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Probing Jet Launching in Neutron Star X-Ray Binaries: The Variable and Polarized Jet of SAX J1808.4–3658
- Source :
- Astrophys.J., Astrophys.J., 2020, 905 (2), pp.87. ⟨10.3847/1538-4357/abc685⟩
- Publication Year :
- 2020
- Publisher :
- HAL CCSD, 2020.
-
Abstract
- We report on an optical photometric and polarimetric campaign on the accreting millisecond X-ray pulsar (AMXP) SAX J1808.4-3658 during its 2019 outburst. The emergence of a low-frequency excess in the spectral energy distribution in the form of a red excess above the disc spectrum (seen most prominently in z, i and R-bands) is observed as the outburst evolves. This is indicative of optically thin synchrotron emission due to a jet, as seen previously in this source and in other AMXPs during outburst. At the end of the outburst decay, the source entered a reflaring state. The low-frequency excess is still observed during the reflares. Our optical (BVRI) polarimetric campaign shows variable linear polarization (LP) throughout the outburst. We show that this is intrinsic to the source, with low-level but significant detections (0.2-2%) in all bands. The LP spectrum is red during both the main outburst and the reflaring state, favoring a jet origin for this variable polarization over other interpretations, such as Thomson scattering with free electrons from the disc or the propelled matter. During the reflaring state, a few episodes with stronger LP level (1-2 %) are observed. The low-level, variable LP is suggestive of strongly tangled magnetic fields near the base of the jet. These results clearly demonstrate how polarimetry is a powerful tool for probing the magnetic field structure in X-ray binary jets, similar to AGN jets.<br />Comment: Accepted for publication in ApJ
- Subjects :
- Black Holes
010504 meteorology & atmospheric sciences
Astrophysics::High Energy Astrophysical Phenomena
FOS: Physical sciences
Synchrotron radiation
Astrophysics
01 natural sciences
Outburst
Pulsar
0103 physical sciences
Binary star
Astrophysics::Solar and Stellar Astrophysics
010303 astronomy & astrophysics
Solar and Stellar Astrophysics (astro-ph.SR)
0105 earth and related environmental sciences
High Energy Astrophysical Phenomena (astro-ph.HE)
Physics
Cygnus
Jet (fluid)
Linear polarization
Astronomy and Astrophysics
Stars
Neutron star
Astrophysics - Solar and Stellar Astrophysics
13. Climate action
Space and Planetary Science
Spectral energy distribution
Astrophysics - High Energy Astrophysical Phenomena
[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Subjects
Details
- Language :
- English
- Database :
- OpenAIRE
- Journal :
- Astrophys.J., Astrophys.J., 2020, 905 (2), pp.87. ⟨10.3847/1538-4357/abc685⟩
- Accession number :
- edsair.doi.dedup.....bcee9508a958a6f71fb29e81b6d3f8db