VLBI structure of PSR B1259-63/LS2883

during the 2007 and 2010

periastron passages

Javier Moldón

Marc Ribó

Josep M. Paredes

Simon Johnston, Ryan Shannon (ATNF -CSIRO)

Adam Deller (NRAO/Berkeley)

High Energy Phenomena in Relativistic Outflows IIIBarcelona – June 28, 2011

● The radio emission from the gamma-ray binary PSR B1259-63.

● VLBI radio observations from 2007 periastron passage.

● Campaign during the 2010-2011 periastron passage.

● Discovery of extended emission from HESS J0632+057.

● Gamma-ray binaries as seen by VLBI.

● Conclusions.

Outline

The gamma-ray binaryPSR B1259-63

The binary system PSR B1259-63/LS 2883

[Moldón et al. 2011, ApJL, 732, L10Negueruela et al. 2011, ApJL, 732, L11]

PSR B1259–63/LS 2883 is a binary system located at 2.3 kpc that contains an Oe star and a 47.7 ms radio pulsar orbiting it every 3.4 yr in a very eccentric orbit.

Non-thermal transient emission up to VHE is detected close to the periastron passage.

[Aharonian et al. 2005, A&A, 442, 1]

PSR B1259-63 shows a double radio pulse, and drastic changes in the Dispersion Measure (DM) and in the Rotation Measure (RM) of the pulses close to each periastron passage.[Johnston et al 2005,MNRAS, 358, 1069]

Pulsed radio emission from PSR B1259-63

Radio pulses disappear around 16 days before the periastron passage, and reappear 15 days after.

Radio pulsar timing provides accurate values for some orbital parameters like f(Mpulsar), e, P, t0, ω. [Wang et al. 2004, MNRAS, 351, 599]

Transient emission from PSR B1259-63/LS 2883

The system displays transient unpulsed optically thin (α≈−0.6) radio emission up to 60 mJy close and after the periastron passage. The radio lightcurve shows two peaks centered aroundτ − 10 and τ + 20 days.

After the second peak the flux density of the unpulsed emission decreases continuously, and it has been detected up to τ + 100 days. ∼

Radio eclipse

Gamma-ray binaries at AU scales

Radio emission in a binary pulsar

An intense shock between the relativistic wind of a non-accreting pulsar and the stellar wind is produced.Particle acceleration at the termination shock leads to synchrotron and inverse Compton emission.

The shocked material is contained by the stellar wind behind the pulsar, producing nebula extending away from the stellar companion.

UV photons from the companion star suffer inverse Compton scattering with the relativistic electrons from the pulsar wind

Adiabatically expanding flow produce the synchrotron emission from radio to X-rays

Expected behaviour at mas scales

The cometary tail changes its direction continuously.

The peak of the emission follows the path of an elliptic orbit.

Astrometric and morphological changes expected

VLBI observations provide images at AU scales at ~2.5 kpc: 1−100 mas 2.5−250 AU

[Dubus 2006, A&A , 456, 801]

VLBI observations ofPSR B1259-63/LS 2883

(The only gamma-ray binary with a confirmed pulsar)

PSR B1259-63 (2007 periastron passage)

We observed PSR B1259–63 with Long Baseline Array (LBA) observations conducted during the 2007 periastron passage at three different orbital phases (T+1, T+21 and T+315).We used 5 antennas of the array. Observations at 2.3 GHz (13 cm).

Run Epoch EpochOrbital phase

A 54309.25 T+1 0.0010

B 54329.18 T+21 0.0170

C 54623.48 T+315 0.2551

A

BC

Run Epoch EpochOrbital phase

A 54309.25 T+1 0.0010

B 54329.18 T+21 0.0170

C 54623.48 T+315 0.2551

PSR B1259-63 (2007 periastron passage)

Radio eclipse

Observations during the 2007 periastron passage were conducted 1 and 20 days after the periastron passage to see variability changes of the transient emission, and 1 year later to find the pulsar position.

A

BC

We have just found extended emission from PSR B1259–63 with Long Baseline Array (LBA) observations conducted during the 2007 periastron passage.

● We confirm that non-accreting pulsars orbiting massive stars can produce variable extended radio emission at AU scales.● The peak of the radio nebula is detected at distances between 10 and 50 AU from the binary system and with a total extension of 50 mas (120 AU).● The discovery of such a structure in PSR B1259–63 reinforces the link with the other known gamma-ray binaries, LS 5039 and LS I +61 303, for which the detection of pulsations is challenging.

VLBI observations of PSR B1259-63 (2007)

[Moldón et al. 2011, ApJL, 732, L10]

Kinematical interpretationA simple kinematic model, using the approximation of a non-turbulent adiabatically expanding flow, as described in Kennel & Coronitti (1984). The flow speed depends only on the magnetization parameter σ when σ << 1. We only consider intertaction with an isotropic polar wind. This first approximation allow us to constrain the orientation of the orbit, given by the longitude of the ascending node, Ω, and the magnetization of the pulsar, σ.

The detected morphology can be accounted for if:≃−40º≃0.005

[Moldón et al. 2011, ApJL, 732, L10]

2010 periastron passage ofPSR B1259-63/LS 2883

We have monitored the orbital variability of the nebula with the LBA during the 2010 periastron passage (Dec 15, 2010). We have 5 observations covering a wide range of true anomalies.

VLBI observations of PSR B1259-63 (2010)

Run Epoch Epoch Orbital phase

A 55524 T-21 0.9833

B 55545 T+0 0.0003

C 55574 T+29 0.0237

D 55600 T+55 0.0447

E 55652 T+107 0.0868

Radio eclipse

B

CD E

A

Pulsar gatingThe data are correlated with pulsar gating, only using the data during the on-pulse or the off-pulse. This technique allows us to enhance the pulsed emission or to eliminate it, and therefore, determine the position of the pulsar inside the nebula.

When we receive the whole set of data, we will separate the pulsed emission from the transient emission for most of the runs. We will also obtain precise astrometry of the pulsar (binary system).

We will obtain the relative position and distance between the pulsar and the nebula.

Discovery of extended emission from HESS J0632+057

HESS J0632+057HESS J0632+057 is a gamma-ray binary composed by a compact object orbiting every 320±5 days the B0pe-type star MWC 148, located at 1.5 kpc.

We conducted ToO e-EVN observations triggered by the February 2011 X-ray outburst. Response timescale since VHE detection = 1 week (7 antennas in Europe, China and South Africa). Second ToO after 1 month to search for variability.

[Moldón et al., in preparation]

● Confirmed association with Be Star

● Confirmed the non-thermal nature of the radio source.

● Discovery of extended emission

Gamma-ray binariesas seen by VLBI

LS I +61 303

Dhawan et al. (2006), VI Microquasar Workshop

(1999)

(2007)

(2000)

Orbital Phase0.0 1.00.5

0.98 0.10 0.23 0.44 0.49 0.72 0.75 0.00

LS 5039

[Ribó et al. 2008, A&A, 481, 17 Moldón et al. 2011, High-Energy Emission from Pulsars and their SystemsMoldón et al., in preparation]

PSR B1259-63

[Moldón et al. 2011, ApJL, 732, L10]

HESS J0632+057

[Moldón et al., in preparation]

Gamma-ray binaries

Pulsar VLBI

LS 5039P

orb = 3.9 days ? periodic

orbital variability

LS I +61 303P

orb = 26.5 days ? periodic

orbital variability

PSR B1259-63P

orb = 3.4 years

(periodic) orbital variability

HESS J0632+057P

orb = 26.5 days ? Extended

1FGL J1018.6-5856P

orb = 16.58 days ? ?

Summary

1. We confirm that non-accreting pulsars orbiting massive stars can produce variable extended radio emission at AU scales.

2. The peak of the radio nebula is detected at distances between 20 and 50 AU from the binary system and with a total extension of 50 mas (120 AU).

3. VLBI radio observations can put constrains on physical parameters of the system.

4. During 2011 we will have the complete dataset to study the morphologic and astrometric changes of the radio emission, and precise astrometry of the binary system.

5. HESS J0632+057 displays extended emission and peak displacement.

6. VLBI observations are a common link, useful to understand the behaviour of gamma-ray binaries.