Transient X-ray sources in the field of the unidentified gamma-ray source TeV J2032+4130 in Cygnus

We present an analysis of Chandra ACIS observations of the field of TeV J2032+4130, the first unidentified TeV source, detected serendipitously by HEGRA. This deep (48.7 ks) observation of the field follows up on an earlier 5 ks Chandra director’s discretionary observation. Of the numerous point-like X-ray sources in the field, the brightest are shown to be a mixture of early and late-type stars. We find that several of the X-ray sources are transients, exhibiting rapid increases in count rates by factors 3–10, and similar in nature to the one, hard absorbed transient source located in the earlier Chandra observation of the field. None of these transient sources are likely to correspond to the TeV source. Instead, we identify a region of diffuse X-ray emission within the error circle of the TeV source and consider its plausible association.     

H.E.S.S. observations of LS 5039

Recent observations of the binary system LS 5039 with the High Energy Stereoscopic System (H.E.S.S.) revealed that its Very High Energy (VHE) γ-ray emission is modulated at the 3.9 days orbital period of the system. The bulk of the emission is largely confined to half of the orbit, peaking around the inferior conjunction epoch of the compact object. The flux modulation provides the first indication of γ-ray absorption by pair production on the intense stellar photon field. This implies that the production region size must be not significantly greater than the gamma-gamma photosphere size (∼1 AU), thus excluding the large scale collimated outflows or jets (extending out to ∼1000 AU). A hardening of the spectrum is also observed at the same epoch between 0.2 and a few TeV which is unexpected under a pure absorption scenario and could rather arise from variation with phase in the maximum electron energy and/or the dominant VHE γ-ray production mechanism. This first-time observation of modulated γ-ray emission allows precise tests of the acceleration and emission models in binary systems. Mathieu de Naurois for the H.E.S.S. Collaboration.     

GMRT observations of four suspected supernova remnants near the Galactic Centre

We have observed two fields – Field I     ,     and Field II     ,     – with the Giant Metrewave Radio Telescope (GMRT) at 330 MHz. In the first field, we have studied the candidate supernova remnant (SNR) G3.1−0.6 and, based on its observed morphology, spectral index and polarization, confirmed it to be an SNR. We find this supernova to have a double ring appearance with a strip of emission on its western side passing through its centre.
We have discovered two extended curved objects in the second field, which appears to be part of a large shell-like structure. It is possibly the remains of an old supernova in the region. Three suspected SNRs, G356.3−0.3, G356.6+0.1 and G357.1−0.2, detected in the MOST 843-MHz survey of the GC region appear to be located on this shell-like structure. While both G356.3−0.3 and G356.6+0.1 seem to be parts of this shell, G357.1−0.2, which has a steeper spectrum above 1 GHz, could be a background SNR seen through the region. Our H  i absorption observation towards the candidate SNR G357.1−0.2 indicates that it is at a distance of more than 6 kpc from us.     

Multiwavelength observations of the two unidentified EGRET sources 3EG J0616-3310 and 3EG J1249-8330

We report on the X-ray and optical observation of the two unidentified EGRET sources 3EG J0616-3310 and 3EG J1249-8330. The X-ray coverage performed by the ESA space telescope XMM–Newton provided ∼150 X-ray sources within each of the two γ-ray error-circles. The optical follow-up carried on with the Wide Field Imager at the ESO/MPG 2.2 m telescope have found no candidate counterpart for 125 of these X-ray sources. Among these, we have selected 9 sources with f _X/f _opt≥100, which we consider promising INS candidates.     

Search for TeV gamma-rays from Geminga pulsar

We present the results of observation of the Geminga pulsar carried out in the TeV energy band during the 6 year period spanning 2000–2006 using the Pachmarhi Array of Cherenkov Telescopes (PACT). A long stretch of data, new computer codes and the “Tempo” package have been used in the present analysis. We have searched for evidence of pulsed emission of γ-rays from the Geminga pulsar using the post-glitch pulsar elements obtained by Jackson and Halpern from X-ray/γ-ray satellite data. We do not see any significant evidence for pulsed emission from the Geminga pulsar at a threshold energy of 825 GeV. In this paper we present our results on the light curve in the TeV energy band, set an upper limit on the time averaged flux of γ-rays, and compare our results with other ground based observations.