Neutron Star Astronomy

1. Neutron Star Astronomy Roberto Mignani University College London Mullard Space Science Laboratory Science with the new HST after SM4

2. The Role of HST in NS Astronomy ID mag Discovery Identification PSR B0531+21 16.6 Steward Cocke et al. (1969) Kitt Pk. Lyndt et al. (1969) PSR B0833-45 23.6 Blanco Lasker (1976) AAT Wallace et al. (1977) PSR B0540-69 22 CTIO Middleditch et al. (1984) NTT Caraveo et al. (1992) Geminga 25.5 CFHT Bignami et al. (1987) NTT Bignami et al. (1993) PSR B0656+14 25 NTT Caraveo et al. (1994) HST Mignani et al. (2000) PSR B0950+08 27.1 HST Pavlov et al. (1996) Subaru Zharikov et al. (2004) PSR B1929+10 25.6 HST Pavlov et al. (1996)HST Mignani et al. (2001) PSR B1055-52 24.9 HST Mignani et al. (1997) - RX J1856-3754 25.7 HST Walter et al. (1997)HST Walter et al. ( 2001) RX J0720-3125 26.7 Keck Kulkarni et al. (1998) VLT Motch et al. (2003) PSR B1509-58 26 VLT Wagner et al. (2000) Gemini Kaplan et al. (2006) RX J1308+2127 28.6 HST Kaplan et al. (2002) - RX J1605+3249 26.8 HST Kaplan et al. (2003) Subaru Motch et al. (2004) PSR J0437-4715 27.0 HST Kargaltzev et al. (2004)HST Kargaltzev et al. (2004) Pre-HST The breakthrough ! Post-HST PSR = “classical” radio pulsars RX = radio-quiet NSs, thermal X-ray emitters

3. The Impact of HST on NS Astronomy HST/STIS VLT/FORS1 B1929+10 • Higher sensitivity wrt pre 10-m class telescopes • Sharper spatial solution • UV + IR access • Timing • Polarimetry (poorly exploited)  All together, capabilities offered only by HST Mignani et al. (2001)

4. Perspectives after SM-4 • By the end of 2008, HST will be the longest-lived astronomical satellite • WFPC2  WFC3 (UV+VIS+IR) • COSTAR  COS (UV) • STISand ACS to be repaired • Spatial resolution: WFC3 (STIS+ACS) • UV: WFC3, COS (STIS+ACS) • IR: WFC3 WFC3 better in UV & IR wrt ACS & NICMOS WFC3 worse in VIS wrt ACS, better wrt WFPC2 • Timing: STIS • Polarimetry: ACS

5. Astrometry Crab Vela The Drilling Pulsars • HST proper motions (parallaxes) measured so far for 8 (4) neutron stars • 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 Mignani et al.(2000)

6. 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 ! • 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)? “Crazy Ivan” pattern PULSAR BLOB

7. The Near-UV • FOC&STIS detected UV emission from middle-aged neutron stars (Mignani et al. 1998; Pavlov et al. 1997; Kargaltsev et al. 2007) RJ tail of the cooling neutron star spectrum. • 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 @>106 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)

8. 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 Msun (Perna et al. 2000) • Disk not resolved by Spitzer (Mignani et al. 2008b) • Detection of debris disks has implications on NS formation and SN models • WFC3 can do a better job More about it in Andy Shearer’s talk Spitzer/IRAC Koptsevich et al. (2001)

9. 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

10. Polarimetry • Optical polarimetry with ACS is a powerful diagnostic to: • test neutron star magnetosphere models • constrain magnetic field geometry • constrain the neutron star rotation angle wrt the sky (iv) investigate pulsar/nebula magneto-dynamical interactions • Observations of PSR B0540-69 performed with WFPC2 (Mignani et al. 2008c) Mignani et al.(2007) polarisation angle (wrt NS axis) dipole angle α HST proper motion Pintr = 75% polarization Pintr = 13% X-ray axis

11. BVI 2.2m/WFI More Goals … BVI ACS/WFC • 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): old NSs, no longer radio-active • Magnetars: transient HE sources, with B ≈ 1014 G • Compact Central Objects: Not Crab-like ! Nature is unclear • Rotating RAdioTransients (RRATs): bursting (otherwise quiescent) radio PSRs • High-B radio PSRs: magnetars by definition not by reputation  UV-to-IR observations become more and more important !  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 Pulone et al.2008

12. 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