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Constraints on X-ray polarization of synchrotron jets from stellar-mass BHs

Constraints on X-ray polarization of synchrotron jets from stellar-mass BHs. Dave Russell niversity of Amsterdam In collaboration with: Dipankar Maitra, Robert Dunn, Sera Markoff, Rob Fender, Fraser Lewis, Piergiorgio Casella, Peter Curran... and some results from a larger collaboration

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Constraints on X-ray polarization of synchrotron jets from stellar-mass BHs

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  1. Constraints on X-ray polarization of synchrotron jets from stellar-mass BHs Dave Russell niversity of Amsterdam In collaboration with: Dipankar Maitra, Robert Dunn, Sera Markoff, Rob Fender, Fraser Lewis, Piergiorgio Casella, Peter Curran... and some results from a larger collaboration 28th June 2011

  2. Let’s start with the conclusions Future spaceborne X-ray polarimeters will* detect variable X-ray polarization from synchrotron emission from the jetsreleased from accreting Galactic black holes *probably X-ray binary – microquasar system I will show: • Sometimes, synchrotron emission from jets can dominate the X-ray • flux of a black hole X-ray binary • This synchrotron emission is polarized at a low, and variable level • The polarization properties can help us understand jet physics

  3. Introducing the 2000 outburst of XTE J1550-564 Well monitored in X-ray, optical and near-infrared (NIR) Optical & infrared data published in Jain et al. 2001; radio in Corbel et al. 2001 X-ray analysis as in Dunn et al. 2010 We can separate disc and jet emission Assumes continuation of the exponential decay of disc flux Jet has optically thin spectrum

  4. Hardness-intensity vs colour-magnitude diagrams Russell, Maitra, Dunn & Fender 2011, MNRAS, in press

  5. Could it be a synchrotron jet dominating X-ray? Russell, Maitra, Dunn & Markoff 2010, MNRAS, 405, 1759 NIR jet flux is proportional to X-ray flux variability amplitude increases here (Kalemci et al. 2001) α (NIR  optical) ~ -0.7 α (optical  X-ray) = -0.7 α (X-ray power law) = -0.7 (photon index = 1.7) α (X-ray power law before) = -0.6 A single power law decreasing in flux by a factor of ten Jet origin of X-ray emission predicted by Markoff, Falcke & Fender 2001 (modelling of multiwavelength SED of XTE J1118+480)

  6. Fender, Gallo & Jonker 2003: Energetics are jet dominated at low luminosities in the hard state A possible revised picture for BH outbursts Jet could dominate X-ray flux in the hard state between

  7. News flash: XTE J1752-223 late X-ray + optical flare 2009-2010 outburst of this new BH transient: Faulkes Telescope monitoring in 4 optical filters α (optical excess) = -0.16 +- 0.29 No change in X-ray PL properties Russell et al. in prep.

  8. Polarization of optically thin synchrotron emission Russell & Fender 2008 Shahbaz et al. 2008 • In NIR, the observed emission can be highly polarized • Depends on magnetic field configuration • Ordered field  up to 70% polarized • Tangled field  ~ no net polarization

  9. New VLT observations of GX 339-4 in 2008 • We observed GX 339-4 in September 2008 during a hard state with VLT+ISAAC •  We detect significant, variable linear polarization in the near-infrared (when the jet dominated) News flash: Polarized γ-ray emission from Cygnus X-1 might be from the jet (Laurent et al. 2011, Science) Polarization strength is very high: 67 +- 30 % !! (0.4-2 MeV) Derived from 58 days of exposure time This would imply a very highly ordered, constant B field at the base of the jet of Cyg X-1 PA is offset from jet axis Resolved radio jet of GX 339-4 (Gallo et al. 2004) • We infer a predominantly tangled, variable magnetic field near the jet base • The PA of polarization is ~ perpendicular to the PA of the resolved radio jet  The magnetic field is approximately parallel to the jet axis (Russell et al. in prep.)

  10. Conclusions revisited • NIR synchrotron emission from jets in BH X-ray binaries is polarized • The results so far suggest: • Near the jet base of GX 339-4, the magnetic field is: •  generally turbulent (only partially ordered) and rapidly changing •  parallel to the jet axis • Near the jet base of Cygnus X-1 (Laurent et al. 2011), the magnetic field is possibly: •  extremely ordered and not rapidly changing •  offset from the jet axis • These magnetic geometry/variability properties are useful for jet models • This polarized synchrotron emission can occasionally dominate the X-ray flux • (This is probably true XTE J1550-564, and possibly XTE J1752-223) • Regular X-ray & optical/NIR monitoring is beneficial, such as SMARTS & Faulkes Future spaceborne X-ray polarimeters like GEMS and NHXM may be able to detect variable X-ray polarization from synchrotron emission from the jets released from accreting Galactic black holes

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