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: o Radio pulsars o Compact central X-ray sources in supernova remnants. o Anomalous X-ray pulsars o Soft gamma repeaters o The Magnificent Seven & Co. o Transient radio sources (RRATs) o …………………… A kind of “GRAND UNIFICATION” is necessary (Kaspi 2010) Kaplan

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

Evolution of PSRs with evolving field Pons, Vigano, Geppert 2012 Three stages: 1. n<=3 Standard + emerging field 2. n>3 Ohmic field decay 3. Oscillating and large n – Hall drift

Additional evidence for field decay Chashkina, Popov (2012) 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 them with prediction of the Pons et al. model.

Evolution of CCOs and field distributions B PSRs+ Magnetars+ Close-by coolers CCOs B HMXBs 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 NSs in 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 Chashkina, Popov 2012 Popov et al. MNRAS 2010 Halpern, Gotthelf (See discussion in )

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 10 5 years. Some PSRs with thermal emission for which additional heating was proposed can be descendants of CCOs with emerged field.

What else can we learn about field decay and/or emerging magnetic field studying properties of populations of different age and comparing them?

Sample of NSs+SNRs 30 pairs: PSR+SNR Popov, Turolla arXiv:

B vs. P 0 All presented estimates are made for standard assumptions: n=const=3. So, field is assumed to be constant, as well as the angle between spin and magnetic axis. Crosses – PSRs in SNRs (or PWN) with ages just consistent with spin-down ages. We assume that P 0 <0.1P Popov, Turolla

Checking gaussian P 0 =0.1 s; σ=0.1 s The data we have is not enough to derive the shape of the P 0 distribution. However, we can exclude very wide and very narrow distributions, and also we can check if some specific distributions are compatible with our results. Here we present a test for a gaussian distribution, which fits the data. Still, we believe that the fine tuning is premature with such data.

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 SNRs were used, i.e. the sample is much younger! Can it explain the difference?

Magnetic field decay and P 0 Igoshev, Popov MNRAS arXiv: One can suspect that magnetic field decay can influence the reconstruction of the initial spin period distribution. Exponential field decay with τ=5 Myrs. =0.3 s, σ P =0.15 s; =12.65, σ B =0.55 τ<10 7 yrs, 10 5 <t10 5 <t<10 7 yrs

Real vs. reconstructed P 0 How long reconstructed initial periods changed due to not taking into account the exponential field decay The amount of field decay necessary to explain this shift is in correspondence with the radio pulsar data (talk by Andrei Igoshev)

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 visible at the age ~few million years? Yes! Emerging magnetic field!!! Then we probably need correlations between different initial parameters

Extensive population synthesis: M7, magnetars, PSRs M7 Magnetars PSRs Using one population it is difficult or impossible to find unique initial distribution for the magnetic field All three populations are compatible with a unique distribution. Popov, Pons et al. 2010

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

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