter of very-high-energy gamma -rays due to its high X-ray and radio flux. The authors ...report observations made between October 2005 and December 2009 with HESS, an array of four imaging atmospheric Cherenkov telescopes. Observations at high energies with the Fermi-LAT instrument in the first 20 months of its operation are also reported. Based on the observations with HESS, 1ES 0414++009 is detected for the first time in the VHE band. An excess of 224 events is measured, corresponding to a significance of 7.8 sigma . The photon spectrum of the source is well described by a power law, with photon index of ... . The integral flux above 200 GeV is ... . Observations with the Fermi-LAT in the first 20 months of operation show a flux between 200 MeV and 100 GeV of ... , and a spectrum well described by a power-law function with a photon index ... . (ProQuest: ... denotes formulae/symbols omitted.)
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