Intermittent Radioemission form Pulsars. Implications for Magnetospheric Models

Transcription

1 Intrmittnt Radiomission form Pulsars Implications for Magntosphric Modls Axl Jssnr, MPIfR Bonn Harald Lsch, LMU Munich, Michal Kramr, MPIfR

2 Spin-down loss: E rot 5 m r ns ns is similar to th powr budgt of th Crab nbula but tims obsrvabl psr luminosity 1 st Solution: Pulsar Spin-down Invisibl for most pulsars! 6 W Powr losss from low n radio wav mittd by rotating magntic dipol (Dutsch 1955, Pacini 1967) B r ns L. dip sin( ) 3.. c 3 Obsrvd: Estimat of surfac B 3. 1 T P P sin B Chang of rotation with tim: d dt. B. r. ns. 3 3 c 3 braking indx. M ns 1.4 n 3 Dipol radiation modl is not a good xplanation! Magntisd Nutron stars do not to oprat in a vacuum! 9 T (Lyn & Smith, 6) (Dutsch 1955)

3 Filds and Currnts in Th Pulsar Magntosphr Filds of an alignd Rotator (P=.539 s, B = T) F 1 I cap 13 V 7 1 n GJ = m 3 11 A Th rotating dipolar B-fild inducs a potntial F which givs ris to a quadrupolar E-fild Nar th surfac chargs can mov only paralll to B, but at T surf 1 6 K and E B 13 V E 31 B m chargs can b frly libratd from th surfac until an quilibrium charg dnsity n GJ is rachd whn th corotating spac chargs shild th lctric fild (Goldrich & Julian 1969) F I cap W Thy scap via opn fild lins abov th polar caps and rturn in an quatorial currnt sht forming a magntosphric currnt systm. Th rotating nutron star gnrats strong filds at its surfac,- capabl of acclrating chargs and driving a larg currnt. Th dissipatd powr is comparabl to th spin-down powr!

4 Evidnc: Radio mission & Magntosphric Currnts Variabl Spin-down of PSR B On: Off: L on = W L dip = W B 31 6 (Gurvich&Istomin 7) 8 T radio mission radio quit 4 L M 5 L or L on r ns ns dn ( dt.35 on dn dt off ) W Estimats for th currnt systm (j= q n GJ c ) I cap = A F = V. I. cap U cap = W Kramr t al. Scinc, 31, 549 (6) ( W incl. GR. Corrctions) ++ changs in puls profils corrlat with changs in spin-down rat ++ (Lyn t. al 1) Radio mission is linkd to magntosphric currnt flow!

5 Modl: Magntosphric Currnts Total currnt is controlld by conductivity s s vacuum dipol MHD: s= E B= no radio mission W xpct s to dpnd on location and currnt dnsity j to b consrvd along fild lins: j= q n GJ c and j B Fluctuating noisy E clos to polar rgions. Kalapotharakos t al. 1

6 Modl: 1-D non- nutral currnt instabilitis Pirc Instability (Pirc 1946) Particls constraind to 1-D motion will gain nrgy until thir collctiv spac charg compnsats th background E. Thir own fild will start to rpl thm until thy com to a stop and anothr 'virtual' cathod is formd Poisson s qn.: Eqn. of motion: de dz z d( ) dz j c m q c (E z (1 )E ) Th procss rpats thrby forming a rgular spacial pattrn of narrow high charg dnsity rgions sparatd by wid low dnsity but high rgions and altrnating E (Mstl (1985), Jssnr (), Blorobodov(8), Luo (8)) Sparation: L p 4(1 ) mc virtual cathod Lvc q(1 )E thicknss (of non-rlativistic rgion) j E c L p r (m ) Lorntz factor variations in th radio mission rgion of PSR B1+51 (Jssnr t al. 1) max. Lorntz factor: max E (1 ) n m c m ax

7 Modl: 1-D non- nutral currnt instabilitis Estimats for PSR B1-51 ( P=.59s, B = T, alignd approximation): x m q 1 1 rad Pirc lngth (m) max. Lorntz factor thicknss of non-rlativistic rgion (Jssnr t al. 1) r/r* thicknss x m =8.7 r ns =.99 L vc q mc (1 )E 1cm sparation L p 4(1 ) j E c 3m Min. dissipation in radio rgion: rad L I cap rad q m c 34 max E (1 ) n m c 134

8 Modl: -D non- nutral currnt instabilitis: rlativistic tim dpndnt flow t x (m) k 1 qn Potntials & F F c t Filds 1 (Lorntz gaug) A A j c t A E F t Linard-Wichrt potntials (qn ) Continuity j q c( n ) t (np) Momntum c (np) q n transport t E Grid: 496 x19 grid, 4 ns in 1 4 stps for L x = 1 m, L y =.13 m, L z =.1 m background fild: E x = 1 6 V/m, Injction n = m -3, particls bing initially at rst. oscillations with l 3 c/w p low -3 & upstram propagation Expct rgular short wav lngth ( cm) & short duration instabilitis

9 Animatd Rlativistic flow instabilitis for strong currnts

10 Evidnc: A Common Shap of Pulsar Spctra Paramtrs of spctral fits for a numbr of pulsars. PSR S t n (Jy) (ns) B B B B B B B B B B B B (Löhmr t al. 6) Nano-shot potntial t t F( t) F (t) With th Havisid function: 1 (t) Spctrum S S( n) 1 ( t t t n) Pulsar Spctra fit nano-shot mission on short timscals rmarkably wll

11 S/N f [MHz] Evidnc: nano shot mission in Crab giant pulss (Efflsbrg 15 GHz obsrvations) CCF of Crab MP Giant Puls at 15 GHz Efflsbrg 5/1/7 :14:4 mjd = f sky = GHz S pak = 68 Jy pak S/N = rms = tim (s) frquncy pattrns: sparation of 4 MHz, width < 4 MHz t [ns] -D cross-corrlation btwn LHC and RHC signals (Jssnr t al. 1).. -. intrfrnc pattrn l c (4MHz) -1 = 7.5m Rgular mission structurs may b obsrvabl at high tim rsolution

12 Summary and Conclusions: Th Magntosphr of Pulsars dominats thir dynamics and our obsrvations 1. Obsrvations may b sn as vidnc, that a non-nutral currnt flowing in th pulsar magntosphr is th caus of radio mission.. Th currnt can contribut about 3-4% of th spin-down nrgy loss of a pulsar. 3. Th currnt is xpctd to xhibit rgular spatial instability pattrns with thin (L vc 1 cm) non-rlativistic high-dnsity rgions sparatd by wid (L p 1m) strtchs of rlativistic flow. 4. Thr is obsrvational vidnc for th xistnc of short timscals and rgular mission pattrns. 5. Th pulsar magntosphr in th mission rgion is not spatially homognous. This will affct mission and propagation mchanisms. Homognous and linar modls ar unsuitabl. 6. Th dscribd solutions ar highly snsitiv to th initial conditions. On xpcts small variations of th currnt dnsity to caus larg fluctuations in th local radio mission. Th pulsar radio mission mchanism is still unclar bcaus it nds holistic modlling: small and larg scals at th sam tim,- and rcnt advancs in computr hard and softwar will allow us to do just that. jssnr@mpifr-bonn.mpg.d

13 Litratur: Pirc : Th Thory and Dsign of Elctron Bams, van Nostrand, (Toronto, Nw York, London 1949) Dutsch, Annals Astrophysiqu,18,1 (1955) Pacini, Natur,16,567 (1967) Hwish, Bll t al., Natur, 17, 79 (1968) Gold, Natur,18,731 (1968) Goldrich & Julian, ApJ, 157, 869 (1969) L. Mstl, t al., MNRAS, 17, 443 (1985) Davidson Physics of non-nutral bams, Imprial Collg Prss, (London 1) A. Jssnr, H. Lsch, Thomas Kunzl 1, ApJ, 547, 959 Jssnr t al. MPE-Rport No. 78, 9-14, MPE Garching () Bckr t al., ApJ, 615,, 98-9 (4) Kramr t al., Scinc, 31, 549 (6) Lyn & Smith, Pulsar Astronomy, 3rd d., CUP, (6) Bloborodov, ApJ 683: L41 L44, (8) Lohmr, t al., Astronomy and Astrophysics, 48, 63 (8) Luo&Mlros, MNRAS. 387, (8) Jssnr, t al., Proc. IAU, 6, pp (1) Jssnr, t al., Astronomy and Astrophysics, 54, id.a6 (1) Lyn, t al., Scinc, 39, 48 (1); Kalapotharakos t al., arxiv: v (1)