Neutron star periods Sergei Popov SAI MSU Kaplan arXiv: 0801.1143 - PowerPoint PPT Presentation

Neutron star periods Sergei Popov SAI MSU

Kaplan arXiv: 0801.1143

Diversity of young neutron stars You ng is o lated ne u tr o n stars can appear in many flav o rs: o R adi o p u lsars o Co mpact central X-ray s ou rces in s u pern o va remnants. o A n o mal ou s X-ray p u lsars o So ft gamma repeaters o Th e Magnificent S even & Co . o T ransient radi o s ou rces ( RRAT s) o …………………… “GRAND U NIFICATION” is welc o med! (Kaspi 2010) S ee a recent review in 1111.1158

C ontents • E pisode 1. Initial spin periods. NSs in SNRs. • E poside 2. Initial spin periods and field decay. • E pisode 3. CCOs and emerging magnetic field • E pisode 4. Close-by cooling INSs: “One second problem”

E pisode 1. Initial spin periods of neutron stars Sergei Popov (SAI MSU) Roberto Turolla (Univ. Padua) arXiv: 1204.0632, 1206.2819

PSRs in SNRs See a review on NSs in SNRs in 1011.3731

CCO s For two sources there are strong indications for large (>~100 msec) initial spin periods and low magnetic fields: 1E 1207.4-5209 in PKS 1209-51/52 and PSR J1852+0040 in Kesteven 79 [see Halpern et al. arxiv:0705.0978] Puppis A Recent list in: 0911.0093

Sample of PSRs+SNRs 30 pairs: PSR+SNR

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

B vs. τ SNR /τ SD Recently, Zhang and Xie (2011) proposed that such a plot can be explained by field decay. We believe that a much more natural explanation is to assume significant P 0 .

Ch ecking gaussian 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. P 0 =0.1 s; σ=0.1 s

Ch ecking flat distrbution Flat between 0.001 and 0.5 s. Very wide distributions in general do not fit the data we have.

E pisode 2. Initial periods and field decay Sergei Popov (SAI MSU) Andrei Igoshev (Radbound Univ. ) arXiv: 1303.5258, 1309.4917

W ide 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?

M agnetic field decay and P 0 One can suspect that magnetic field decay can influence the reconstruction of the initial spin period distribution. Exponential field decay with τ=5 Myrs. <P 0 >=0.3 s, σ P =0.15 s; <log B 0 /[G]>=12.65, σ B =0.55 τ<10 7 yrs, 10 5 <t 10 5 <t<10 7 yrs I goshev, Popov MNRAS arXiv: 1303.5258

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

A not h er option: emerging field The problem is just with few (6) most long-period NSs. I s 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

E pisode 3. CCO s and emerging magnetic fields Sergei Popov (SAI MSU) Roberto Turolla (Univ. Padua) arXiv: 1206.2819

NS birth rate [ Keane, Kramer 2008, arXiv: 0810.1512]

E volution of CCO s Popov et al. MNRAS 2010 Halpern, Gotthelf Chashkina, PSRs+ Popov 2012 Magnetars+ Close-by coolers CCOs HMXBs B B 10 10 10 12 10 11 10 13 Among young isolated NSs about 1/3 can be related to CCOs. I f 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 many sources with such properties. The only good example - SAX J0635+0533. An old CCO? Possible solution: emergence of magnetic field (see Ho 2011).

W h ere are old CCO s? Y akovlev, Pethick 2004 According to cooling studies they have to be bright till at least 10 5 years. But only one candidate (2XMM J104608.7-594306 Pires et al.) to be a low-B cooling NS is known (Calvera is also a possible candidate). We propose that a large set of data on HMXBs and cooling NSs is in favour of field emergence on the time scale 10 4 ≤ τ ≤ 10 5 years. Some PSRs with thermal emission for which additional heating was proposed can be descendants of CCOs with emerged field.

E merged pulsars in t h e P-Pdot diagram Emerged pulsars are expected to have P~0.1-0.5 sec B~10 11 -10 12 G Negative braking indices or at least n<2. About 20-40 of such objects are known. Parameters of emerged PSRs: similar to “injected” PSRs (Vivekanand, Narayan, Ostriker). The existence of significant fraction of “injected” pulsars formally do not contradict recent pulsar current studies (Vranesevic, Melrose 2011). Part of PSRs supposed to be born with long (0.1-0.5 s) spin periods can be matured CCOs. Espinoza et al. arXiv: 1109.2740

E pisode 4. C lose-by cooling NSs and “ O ne second problem” Sergei Popov (SAI MSU) Co-authors: Jose Pons et al. arXiv: 1309.4917

M agnetic field decay A m o del based o n t h e initial field-dependent decay can pr o vide an ev o l u ti o nary link between different p o p u lati o ns (P o ns et al.). arXiv: 0710.4914 ( A g u ilera et al.)

Ex tensive population synt h esis W e want to make extensive population synthesis studies using as many approaches as we can to confront theoretical models with different observational data  L o g N – L o g S f o r cl o se-by y ou ng c oo ling is o lated ne u tr o n stars  L o g N – L o g L distrib u ti o n f o r galactic magnetars  P-Pd o t distrib u ti o n etc. f o r n o rmal radi o p u lsars M NRAS 401, 2675 (2010) arXiv: 0910.2190 S ee a review o f t h e p o p u lati o n synt h esis tec h niq u e in P o p o v, Pr o k ho r o v Physics Uspekhi v o l. 50, 1123 (2007) [ ask me f o r t h e P DF file, if necessary - it is n o t in t h e arXiv]

C ooling curves wit h decay Magnetic field distribution is more important than the mass distribution.

L og N – L og S with heating L o g N – L o g S f o r 7 different D ifferent magnetic field distrib u ti o ns. magnetic fields. 1. 3 10 12 G 2. 10 13 G 3. 3 10 13 G 4. 10 14 G 5. 3 10 14 G 6. 10 15 G 7. 3 10 15 G [ Th e c o de u sed in P o sselt et al. A & A (2008) wit h m o dificati o ns]

F itting Log N – Log S W e try t o fit t h e L o g N – L o g S wit h l o g-n o rmal magnetic field distrib u ti o ns, as it is o ften d o ne f o r P SR s. W e cann o t select t h e best o ne u sing o nly L o g N – L o g S f o r cl o se-by c oo ling NS s. W e can select a c o mbinati o n o f parameters.

L og N – L og L for magnetars W e u sed t h e same initial magnetic field distrib u ti o ns. Cu rves are s ho wn f o r t h ree l o g-n o rmal distrib u ti o ns wit h and wit hou t a “ transient ” be h avi ou r. I t is ass u med t h at t h e t o tal l u min o sity can be well appr ox imated by t h e energy release d u e t o field decay. I t is seen t h at t h e same l o g-n o rmal distrib u ti o ns can reas o nably well describe t h e data f o r magnetars. D ata p o ints fr o m t h e Mc G ill catal o g u e. L imits - fr o m M u n o et al. (2008)

P-P dot tracks Kaplan & van Kerkwijk arXiv: 0909.5218 Co l o r o n t h e track enc o des s u rface temperat u re. T racks start at 10 3 years, and end at ~3 10 6 years.

Population synt h esis of PSRs B est m o del: <l o g( B 0 / [ G ])>= 13.25, σ l o g B 0 =0.6, <P 0 >= 0.25 s, σ P0 = 0.1 s

T he “one second” problem T w o types o f s ou rces are o bserved: • R adi o p u lsars (P<1 sec) • Magnificent S even (P>1 sec) No cl o se-by c oo ling NS s in t h e range ~-0.5 <l o g P< ~0.5 Kaplan arXiv: 0801.1143

P-P dot diagram for coolers Th is is a P-Pd o t diagram f o r cl o se-by c oo ling NS s acc o rding t o ou r m o del. Nu mbers c o rresp o nd t o t h e o bserved s ou rces.

I nitial magnetic fields of the modeled coolers Th e pl o t s ho ws t h e distrib u ti o n o f t h e initial magnetic fields o f NS s w h ic h c o ntrib u te t o t h e L o g N – L o g S diagram in t h e range ~0.1-10 cts/s O bvi ou sly, t h ere is t h e same pr o blem as wit h t h e peri o d distrib u ti o n.

New calculations New cooling models (Pons, Vigano). Now low-B NSs are hotter than before, and high- B NSs are colder. Still, it is not possible to explain the P-Pdot data. Fine tuning is necessary.

E volution wit h out h eating Kaspi-like population Kaspi-like population with additional peak at B=10 14 G and small dispersion Calculations with new cooling curves from the St.Petersburg group (Sternin, Yakovlev et al.) can easily explain the Log N – Log S, but cannot the P-Pdot without finetuning for the B-distribution (curves are not sensitive to B, so it is important only for spin evolution).