Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userConstraints on particle acceleration in SS433/W50 from MAGIC and H.E.S.S. observations
105
0
0.0
(
0
)
Added by
Alicia L\\'opez-Oramas
Publication date
2017
fields
Physics
and research's language is
English
Authors
MAGIC Collaboration: M. L. Ahnen
Ask ChatGPT about the research
No Arabic abstract
The large jet kinetic power and non-thermal processes occurring in the microquasar SS 433 make this source a good candidate for a very high-energy (VHE) gamma-ray emitter. Gamma-ray fluxes have been predicted for both the central binary and the interaction regions between jets and surrounding nebula. Also, non-thermal emission at lower energies has been previously reported. We explore the capability of SS 433 to emit VHE gamma rays during periods in which the expected flux attenuation due to periodic eclipses and precession of the circumstellar disk periodically covering the central binary system is expected to be at its minimum. The eastern and western SS433/W50 interaction regions are also examined. We aim to constrain some theoretical models previously developed for this system. We made use of dedicated observations from MAGIC and H.E.S.S. from 2006 to 2011 which were combined for the first time and accounted for a total effective observation time of 16.5 h. Gamma-ray attenuation does not affect the jet/medium interaction regions. The analysis of a larger data set amounting to 40-80 h, depending on the region, was employed. No evidence of VHE gamma-ray emission was found. Upper limits were computed for the combined data set. We place constraints on the particle acceleration fraction at the inner jet regions and on the physics of the jet/medium interactions. Our findings suggest that the fraction of the jet kinetic power transferred to relativistic protons must be relatively small to explain the lack of TeV and neutrino emission from the central system. At the SS433/W50 interface, the presence of magnetic fields greater 10$mu$G is derived assuming a synchrotron origin for the observed X-ray emission. This also implies the presence of high-energy electrons with energies up to 50 TeV, preventing an efficient production of gamma-ray fluxes in these interaction regions.
rate research
Read More
The microquasar SS433 features the most energetic jets known in our Galaxy. A large fraction of the jet kinetic power is delivered to the surrounding W50 nebula at the jet termination shock, from which high-energy emission and cosmic-ray production have been anticipated. Here we report on the detection of a persistent gamma-ray signal from the direction of SS433/W50 with the Fermi Large Area Telescope. The steady flux and a narrow spectral energy distribution with a maximum around 250 MeV suggest that gamma-rays are rendered by the bulk jet kinetic power through proton-proton collisions at the SS433/W50 interaction regions. If the same mechanism is operating in other baryon-loaded microquasar jets, their collective contribution may represent a significant fraction of the total galactic cosmic-ray flux at GeV energies.
SS433, located at the center of the supernova remnant W50, is a close proximity binary system consisting of a compact star and a normal star. Jets of material are directed outwards from the vicinity of the compact star symmetrically to the east and west. Non-thermal hard X-ray emission is detected from lobes lying on both sides. Shock accelerated electrons are expected to generate sub-TeV gamma rays through the inverse-Compton process in the lobes. Observations of the western X-ray lobe region of SS433/W50 system have been performed to detect sub-TeV gamma-rays using the 10m CANGAROO-II telescope in August and September, 2001, and July and September, 2002. The total observation times are 85.2 hours for ON source, and 80.8 hours for OFF source data. No significant excess of sub-TeV gamma rays has been found at 3 regions of the western X-ray lobe of SS433/W50 system. We have derived 99% confidence level upper limits to the fluxes of gamma rays and have set constraints on the strengths of the magnetic fields assuming the synchrotron/inverse-Compton model for the wide energy range of photon spectrum from radio to TeV. The derived lower limits are 4.3 microgauss for the center of the brightest X-ray emission region and 6.3 microgauss for the far end from SS433 in the western X-ray lobe. In addition, we suggest that the spot-like X-ray emission may provide a major contribution to the hardest X-ray spectrum in the lobe.
The formation mechanism of the W50/SS433 complex has long been a mystery. We propose a new scenario in which the SS433 jets themselves form the W50/SS433 system. We carry out magnetohydrodynamics simulations of two-side jet propagation using the public code CANS+. As found in previous jet studies, when the propagating jet is lighter than the surrounding medium, the shocked plasma flows back from the jet tip to the core. We find that the morphology of light jets is spheroidal at early times, and afterward, the shell and wings are developed by the broadening spherical cocoon. The morphology strongly depends on the density ratio of the injected jet to the surrounding medium. Meanwhile, the ratio of the lengths of the two-side jets depends only on the density profile of the surrounding medium. We also find that most of the jet kinetic energy is dissipated at the oblique shock formed by the interaction between the backflow and beam flow, rather than at the jet terminal shock. The position of the oblique shock is spatially consistent with the X-ray and TeV gamma-ray hotspots of W50.
Axion-like particles are hypothetical new light (sub-eV) bosons predicted in some extensions of the Standard Model of particle physics. In astrophysical environments comprising high-energy gamma rays and turbulent magnetic fields, the existence of axion-like particles can modify the energy spectrum of the gamma rays. This modification would take the form of an irregular behavior of the energy spectrum in a limited energy range. Data from the H.E.S.S. observations of the distant BL Lac PKS 2155-304 are used to derive conservative upper limits on the strength of the axion-like particle coupling to photons. This study gives rise to the first exclusions on axion-like particles from gamma-ray astronomy. The derived constraints apply to both light pseudo-scalar and scalar bosons that couple to the electromagnetic field.
The W50/SS433 system is an unusual Galactic outflow-driven object of debatable origin. We have used the Australia Telescope Compact Array (ATCA) to observe a new 198 pointing mosaic, covering $3^circ times 2^circ$, and present the highest-sensitivity full-Stokes data of W50 to date using wide-field, wide-band imaging over a 2 GHz bandwidth centred at 2.1 GHz. We also present a complementary H$alpha$ mosaic created using the Isaac Newton Telescope Photometric H$alpha$ Survey of the Northern Galactic Plane (IPHAS). The magnetic structure of W50 is found to be consistent with the prevailing hypothesis that the nebula is a reanimated shell-like supernova remnant (SNR), that has been re-energised by the jets from SS433. We observe strong depolarization effects that correlate with diffuse H$alpha$ emission, likely due to spatially-varying Faraday rotation measure (RM) fluctuations of $ge48$ to 61 rad m$^{-2}$ on scales $le4.5$ to 6 pc. We also report the discovery of numerous, faint, H$alpha$ filaments that are unambiguously associated with the central region of W50. These thin filaments are suggestive of a SNRs shock emission, and almost all have a radio counterpart. Furthermore, an RM-gradient is detected across the central region of W50, which we interpret as a loop magnetic field with a symmetry axis offset by $approx90^{circ}$ to the east-west jet-alignment axis, and implying that the evolutionary processes of both the jets and the SNR must be coupled. A separate RM-gradient is associated with the termination shock in the Eastern ear, which we interpret as a ring-like field located where the shock of the jet interacts with the circumstellar medium. Future optical observations will be able to use the new H$alpha$ filaments to probe the kinematics of the shell of W50, potentially allowing for a definitive experiment on W50s formation history.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
