New Insights from the Optical Study of Spiders

Transcription

1 New Insights from the Optical Study of Spiders Rene Breton University of Manchester with many collaborators (V. Dhillon, J. Hessels, M. van Kerkwijk, M. Roberts, ) EWASS 25 June 2015 SDO/AIA/AEI

2 Why Do Pulsar Masses Matter? Our understanding of fundamental physics in the regime of a neutron star s centre is rather poor. hyperon star strange star quark hybrid star s u p e r c o color superconducting strange quark matter (u,d,s quarks) 2SC CSL gcfl LOFF Σ,Λ,Ξ,Δ n,p,e, µ n d u,d,s quarks 2SC CFL H CFL CFL K + CFL K 0 CFL π 0 N+e N+e+n u c t K i n,p,e, µ n π g p r o t o n traditional neutron star n superfluid s R ~ 10 km crust neutron star with pion condensate Fe 10 6 g/cm Hydrogen/He atmosphere nucleon star g/cm 3 g/cm 3

3 The Equation of State Measuring both mass and radius in a given neutron star is experimentally difficult. Statistical properties of radii and masses can independently restrain the phase space. Maximum mass Range of radii Demorest et al. 2010

4 Cumulative Pulse Pr ~10 million pulses sum Spiders: Black Widows and Redbacks Rotational Phase: ms Zo Eclipse Ingress Short, circular orbits (75 minutes - 15 hours) Large spin-down luminosity (Edot = few 1034 erg/s) Radio eclipses (0-70% of the orbit) Optical flux/colour modulation Orbital Phase: 0-4.8hr Fast millisecond pulsars ( 5 ms) Eclipse Egress Pulsar in the main eclipse ~50% of the orbit at 92cm Black Widows Redbacks Art (See J. Hessels talk) Very low companion mass (~0.02 M )? Low companion mass (~0.2 M ) Some show state transitions MSP LMXB (see A. Archibald s talk)

5 Origin and Fate of Spiders 1000 PSR-WD Land (Tauris & Savonije 1999) Orbital Period (Hours) Black Widow County Redback Realm Companion Mass (M ) 1 (see e.g. Istrate et al. 2014) (More in T. Tauris talk)

6 Origin and Fate of Spiders Redbacks unlikely to turn black widows because of evolution timescale. (Benvenuto 2015 vs Chen et al. 2013). Irradiation (from pulsar spin 1000down) required to sweep the PSR-WD Land companion of normal evolution track. (Tauris & Savonije 1999) (Black widow) companions are essentially semi-degenerate helium stars with small hydrogen 100 envelope. Orbital Period (Hours) Black Widow County 10 Redback Realm Companion Mass (M ) 1 (see e.g. Istrate et al. 2014) (More in T. Tauris talk)

7 How to Measure Masses Pulsar radio timing 5 Keplerian parameters Unknown masses and orbital inclination Optical follow-up of the companion Light curves orbital inclination Spectroscopy mass ratio (from projected velocity)

8 Difficulty #1: Light Curve Modelling Irradiated model works well to first order but Short timescale variability Spotty surface Asymmetric light curve Flickering Difficult to reconcile max/min Hinders orbital inclination measurement PSR J Romani et al. (2012) (see also Romani al. 2015)

9 Difficulty #1: Light Curve Modelling Irradiated model works well to first order but Short timescale variability Spotty surface Asymmetric light curve Flux variability but no/little colour change (difficult to reconcile with eclipses) Hinders orbital inclination measurement PSR J Tang et al. (2014)

10 Difficulty #1: Light Curve Modelling Irradiated model works well to first order but Short timescale variability Spotty surface Asymmetric light curve Asymmetric light curve Hinders orbital inclination measurement Breton et al. (in prep)

11 Difficulty #2: Spectroscopic Modelling The projected companion velocity doesn t track the centre of mass Solution: use ICARUS to model spectrum directly Spectral features departing from LTE Where is the centre of light? Hinders mass ratio measurement van Kerkwijk et al. (2011)

12 Difficulty #2: Spectroscopic Modelling The projected companion velocity doesn t track the centre of mass Solution: use ICARUS to model spectrum directly Spectral features departing from LTE Hinders mass ratio measurement Emission cores van Kerkwijk et al. (2011)

13 The Pulsar Mass Landscape PSR-NS PSR-WD Redbacks Redbacks PSR-NS tend to be less massive (simply evolution ) Tantalising evidence for black widows (and redbacks ) to be more massive Black widows Black widows

14 Future Prospects: How Light/Heavy? SKA should multiply the number of known binary pulsars by ~100 Catching light/heavy pulsars PSR-NS Statistical analysis of the mass distribution PSR-WD Redbacks Black widows Tauris et al. (2015)

15 Future Prospects: How Light/Heavy? SKA should multiply the number of known binary pulsars by ~100 Catching light/heavy pulsars PSR-NS Statistical analysis of the mass distribution PSR-WD Redbacks Black widows Tauris et al. (2015)

16 Conclusions & Open Questions 3(4) transitioning LMXB-pulsars systems so far All are redback-type Can black widows experience state transition? What does trigger the state transition? Is the radio pulsar still `on but screened, or has it turned `off What is happening in the accretion state? Is the radio pulsar still `on but screened, or has it turned `off Is the neutron star accreting? Is a jet being launched?