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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 28 th June 2011
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Let’s start with the conclusions Future spaceborne X-ray polarimeters will* detect variable X-ray polarization from synchrotron emission from the jets released from accreting Galactic black holes 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 *probably
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Optical & infrared data published in Jain et al. 2001; radio in Corbel et al. 2001 X-ray analysis as in Dunn et al. 2010 Introducing the 2000 outburst of XTE J1550-564 Well monitored in X-ray, optical and near-infrared (NIR) We can separate disc and jet emission Assumes continuation of the exponential decay of disc flux Jet has optically thin spectrum
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Russell, Maitra, Dunn & Fender 2011, MNRAS, in press Hardness-intensity vs colour-magnitude diagrams
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Could it be a synchrotron jet dominating X-ray? NIR jet flux is proportional to X-ray flux variability amplitude increases here (Kalemci et al. 2001) Russell, Maitra, Dunn & Markoff 2010, MNRAS, 405, 1759 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)
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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
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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.
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Polarization of optically thin synchrotron emission Shahbaz et al. 2008 In NIR, the observed emission can be highly polarized Depends on magnetic field configuration Ordered field up to 70% polarized Russell & Fender 2008 Tangled field ~ no net polarization
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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.) 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) Resolved radio jet of GX 339-4 (Gallo et al. 2004) New VLT observations of GX 339-4 in 2008 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
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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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