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

BHsDave 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

Let’s start with the conclusionsFuture 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 systemI 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

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 J1550-564Well 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

Russell, Maitra, Dunn & Fender 2011, MNRAS, in press

Hardness-intensity vs colour-magnitude diagrams

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) ~ -0.7α (optical X-ray) = -0.7α (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 tenJet origin of X-ray emission predicted by Markoff, Falcke & Fender 2001

(modelling of multiwavelength SED of XTE J1118+480)

Fender, Gallo & Jonker 2003:Energetics are jet dominated at low luminosities in the hard state

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Jet could dominate X-ray flux in the hard state between

News flash: XTE J1752-223 late X-ray + optical flare

2009-2010 outburst of this new BH transient:

Faulkes Telescope monitoring in 4 optical filtersα (optical excess) = -0.16 +- 0.29No change in X-ray PL propertiesRussell et al. in prep.

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

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

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