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: james.miller-jones@curtin.edu.au

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

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)

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)

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

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

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

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

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

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

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

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

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

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

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

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!

Visibility plane

• Amplitude decreases, minimum shifts to shorter baselines

Miller-Jones et al. 2011

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)

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

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

qq

k

r

a

SS

cos1cos1

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

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?

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