10 research outputs found
H.E.S.S. Observations of LS 5039
Recent observations of the binary system LS5039 with the High Energy Stereoscopic System (H.E.S.S.) revealed that its Very High Energy (VHE) gamma-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 gamma-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 gamma-ray production mechanism. This first-time observation of modulated gamma-ray emission allows precise tests of the acceleration and emission models in binary systems
Towards a population of HMXB/NS microquasars as counterparts of low-latitude unidentified EGRET sources
The discovery of the microquasar LS 5039 well within the 95% conficence
contour of the Unidentified EGRET Source (UES) 3EG J1824-1514 was a major step
towards the possible association between microquasars (MQs) and UESs. The
recent discovery of precessing relativistic radio jets in LS I +61 303, a
source associated for long time with 2CG 135+01 and with the UES 3EG
J0241+6103, has given further support to this idea. Finally, the very recently
proposed association between the microquasar candidate AX J1639.0-4642 and the
UES 3EG J1639-4702 points towards a population of High Mass X-ray Binary
(HMXB)/Neutron Star (NS) microquasars as counterparts of low-latitude
unidentified EGRET sources.Comment: 12 pages, 7 figures. Proceedings of the Conference "The
Multiwavelength Approach to Unidentified Gamma-ray Sources", to appear in the
journal Astrophysics and Space Scienc
Multiwavelength Observations of Gamma-ray Binary Candidates
There are currently only six known high mass X-‐ray binaries (HMXBs) that also exhibit MeV, GeV, and/or TeV emission ("gamma-‐ray binaries"). Expanding the sample of gamma-‐ray binaries and identifying unknown Fermi sources are currently of great interest to the community. Based upon their positional coincidence with the unidentified Fermi sources 1FGL J1127.7-‐6244c and 1FGL J1808.5-‐1954c, the Be stars HD 99771 and HD 165783
have been proposed as gamma-‐ray binary candidates. During Fermi Cycle 4, we have performed multiwavelength
observations of these sources using XMM-‐Newton and the CTIO 1.5m telescope. We do not confirm high energy emission from the Be stars. Here we examine other X-‐ray sources in the X-‐ray sources in the field of view that are potential counterparts to the Fermi sources