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Unifying neutron stars

Unifying neutron stars. Sergei Popov (SAI MSU) in collaboration with: Andrei Igoshev (SPbSU), and Roberto Turolla (Univ. Padova). Diversity of young neutron stars. Young isolated neutron stars can appear in many flavors: Radio pulsars Compact central X-ray sources

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Unifying neutron stars

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  1. Unifying neutron stars Sergei Popov (SAI MSU)in collaboration with:Andrei Igoshev (SPbSU),and Roberto Turolla (Univ. Padova)

  2. Diversity of young neutron stars • Young isolated neutron starscan appear in many flavors: • Radio pulsars • Compact central X-ray sources • in supernova remnants. • Anomalous X-ray pulsars • Soft gamma repeaters • The Magnificent Seven & Co. • Transient radio sources (RRATs) • …………………… Kaplan 0801.1143 A kind of “GRAND UNIFICATION” is necessary (Kaspi 2010)

  3. Bernal, Page, Lee Pons et al. Aguilera et al. • Field decay • Emerging magnetic field • Toroidal magentic field Three main ingredients:

  4. Evolution of PSRs with evolving field • Three stages: • n<=3 Standard + emerging field • n>3 Ohmic field decay • Oscillating and large n – Hall drift Pons, Vigano, Geppert 2012

  5. Additional evidence for field decay It is possible to use HMXBs to test models of field decay on time scale >1 Myr (Chashkina, Popov 2012). We use observations of Be/X-ray binaries in SMC to derive magnetic field estimates, and compare themwith prediction of the Pons et al. model. Chashkina, Popov (2012)

  6. Evolution of CCOs and field distributions Popov et al. MNRAS 2010 Halpern, Gotthelf Chashkina,Popov 2012 PSRs+Magnetars+Close-by coolers CCOs HMXBs B B 1010 1012 1011 1013 Among young isolated NSs up to 1/3 can be related to CCOs.If they are anti-magnetars, then we can expect that 1/3 of NSsin HMXBs are also low-magnetized objects.They are expected to have short spin periods <1 sec.However, there are no such sources with such properties. Possible solution: emergence of magnetic field (See discussion in 1206.2819)

  7. Additional evidence for emerging field Yakovlev, Pethick 2004 Where are older hot CCOs? According to cooling studies they have to be bright till at least 105 years. Some PSRs with thermal emission for which additional heating was proposed can be descendants of CCOs with emerged field.

  8. What else can we learn about field decay and/oremerging magnetic fieldstudying properties of populations of different ageand comparing them?

  9. Sample of NSs+SNRs 30 pairs: PSR+SNRPopov, Turolla arXiv: 1204.0632

  10. B vs. P0 All presented estimatesare made for standardassumptions: n=const=3.So, field is assumed to beconstant, as well as the anglebetween spin and magnetic axis.Crosses – PSRs in SNRs (or PWN) with ages justconsistent with spin-down ages.We assume that P0<0.1P Popov, Turolla

  11. Checking gaussian The data we have is not enoughto derive the shape of theP0 distribution.However, we can excludevery wide and very narrowdistributions, and also wecan check if some specificdistributions are compatible withour results.Here we present a test fora gaussian distribution,which fits the data.Still, we believe that thefine tuning is prematurewith such data. P0=0.1 s; σ=0.1 s

  12. Wide initial spin period distribution Noutsos et al. Based on kinematic ages. Mean age – few million years.Note, that in Popov & Turolla (2012) only NSs in SNRswere used, i.e. the sample is much younger!Can it explain the difference?

  13. Magnetic field decay and P0 One can suspect that magnetic field decay can influence the reconstructionof the initial spin period distribution. Exponential field decay with τ=5 Myrs. <P0>=0.3 s, σP=0.15 s; <log B0/[G]>=12.65, σB=0.55 τ<107 yrs, 105<t 105<t<107 yrs Igoshev, Popov MNRAS arXiv: 1303.5258

  14. Real vs. reconstructed P0 How long reconstructed initial periodschanged due to not taking into accountthe exponential field decay The amount of field decay necessaryto explain this shift is in correspondencewith the radio pulsar data(talk by Andrei Igoshev)

  15. Another option: emerging field The problem is just with few (6)most long-period NSs. Is it possible to hide them when they are young, and make them visibleat the age ~few million years? Yes! Emerging magnetic field!!!Then we probably need correlations betweendifferent initial parameters

  16. Extensive population synthesis:M7, magnetars, PSRs Using one populationit is difficult or impossibleto find unique initialdistribution for themagnetic field M7 M7 Magnetars All three populations arecompatible with aunique distribution. PSRs Popov, Pons et al. 2010

  17. The “one second” problem • Two types of sources are observed: • Radio pulsars (P<1 sec) • Magnificent Seven (P>1 sec) No close-by cooling NSsin the range ~-0.5 <log P< ~0.5

  18. Conclusions • Studies of the magnetic field distribution in HMXBs provide evidence in favour of decaying field and in favour of emerging field • Absence of evolved hot CCO-like sources argues in favour of emerging magnetic field • Comparison of the initial spin period distributions obtained for very young NSs (in SNR) and for older pulsars with known kinematic ages argues in favour of the field decay or/and emerging field • We need more detailed population synthesis studies • We need larger observational statistics

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