Neutron Star Astronomy

Roberto Mignani

University College London Mullard Space Science Laboratory

Science with the new HST after SM4

The Role of HST in NS Astronomy

ID mag Discovery

PSR B0531+21 16.6 Steward Cocke et al. (1969) PSR B0833-45 23.6 Blanco Lasker (1976)

Identification

Kitt Pk. Lyndt et al. (1969) AAT Wallace et al. (1977) PSR B0540-69 22 CTIO Geminga 25.5 CFHT Middleditch et al. (1984) Bignami et al. (1987) NTT Caraveo et al. (1992) NTT Bignami et al. (1993)

PSR B0656+14 25

NTT

PSR B0950+08 27.1 HST PSR B1929+10 25.6 HST PSR B1055-52 24.9 HST RX J1856-3754 25.7 HST

RX J0720-3125 26.7 Keck PSR B1509-58 26 VLT

RX J1308+2127 28.6 HST RX J1605+3249 26.8 HST PSR J0437-4715 27.0 HST

The breakthrough !

Caraveo et al. (1994)

Pavlov et al. (1996) Pavlov et al. (1996) Mignani et al. (1997) Walter et al. (1997)

Kulkarni et al. (1998) Wagner et al. (2000)

Kaplan et al. (2002) Kaplan et al. (2003) Kargaltzev et al. (2004)

PSR

= “classical” radio pulsars

HST Mignani et al. (2000)

Subaru Zharikov et al. (2004) -

HST Mignani et al. (2001) HST Walter et al. ( 2001)

VLT Motch et al. (2003) Gemini Kaplan et al. (2006) Subaru Motch et al. (2004)

HST Kargaltzev et al. (2004)

RX

= radio-quiet NSs, thermal X-ray emitters

The Impact of HST on NS Astronomy

• Higher sensitivity wrt pre 10-m class telescopes

HST/STIS

• Sharper spatial solution

VLT/FORS1 B1929+10

• UV + IR access • Timing • Polarimetry (poorly exploited)

Mignani et al. (2001)



All together, capabilities offered only by HST

Perspectives after SM-4

• By the end of 2008, HST will be the longest-lived astronomical satellite – WFPC2 – COSTAR   WFC3 (UV+VIS+IR) COS (UV) – STIS and ACS to be repaired • Spatial resolution: WFC3 (STIS+ACS) • UV: • IR: WFC3 better in UV & IR wrt ACS & NICMOS WFC3 worse in VIS wrt ACS, better wrt WFPC2 • Timing:

STIS

• Polarimetry: WFC3, COS (STIS+ACS) WFC3

ACS

Astrometry

• HST proper motions (parallaxes) measured so far for 8 (4) neutron stars

12.5

±0.4

PSR B0833-45 PSR B0656+14 Geminga PSR B1929+10 51.8

±1.1

43 ±2 3.4

±0.7

PM accuracy comparable to VLBI 171.0

±6 6 ±2 Only optical PM feasible 107.3

±1.4

The Drilling Pulsars

107.8

±1.2 2.8±0.9

Only optical PM feasible RX J0720-3125 RX J1605.3+3249 155 ±3 RX J1856-3754 333 ±1 6.2

±0.6

Mignani et al.(2000)

Only optical PM feasible Only optical PM feasible

• WFC3 (ACS) can enlarge the sample with a much better accuracy – Confirm NS identifications – Localization of NS birth place – NS velocity  ISM accretion or not. Important for RX neutron stars – Hints on SN dynamics and progenitor core collapse

Neutron Stars Nebulae

• WFC3 (ACS) can resolve the structure and variability of the Pulsar Wind Nebulae, as WFPC2 did for the Crab. Only chance for distant PWNe !

PULSAR “Crazy Ivan” pattern BLOB • WFPC2 also found evidence of optical variability also in the B0540-69 PWN (De Luca et al. 2007;Mignani et al. 2008a) • Genuine variability in the nebula ?

• Expanding optical jet from the pulsar (v=22000 km/s)?

The Near-UV

• FOC&STIS detected neutron star UV emission al. 1998; Pavlov et al. 1997; Kargaltsev et al. 2007) spectrum.

from middle-aged neutron stars (Mignani et  RJ tail of the cooling • • Fitting the thermal spectrum yields: - coupled with the distance, the surface thermal map - coupled with age, the neutron star cooling rate - NS conductivy, core composition, EOS UV COS (STIS,ACS) observations are critical to: - constrain cooling @>10 6 yrs (too cold for X-rays), where different models predict different slopes - investigate NS re-heating (Kargaltsev et al. 2004)

Optical (colder&larger) X-rays (hotter&smaller)

The Near-IR

• NICMOS discovered IR emission from NSs (Koptsevich et al. 2001), the first after the Crab • E.g., for B0656+14 the IR is a hint of a debris disk of ≈2 10 -4 M sun (Perna et al. 2000) • Disk not resolved by Spitzer (Mignani et al. 2008b)

More about it in Andy Shearer’s talk

• Detection of debris disks has implications on NS formation and SN models • WFC3 can do a better job

Koptsevich et al. (2001) Spitzer/IRAC

Timing

• Multi-λ timing allows to study the light curve λ -dependance • Important inputs on emission models from NS magnetosphere • STIS observations have detected for the first time UV pulsations from neutron stars (Kargaltsev et al. 2005;, Shibanov et al. 2006; Romani et al. 2005) • UV time-resolved spectroscopy allows to weight different emission processes

Polarimetry

• Optical polarimetry with ACS is a powerful diagnostic to: (i) test neutron star magnetosphere models (ii) constrain magnetic field geometry (iii) constrain the neutron star rotation angle wrt the sky (iv) investigate pulsar/nebula magneto-dynamical interactions Mignani et al.(2007)

dipole angle α polarisation angle (wrt NS axis) HST proper motion P intr = 75% polarization P intr = 13% X-ray axis

• Observations of PSR B0540-69 performed with WFPC2 (Mignani et al. 2008c)

More Goals …

• While keeping the course on “classical” PSRs, there are other challenges to face • Many more classes of radio-quiet NSs are now known • Isolated Cooling NS (ICONSs): • Magnetars: • Compact Central Objects: • Rotating RAdioTransients (RRATs): • High-B radio PSRs: old NSs, no longer radio-active transient HE sources, with B ≈ 10 14 G Not Crab-like ! Nature is unclear bursting (otherwise quiescent) radio PSRs magnetars by definition not by reputation    UV-to-IR observations become more and more important !

Pulone et al.2008

Critical to determine the NS nature (isolated, binary, isolated+disk) HST archaeo-astronomy to identify (via PM) NS parental clusters, study their properties, trace the origin of the NS diversity

Conclusions

• HST has played so far a fundamental role in NS astronomy • After SM4, HST can play a role as (or even more) fundamental – The WFC3 (with ACS) will be unique for astrometry and stellar population studies – WFC3+COS will allow to obtain NSs multi-λ SED, especially in the crucial UV and IR bands – The repaired ACS+STIS will offer timing+polarimetry, crucial for NS astronomy and so far little explored due to technical failures • HST has posed the questions, now it can find the answers