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Resolving the jets of Circinus X-1 with Very Long Baseline Interferometry

Resolving the jets of Circinus X-1 with Very Long Baseline Interferometry. James Miller-Jones Collaborators: A. Moin , S. Tingay , C. Reynolds, C. Phillips, A. Tzioumis , R. Fender, J. McCallum, G. Nicolson, V. Tudose. Email: james.miller-jones@curtin.edu.au. Why study X-ray binaries?.

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Resolving the jets of Circinus X-1 with Very Long Baseline Interferometry

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  1. Resolving the jets of Circinus X-1 with Very Long Baseline Interferometry James Miller-Jones Collaborators: A. Moin, S. Tingay, C. Reynolds, C. Phillips, A. Tzioumis, R. Fender, J. McCallum, G. Nicolson, V. Tudose Email: james.miller-jones@curtin.edu.au

  2. Why study X-ray binaries? • Jets observed throughout the visible Universe • Universal coupling to the process of accretion • Open questions: • Accretion/ejection coupling • Jet launching, acceleration, collimation • Multi-wavelength studies couple inflow, outflow • Timescales scale with compact object mass • XRBs evolve on human timescales: unique probe • Application to AGN (scaling relations) • Also: • Feedback of matter and energy to the ISM • Probes of strong gravity • End products of binary evolution • Implications for black hole formation Image credit: R Hynes Image credit: R Hynes

  3. What can the radio tell us? • Band in which emission is dominated by the jets • Probe of high-energy processes • Outbursts • Resolving power: morphology • Jet collimation, propagation, energetics • Jet/disc coupling in transition states • Hard/quiescent states: • Radio/X-ray correlations • Point-like, faint, yet persistent radio sources • Astrometry • Large-scale structure • Jet/ISM interactions, calorimetry Blundell & Bowler (2004) Dubner et al. (1998)

  4. Powerful outflows from NS • Typically fainter than BH • Powerful jets seen in highly-accreting Z-sources • No evidence to date for ejecta at state transitions • Sco X-1: • Working surfaces move out at 0.5 c • Unseen flow at >0.95c lights them up following core flaring Migliari & Fender (2006) Fomalont et al. (2001)

  5. Circinus X-1 • Neutron star X-ray binary • Confirmed by the presence of Type I X-ray bursts • Nature of the companion is still debated • B5-A0 supergiant? • Distance uncertain • >8 kpc (HI absorption) • 7.8-10.5 kpc (bursts) • 4.1 kpc (X-ray column) • Eccentric orbit (16.6d) • Flares at periastron Linares et al. 2010

  6. Inclination angle • Thought to be close to edge-on from the X-rays • Dipping behaviour • Spectral changes on egress from dips • P Cygni profiles of disk lines Brandt & Schulz 2000 Shirey et al. 1999

  7. Galactic environment • Close to the SNR G321.9-0.3 • Early suggestions that this was the SNR created when the NS was born • Requires proper motion in the range 15-75 mas/yr • Ruled out by HST upper limit of <5mas/yr (Mignani et al. 2002) • Unrelated objects

  8. Resolved radio jets • NW-SE alignment • Arcsecond scales • Variable morphology • Variation of jet axis • No obvious evidence for precession • Outbursts near orbital phases 0.0 and 0.5 Tudose et al. 2008

  9. Jets have inflated a nebula • Jets interact with the surroundings, inflating a lobe • Calorimetry: age < 105 yr, jet power >1035 erg/s Tudose et al. 2006

  10. Jets also in the X-rays • Coincident with radio jets • Morphology suggests a terminal shock on contact with ISM • Wide opening angle: poor collimation or precession • Jet power 3x1035 < Pjet < 2x1037 erg/s Sell et al. 2010

  11. Jets may be ultra-relativistic! • Time delay between core and lobe flaring suggests G>15! • Unseen energising flow • Most relativistic flow known in the Galaxy • Requires q<5o • Implies vjet ≠ vesc • Luminosity >35 LEdd if isotropic Fender et al. 2004

  12. First southern-hemisphere e-VLBI • Radio flares reached ~Jy levels from 1975-1985 • Lower-level activity (mJy-level) until 2006, when flares again reached Jy levels • Triggered 1.6, 8.4-GHz e-VLBI • PA, AT, MP, HO • Compact radio source: • 60 ± 15 mas • 11 mJy (1.6 GHz) • 12-70h after periastron • 0.03<f<0.18 Phillips et al. 2007

  13. Follow-up phase-resolved VLBI • Monitoring campaign over full binary orbit • Only detected at/after periastron passage • Unresolved, compact source • Noconstant quiescent component • Anyultra-relativistic flow must be dark Moin et al. 2011

  14. ToO e-VLBI observations • 8.4 GHz; less scattering, higher angular resolution • e-VLBI LBA observations • 14 hour run (2010/07/28) • 5 antennas (AT, CD, HO, MP, TI), but Tid failed • Orbital phase 0.046-0.082 • Flux density decays from 210 to 80 mJy/beam Miller-Jones et al. 2011

  15. Resolving the jets with the LBA • Resolved jets along a position angle of 112 degrees • Expansion between the two halves of the observation • Expansion speed 35 mas/day Miller-Jones et al. 2011

  16. Simulations: is it real? • Sparse array (4 antennas, 6 baselines) • Use simulations to assess effects of sparse uv-coverage: • Decaying point source cannot reproduce extended structure • One-sided jet cannot reproduce bipolar structure • Moving components smear out the emission • appears fainter • locus appears slightly curved • cannot give bipolar structure • Observed structure is real! • Replace first-half visibilities with second-half model • Extended emission would have been seen if present • Expansion is real!

  17. Visibility plane • Amplitude decreases, minimum shifts to shorter baselines Miller-Jones et al. 2011

  18. What are we seeing? • Unlikely to be a compact, steady jet as in GRS 1915+105 • We see expansion between first and second halves • Probably not flat spectrum; usually optically thin by phase 0.05 • Likely outward motion of expanding, optically-thin ejecta Dhawan et al. (2000)

  19. Symmetric structure • Symmetric structure appears to be real • Are we seeing: • A bipolar ejection? • The symmetric brightness profile of the approaching jet? • Can’t determine from astrometry alone • Observations not phase-referenced • No absolute astrometric parameters for the binary • To hide receding jet needs • Extreme Doppler deboosting • Cloud of free-free absorbing material • Symmetry of expansion makes bipolar ejection scenario most plausible

  20. Ultra-relativistic flow? • 400 mas/d flow should be smeared over 63 beams in 14h • Expansion between two halves suggests 35 mas/d • Assuming ejection at orbital phase zero gives 16 mas/d • No downstream lobes seen to be brightened by G>15 flow • Symmetry also argues against ultra-relativistic flow: • Should not see receding jet: • Unless source is at ~10kpc and proper motion is 35mas/d: • inclination angle is moderate • jets are only mildly relativistic

  21. Opening angle • Jets unresolved • Implies q<20o • X-ray caps have 35o opening angle • Possible precession? • ATCA jet position angle 129 ± 13 degrees • No unequivocal evidence for precession • Requires more VLBI sampling to verify this Sell et al. 2010

  22. Follow-up work • 3 LBA observations in 2011 May • Triggered by e-VLBI • Time-resolved to track moving jet components • Orbital phases 0.10, 0.15, 0.21 • Resolved jets in epoch 1 • Different PA: precession? • Astrometry suggests significant peculiar velocity (160-320 km/s): natal kick?

  23. Conclusions • We have resolved the jets on mas scales for the first time • Symmetric, expanding structure • Appears only mildly relativistic • Ultra-relativistic flow model is becoming ever less plausible • Ruled out by Occam’s razor? • Time-resolved LBA observations around periastron can directly measure component speed and inclination angle • Hints of precession of the jets – follow-up required • Hints of a significant peculiar velocity suggest a natal kick

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