3.9 day orbital modulation in the TeV gamma-ray flux and spectrum from the X-ray binary LS 5039
By T. H. C. Aharonian, et al. 2006
157 citations recorded by the source corpus.
New observations of LS 5039, a High Mass X-ray Binary comprising a massive star and compact object, were carried out with the High Energy Stereoscopic System of Cherenkov Telescopes (H.E.S.S.) in 2005 at very high energy (VHE) gamma-ray energies. These observations reveal that its flux and energy spectrum are modulated with the 3.9 day orbital period of the binary system. This is the first time in gamma-ray astronomy that orbital modulation has been observed, and periodicity clearly established using ground-based gamma-ray detectors. The VHE gamma-ray emission is largely confined to half of the orbit, peaking around the inferior conjunction epoch of the compact object. For this epoch, there is also a hardening of the energy spectrum in the energy range between 0.2 TeV and a few TeV. The flux vs. orbital phase profile provides the first clear indication of gamma-ray absorption via pair production within an astrophysical source, a process which is expected to occur if the gamma-ray production site is situated within ~1 AU of the compact object. Moreover the production region size must be not significantly greater than the binary separation (~0.15 AU). Notably, these constraints are also considerably smaller than the collimated outflows or jets (extending out to ~1000 AU) observed in LS 5039. The spectral hardening could arise from variations with phase in the maximum electron energies, and/or the dominant VHE gamma-ray production mechanism.
Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics
View Paper: https://www.semanticscholar.org/paper/13d4c566f18200aa23d9f98d641ca2b83e9d6fd7
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Citations in the corpus
- Teraelectronvolt Astronomy (2010, methodology): “In one case — GRB 060602B — an (unusually soft) GRB occurred in the field of view of ongoing observations of the H.E.S.S. telescope, however, without giving rise to a detectable signal (Aharonian et al. 2009).”
- Gamma-ray binaries and related systems (2013, background): “Gamma-ray binaries and related systems 41 Hadronic processes have not been favoured for several reasons (but see Kawachi et al. 2004; Bednarek 2005; Romero et al. 2005; Aharonian et al. 2006; Chernyakova et al. 2006b for models considering hadronic emission in gamma-ray binaries).”