44th Rencontres de Moriond

44th Rencontres de Moriond
Magnetars Sandro Mereghetti INAF, IASF-Milano 44th Rencontres de Moriond La Thuile – February 1-8, 2009

S.Mereghetti - La Thuile - Feb.2009
Outline Introduction Soft Gamma-ray Repeaters Anomalous X-ray Pulsars Magnetars and GRBs Recent results SGR : the reactivation AXP : a new Giant Flare ? S.Mereghetti - La Thuile - Feb.2009

What is a “Magnetar” ? (Isolated) neutron stars where the main source of energy is the magnetic field most observed NS have B = G and are powered by accretion, rotational energy, residual internal heat In Magnetars B = G cfr. the strongest man-made magnetic fields: ~5 105 G (steady) ~107 G (for a few ms) S.Mereghetti - La Thuile - Feb.2009

Main manifestations of Neutron Stars:
(Radio) Pulsars - Powered by rotational energy >1700 pulsars observed in radio (+ several Pulsar Wind Nebulae) the youngest seen also at higher energies mostly isolated typical rotation periods: ms – 5 s Accreting X-ray binaries - Powered by gravitational energy several hundreds in High Mass and Low Mass X-ray binaries many are transients typical rotation periods s Magnetars do not fit in these two categories ! S.Mereghetti - La Thuile - Feb.2009

Two classes (?) of Magnetars:
Soft Gamma-ray Repeaters Discovered in 1979 as transient sources of hard X-ray bursts and giant flares (GF) 5 confirmed SGRs (3 emitted a GF ) Anomalous X-ray Pulsars Identified in the 90’s as a peculiar class of persistent X-ray pulsar with no signs of binary companions 9 confirmed AXPs (3 in SNRs, 3 transients) [ see Mereghetti 2008, Astr. & Astroph. Reviews 15, 225 ] S.Mereghetti - La Thuile - Feb.2009

SGRs Soft Gamma-ray Repeaters
S.Mereghetti - La Thuile - Feb.2009

SGRs emit short ( < 1 s ) repeating bursts of hard X / soft gamma- rays with soft spectrum (compared to GRBs) Hurley et al. 1999 Bursts Lx ~ 1040 – erg/s  Super Eddington for a NS spectra at E>10 keV well fit by thermal brem. with kT~30 keV S.Mereghetti - La Thuile - Feb.2009

Location and discovery date of the 5 SGRs 1979 SGR 1998 SGR 2008 SGR SGR SGR NEW S.Mereghetti - La Thuile - Feb.2009

Besides the bursts, SGRs have “persistent” X-ray emission Lx ~ 1035 – erg/s [extends up to ~ 200 keV] Pulsations – 8 sec  Rotating Neutron stars Long term spin down – s/s small long term variability in 3 SGRs large variations in 2 “transient” SGRs S.Mereghetti - La Thuile - Feb.2009

… and sometimes emit “Giant Flares” Only three observed 1979 March SGR L peak ~ erg/s ETOT ~ erg 1998 August SGR L peak > erg/s ETOT > erg 2004 December 27 – SGR L peak ~ erg/s ETOT ~ erg S.Mereghetti - La Thuile - Feb.2009

AXPs Anomalous X-ray Pulsars
Recognized in 1995 as a new class of pulsars with properties different from those of the other known classes of neutron stars Mereghetti & Stella 1995, ApJ 442, L17 van Paradijs, Taam & van den Heuvel 1995, A&A 299, L41 S.Mereghetti - La Thuile - Feb.2009

Main properties of the AXPs No evidence for companion stars (very faint IR ctps, no Doppler delays in pulses) Rotational period of a few seconds (5-12 s) Secular spin-down (0.05-4) x s/s Lx ˜ erg s-1 >> Rotational Energy Loss soft X-ray spectrum (kT~0.5 keV) + hard tail up to 200 keV 3 are in Supernova Remnants 3 are transients S.Mereghetti - La Thuile - Feb.2009

The AXPs have properties very similar to those of the “quiescent” counterparts of SGRs  Bursts from AXPs were expected …. S.Mereghetti - La Thuile - Feb.2009

1E , Kaspi et al. 2003, ApJ 588, L93 1E Gavriil et al. 2005, …and indeed short bursts from AXPs were finally discovered with RXTE S.Mereghetti - La Thuile - Feb.2009

Summary Both SGRs and AXPs are well explained by the Magnetar model Steady dissipation of magnetic field  surface heating  persistent X-ray emission NS crust fractures  short bursts Large scale magnetic dissipation  Giant flares Duncan & Thompson 1992, ApJ 392, L9 Thompson & Duncan 1995, MNRAS 275, 255 Thompson et al. 2000, ApJ 543, Thompson, Lyutikov and Kulkarni 2002, ApJ 574, 332. S.Mereghetti - La Thuile - Feb.2009

Outline Introduction Soft Gamma-ray Repeaters Anomalous X-ray Pulsars Magnetars and GRBs afterglows from Giant Flares SGRs and short GRBs newly born magnetars as GRBs central engine ……. Recent results SGR reactivation A new Giant Flare ? S.Mereghetti - La Thuile - Feb.2009

SGR – GRB connection: it is not a recent idea…. “Pre-BATSE era” Mazets et al 1982, Ap&SS 84, 173 This was before BATSE !! Class of short/hard bursts was already recognized – accounted to 10% of Venera GRB sample Galactic vs extragalactic origin of GRBs not solved yet - Long GRB believed as galactic NS (sudden accretion of plasma accumulated outside magnetosphere / comets / thermonuclear explosions etc…) Later reconsidered by Duncan (2001 , AIP Texas Symp.) and Eichler (2002 MNRAS) S.Mereghetti - La Thuile - Feb.2009

1979 March SGR L peak ~ erg/s 1998 August SGR L peak > erg/s 2004 December 27 – SGR L peak ~ erg/s S.Mereghetti - La Thuile - Feb.2009

Initial pulse saturated the instrument 2.8 light seconds Mereghetti et al. 2005, ApJ 624, L105 SGR Giant Flare 2004 Dec 2004 Initial pulse backscattered by the Moon S.Mereghetti - La Thuile - Feb.2009

A large fraction of the SHORT GRBs could be Giant Flares from SGRs in external galaxies Giant Flares with the luminosity of the Dec 27 event at few tens of Mpc would appear as short bursts if only the initial pulse is detected. S.Mereghetti - La Thuile - Feb.2009

Distance of SGR Corbel & Eikenberry 2004 ~ 15 kpc (based on associations with other objects) Distance of G (which is not a SNR, but a wind nebula powered by the LBV star) is well determined 15.1 [ ] kpc. d of SGR assumes that it is a member of the cluster of massive stars to which also the LBV belongs. S.Mereghetti - La Thuile - Feb.2009

How many short GRBs are GF ? but large uncertainty on rate of GF: Nakar et al. 2005 Nakar et al – rate di Hyper-Giant-Flares  from 10% to 100% of short GRBs could be GF S.Mereghetti - La Thuile - Feb.2009

Outline Introduction Magnetars and GRBs Recent results (…of our group) SGR : reactivation AXP : a new Giant Flare ? S.Mereghetti, A.Tiengo, P. Esposito, G.Vianello at IASF MILANO D. Gotz, G.L.Israel, N.Rea, R.Turolla, S.Zane, L.Stella, K. Hurley, & al…. S.Mereghetti - La Thuile - Feb.2009

SGR S.Mereghetti - La Thuile - Feb.2009

SGR 1627-41: the Transient SGR
Discovered in 1998 (Woods et al. 1999); active only a few weeks and quiescent since then Spin Period could not be found No identified optical/NIR counterparts (Wachter et al 2004) Long term decrease in X-ray luminosity interpreted as cooling after crust heating by the bursts (Kouveliotou et al. 2003) Giant Flare  radio VLA position  IR ctp nailed down (Subaru / VLT) S.Mereghetti - La Thuile - Feb.2009

SAX, ASCA and Chandra data spanning 4 years (Kouveliotou et al. 2003) Model of cooling after the deep crustal heating occurred during the active period (Lyubarsky, Eichler & Thompson 2002) S.Mereghetti - La Thuile - Feb.2009

SGR : New outburst in May 2008 Esposito et al. 2008a, MNRAS S.Mereghetti - La Thuile - Feb.2009

Comparison of X-ray flux decays after strong bursting episodes in different magnetars (Esposito et al. 2008, MNRAS, 390, L34) S.Mereghetti - La Thuile - Feb.2009

XMM Target of Opportunity performed as soon as visibility constraints allowed it (Esposito et al. 2009, ApJ 690, L105) Discovery of the long-sought pulsations... … and diffuse soft X-ray emission from SNR P = 2.6 s S.Mereghetti - La Thuile - Feb.2009

AXP 1E S.Mereghetti - La Thuile - Feb.2009

(Gelfand & Gaensler 2007) X-rays - Chandra RADIO SNR G NIR S.Mereghetti - La Thuile - Feb.2009

Halpern et al 2007) Pulsations and spin-down [discovered in radio] confirm that 1E1547 is an AXP (Camilo et al 2007) S.Mereghetti - La Thuile - Feb.2009

on Jan 22 many bursts were detected from 1E by ~all satellites Swift Gronwall et al. GCN 8833 Fermi Connaughton GCN 8835, von Kienlin & Connaughton GCN 8838, INTEGRAL - Savchenko et al. GCN 8837, Mereghetti et al. GCN 8841 Suzaku Terada et al. GCN 8845, Konus-WIND - Golenetskii et al. GCN 8851, RHESSI Bellm et al. GCN 8857 S.Mereghetti - La Thuile - Feb.2009

1E 1547-5408 - “SGR-like” bursts on Jan 22
INTEGRAL SPI-ACS E>80 keV S.Mereghetti - La Thuile - Feb.2009

1E a new Giant Flare ?? Mereghetti et al. GCN 8841 INTEGRAL SPI-ACS E>80 keV S.Mereghetti - La Thuile - Feb.2009

1E 1547-5408 - Swift/XRT follow-up
2-10 keV SUPER - PRELIMINARY !!! S.Mereghetti - La Thuile - Feb.2009

Expanding X-ray rings Tiengo, SM, et al. GCN 8848 S.Mereghetti - La Thuile - Feb.2009

X-ray halos from interstellar dust scattering
OBSERVER X-RAY SOURCE  DUST D = x Ds Ds S.Mereghetti - La Thuile - Feb.2009

Earth ionosphere disturbance caused by 1E1547 flare
Chackrabarti et al. GCN 8881 S.Mereghetti - La Thuile - Feb.2009

Summary of results SGR discovery of P=2.6 s (2nd fastest magnetar) X-ray emission shows that SNR is more extended than desumed from radio data  the SGR is at the center AXP strong burst with pulsed tail (P=2.1 s) might be a Giant Flare (1st from an AXP) Expanding dust scattering rings  properties of GF in X-ray (never observed before), distance S.Mereghetti - La Thuile - Feb.2009

CONCLUSIONS AXPs and SGRs  single class of objects (MAGNETARS) containing the highest magnetic fields observed in the Universe (~1015 G) Physics of High B fields Astrophysics of Neutron Stars and endpoints of massive stars MAGNETAR – GRBs connections: some of the Short GRBs are GF central engines of long GRBs “afterglows” in GFs Many new results in the last few months… cooperation from the sources + fast reaction of observations …and more to come Gravit. waves, UHE CR, neutrinos,… S.Mereghetti - La Thuile - Feb.2009

EXTRA SLIDES S.Mereghetti - La Thuile - Feb.2009

Energy in initial spike
3 Giant Flares from SGRs Energy in initial spike Energy in pulsating tail 1979 March 5 SGR erg erg 1998 August 27 SGR > erg erg 2004 Dec. 27 SGR erg 1044 erg Despite the x100 stronger initial spike of the 2004 GF, the energy in the tail is of the same order of the other SGRs !!  “magnetically trapped fireball” with similar B intensity S.Mereghetti - La Thuile - Feb.2009

Mereghetti, Esposito, Tiengo 2006, astro-ph/ S.Mereghetti - La Thuile - Feb.2009

SGR X-RAY FLUX PHOTON INDEX PERIOD TIME (years) S.Mereghetti - La Thuile - Feb.2009

Magnetar formation (a rare event…?)
Standard Scenario - Duncan & Thompson 1992, ApJ 392, L9 Requires a “proto-NS” spinning very rapidly ms Convection + differential rotations  efficient dynamo  can produce B~1015 G Dipole energy losses cause a rapid spin-down to P>10 s in 104/B215 yrs Rossby Number = Rotation Period / Convective overturn <~ 1  efficient dynamo DT92 predicted high recoil velocity (~1000 km/s) – several possible mechanisms Anisotropic mass loss due to gravitational instability (close to breakup rotation) Anisotropic neutrino emission Magnetized winds/jets DT92 suggested high speed SGR would escape galactic disk and populate halo and responsible for GRBs S.Mereghetti - La Thuile - Feb.2009

The “standard” formation scenario predicted high recoil velocities ~1000 km/s Seemed consistent with offset from SNR centers However the claimed associations of three SGRs with SNRs are no more considered reliable (and the AXPs with SNRs are at the center) S.Mereghetti - La Thuile - Feb.2009

Proper motion of AXP XTE J1810 measured with VLBA Helfand et al 2007, ApJ – astro-ph/ 13.5 +/- 1 mas / yr D ~ 3.5 kpc  VT ~ 200 km/s S.Mereghetti - La Thuile - Feb.2009

Rotational energy ½ I Ω2 = P-2(ms) erg Magnetically dominated, neutrino-driven outflow extracts rotational energy in a few seconds  implications for GRB models,  energetics of supernovae S.Mereghetti - La Thuile - Feb.2009

No evidence that the SNRs associated to Magnetars are more energetic than “standard” SNRs Vink & Kuiper 2006, MNRAS 370, L14 S.Mereghetti - La Thuile - Feb.2009

Alternative origin for high B field
“Fossil field” MNRAS 367, 1323 (2006) Magnetars could be the descendant of massive stars with high magnetic field similar to what is believed to happen for white dwarfs S.Mereghetti - La Thuile - Feb.2009

Observations supporting a Magnetars origin from very massive stars
2 (or 3?) SGRs possibly associated with massive star clusters (Corber & Eikenberry 2004, Vrba et al. 2000, Klose et al. 2004) cluster age <4.5 Myrprogenitor >50 Msun <10 Myr  >20 Msun HI shell around AXP 1E1048: (Gaensler et al. 2005) ISM cavity due to wind of Msun star AXP in Westerlund 1 (Muno et al. 2006) 4 Myr  >40 Msun  Magnetars compete with BH as remains of massive stars important mass loss in pre-SN or SN explosion? highly rotating cores ? S.Mereghetti - La Thuile - Feb.2009

INTEGRAL SPI Anti Coincidence Shield (ACS) (512 kg, 91 BGO blocks) The ACS is also used as an omni-directional GRB detector ( E > 80 keV) Provides: 50 ms light curve No direction information No energy information S.Mereghetti - La Thuile - Feb.2009

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