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 starscan appear in many flavors:

o Radio pulsars o Compact central X-ray sources in supernova remnants. o Anomalous X-ray pulsarso Soft gamma repeaterso The Magnificent Seven & Co.o Transient radio sources (RRATs)o ……………………

A kind of “GRAND UNIFICATION” is necessary (Kaspi 2010)

Kaplan 0801.1143

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 field2. n>3 Ohmic field decay3. 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 themwith prediction of the Pons et al. model.

Evolution of CCOs and field distributions

B

PSRs+Magnetars+Close-by coolersCCOs

1010 1012 B1011 1013

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 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

Chashkina,Popov 2012

Popov et al. MNRAS 2010

Halpern, Gotthelf

(See discussion in 1206.2819)

Additional evidence for emerging field

Yak

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v, P

ethi

ck 2

004

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 proposedcan be descendants of CCOs with emerged field.

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

Sample of NSs+SNRs

30 pairs: PSR+SNR

Popov, Turolla arXiv: 1204.0632

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

Checking gaussian

P0=0.1 s; σ=0.1 s

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.

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?

Magnetic field decay and P0

Igoshev, Popov MNRAS arXiv: 1303.5258

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

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)

Another option: emerging fieldThe 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

Extensive population synthesis:M7, magnetars, PSRs

M7 M7

Magnetars

PSRs

Using one populationit is difficult or impossibleto find unique initialdistribution for themagnetic field

All three populations arecompatible with aunique distribution.

Popov, Pons et al. 2010

The “one second” problemTwo 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

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