Magnetars

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Magnetars

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

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Outline

• Introduction
• Soft Gamma-ray Repeaters
• Anomalous X-ray Pulsars
• Magnetars and GRBs
• Recent results
• SGR 1627-41 the reactivation
• AXP 1547-48 a new Giant Flare ?

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What is a Magnetar ?

• (Isolated) neutron stars where the main source of
  energy is the magnetic field
• most observed NS have B 109 - 1012 G and
  are powered by accretion, rotational energy,
  residual internal heat
• In Magnetars B 1014 - 1015 G
• cfr. the strongest man-made magnetic fields5
  105 G (steady) 107 G (for a few ms)

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Main manifestations of Neutron Stars

• (Radio) Pulsars -
• Powered by rotational energy gt1700
  pulsars observed in radio ( several Pulsar Wind
  Nebulae)the youngest seen also at higher
  energiesmostly isolated typical rotation
  periods 1.5 ms 5 s
• Accreting X-ray binaries - Powered by
  gravitational energyseveral hundreds in High
  Mass and Low Mass X-ray binariesmany are
  transientstypical rotation periods 0.1-1000 s
  

Magnetars do not fit in these two categories !
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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 90s 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
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SGRsSoft Gamma-ray Repeaters
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SGRs emit short ( lt 1 s ) repeating bursts
of hard X / soft gamma- rays with soft spectrum
(compared to GRBs)
Bursts Lx 1040 1041 erg/s ? Super
Eddington for a NS
spectra at Egt10 keV well fit by thermal brem.
with kT30 keV
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Location and discovery date of the 5 SGRs
NEW
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Besides the bursts, SGRs have persistent
X-ray emission
Lx 1035 1036 erg/s extends up to
200 keV Pulsations 2.6 8 sec ? Rotating
Neutron stars Long term spin down 10-11
10-10 s/s small long term variability in 3
SGRs large variations in 2 transient
SGRs
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and sometimes emit Giant Flares
Only three observed
1979 March 5 - SGR 0526-66 L peak 4 1044
erg/s ETOT 5 1044 erg 1998 August 27 -
SGR 190014 L peak gt 8 1044 erg/s ETOT gt
3 1044 erg 2004 December 27 SGR 1806-20 L
peak 2-5 1047 erg/s ETOT 2-5 1046 erg
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AXPsAnomalous 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, AA 299,
L41
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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 10-11 s/s
• Lx 1034 - 1036 erg s-1 gtgt Rotational
  Energy Loss
• soft X-ray spectrum (kT0.5 keV) hard tail
  up to 200 keV
• 3 are in Supernova Remnants
• 3 are transients

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The AXPs have properties very similar to
those of the quiescent counterparts of SGRs
? Bursts from AXPs were expected .
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and indeed short bursts from AXPs were finally
discovered with RXTE
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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, 340 Thompson, Lyutikov
and Kulkarni 2002, ApJ 574, 332.
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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 1627-41 reactivation
• A new Giant Flare ?

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SGR GRB connection it is not a recent
idea.
Mazets et al 1982, ApSS 84, 173
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1979 March 5 - SGR 0526-66 L peak 4 1044
erg/s 1998 August 27 - SGR 190014 L peak
gt 8 1044 erg/s 2004 December 27 SGR
1806-20 L peak 2-5 1047 erg/s
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SGR 1806-20 Giant Flare 2004 Dec 2004
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A large fraction of the SHORT GRBs could be Giant
Flares from SGRs in external galaxies
Giant Flares with the luminosity of the 2004
Dec 27 event at few tens of Mpc would appear as
short bursts if only the initial pulse is
detected.
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Distance of SGR 1806-20
Corbel Eikenberry 2004
15 kpc (based on associations with other
objects)
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How many short GRBs are GF ?
but large uncertainty on rate of GF
? from 10 to 100 of short GRBs could be GF
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Outline

• Introduction
• Magnetars and GRBs
• Recent results (of our group)
• SGR 1627-41 reactivation
• AXP 1547-48 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.
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SGR 1627-41
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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)

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SAX, ASCA and Chandra data spanning 4 years
Model of cooling after the deep crustal heating
occurred during the active period (Lyubarsky,
Eichler Thompson 2002)
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Comparison of X-ray flux decays after
strong bursting episodes in different magnetars
(Esposito et al. 2008, MNRAS, 390, L34)
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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
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AXP 1E1547-5408
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1E 1547-5408 (Gelfand Gaensler 2007)
X-rays - Chandra
RADIO SNR G327.24-0.13
NIR
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1E 1547-5408
Pulsations and spin-down discovered in radio
confirm that 1E1547 is an AXP (Camilo et al
2007)
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on Jan 22 many bursts were detected from 1E
1547-5408 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
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1E 1547-5408 - SGR-like bursts on Jan 22
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1E 1547-5408 - a new Giant Flare ??
Mereghetti et al. GCN 8841
INTEGRAL SPI-ACS Egt80 keV
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1E 1547-5408 - Swift/XRT follow-up
2-10 keV
SUPER - PRELIMINARY !!!
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Expanding X-ray rings
Tiengo, SM, et al. GCN 8848
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X-ray halos from interstellar dust scattering
?s
OBSERVER
X-RAY SOURCE
?
DUST
D x Ds
Ds
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Earth ionosphere disturbance caused by 1E1547
flare
Chackrabarti et al. GCN 8881
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Summary of results

• SGR 1627-41
• discovery of P2.6 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 1547-58
• strong burst with pulsed tail (P2.1 s) might be
  a Giant Flare (1st from an AXP)
• Expanding dust scattering rings ? properties of
  GF in X-ray (never observed before), distance

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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,

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EXTRA SLIDES
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3 Giant Flares from SGRs
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
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Mereghetti, Esposito, Tiengo 2006,
astro-ph/0608364
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Magnetar formation(a rare event?)
Standard Scenario - Duncan Thompson 1992,
ApJ 392, L9

• Requires a proto-NS spinning very rapidly
  0.6-3 ms
• Convection differential rotations ? efficient
  dynamo ? can produce B1015 G
• Dipole energy losses cause a rapid spin-down
  to Pgt10 s in 104/B215 yrs

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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)
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Proper motion of AXP XTE J1810 measured with
VLBA
13.5 /- 1 mas / yr D 3.5 kpc ? VT 200
km/s
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• Rotational energy ½ I O2 3 1052 P-2(ms) erg
• Magnetically dominated, neutrino-driven outflow
  extracts rotational energy in a few seconds
• ? implications for GRB models,
• ? energetics of supernovae

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No evidence that the SNRs associated to Magnetars
are more energetic than standard SNRsVink
Kuiper 2006, MNRAS 370, L14
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Alternative origin for high B field
Fossil field
Magnetars could be the descendant of massive
stars with high magnetic field similar to what
is believed to happen for white dwarfs
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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)1806-20 cluster
  age lt4.5 Myr?progenitor gt50 Msun190014
  lt10 Myr ? gt20 Msun
• HI shell around AXP 1E1048 (Gaensler et al.
  2005) ISM cavity due to wind of 30-40 Msun
  star
• AXP in Westerlund 1 (Muno et al. 2006) 4 Myr ?
  gt40 Msun
• ? Magnetars compete with BH as remains of massive
  stars important mass loss in pre-SN or SN
  explosion?highly rotating cores ?

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INTEGRAL SPI
Anti Coincidence Shield (ACS) (512 kg, 91 BGO
blocks)

• The ACS is also used as an
• omni-directional GRB detector
• ( E gt 80 keV)
• Provides
• 50 ms light curve
• No direction information
• No energy information