1I Compstar meeting, Wroclaw 2008 Prospects of inferring dense matter properties from NS cooling: the magnetar masquerade the magnetar masquerade José A. Pons (U. Alicante, Spain) In coll. with D. Aguilera, J.A. Miralles, U. Geppert

2I Compstar meeting, Wroclaw 2008 Reminder: What we see is NOT the NS, we see an e.m. spectrum (actually, a part of it),formed in the star’s surface (or a fraction of it), or in the magnetosphere, or radiation from accreting material … or everything together. It is crucial to understand the physics of the crust, atmosphere, magnetosphere …. to have reliable models. Can we really say anything about high density/exotic matter with current NS emission/cooling models ?

3I Compstar meeting, Wroclaw 2008  Last 10 years: increasing evidence of B field influencing (surface/magnetospheric) thermal spectra. Non trivial B fields.  Cooling of magnetized NSs just beginning to be considered, not yet in a fully consistent way Until recently only 1D cooling, and decoupled B-T evolution, with some prescription to deal with anisotropy as a boundary condition.  Joule heating is usually not considered because: Magnetic energy << thermal energy content, large electrical conductivity, large scale structure … BUT in the crust and envelope of a NS this is not true. Reminder: Neutron Stars DO have magnetic fields

4I Compstar meeting, Wroclaw 2008 What we believe now:  in “low field NSs” (B<10 12 G) 1D models are reasonably correct (anisotropy,if any, in the envelope) Joule heating by crustal magnetic field decay, if effective, only in NSs too cool to be observable.  in “magnetars” (B>10 14 G) Some consensus in the fact that they are “too hot for their age” and the magnetic energy is maintaining the high temperature What happens to intermediate B objects ? (Which, by the way, are those used to establish constraints on exotic matter: radius estimates, cooling curves …)

5I Compstar meeting, Wroclaw 2008

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9 THERMAL STRUCTURE 2D radiation transport to obtain the distribution of T (Geppert, Küker, Page, 2004,2007, Perez-Azorin et al. 2005, 2006a, 2006b) F =       b    b   b  b    b   Isothermal surfaces aligned with B: Strong dependence on B field geometry !

10I Compstar meeting, Wroclaw 2008

11I Compstar meeting, Wroclaw 2008 Crustal B field evolution  Superconducting dynamics of the core is very complex (vortex/fluxoid interaction, type I or II ?…)  To begin, consider the currents in the crust after birth.  Physics well (?) known: “free” electrons in a solid lattice, ions are fixed and e- move as a 1-component plasma  Currents will evolve with time and dissipate in shorter timescales than the B field anchored in the core (larger conductivity).

12I Compstar meeting, Wroclaw 2008 Crustal B field evolution  Conductivity varies many orders of magnitude  Magnetization parameter varies with time and can be large  Hall induction equation.

13I Compstar meeting, Wroclaw 2008 B field evolution  Diffusive (parabolic) terms.  C,D non-linear (Hall) terms  Toroidal field subject to an “advective” term proportional to the resistivity gradient.  Decomposition into poloidal+toroidal components.  For purely toroidal fields D=0 and (homogeneous charge density), C becomes Burgers Eq.

14I Compstar meeting, Wroclaw 2008 B field evolution: weak field  B(pole)=1e13 G Pons & Geppert, 2007, A&A

15I Compstar meeting, Wroclaw 2008 B field evolution: intermediate field  B(pole)=1e14 G Pons & Geppert, 2007, A&A

16I Compstar meeting, Wroclaw 2008 B field evolution: strong field  B(pole)=1e15 G Pons & Geppert, 2007, A&A

17I Compstar meeting, Wroclaw 2008 B field evolution: dissipation rate

18I Compstar meeting, Wroclaw 2008

19I Compstar meeting, Wroclaw 2008 Joule heating ? Do the easy thing first: energy balance Joule heating ? Do the easy thing first: energy balance Prediction: slope=1/2 in a logT-logB plot ?? Data? We have about 30 NSs (7 magnificents, 3 musketeers, RRATs, 7 AXPs, 2 SGRs, some radio- pulsars …) with reported thermal emission and B.

20I Compstar meeting, Wroclaw 2008 Joule heating effective in many NSs ? Crust size = 1 km Bint = 15 x Bdip B decay time 1 Myr  Pons, Link, Miralles, Geppert, 2007, Phys. Rev. Lett.

21I Compstar meeting, Wroclaw 2008 Joule heating working in many NSs ?

22I Compstar meeting, Wroclaw 2008

23I Compstar meeting, Wroclaw 2008

24I Compstar meeting, Wroclaw 2008 Coupled B-T evolution: first results

25I Compstar meeting, Wroclaw 2008 Light curves

26I Compstar meeting, Wroclaw 2008 Orientation and light curves Sinusoidal light curves give information about the axis orientation (small O+B or (unlikely) O=B=90), but irregular light curves give more information. Dipolar Quadrupolar

27I Compstar meeting, Wroclaw 2008 RXS J1308 (RBS1223): Evidence of quadrupolar T distribution ? RXS J1308 (RBS1223): Evidence of quadrupolar T distribution ? Two asymmetric minima cannot be explained with purely axisymmetric dipolar T distribution

28I Compstar meeting, Wroclaw 2008 B field evolution: braking index

29I Compstar meeting, Wroclaw 2008 Summary Evolution of B field unavoidable. Fast/moderate B field dissipation in the crust during the first Myr of a NS life. Are INS with B=1e13 G just old magnetars ? Are magnetars in the “Hall phase” ? Hall drift displaces field towards surface/poles/equator and there is increased magnetospheric activity. Observational evidence of B-T correlation. Old radio-pulsars more abundant at B=1e12 G, where are the thermally emitting young pulsars ? (maybe their initial fields were 10 times larger). Joule heating by B field decay accounts for observed properties. Simple energy argument and cooling simulations agree. Overall evolution consistent with other evidences for strong crustal fields (magnetar activity, small hot spots or hot equatorial rings, toroidal components, higher order multipoles, large braking index). DIRECT URCA (or other fast cooling processes) can be hidden by crustal currents dissipation plus the effect of core/crust magnetic insulation. Better understanding of cooling coupled to B field evolution is needed to establish “serious” constraints on exotic matter based on NS properties. !! Otherwise inferred constraints of gaps, rapid or fast cooling, NS radius, crust size, etc… significantly biased.