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 XMM
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. (2003) I
C
- pn
RX J0720.4–3125 variable with pulse phase and over years Haberl et al. (2004), Hohle et al. (2012)
RX J1605: multiple lines Haberl et al. The origin of the absorption features
Proton cyclotron absorption line ? In the case of proton scattering harmonics should be greatly suppressed.
Atomic line transitions ? Hydrogen-like elements ?
Mixture ? van Kerkwijk & Kaplan 2007, Ap&SS 308, 191
In any case B ≈ 1013 – 1014 G Magnetic fields Unique opportunity to estimate B in two independent ways: • Magnetic dipole braking (P, dP/dt) • Proton cyclotron absorption → B = 1.6·1011 E(eV)/(1–2GM/c2R)1/2
B E B Object P dip cyc [eV] cyc Bcyc/Bdip [1013 G] [1013 G] [s] RX J0420.0–5022 3.45 1.0 ? RX J0720.4–3125 8.39 2.4 280 5.6 2.3 RX J0806.4–4123 11.37 2.5 430/306a) 8.6/6.1 2.4-3.4 1RXS J1308.8+2127 10.31 3.4 300/230a) 6.0/4.6 1.4-1.8 RX J1605.3+3249 3.39 450/400b) 9/8 RX J1856.5–3754 7.06 1.5 – – 1RXS J2143.0+0654 9.43 2.0 750 15 7.5
a) Spectral fit with single line / two lines b) With single line / three lines at 400 eV, 600 eV and 800 eV Magnetars: the most extreme NSs general properties
• Swift- COMPTE Two classes of sources: AXPs and XRTINTEGRA L SGRs (now unified?), ~20 known L • bright X-ray pulsars (in quiescence) Lx ~ 1033-1036 erg/s Fermi- LAT • strong soft and hard X-ray emission
• pulsed fractions ranging from ~2-80% (Abdo et al. 2010) • x/gamma-ray bursts and flares
• • rotating with periods of ~2-12s • period derivatives of ~10-13-10-11 s/s • magnetic fields of ~1014-1015 Gauss • glitches and timing noise (Israel et al. 2010) • faint infrared/optical emission (K~20; sometimes pulsed and transient) (see Woods & Thompson 2006, Mereghetti 2008, Rea & Esposito 2011 , Turolla SZ Watts 2015 for reviews) Why SGRs/AXPs may be ‘magnetars’?
1. Original suggestion driven by the extreme properties of SGRs bursts and flares (Duncan & Thomson ’92-’95) 2. Their X-ray luminosity is by far (~100) larger than their rotational energy resevoir . 3. No evidence for a companion star. Another energy source is needed to explain their emission! 2 6 4 2 2 2 2B R sin E m rot 3c3 3c3 LX Erot I Neutron star formation & Magnetars most observed NS have B = 109 - 1012 G and are powered by accretion, rotational energy, residual internal heat
In Magnetars: external field:13 B = 1014 - 1015 G B BQED 4.41 10 G : quantum effects important internal field: B > 1015 G
Those huge fields are believed to form either via alpha-dynamo mechanisms soon after birth or as fossil fields from a very magnetic progenitor
. Strong convection in a rapidly rotating (P ~ 1 ms) newborn neutron star generates a very strong magnetic field via dynamo action (Duncan & Thomson 1992; Thomson & Duncan 1995)
. Probably associated with massive progenitors, M 25 Msun (Lose et al, 2004; Eikenberry et al, 2005, Gaensler et al 2005)) SGR1900+14
SGR0526-66
SGR1806-20
Young stellar clusters: AXPs-SGRs nests ?
If SGR-cluster is confirmed:
1. Progenitor mass is >20Msun 2. Age < 105 yr 3. High metallicity SGRs/SNRs Associations (?) SGR 0526-66 / N49 SGR 1806-20/G10.0 0.3 SGR 1900+14/G42.8+0.6
(Kulkarni et al. 2003)
(Kaplan et al. 2002)
(Hurley et al. 1999) SGR 1627-41 /G337.0-0.1
(Woods et al. 1999) Magnetars’ outbursts
(updated from Rea & Esposito 2011) Magnetars: different types of X/-ray bursts
Short bursts • most common • they last ~0.1s • peak ~1041 ergs/s • soft -rays thermal spectra
Intermediate bursts • last 1-40 s • peak ~1041-1043 ergs/s • abrupt on-set • usually soft, thermal -ray spectra
Giant Flares • peak energy > 3x1044 ergs/s • output of high energy only exceeded by blazars and GRBs • <1 s initial peak (~2ms substructures) • rapid hard/soft spectral evolution • burst tail can last > 500s, with NS spin pulsations. The SGRs Giant Flares: 3 so far SGR 0526-66: 5 March 1979 SGR 1900+14: 27 August 1998
SGR 1806-20: 27 December 2004 The Earth responding to magnetar flares The Earth responding to magnetar flares
Indeed, during the first half of the decay phase of the flare a 7.5 s periodicity is observed in the magnetic field over a magnetically quiet period, near the South Pole at 400 km altitude.
This observation can be explained by a mechanism through which the oscillating flux of ionizing γ- rays could alter the ionospheric conductivity and hence cause oscillat- ing perturbations in the current- generated magnetic (Mandea & Balasis 2006, Geophysical Journal) field. NEWS? MAGNETARS VARIETY?? NUMBER? SGRs, AXPs: a change of perspective
“Magnetar activity” (bursts, outbursts, …) detected in the past only in high-B sources 13 (Bp > 5x10 G) : AXPs+SGRs () PSR J1846-0258, PSR J1622-4950 ()
Three “low-field” magnetars recently discovered (Rea et al. 2010, 2012, 2013) 13 – Bp ≤ 10 G, τ 1 -10 Myr SGR 0418+5729 and SGR1822-1606
• SGR 0418+5729: 2 bursts detected on 2009 June 05 with Fermi/GBM, spin period of 9.1 s with RXTE within days (van der Horst et al. 2010) • Ṗ ~ 5.14x10-15 s/s 12 Bp = 7 x10 G SGR 1822
(Rea, SZ et al. 2013) SGR 0418
• SGR1822-1606: outburst in July 2011 • Monitored with Swift, RXTE, Suzaku, XMM-Newton and Chandra • P = 8.44 s Ṗ = 8.3x10-14 s/s
13 Bp = 2.7x10 G (second weakest Magnetar-like activity detected after SGR 0418) in two RPPs (Gavriil et al. 2008, Levin et al. 2010) (Rea, SZ et al 2012) SGR 0418+5729 and SGR1822-1606 It is clear that the dipolar B value is not enough to explain the variety in phenomenology: why some “high B” pulsars do not display bursts, while some “low field” SGRs do? A Magnetar at Work
•
What really matters is High
the internal toroidal - field Bφ PSR B
• A large Bφ induces a rotation of the surface layers
• Deformation of the crust fractures SGR/AXP bursts/twist of the external field Calculation of magnetic stresses acting on the NS crust at different times (Perna & Pons 2011; Pons & Perna 2011) Max stress substained by the crust as in Chugunov B Horowitz 2010 Activity strongly enhanced when Btor,0 > Bp,0
16 Btor,0 = 2.5x10 G 14 Bp,0 = 2.5x10 G Pons & Perna (2011)
14 Can we have a large B Btor,0 = 8x10 G tor 14 Bp,0 = 1.6x10 G associated with a low dipolar Bp? “low-field” SGRs as Old Magnetars (Turolla, SZ et al. 2011, Rea, SZ et al 2012) Observed . Low dipole field (B < 7.5x1012 G) . Large age (> 1-20 Myr) . Weak bursting activity (only 2 faint bursts)
2D simulations of NS magneto-thermal evolution:
. P, Ṗ and Bp from magneto-rotational evolution consistent with observed values age ~ 0.5 Myr of SGR 1822 age ~ 1 Myr for SGR 0418 Btor 10-100 times larger than Bdip SGR0418+5729 Phase-energy image
67ks XMM observation in Aug 2009 (after the outburst of June 2009) X-raySIMILAR ABSORPTION LINES LINE INwith RXJ0720, strong energy Borghese et al 2015 VARIABILITY with phase, UNPRECEDENTED amongand neutron SGR stars1822, (including Rodriguez, accreting SZpulsars) et al, 2015 PROTON CYCLOTRON resonant scattering in a MAGNETAR LOOP Bsurf >2x1014 G (2x1014 G< B < 1015 G in the loop)
(Tiengo, SZ et al, Science, 2013) Inferences
SGR 0418+5729 (and few other recently added) is a low-B source (dipolar B!): more than 20% of known radio PSRs have a stronger SGR 1822 Bp
Their properties compatible SGR 0418 with aged magnetars ≈ 1 Myr old A continuum of magnetar- like activity across the P-Ṗ diagram Which are the broader consequences of these discoveries?
** SN explosions A large number of strong-B neutron stars call for a revision of a key ingredient of the NS formation model: an extreme internal B should then be a common place rather than an exception
** GW radiation from newly born magnetars The GW background radiation produced by the formation of highly magnetic neutron stars is probably underestimated given the recent results.
** Gamma-ray bursts If a large fraction of the formed neutron stars have a strong B-field, GRBs caused by the formation of such stars are way more frequent than predicted.
** Massive Stars If strong-B neutron stars are formed by the explosion of highly magnetic stars, there should be many more of such stars than predicted thus far NEXT STEPS, OPEN QUESTIONS, BREAD FOR THEORETICIENS, FUTURE PERSPECTIVES, … Too Many INSs Around ?
The different manifestations of INS may reflect – intrinsic differences in the way they are born (e.g. mass, initial spin period, magnetic field) – Different formation channels? – diverse interactions with the surrounding medium (SNR ejecta, fallback, …) – evolution (of B, P, temperature, …) – a mixture of the above -1 • Core-collapse supernova rate, βCCSN = 1.9±1.1 century
-1 -1 • βPSR ~ 1.4 century , βRRAT ~ 2.8 century , βmag ~ 0.3 -1 -1 -1 century , βCCO ~ 0.04 century , βXDINS ~ 2 century (Popov, Turolla & Possenti 2006; Keane & Kramer 2008)
-1 βTOT = βPSR + βRRAT + βmag + βCCO + βXDINS ~ 6.5 century > βCCSN
Evolutionary link among at least some of the INS classes Variety in unity, or the NSs Jigsaw
SGRs/AXPs XDINSs
RPPs CCOs
RRATs HBPSRs Getting to GUNS ?
Grand Unification (of) Neutron Stars !
• Present knowledege of SN explosion mechanism insufficient to predict initial NS parameters
• Use different approaches (population synthesis, cooling curves, P-Ṗ diagram) to confront (magneto- thermal) NS evolutionary models with observations
• Pinpoint key initial parameters and check possible evolutionary links among NS classes 1) Thermal emission
• Best observed, e.g., in middle-aged NS and XDINS (Potekhin 2011) • About 40 “coolers” (Vigano’+ 2014): 11 RPP 7 XDINS 4 CCOs 17-18 AXPs/SGRs
• Uncertainties / caveats: • Ages • Distances • Atmosphere composition and magnetization • Non-uniform sample
• No evidence for fast cooling, ….but data may not exclude it (Cas-A, Kostas, B. Posselt) Magneto-thermal evolution of INS
Aguilera+ 2008, Pons & Geppert 2007, Pons+ 2009,2013, Vigano’+2012, 2014, Gullon et al, 2015, Elfritz talk …..
Explain variety of INS (timing and radiative properties) by coupled evolution of T and B Variety of initial B, M and envelope composition Evolutionary links between different classes S.Mereghetti - NS2014 St.Petersburg 2) X-ray spectral lines in INS o A formidable diagnostic tool… (in principle! ) See, e.g., accreting NS, where lines are well established and interpreted as cyclotron resonance features from electrons in B≈1012-1013 G o Lines reported in different classes of isolated NS: (CCOs, XDINSs, AXPs/SGRs, RRAT, RPPs)
a variety of different and complex situations (sometimes unclear/controversial detections and results ) - no unique interpretation X-ray lines in INS • CCOs: – Harmonically-spaced absorption lines in 1E 1207
(Sanwal+2002, Mereghetti+2002, Bignami+2003, De Luca+ 2004, Mori+ 2005)
P=0.4 s, Pdot=2 x 10-17 s/s (Gotthelf+ 2013)
electron cyclotr. line in B≈1011 G
– time-variable phase-dependent feature in PSR J0821 (in Pup A) emiss. at 0.75 keV or abs. 0.45 keV ?
(Gotthelf & Halpern 2009, De Luca+2012, Gotthelf+ 2013) X-ray lines in INS • XDINS: – Most have broad absorption lines – Proton cyclotron lines or atomic transitions in B ≈1013 G – No lines in RX J1856
• Magnetars: 1E 1048 NuSTAR ( An+2014) – A few unconfirmed claims in phase-resolved spectra of persistent emission
– Transient features during (some) bursts (E ≈14 keV) Recently confirmed with NuSTAR – Strong phase-dependent line in SGR 0418 (“low Pdot magnetar”) X-ray lines in INS • RRAT PSR J1819 - absorption line at 1 keV (McLaughlin+ 2005, Rea+ 2009, Camero- Arranz+ 2013) PSR J1740+1000 (Kargaltsev+ 2012)
• Normal RPP:
– PSR J1740+1000 phase-dependent line at 0.5-07 keV (Kargaltsev+ 2012)
– Fermi pulsar PSR J0633+0632
– Double pulsar PSR J0737- 3039 – etc Caveat for broad lines in thermal spectra
• Vigano’+ 2014 Inhomogeneous surface temperature distributions can produce spectra which may mimic broad absorption lines XDIN RXJ 0806
BB + line non-uniform (removed) surface T ATHENA+ (ESA L2): - a view of the hot and energetic Universe - NSs line searches approved among the instrument requirements (WG Galactic observational science Bozzo, Schope) 3) X-ray variability in INS • Distinctive property of magnetars – bursts / flares – Transients / variable “persistent”
• Variability seen also in NS of other different classes, e.g.: – PSR J1846 (RPP) – RXJ 0720 (XDINS) – RCW 103
• Possibly all related to dynamic manifestations of magnetic fields
S.Mereghetti - NS2014 St.Petersburg BURSTS Rapid magnetic field reconfiguration is an integral part of the -ray bursts Slow magnetic evolution builds up stresses in the system, some of which are released catastrophically in bursts, which must either be driven by or result in rapid magnetic field reconfiguration. Precise trigger mechanism? Three main locations (and associated families of instabilities) Turolla, SZ, Watts 2015 for a review
1. The magnetic field evolves into an unstable configuration within the liquid core of the star which is then susceptible to a large-scale magnetohydrodynamical instability (but: superconductivity, crustal currents, high core field?) 2. The decay of the core field places magnetic stresses on the solid crust of the star . The crust can deform elastically to accommodate this up to a certain point, then ruptures catastrophically once its breaking strain is exceeded 3. The core and crust evolve smoothly, and that stress builds up instead in the magnetosphere. Stress release is then envisaged as taking place via a plasma instability involving spontaneous magnetic reconnection Giant Flare Seismology Sky & Telescope
High Frequency QPOs at ~ 92.5, 30 and 18 Hz, detected with RXTE 200 – 300 s after the flare (Israel et al 2005) Courtesy A Watts QPOs turn out to be a common feature of all 3 GFs
• Marginal detection of 20-25 ms period oscillations during the very first 0.2s of the 5th March 1979 event (Barat et al. 1983)
• QPOs in the SGR 1900+14 GF; ~ 84 Hz (rms 26%) lasting 1s and starting 1 min after the spike of the flare Also in this case they are spin-phase dependent
(Strohmayer & Watts 2005, 2006, Watts & Strohmayer 2006) QPOs as seismic oscillations • Most probably due to magneto-torsional seismic oscillations excited by a crack in the crust • Very similar to the oscillations excited by Earthquakes • Toroidal modes were detected for the first time in 1960 during the devastating Chilean earthquake; fundamental period of 43min.
Period of the fundamental (l=2, 2 0.87 0.13M1.4R10 n=0) toroidal oscillation for a P 0 33.6R10 ms (2 t ) 1 1/ 2 non-rotating, non-magnetic star: (1.71 0.71M1.4R10 )
Considering also the 1/ 2 1/ 2 2 magnetic fields, higher order 6 B P 0 P 0 1 oscillations can be very ( t ) ( t ) l 2 l(l 1) B roughly addressed as:
relation between M, R and B (McDermott et al. 1988, Duncan 1998, Thompson & Duncan 2001; Lattimer & Prakash 2001; Duncan 1998; Israel et al. 2005; Strohmayer & Watts 2005) NSs Asteroseismology
Courtesy of A Watts Stellar structure equations
Equation of state (EOS) Nucleonic
Strange cores Chiral EFT models
Quark stars Small Bursts Asteroseismology
• Oscillation searches are complicated by the ‘burst envelope’.
• Traditional method (Monte Carlo simulations of lightcurves) fails
Courtesy of A Watts Oscillations in burst storms • Stacking consecutive bursts in most active periods: significant oscillations (final p < 0.001) in frequency range (93-127 Hz) found in giant flares (Huppenkothen et al. 2014a)
• Similar signals in RXTE data of SGR 1806- 20/SGR 1900+14 bursts (Huppenkothen et al. 2014b).
Fermi GBM data of burst storm • Global modes excited from SGR J1550-5418, Jan. 2009 by burst storms? (Kaneko et al. 2010, van der Horst Excitation threshold? et al. 2012 ) Coupling to emission mechanism?/ Courtesy of A Watts • LOFT: Large Observatory For • eXTP: enhanced X-ray timing x-ray Timing (ESA) and polarimetry mission (CAS)
Large collimated area, 10 m2 3m2 area for timing, soft xray response, polarimetry
Also LOFT-P (10m2) proposed to NASA 4) X-ray polarimetry
From top to bottom: comparison of the pulse profile, polarization degree, polarization angle and photon spectrum for two models with: Δϕ=0.7 rad,β=0.4 (solid line) Δϕ=1.3 rad,β=0.3 (dotted line). The filled circles with error bars denote the simulated XIPE data obtained from model A. All quantities refer to the 2–6 keV energy range.
From Taverna, Muleri, Turolla, Soffitta, Fabiani, Nobili, 2013 QED in magnetars and NS
MAGNETOSPHERIC EMISSION: Light curve, degree and angle of polarization expected from a magnetar in the ‘twisted magnetosphere’ model ( = 1.3 rad, = 0:5, = 60 and = 30). Data points are generated assuming a 1 Ms eXTP observation and following the blue line, which represents the model including vacuum polarization (QED). Points are then fitted with models including (red line) or not (green line) QED; the latter is excluded with high confidence (2 = 0.90 QED ON, 2 = 17.62 QED OFF). See Taverna et al 2014 QED in magnetars and NS
Linear polarization for hydrogen atmospheres with Teff=106.5 K neutron stars and magnetic moment 30 degrees from the line of sight (Heyl et al 2005) XIPE, The X-ray Imaging Polarimetry Explorer
Selected by ESA as a candidate for a M4 CV mission Launch in 2026 Science Study Team:
Paolo Soffitta (PI, Italy) Ronaldo Bellazzini (Italy) Thierry Courvoisier (Switzerland) Rene' Goosmann (France) Giorgio Matt (Italy) Victor Reglero (Spain) Andrea Santangelo (Germany) Gianpiero Tagliaferri (Italy) Jacco Vink (Netherlands) Silvia Zane (UK) Andrea Santovincenzo (ESA) David Lumb (ESA) Jonan Larranaga (ESA) Ivo Ferreire (ESA) Tim Oosterbroek (ESA) Erik Kuulkers (ESA)
PLEASE JOIN US AT http://www.isdc.unige.ch/xipe/ and in Valencia next month Other polarimetry missions proposed worldwide
- eXTP (CAS, approval discussed ~2017?) - Prays (NASA SMEX) - IXPE (NASA SMEX)
01/2015: NASA has selected three proposals, SPHEREx, IXPE and PRAXyS, for the SMEX mission that is expected to be launched not earlier than 2020 ASTRO-H- HITOMI (LOST?):
launched in 2015 soft and hard X-ray telescopes + different detectors to provide wide band coverage Calorimeter: DE ≈ 5 eV in 0.3-10 keV band
NICER:
Neutron star Interior Composition ExploreR on ISS in 2017 Mission devoted to NS timing+spectroscopy
EROSITA .... Conclusions
INSs are intriguing objects, and unique laboratories to test our knowledge on the physics of matter under extreme gravitational and magnetic fields.
We finally understood that behind the powerful magnetar emission there is not just the magnetic strength measured at large scale, but there are other important parameters: i.e. field geometry and evolution.
Many normal pulsars might be hiding a magnetar inside, and may turn out to be active and flaring at any time, with all the due consequences.
X-ray magneto-thermal evolution, spectroscopy and lines, variability, seismology, polarimetry in INS may be the key to a self consistent GUNS and to QCD/QED understanding thanks! Simulation of the LAD capabilities: magnetar astroseismology
Courtesy of G.L. Israel