Magnetars in Binaries

Wei Wang

National Astronomical Observatories, China

High Throughput X-ray Astronomy in the eXTP Era conference

Rome, Feb 6-8 2017

Contents

• Magnetar family: isolated magentars (AXP & SGR); accreting magnetars in binaries

• Superslow pulsation X-ray pulsars

• Super-luminous X-ray pulsars: extragalactic magnetars

• Prospects for eXTP

Pulsar FamilyAnomalous X-ray pulsars(AXPs) & Soft gamma

repeaters (SGRs)

Millisecond pulsars

Radio young pulsars

Observed characteristics of AXPs and SGRs

• Pspin = 2 – 12 sec

• period derivatives: 10-14 – 10-10 s/s

• Dipole magnetic field: 1013 – 1015 G

• They have a persistent X-ray luminosity (1033-1035 erg/s) higher than their spin-down power – different from other pulsars!

• X-ray Bursts/flares are detected:

luminosity > 1037 erg/s

giant bursts Lx > 1042 erg/s

• No companion

• Magnetic field provides energy

• Isolated magnetars !

Pulsar populations

single binary

MSPs

Young pulsars

magnetars

LMXBs

HMXBsAccreting magnetars

？

Magnetars in binaries:accreting magnetars

• Superslow pulsation X-ray pulsars (Pspin>1000 s)

• Super-luminous X-ray pulsars :

extragalactic magnetars

• Neutron stars in high-mass X-ray binaries:

Be X-ray transients

(main-sequence companion star)

Supergiant binaries

(supergiant companion)

Corbet diagram

Pspin ≈0.1 - 1000 sec

The Pspin- Porbit diagram for Superslow X-ray pulsars in HMXBs

Recently some very slowly pulsation neutron stars are discovered in some binaries: Pspin>1000 s !

2S 0114+65 : 9700 s(Wang 2011)

4U 2206+54 : 5560 s

SXP 1062: 1062 sX-ray transient (Haberl et al. 2012)

(Wang 2009;Wang 2010;Wang 2013)

Spin-up trend of 2S 0114+65 from 1986 - 2008

6.2x10-7 s s-1

8.9x 10-7 s s-1

1.06x 10-6 s s-1

Spin-up trend seems acceleratingin last 20 years

Wang 2011

Fast spin period evolution of these pulsars:

Spin-down trend of 4U 2206+54 in last 20 years

Average Spin–down rate of 5x10-7 s s-1

(Wang 2012,2013; Reig et al. 2012)

Phase-shift method finds the spin-down behavior in haft year in 4U 2206+54 (2006 May -Dec): \dot P ~ (6± 2)x10-7 s s-1

Be X transient SXP 1062• Located in the Small Magellanic Cloud, associated with a SNR ( 2-4x104 yr)

• A large spin-down rate of 3x10-6 s/s during an outburst in 2010.

Haberl et al. 2012

From 2010-2012average rate:~ 10-7 s/s

Sturn et al. 2013

• 1E 1613.48−5055 in a young supernova remnant RCW 103 (Central Compact Object, CCO)

P = 6.67 hours

(single or binary?)

Other candidates of superslow pulsation pulsars

Magnetar activity in 1E 1613.48−5055

2016 June 22

Rea et al. 2016D’Ai et al. 2016

CCO in RCW 103 should be a magnetar!

Possible picture:Fall-back accretion after the supernova explosion (Tong, Wang, + 2016 ApJ)

Origin of spin period in X-ray pulsarsStandard evolution of neutron star binaries:a) ejector state: spin-down like radio pulsars;b) propeller state: spin-down by interaction between magnetosphere

and stellar winds;c) accretor state: Pspin reaches a critical value; switch on as X-ray

pulsars as observed.

(Pringle & Rees 1972 Ghosh & Lamb 1978)

The maximum spin period which can be reached in different observed conditions (magnetic field; accretion rate) : from several seconds up to near 1000 s.Then what channels produce the long spin period higher 1000 s ? It is a key question we need understand here.

Why special for superslow pulsation X-ray pulsars？

What is physical origin for long spin period?

• Li & van den Heuvel (1999): born as a magnetar with B>1014 G, allow for the neutron star to spin down slower than 1000 s in Myrs, and field decays to 1012 G at present (difficulty in time scales)

• Ikhsanov (2007): a phase “subsonic propeller” between the transition from known supersonic propeller state to accretorstate would allow for the long spin period :

Applying the above formulae to the case of 4U 2206+54/2S 0114+65, one derives the magnetic field of higher than ~ 1014 G!

Alternative approaches:• Spin-down rate in accreting state in standard model

(Lipunov 1992)

• Recently , a new theory of quasi-spherical accretion for X-ray pulsars is developed (Shakura et al. 2012):the magnetic field in wind-fed neutron star systems is given by

However, with both approaches we still find the derived magnetic field of

> 1014 G for 4U 2206+54; SXP 1062; 2S 0114+65

These super-slow pulsation pulsars then are defined as accreting magnetars.

2. Ultra-luminous X-ray sources (ULXs)

M31 X-rays

ULXs : X-ray luminosity > 1039 erg/s(1) intermediate mass BH 100-1000 M⊙;(2) 10 M⊙ BH and jet effect

A neutron star discovered in a ULX in M82

NuStar found a pulsation of 1.37 s in X-ray toward M82 X-2(Bachetti et al. 2014) .

Lx ~ 1040 erg/s; Orbital period: 2.5 day Neutron star mass 1.4 M⊙; Ledd~ 1038 erg/sRequiring an ultra-strong magnetic field >1014 G to produce high X-ray luminosity

• ULX NGC 7793 P13: (Furst et al. 2016)

P=0.42 s, Lx =1040 erg/sspin-up: \dot P= -2x10-11 s/s

• ULX-1 in NGC 5907: (Israel et al. 2016)

P=1.43 (2003), P=1.13 (2014) ( \dot P= -8x10-10 s/s )Lx=1041 erg/s (500*LEdd)

• Strong multipolar magnetic field (similar to magnetars) needed

• Many ULXs may harbor neutron stars – super-luminous X-ray pulsars – extragalactic accreting magnetars

Ultra-luminous X-ray bursts NGC 4636 d=14 Mpc (Irwin et al. 2016)

Lx ~ 1039 -1040 erg/s; durations ~ 1 hr; rise time <1 min

Origins: X-ray flares in magnetars (similar to observed flares in AXP and SGR)? - extragalactic magnetars?

Magnetar studies in binaries with eXTP

• Magnetars: AXP/SGR

powered by magnetic energy

• Accreting magnetar candidates powered by accretion not magnetic energy:

• Identifying a real magnetar in accreting systems requires –

searching for features of magnetar activities :

X-ray bursts

accreting neutron stars with high dipole magnetic field

Science goals

• Find more candidates with WFM

• Detect X-ray bursts in accretion magnetar systems with WFM

• Timing: spin evolution of accretion magnetars, QPOs

• Precise spectral measurements to find cyclotron absorption lines with LAD and SFA

• Better X-ray spectra and timing for ULX pulsars /bursts with LAD and SFA: weak sources (1-10x10-12

erg/cm2/s, 0.5-10keV)

– search for extragalactic magnetars

Thank you for your attention!