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تسجيل مستخدم جديدDiscovery of a variable X-ray counterpart to HESS J1832-093: A new gamma-ray binary?
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The TeV gamma-ray point source HESSJ1832-093 remains unidentified despite extensive multi-wavelength 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 XMMUJ183245-0921539 and its relation to HESSJ1832-093, we performed deeper follow-up observations in X-rays with Chandra and Swift to improve source localisation and to investigate time variability. We observed an increase of the X-ray flux by a factor ~6 in the Chandra data compared to previous observations. The source is point-like for Chandra and its updated position is only 0.3 offset from 2MASS J18324516-0921545, confirming the association with this infrared source. Subsequent Swift ToO observations resulted in a lower flux, again compatible with the one previously measured with XMM-Newton, indicating a variability timescale 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. Further observations to characterise the optical counterpart as well as to search for orbital periodicity are needed to confirm this scenario.
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We investigate the nature of the unidentified very-high-energy (VHE) gamma-ray object, HESS J1832-093, in a multi-wavelength context. Based on X-ray variability and spectral index ($Gamma_Xsim,1.5$), and its broad-band spectrum (which was remarkably
similar to HESS J0632+057, a confirmed gamma-ray binary), HESS J1832-093 has been considered to be a strong gamma-ray binary candidate in previous works. In this work, we provide further evidence for this scenario. We obtained a spectrum of its IR counterpart using Gemini/Flamingo, finding absorption lines that are usually seen in massive stars, in particular O stars. We also obtained a rather steep ATCA spectrum ($alpha=-1.18^{+1.04}_{-0.88}$) which prefers a gamma-ray binary over an AGN scenario. Based on spatial-spectral analysis and variability search, we found that 4FGL J1832.9-0913 is possible to be associated with SNR G22.7-0.2 rather than with HESS J1832-093 only.
The region around the supernova remnant (SNR) W41 contains several TeV sources and has prompted the H.E.S.S. Collaboration to perform deep observations of this field of view. This resulted in the discovery of the new very high energy (VHE) source HES
S J1832-093, at the position $rm RA=18^h 32^m 50^s pm 3^s_{stat} pm 2^s_{syst}, rm Dec=-9^circ 22 36 pm 32_{stat} pm 20_{syst} (J2000)$, spatially coincident with a part of the radio shell of the neighboring remnant G22.7-0.2. The photon spectrum is well described by a power-law of index $Gamma = 2.6 pm 0.3_{rm stat} pm 0.1_{rm syst}$ and a normalization at 1 TeV of $Phi_0=(4.8 pm 0.8_{rm stat}pm 1.0_{rm syst}),times,10^{-13},rm{cm} ^{-2},s^{-1},TeV^{-1}$. The location of the gamma-ray emission on the edge of the SNR rim first suggested a signature of escaping cosmic-rays illuminating a nearby molecular cloud. Then a dedicated XMM-Newton observation led to the discovery of a new X-ray point source spatially coincident with the TeV excess. Two other scenarios were hence proposed to identify the nature of HESS J1832-093. Gamma-rays from inverse Compton radiation in the framework of a pulsar wind nebula scenario or the possibility of gamma-ray production within a binary system are therefore also considered. Deeper multi-wavelength observations will help to shed new light on this intriguing VHE source.
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