Observational Properties of Isolated Neutron Stars. XDINSs and MAGNETARSs Silvia Zane, MSSL, UCL S. Mereghetti, R. Turolla, F. Haberl, and on behalf of a large team Compstar – Istanbul , 24-29 April 2016 o Introduction on Galactic Isolated Neutron Stars: the zoo o XDINSs properties o SGRs/AXPs as “magnetars”, the most extreme compact objects o Perspective for magnetars future missions/ astroseismology /polarimetry ? Neutron Stars are extreme objects.. NSs have a complex structure, with different particle species and states of matter in different density regimes. Outer parts: an elastic crust of neutron rich atomic nuclei, permeated by superfluid neutrons. Outer core: here protons form a superconducting fluid which co-exists with superfluid neutrons and a relativistic electron gas. The deep core of the star likely contains exotic components as hyperons and deconfined quarks. Matter reaches supra-nuclear densities, not reproducible in a terrestrial lab! Unique window to study QCD! Magnetic field tree 0.6 G – The Earth magnetic field measured at the North pole 100 G – A common hand-held magnet like those used to stick papers on a refrigerator’s door 107 G – The strongest man-made field ever achieved, made using focused explosive charges, lasting only 4-8 s 1012 G – Typical neutron star dipolar magnetic fields 1014 -1015 G - Magnetars fields Unique window to study the physics of plasma embedded in very high magnetic and gravitational fields Radiative Transfer in Ultra-Strong B-Fields 9 1) B B0 2.35 10 G: we enter the strongly-magnetized regime • Ec > atomic orbit of electrons Increasing B • Atomic structure distorted, medium anisotropic • Radiation propagates as 2 NORMAL MODES, the ordinary and the extraordinary one. 13 2) B BQED 4.41 10 G : we enter the quantizing regime 2 • Ec > mec (electron rest mass) • Exotic quantum effects Ex: photon splitting and vacuum polarization. - + Photons are temporarily converted e e into e - - e+ pairs • change in the refractive index, • Induced linear polarization, • Single photon pair production, etc.. How do we measure neutron stars’ magnetic fields? æ 2 6 ö ˙ 8p Rns 2 2 PP = ç ÷ B0 sin a è 3c 3I ø Isolated neutron stars: P-Pdot diagram Harding (2013) æ 2 6 ö ˙ 8p Rns 2 2 PP = ç ÷ B0 sin a è 3c 3I ø First seen neutron stars… • OPTICAL 1942: Crab pulsar The “south, preceding star” V≈16 at the center of the Crab Nebula (Baade 1942, Minkowsi 1942) First seen neutron stars… • OPTICAL 1942: Crab pulsar • X-RAYS 1962: Sco X-1 (Giacconi+ 1962) 1964: Tau X-1 (Bowyer+ 1964) 1967 June: Crab PSR at > 20 keV (Fishman+ 1969) The INS Zoo For about 25 years radio pulsars have been the most common manifestation of INSs Starting from the early ‘90s, other classesMagnetism of INSs were discovered with properties much at variance with those of PSRs (e.g. Kaspi 2010, Harding 2013) Magnetars Thermally emitting INSs (SGRs/AXPs) (XDINSs) Residual heat Residual Radiopulsars (PSRs) Central Compact Objects Rotating Radio Transients (CCOs) (RRaTs) Radio Pulsars (including HBPSRs) • More than 2000 discovered in the radio, ~ 100 in the X-rays • Bulk of the INSs population (most likely birth parameters, lifetime,…) 8 14 • Wide range of P ( 1ms-10 s) and Bp ( 10 -10 G) • X-ray emission • Thermal (~ 0.1 keV), from » hot spots (MSPs, relatively old PSRs) » the entire cooling surface (relatively young PSRs) • Non-thermal, from the magnetosphere • High-B PSRs are “normal” RPPs with a field in the magnetar range 13 (~ 20 with Bp > 5x10 G) but no detected magnetar-like activity Rotating Radio Transients (RRaTs) • About 80 known, “normal” radio pulsars with an exceedingly high nulling fraction (> 99%, Burke-Spolaor 2013), i.e. they emit sporadic, single radio pulses (McLaughlin et al. 2006) • P ~ 0.5-7 s, B ~ 1012-1014 G, τ ~ 0.1-3 Myr • PSR J1819-1458 (P = 4.3 s, B = 5x1013 G) detected in X-rays (McLaughlin et al. 2007, Miller et al. 2013) – Thermal spectrum (T ~ 140 eV, RBB ~ 8 km) – One (two ?) absorption feature @ ~ 1 keV – LX > Ė (?) – Bright PWN (Rea et al. 2009) Central Compact Objects (CCOs) • INS X-ray sources at the centre of SNRs, 8 found 4 • Young (SNR age τSNR < 10 yr) • Radio-silent, no counterpart at other wavelengths • Steady, thermal spectrum, quite large pulsed fraction, absorption lines in some sources • P and Ṗ measured (or constrained) in 3 sources (Pup A, Kes 79, 1E 1207; Gotthelf 2010, Halpern & Gotthelf 2010, 2011) • P ~ 0.1 -0.4 s • B 3-10x1010 G, the “anti-magnetars” • LX > Ė, τ >> τSNR Thermally-emitting INSs (XDINSs) • A legacy of ROSAT: the discovery of 7 radio quiet NSs (hence the nickname “Magnificent Seven”, or M7) Haberl et al. (1997) PSPC cts/s HR1 HR2 Name 0.15 ± 0.01 -0.96 ± 0.03 -0.45 ± 0.73 RX J0420.0-5022 0.23 ± 0.03 -0.06 ± 0.12 -0.60 ± 0.17 RBS1774 = 1RXS J214303.7+065419 0.29 ± 0.02 -0.20 ± 0.08 -0.51 ± 0.11 RBS1223 = 1RXS J130848.6+212708 0.38 ± 0.03 -0.74 ± 0.02 -0.66 ± 0.08 RX J0806.4-4123 0.78 ± 0.02 -0.67 ± 0.02 -0.68 ± 0.04 RBS1556 = RX J1605.3+3249 1.82 ± 0.02 -0.82 ± 0.01 -0.77 ± 0.03 RX J0720.4-3125 3.08 ± 0.02 -0.96 ± 0.01 -0.94 ± 0.02 RX J1856.5-3754 Soft X-ray spectrum + faint in optical Thermally-emitting INSs (XDINSs) • Soft X-ray sources, thermal spectrum, T ~ 50-100 eV, RBB ~ 5-10 km • Faint optical counterparts (mv > 25) • Close-by, D 150-500 pc • Slow rotators, P ~ 3-11 s, Ṗ 10-13 s/s 13 – Bp ~ 1.5-3.5x10 G, τ ~ a few Myr, τkin ~ 5-10 times shorter • Broad absorption features @ 300-700 eV – Proton cyclotron/Atomic transitions ? (Turolla 2009, Kaplan & Van Kerkwijk 2011) • Steady, long-term spectral changes in RX J0720 – Precession (Haberl et al 2006) ? Glitch (Van Kerkwijk et al. 2007, Hohle et al. 2012) ? • Radio-silent – Intrinsically radio-quiet ? Misaligned PSRs ? (Kondratiev et al. 2009) Thermal X-ray spectrum Haberl et al. (1997) Walter et al. (1996) Blackbody-like X-ray spectra without non-thermal component! XMM EPIC Best candidates for „genuine“ cooling INSs with nearly undisturbed emission from stellar surface - LETGS pn a Chandr Photon Energy (keV) RX J1856: Spectrum constant over time scales of years Haberl (2006) RX J1856: No narrow absorption features ! Burwitz et al. (2003,2004) Proper motions, distances and velocities RX J1856.5-3754 HST Bowshock Nebula VLT Kerkwijk & Kulkarni (2001) B = 25.2 Proper motion = 330 mas y–1 Parallax 8.16 +0.9/-0.8 mas (1σ) Distance = 123 +11/–15 pc Tangential space velocity = 254 km s–1 Kinematic age from back tracing to possible birth place ≈ 5·105 y Walter et al. 2010 see also Walter 2001, Kaplan et al. (2002), Walter & Lattimer 2002, van Kerkwijk & Kaplan (2007) The inhomogenous Interstellar Medium Henbest & Couper 1994 Lallement et al. 2003 (NaI D-line) z=0 pc Breitschwerdt et al. 2005 ~1700 pc Ophiuchus Taurus dark clouds clouds Pleiades bubble Loop I Lupus Tunnel Tunnel to GSH 238+00 S.Coalsack Lupus ~1300 pc clouds Galactic center Chameleon Within one kpc The close Galactic center around the sun solar neighbourhood Distance estimates from X-ray absorption N(H) [1020cm-2] Distance [pc] RX J1856.5-3754 0.7 (0L) 120–140 RX J0420.0-5022 1.6 (1L) 320–350 RX J0720.4-3125 1.2 (1L) 230–280 RX J0806.4-4123 1.0 (1L) 230–260 RBS 1223 4.3 (1L) >400 RX J1605.3+3249 2.0 (3L) 320–400 Posselt et al. 2007, Ap&SS 308, 171 RBS 1774 2.4 (1L) 380–440 Proper motions, distances and velocities ---------------------------------------------------------------------- Object μ distance vT mas y-1 pc km s-1 ---------------------------------------------------------------------- RX J0420.0–5022 <1232 (300–370)1 <200 RX J0720.4–3125 108±1 360 +172/-88 184 280 +210/-85 1434 RX J0806.4–4123 <862 (210–275)1 <96 RX J1308.8+2127 220±252 (400-800)1 417-835 RX J1605.3+3249 155±3 (300–415)1 286 RX J1856.5–3754 331±2 123 +11/-153 193 RX J2143.0+0654 (365–455)1 ---------------------------------------------------------------------- 1constraints from absorption Radio Pulsars 2X-ray measurements (Chandra) Motch et al. 2009 (A&A 497, 423) 3from Walter et al. 2010 4from Eissenbeiß 2011 (PhD thesis) High transverse speeds: No significant heating due to accretion from ISM !! X-ray pulsations 8.39 s 11% variable 11.37 s 6% 10.31 s 18% 3.45 s 13% Non-uniform temperature distribution on neutron star surface? Timing and Magnetic fields 19 1/2 Magnetic dipole braking → Bdip = 3.2·10 (P ·dP/dt) τchar = P/2(dP/dt) Object P dP/dt τchar Bdip Ref. Kinematic [s] [10–13 ss–1] [Myr] [1013 G] Age [Myr] RX J0420.0–5022 3.45 0.28(3) 2.0 1.0 1 RX J0720.4–3125 8.39 0.698(2) 1.9 2.4 2 0.85 RX J0806.4–4123 11.37 0.55(30) 3.3 2.5 3 1RXS J1308.8+2127 10.31 1.120(3) 1.5 3.4 4 RX J1605.3+3249 3.39 RX J1856.5–3754 7.06 0.297(7) 3.8 1.5 5 0.46 1RXS J2143.0+0654 9.43 0.4(2) 3.7 2.0 6 1Kaplan & van Kerkwijk 2011, ApJ 740, L30 2Kaplan & van Kerkwijk 2005a, ApJ 628, L45; van Kerkwijk et al. 2007, ApJ 659, L149 3 Kaplan & van Kerkwijk 2009b, ApJ 705, 798 4 Kaplan & van Kerkwijk 2005b, ApJ 635, L65 5 van Kerkwijk & Kaplan 2008, ApJ 673, L163 6 Kaplan & van Kerkwijk 2009a, ApJ 692, L62 XMM-Newton observations of the M7: absorption features XMM - RBS 1223 Ne EW = 150 eV w Pulse phase ton variations EP Haberl et al.