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SGRsSGRs andand AXPsAXPs: : MassiveMassive RotatingRotatingWhite White DwarfsDwarfs versus versus MagnetaresMagnetares

Manuel Manuel MalheiroMalheiro, Jorge , Jorge RuedaRueda, Remo , Remo RuffiniRuffiniICRA ICRA SapienzaSapienza UniversitUniversitáá didi Roma, Roma, ICRANetICRANet, ITA, ITA

http://arxiv.org/abs/1102.0653http://arxiv.org/abs/1102.0653

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.I – Recent Observations: SGR 0418+5729, Massive

and Highly Magnetized White Dwarf Pulsar.

VI – Conclusions.

III – SGRs and AXPs as fast rotating-poweredMagnetic White Dwarf Pulsars.

IV – Outbursts mechanism: change of rotationalenergy from normal glitches (spin up events).

V – Issues of Magnetar and White Dwarf Models.

II – Magnetar x White Dwarf Physical Scales.

I – Recent Observations: SGR 0418+5729, Massiveand Highly Magnetized White Dwarf Pulsars.

•• SGR 0418+5729 SGR 0418+5729 withwith PeriodPeriod P = 9.04 s P = 9.04 s withwith a a lowlow surfacesurfacemagneticmagnetic fieldfield B < 7.5 x 10B < 7.5 x 1012 12 G.G.

•• LargeLarge spin spin downdown: : anan upperupper limitlimit dP/dtdP/dt < 6.0 < 6.0 x10x10--1515s/ss/s•• OldOld star star amongamong SGRsSGRs: : characteristiccharacteristic age t~ 24 age t~ 24 MyrMyr•• LuminosityLuminosity LLxx = 6.2 x 10= 6.2 x 1031 31 erg/serg/s•• LLxx~ 200 ~ 200 dEdErotrot/dt/dt•• To To explainexplain thethe luminosityluminosity anan interior interior toroidaltoroidal magneticmagnetic fieldfield 100 100

times times largerlarger thanthan thethe surfacesurface magneticmagnetic fieldfield is is neededneeded..•• HighHigh TemperatureTemperature T = 0.67 KeV similar to T of T = 0.67 KeV similar to T of newnew SGRsSGRs. .

N. Era, P. N. Era, P. EspositoEsposito, R. , R. TurollaTurolla, , etet al. al. ScienceScience, 330, 994 (2010), 330, 994 (2010)

Massive and Highly Magnetized White Dwarf Pulsars.

•• Catalogue of more Catalogue of more thanthan 100 100 isolatedisolated massivemassive whitewhitedwarfsdwarfs andand 25% are 25% are magneticmagnetic (M. (M. NalezytyNalezyty andand J. J. MadejMadej2004) 2004)

•• four four mostmost massivemassive whitewhite dwarfsdwarfs M > 1.3 M > 1.3 MMsunsun are are magneticmagnetic withwith B ~ 10B ~ 106 6 --10109 9 GG

•• MagneticMagnetic whitewhite dwarfsdwarfs havehave higherhigher temperaturestemperatures T~10T~1055 K K •• AE AE AquariiAquarii : : HardHard XX--RayRay White White DwarfDwarf Pulsar Pulsar foundfound byby

SuzakuSuzaku (Y. (Y. TeradaTerada etet al. 2008). al. 2008). VeryVery fastfast andand highhigh B.B.•• Similar Similar propertiesproperties of SGR 0418+5729: P = 33 s, of SGR 0418+5729: P = 33 s,

dP/dtdP/dt = 5.64 10= 5.64 10--14 14 s/ss/s, , LLxx~10~103131 erg/serg/s (< 4 Kev),(< 4 Kev),B = 3 B = 3 x10x1088 G , T~ 0.5 KeVG , T~ 0.5 KeVcharacteristiccharacteristic age t~ 9.4 age t~ 9.4 MyrMyr

Pulsed fraction PF = (I_max - I_min)/(I_max + I_min)

II – Magnetar x White Dwarf Physical Scales.

•• MoriniMorini (1988) (1988) andand PaczynskiPaczynski (1990) (1990) –– MassiveMassive fastfastrotatingrotating highlyhighly magnetizedmagnetized whitewhite dwarfdwarf for 1E 2259+586 for 1E 2259+586 (AXP) at SNR (AXP) at SNR G109G109.1.1--1.0 (1.0 (periodperiod of P = 6.98 s)of P = 6.98 s)

• Kepler frequency W k = (G M/R3) ½ ~ (G r ) ½ ; W < WkP ~ 1 s , the average density r > 108 g/cm3 .

• Low density stars cannot spin fast .

• High density and massive white dwarfs: M= 1.4 Msun andmaximal radius R ~ 1000Km = 102 RNS. • Momentum of Inertia INS ~ M R2 = 1045 g.cm2

• IWD = 104 INS = 1049 g.cm2

ObservedObserved LongLong PeriodsPeriods as a as a manifestationmanifestation of of thethe lowlow whitewhite dwarfdwarfmassmass densitiesdensities –– cannotcannot spin spin fasterfaster thanthan twotwo secondsseconds ((BoshkayevBoshkayev, , RuedaRueda, , andand RuffiniRuffini))

First red point – AXP unconfirmed - CXOU J171405.7-381031, P= 3.825 s

New scale of rotational energy losses

New scale of dipolar magnetic field

White Dwarf Magnetar

Soft Gamma Repeaters

Anomalus X-Ray Pulsars

VeryVery DifferentDifferent MagneticMagnetic FieldField ScalesScalesWhite Dwarfs Magnetars

White Dwarf Model – no more ultra-strong magnetic fields, all undercritical !!!

III – SGRs and AXPs as fast rotating-poweredmagnetic white dwarf Pulsars.

White Dwarf Pulsar - dErot/dt ~10^2 to 10^5 Lx•Blue squares: SGR 1627-41 (P=2.6 s), 1E 1547.0-4950 (P=4.33s)•PSR 1627-41 (P=2.07 s) (the faster SGRs and AXPs)

White Dwarfs Neutron Star

EfficiencyEfficiency η η = = LLxx /(/(dEdErotrot/dt/dt) as a ) as a functionfunctionof of thethe star age.star age.

Magnetar Model – η η is is multipliedmultiplied byby 10^4 10^4 becausebecause smallsmall m. m. inertiainertia II

PredictionPrediction of of spinspin--downdownlowerlower limitlimit of SGR 0418+5729of SGR 0418+5729

•Maximal value of the Efficiency is one: Lx= dErot/dt

• Lower limit for Surface Dipolar Magnetic Field.

1.05 x 108 G < B < 7.47 x 108 G

Lx P3 /(4 π2 I) < dP/dt < 6.0 x 10-15 s/s

1.18 x 10-16 s/s < dP/dt < 6.0 x 10-15 s/s

IV – Outbursts mechanism: change of rotationalenergy from glitches (spin-up events).

Delta E_rot = -2*pi^2*I*(Delta P/P)/P^2

ObservedObserved andand PredictedPredicted GlitchesGlitches

VV-- IssuesIssues of of MagnetarMagnetar ModelModel

•• InconclusiveInconclusive measurementsmeasurements of of cyclotroncyclotron resonanceresonancelineslines to to estimateestimate thethe magneticmagnetic fieldfield strengthstrength. .

•• No No highhigh--energyenergy gammagamma emissionemission of of MagnetarsMagnetars foundfoundrecentlyrecently byby Fermi Fermi sattelitesattelite..

•• NotNot viableviable to relate to relate magnetarsmagnetars to to thethe energyenergy of of supernovasupernova remnantsremnants, to , to formationformation of of BlackBlack HolesHoles ororto to GammaGamma Ray Ray BurstBurst ((controversialcontroversial).).

•• VeryVery hot stars hot stars andand almostalmost withwith thethe samesame temperaturetemperature::notnot explainedexplained byby neutronneutron star star thermalthermal evolutionevolution..

•• R R factorfactor ((emissionemission area/totalarea/total areaarea of of thethe star) is star) is smallsmall ((1010--66 --1010--55) ) butbutat at samesame orderorder of of thethe sunsun; ; effectiveeffective circular circular areaarea of of thethe XX--rayray spot of spot of radiusradius ~ 1 ~ 1 -- 3.2 Km . 3.2 Km .

•• TheThe emissionemission is is notnot radiallyradially beamedbeamed; ; notnot justjust fromfrom thethe surfacesurface butbutalsoalso fromfrom thethe corona of corona of thethe hot spot. hot spot. PulsedPulsed fractionfraction smallersmaller thanthanoneone, as , as observedobserved in in SGRs/AXPsSGRs/AXPs, , andand alsoalso in AE in AE AquariiAquarii whitewhitedwarfdwarf pulsar (pulsar (sinusoidalsinusoidal pulsedpulsed flux in flux in softsoft XX--raysrays E< 4 KeV). E< 4 KeV).

•• SpectralSpectral featuresfeatures of of thethe persistentpersistent emissionemission of SGRs/AXPs for E< of SGRs/AXPs for E< 10 KeV well fited by the superpositon10 KeV well fited by the superpositon of a blackbody and a high of a blackbody and a high energy power law tail, or two blackbodies. Such a spectral featuenergy power law tail, or two blackbodies. Such a spectral feature re is also seeis also seen in AE n in AE AquariiAquarii ((TeradaTerada etet al., 2008), al., 2008), withwith spikyspikypulsationspulsations (E < 4 KeV). (E < 4 KeV). ThisThis whitewhite dwarfdwarf is is alsoalso emmitingemmiting uptouptoTeVTeV regionregion ((KashiamaKashiama etet al., al., PRD83PRD83, 023003, 2011). , 023003, 2011). MoreMore workworkneededneeded to to explainexplain thethe 2020--200 KeV 200 KeV persistentpersistent flux of flux of SGRs/AXPSGRs/AXP. .

•• QPOsQPOs frequenciesfrequencies in in thethe decaydecay tailstails of of SGRsSGRs giantgiant flaresflares..

IssuesIssues of White of White DwarfDwarf ModelModel

PossiblePossible connectionconnection to to supernovasupernova remnantsremnants

•• CharacteristicCharacteristic ages of ages of SGRs/AXPsSGRs/AXPs are are reasonablereasonable in in agreementagreement withwithages of SNR (SGR 0526ages of SNR (SGR 0526--66 to SNR 66 to SNR N49N49, 1E 1547, 1E 1547--54 to 54 to G327G327.24.24--013, 1E 1841013, 1E 1841--045 to 045 to Kes73Kes73, 1E 2259+586 to , 1E 2259+586 to G109G109.1.1--1.0).1.0).

•• PossiblePossible scenarioscenario thatthat SGRs/AXPsSGRs/AXPs andand SNR SNR originateoriginate fromfrom a a veryveryclose close binarybinary systemsystem composedcomposed of a of a whitewhite dwarfdwarf andand a companion a companion late evolved star, close to the process of gravitational collapslate evolved star, close to the process of gravitational collapse.e.

•• TheThe companioncompanion stars stars collapsecollapse eithereither to a to a neutronneutron star star oror blackblack holeholeandand thethe whitewhite dwarfdwarf is is expelledexpelled withwith largelarge runawayrunaway velocityvelocity ~ 1000 ~ 1000 Km/sKm/s ..

•• TheThe whitewhite dwarfdwarf does does notnot participateparticipate eithereither to to thethe gravitationalgravitationalcollapsecollapse nornor to the formation of SNR.to the formation of SNR.

•• TheThe collisioncollision of of thethe whitewhite dwarfdwarf withwith surroundingsurrounding material of SNR material of SNR ((includingincluding planetsplanets) ) maymay wellwell produceproduce largelarge glitchesglitches andand burstburstactivityactivity..

VII VII -- ConclusionsConclusions• SGR 0418+5729 is an authentic Rosetta Stone for deciphering the

energy sources of SGRs and AXPs. • The similiarity of the observational properties between SGR

0418+5729 and the white Dwarf pulsar AE Aquarii reopens the SGRsand AXPs description as rotation-powered white dwarf pulsars.

• SGRs and AXPs observed long periods are well in agreement andexplained by massive, fast rotating, and highly magnetized whitedwarfs.

• Dipolar magnetic fields all undercritical for SGRs/AXPs as whitedwarfs pulsars.

• A theoretical predicition for the lower limit of the first derivative of the rotational period of SGR 0418+5729 is obtained in the white dwarf model.

• The energetics of all SGRs and AXPs, including their outburst , are well explained by the change of the rotational energy of white dwarfs, associated to the observed sudden spin-up changes of the rotational frequency ( normal glitches).