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

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 Dubner et al. (1998) Blundell & Bowler (2004)

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 10 35 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 3x10 35 < P jet < 2x10 37 erg/s Sell et al. 2010

11. Jets may be ultra-relativistic! Time delay between core and lobe flaring suggests  >15! Unseen energising flow Most relativistic flow known in the Galaxy Requires  <5 o Implies v jet ≠ v esc Luminosity >35 L Edd 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 Phillips et al. 2007 PA, AT, MP, HO Compact radio source: 60 ± 15 mas 11 mJy (1.6 GHz) 12-70h after periastron –0.03<  <0.18

13. Follow-up phase-resolved VLBI Monitoring campaign over full binary orbit Moin et al. 2011 Only detected at/after periastron passage Unresolved, compact source No constant quiescent component Any ultra-relativistic flow must be dark

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  >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  <20 o X-ray caps have 35 o 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