Resolving the jets of Circinus X-1 with Very Long Baseline Interferometry
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Resolving the jets of Circinus X-1 with Very Long Baseline Interferometry
James Miller-JonesCollaborators: A. Moin, S. Tingay, C. Reynolds, C. Phillips,
A. Tzioumis, R. Fender, J. McCallum, G. Nicolson, V. Tudose
Email: [email protected]
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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
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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)
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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)
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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
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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
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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
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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
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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
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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
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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
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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<f<0.18
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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
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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
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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
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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!
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Visibility plane
• Amplitude decreases, minimum shifts to shorter baselines
Miller-Jones et al. 2011
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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)
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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
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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
k
r
a
SS
cos1cos1
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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
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Follow-up work
• 3 LBA observations in 2011 May
• Triggered by e-VLBI ra
ra
q
cos
• 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?
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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