
b833fcd09b217401fe0b3d0778efda21.ppt
- Количество слайдов: 55
Magnetars Sandro Mereghetti INAF, IASF-Milano 44 th Rencontres de Moriond La Thuile – February 1 -8, 2009
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 ? 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 = 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 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: 1. 5 ms – 5 s tw se go ate oc t fit no the in • Accreting X-raydo s binaries energy Poweredetar n by gravitational ag M several hundreds in High Mass and Low Mass X-ray binaries many are transients typical rotation periods 0. 1 -1000 s S. Mereghetti - La Thuile - Feb. 2009 s! rie
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 – 1041 erg/s Super Eddington for a NS spectra at E>10 ke. V well fit by thermal brem. with k. T~30 ke. V S. Mereghetti - La Thuile - Feb. 2009
Location and discovery date of the 5 SGRs 1979 SGR 1900+14 1979 SGR 1806 -20 1998 SGR 1627 -41 2008 SGR 0501+45 NEW 1979 SGR 0526 -66 S. Mereghetti - La Thuile - Feb. 2009
Besides the bursts, SGRs have “persistent” X-ray emission Lx ~ 1035 – 1036 erg/s [extends up to ~ 200 ke. V] 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 S. Mereghetti - La Thuile - Feb. 2009
… 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 1900+14 L peak > 8 1044 erg/s ETOT > 3 1044 erg 2004 December 27 – SGR 1806 -20 L peak ~ 2 -5 1047 erg/s ETOT ~ 2 -5 1046 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, Ap. J 442, L 17 van Paradijs, Taam & van den Heuvel 1995, A&A 299, L 41 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 10 -11 s/s • Lx ˜ 1034 - 1036 erg s-1 >> Rotational Energy Loss • soft X-ray spectrum (k. T~0. 5 ke. V) + hard tail up to 200 ke. V • 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
1 E 2259+586, Kaspi et al. 2003, Ap. J 588, L 93 1 E 1048 -59 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, Ap. J 392, L 9 Thompson & Duncan 1995, MNRAS 275, 255 Thompson et al. 2000, Ap. J 543, 340 Thompson, Lyutikov and Kulkarni 2002, Ap. J 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 1627 -41 reactivation – A new Giant Flare ? S. Mereghetti - La Thuile - Feb. 2009
SGR – GRB connection: it is not a recent idea…. Mazets et al 1982, Ap&SS 84, 173 “Pre-BATSE era” S. Mereghetti - La Thuile - Feb. 2009
1979 March 5 - SGR 0526 -66 L peak ~4 1044 erg/s 1998 August 27 - SGR 1900+14 L peak > 8 1044 erg/s 2004 December 27 – SGR 1806 -20 L peak ~ 2 -5 1047 erg/s S. Mereghetti - La Thuile - Feb. 2009
Initial pulse saturated the instrument Mereghetti et al. 2005, Ap. J 624, L 105 2. 8 light seconds SGR 1806 -20 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 2004 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 1806 -20 Corbel & Eikenberry 2004 ~ 15 kpc (based on associations with other objects) S. Mereghetti - La Thuile - Feb. 2009
How many short GRBs are GF ? but large uncertainty on rate of GF: Nakar et al. 2005 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 1627 -41: reactivation – AXP 1547 -48: a new Giant Flare ? S. Mereghetti - La Thuile - Feb. 2009 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….
SGR 1627 -41 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) 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 1627 -41: New outburst in May 2008 Esposito et al. 2008 a, 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, L 34) S. Mereghetti - La Thuile - Feb. 2009
XMM Target of Opportunity performed as soon as visibility constraints allowed it (Esposito et al. 2009, Ap. J 690, Discovery of the long-sought pulsations. . . … and diffuse soft X-ray emission from SNR P = 2. 6 s S. Mereghetti - La Thuile - Feb. 2009 L 105)
AXP 1 E 1547 -5408 S. Mereghetti - La Thuile - Feb. 2009
1 E 1547 -5408 X-rays - Chandra (Gelfand & Gaensler 2007) RADIO SNR G 327. 24 -0. 13 NIR S. Mereghetti - La Thuile - Feb. 2009
1 E 1547 -5408 Halpern et al 2007) Pulsations and spindown [discovered in radio] confirm that 1 E 1547 is an AXP (Camilo et al 2007) S. Mereghetti - La Thuile - Feb. 2009
on Jan 22 many bursts were detected from 1 E 1547 -5408 by ~all satellites Swift - Fermi - Gronwall et al. GCN 8833 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
1 E 1547 -5408 - “SGR-like” bursts on Jan 22 INTEGRAL SPI-ACS E>80 ke. V S. Mereghetti - La Thuile - Feb. 2009
1 E 1547 -5408 - a new Giant Flare ? ? Mereghetti et al. GCN 8841 INTEGRAL SPI-ACS E>80 ke. V S. Mereghetti - La Thuile - Feb. 2009
1 E 1547 -5408 - Swift/XRT follow-up RY A !!! IN M ER UP PR - LI E S S. Mereghetti - La Thuile - Feb. 2009 2 -10 ke. V
Expanding X-ray rings Tiengo, SM, et al. GCN 8848 S. Mereghetti - La Thuile - Feb. 2009
X-ray halos from interstellar dust scattering s OBSERVER DUST D = x Ds S. Mereghetti - La Thuile - Feb. 2009 X-RAY SOURCE Ds
S. Mereghetti - La Thuile - Feb. 2009
Earth ionosphere disturbance caused by 1 E 1547 flare Chackrabarti et al. GCN 8881 S. Mereghetti - La Thuile - Feb. 2009
Summary of results • SGR 1627 -41 – discovery of P=2. 6 s (2 nd 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 (P=2. 1 s) might be a Giant Flare (1 st from an AXP) – Expanding dust scatterings 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
S. Mereghetti - La Thuile - Feb. 2009
EXTRA SLIDES S. Mereghetti - La Thuile - Feb. 2009
3 Giant Flares from SGRs Energy in initial spike Energy in pulsating tail 1979 March 5 SGR 0526 -66 1. 6 1044 erg 4 1044 erg 1998 August 27 SGR 1900+14 > 7 1043 erg 5 1043 erg 2004 Dec. 27 SGR 1806 -20 2 1046 erg 1044 erg Despite the x 100 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/0608364 S. Mereghetti - La Thuile - Feb. 2009
X-RAY FLUX PHOTON INDEX PERIOD SGR 1806 -20 S. Mereghetti -(years)- Feb. 2009 TIME La Thuile
Magnetar formation (a rare event…? ) Standard Scenario - Duncan & Thompson 1992, Ap. J 392, L 9 Requires a “proto-NS” spinning very rapidly 0. 6 -3 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/B 215 yrs 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- La Thuile - Feb. 2009 SNRs are at the center) S. Mereghetti the AXPs with
Proper motion of AXP XTE J 1810 measured with VLBA Helfand et al 2007, Ap. J – astro-ph/0703336 13. 5 +/- 1 mas / yr D ~ 3. 5 kpc VT ~ 200 km/s S. Mereghetti - La Thuile - Feb. 2009
Rotational energy ½ I Ω 2 = 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 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, L 14 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) 1806 -20 cluster age <4. 5 Myr progenitor >50 Msun 1900+14 <10 Myr >20 Msun • HI shell around AXP 1 E 1048: (Gaensler et al. 2005) ISM cavity due to wind of 30 -40 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 ke. V) Provides: • 50 ms light curve • No direction information • No energy information S. Mereghetti - La Thuile - Feb. 2009