arXiv:astro-ph/9909484v1 29 Sep 1999 hc hudb rudsaeo eto tr ec,rdopulsa radio Hence, . neutron of state ground a be should which r Ss ,sm rbesi usreiso ehns a esettle be can mechanism emission in problems some 1, BSSs, are n t nuheeg.Frpoeioswt ail oaiginrc ma inner a star and rotating neutron down, rapidly a spins Such with it when progenitors supernovae. t For after shock, stalled a products energy. the semifinished forming enough behind by deposition its emission energy and neutrino neutrino of additional power rotation, the of effect negligible tbe‘arn fsrn neato ofie tts fti ass this If states. confined do interaction up, strong of numbers of equal ‘hadron’ nearly stable of soon composed stars (SQM), neutron matter quark be to thought popularly are , as named trseai o ai pulsar radio for scenario star ido eeta oiswt masses with bodies celestial of kind atrt Q a ueteipreto ntecr-olpesuper core-collapse the in imperfection the cure can stars? SQM strange to bare matter supernovae: after produced Pulsars could r o oiaysrnestars, strange solitary For oneog,wudteaceinot h ufc epossibl be surface the star. onto strange newborn the of would rotation enough, rapid down the is one second cylinder ti aua oepc htteqaksraeo eyyugstr young very a is of star surface a the of that envelope expect an to natural from is rate it ejection mass the First, tag tr ihprosgetrta scnaceesurroun accrete can 5s than greater periods with stars strange n16s oeosrain ae in c are later observed this observations stars of in More kind developed such 1960s. of quantum) in One and stars. compact of (i.e., theory theories greatest Two m wn otedvlpeto h arncqakmdli 90 n 1 and 1960s in model quark hadronic the of development the to Owing ti drse htasrneqakcr ssrone yanorm a by surrounded is core quark strange a that addressed is It r < hr r w esn o st nvtbysgetta strange a that suggest inevitably to us for reasons two are There 1 usr a be may pulsars tag tr uhasgeto a ecekdb ute obs further by checked be can suggestion a Such star. strange usr.Bcueo togmgei field, magnetic explos strong of in Because produced stars pulsars. strange young emission, . easily c r < r ti eivdta usr r eto tr rsrnestar strange or stars neutron are pulsars that believed is It l A-K on ejn srpyia etradDprmn fAs of Department and Center Astrophysical Beijing joint CAS-PKU efind we , edsigihdi observation. in distinguished be l usiuigterdu fmagnetosphere of radius the Substituting . rsne nIUClouu 7:Pla srnm n Beyon and Astronomy Pulsar 177: Colloquium IAU in Presented P aesrnestars strange bare 1 r usr aeSrneStars? Strange Bare Pulsars Are > 0 M uut3 epme ,19,Bn,Germany Bonn, 1999, 3, Setpember – 30 August γ . . 7 rybrtmyapa simultaneously appear may burst -ray 1 8 oee,br tag tr BS a also can (BSS) stars strange bare However, . M svr ml eas fvr togeeto rudtesa.If star. the around ejection strong very of because small very is . eigUiest,Biig108,China 100781, Beijing University, Peking 8 − 3 / ∼ 7 X ..X,GJ io .Zhang B. Qiao, G.J. Xu, R.X. o yia usrvle,where values, pulsar typical for 1 ryand -ray ie,srnesaswtotcut.Det ai oaina rotation rapid to Due crust). without stars strange (i.e., M ⊙ radius , two γ rybnscnre h xsec fplasi h aue a nature: the in pulsars of existence the confirmed bands -ray Abstract oa-rsswudsil h oa aso naccreting an of caps polar the shield would polar-crusts ∼ 0k,admgei fields magnetic and km, 10 1 r m nywe h oaino tag tri slowed is star strange a of rotation the when Only h ortto radius co-rotation the , usr htwr icvrdb ai astronomers radio by discovered were that pulsars igmatter. ding e. ossol ebr hnte c sradio as act they when bare be should ions ervations. mto stu,srnestar strange true, is umption ihcut.Hwvrw ugs eethat here suggest we However crusts. with s nesa snal o opeey bare completely) (or nearly is star ange efial hs-ovre oasrnestar strange a to phase-converted finally be y n n tag urs a ea absolutely an be may quarks, strange and wn, h rcs fpaetasto rmneutron from transition phase of process The ssrie rmsproa ih estrange be might supernovae from survived rs 4 h odtosfrapsil crto are accretion possible a for conditions The fe h discoveries. the after eyhg onatrasproa therefore supernova, a after soon high very . u odc oad ucsflexplosion successful a towards conduce hus lmte rs ntecnetoa strange conventional the in crust matter al M nuyrsle ntefraino the of formation the in resulted entury oaparadigm r,nurnsasmgtb omdas formed be might stars neutron ore, d . tra ai usrsol ebare. be should pulsar radio a as star 2 8 tag trcnsffiinl enhance sufficiently can star strange , 3 well saceinrt n10 in rate accretion is ,srnesasadnurnstars neutron and stars strange 2, , 7s ti ojcue htstrange that conjectured is it 970s, c srdopulsars radio as act ∼ 10 r c 12 4 n h aiso light of radius the and , o rgntr with progenitors For . ase.Sc objects, Such gausses. tronomy, 1 d si h nature, the in is M dstrong nd . − 8 0 = 2 8 fpulsars If . M ⊙ . 1 only 01, 5 · The . yr − 1 . As s quark is a little more massive than that of u and d quarks, there are a few electrons in the chemical equilibrium of SQM in order to keep the matter neutral. The electromagnetic force participated in makes the structure of strange quark matter more interesting and attractive. It is found6 that the number density of 35 18 9.49×10 −3 7.18×10 −1 n ∼ 3 , E ∼ 2 , z electrons above quark surface e (1.2z11+4) cm and the electric field (1.2z11+4) V cm where , in 10−11 cm, is a measured height above the surface. These analytical results are valuable if we are concerned about physical processes near the quark surfaces of strange stars.

An accreting pulsar: with two polar-crusts? As for strange stars in binaries, they could be accretion powered X-ray sources with two polar-crusts2. In some cases, the intermittent phase transition in polar-crust could result in a burst process when one of the crusts is heavier than that the Coulomb force can support. GRO J1744-28 is an ideal example for studying such process. The observational phase-lag in GRO J1744-28 may be a strong evidence of the electric gap between strange quark matter and polar-crust. The bursting can cause matter to enough expand and to drag matter to latter phase. Such phase-lag can be calculated to be ∼ 60o if an expanded crust is ∼ 1 km.

Conclusion We suggested that radio pulsars might be bare strange stars, and that accreting strange stars have two polar-crusts. Bare strange stars and neutron stars are distinguishable in observation because their surfaces differ in many ways, such as the electrodynamics, the thermodynamics, and the composition (see, Xu, Qiao & Zhang in this peroceding). Detailed research on this topic should be interesting and necessary.

We thank Mr. B.H. Hong, Dr. J.L. Han, and other members in our pulsar group. This work is supported by NSFC (No. 19803001, N0.19910211260-570-A03), by the Climbing project of China, by Doctoral Program Foundation of Institution of Higher Education in China and by the Youth Foundation of PKU.

[1] Alcock, C., Farhi, E., Olinto, A. 1986, ApJ, 310, 261 [2] Xu, R.X., Qiao, G.J. 1998, Chin Phys Lett, 15, 934 [3] Xu, R.X., Qiao, G. J., Zhang, B. 1999, ApJ, 522, L109 [4] Xu, R.X. et al. 1999, in K.S. Cheng (eds) Pacific Rim Conf. on Stellar Astrophysics, Kluwer Publishers, in press [5] Usov, V.V., 1998, Phys Rev Lett, 80, 230 [6] Xu, R.X., Qiao, G.J. 1999, Chin Phys Lett, 16, 778

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