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Register a new userPair Cascades in the Disk Environment of the Binary System PSR B1259-63/LS 2883
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PSR B1259-63/LS 2883 is a very high energy (VHE; $E > 100$ GeV) {gamma}-ray emitting binary consisting of a 48 ms pulsar orbiting around a Be star with a period of $sim3.4$ years. The Be star features a circumstellar disk which is inclined with respect to the orbit in such a way that the pulsar crosses it twice every orbit. The circumstellar disk provides an additional field of target photons which may contribute to inverse Compton scattering and {gamma}{gamma}-absorption, leaving a characteristic imprint in the observed spectrum of the high energy emission. At GeV energies, the source was detected for the first time during the previous periastron passage which took place on December 15, 2010. The Fermi Large Area Telescope (LAT) reported a spectacular and unexpected {gamma}-ray flare occurring around 30 days after periastron and lasting for about 7 weeks. In this paper, we study the signatures of Compton-supported, VHE {gamma}-ray induced pair cascades in the circumstellar disc of the Be star and their possible contribution to the GeV flux. We show that cascade emission generated in the disk cannot be responsible for the GeV flare, but it might explain the GeV emission observed close to periastron. We also show that the {gamma}{gamma}-absorption in the disk might explain the observed TeV light curve.
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PSR B1259-63/LS 2883 is a very high energy (VHE; E > 100 GeV) gamma-ray emitting binary consisting of a 48 ms pulsar orbiting around a Be star with a period of 3.4 years. The Be star features a circumstellar disk which is inclined with respect to the orbit in such a way that the pulsar crosses it twice every orbit. The circumstellar disk provides an additional field of target photons which may contribute to inverse Compton scattering and gamma-gamma absorption, leaving a characteristic imprint in the observed spectrum and light curve of the high energy emission. We study the signatures of Compton-supported, VHE gamma-ray induced pair cascades in the circumstellar disc of the Be star and their possible contribution to the GeV flux. We also study a possible impact of the gamma-gamma absorption in the disk on the observed TeV light curve. We show that the cumulative absorption of VHE gamma-rays in stellar and disk photon fields can explain the modulation of the flux at the periastron passage.
Observing the famous high-mass, eccentric X-ray and gamma-ray binary PSR B1259-63/LS 2883 with Chandra, we detected X-ray emitting clumps moving from the binary with speeds of about 0.1 of the speed of light, possibly with acceleration. The clumps are being ejected at least once per binary period, 3.4 years, presumably around binary periastrons. The power-law spectra of the clumps can be interpreted as synchrotron emission of relativistic electrons. Here we report the results of 8 observations of the clumps in 2011-2017 (two binary cycles) and discuss possible interpretations of this unique phenomenon.
Aim. In this paper we present very high energy (VHE; E>100 GeV) data from the gamma-ray binary system PSR B1259-63/LS 2883 taken around its periastron passage (15th of December 2010) with the High Energy Stereoscopic System (H.E.S.S.) of Cherenkov Telescopes. We aim to search for a possible TeV counterpart of the GeV flare detected by the Fermi LAT. In addition, we aim to study the current periastron passage in the context of previous observations taken at similar orbital phases, testing the repetitive behavior of the source. Methods. Observations at VHE were conducted with H.E.S.S. from 9th to 16th of January 2011. The total dataset amounts to around 6 h of observing time. Results. The source is detected in the 2011 data at a significance level of 11.5sigma revealing an averaged integral flux above 1 TeV of (1.01 pm 0.18_{stat} pm 0.20_{sys}) times 10^{-12} cm^{-2}s^{-1}. The differential energy spectrum follows a power-law shape with a spectral index Gamma = 2.92 pm 0.30_{stat} pm 0.20_{sys} and a flux normalisation at 1 TeV of N_{0} = 1.95 pm 0.32_{stat} pm 0.39_{sys}) times 10^{-12} TeV^{-1} cm^{-2} s^{-1}. The measured lightcurve does not show any evidence for variability of the source on the daily scale. Conclusions. The measured integral flux and the spectral shape of the 2011 data are compatible with the results obtained around previous periastron passages. The absence of variability in the H.E.S.S. data indicates that the GeV flare observed by Fermi LAT in the time period covered also by H.E.S.S. observations originates in a different physical scenario than the TeV emission. Additionaly, new results compared to those obtained in the observations which were performed in 2004 at a similar orbital phase, further support the hypothesis of the repetitive behavior of the source.
We examine changes of the $gamma$-ray intensity observed from the direction of the binary system PSR B1259-63/LS 2883 during campaigns around its three periastron passages. A simple and straightforward method is applied to the published data obtained with the Imaging Atmospheric Cherenkov Technique. Regardless of many issues of the detection process, the method works only with numbers of very high energetic photons registered in the specified regions. Within the realm of this scheme, we recognized changes attributable to the variations of the intrinsic source activity at high levels of significance.
We present the analysis of the Chandra X-ray Observatory observations of the eccentric gamma-ray binary PSR B1259-63/LS 2883. The analysis shows that the extended X-ray feature seen in previous observations is still moving away from the binary with an average projected velocity of about 0.07c and shows a hint of acceleration. The spectrum of the feature appears to be hard (photon index of 0.8) with no sign of softening compared to previously measured values. We interpret it as a clump of plasma ejected from the binary through the interaction of the pulsar with the decretion disk of the O-star around periastron passage. We suggest that the clump is moving in the unshocked relativistic pulsar wind (PW), which can accelerate the clump. Its X-ray emission can be interpreted as synchrotron radiation of the PW shocked by the collision with the clump.
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