Neutron Stars and Debris Disks Andy Shearer and Vitaly Neustroev Centre for Astronomy NUI, Galway Ireland 22/02/2019

Debris Disks and Pulsar Theory Underlying pulsar theory unchanged for 40 years rapidly rotating magnetised neutron star radio energy emission - coherent synchrotron high energy emission - incoherent synchrotron or curvature radiation No agreement on how. Probably the only point of agreement between all these theories is the association of pulsars with magnetized, rotating neutron stars - Lyutikov, M., Blandford, R., & Machabeli, G., 1999, MNRAS, 305, 338 Understanding now helped by Rotating Radio Transients - RRATs AXPs Transient pulsars and transient phenomena ..... 22/02/2019

Some Background Pulsar-disk systems have been proposed for over 25 years Debris Disks - either fossil disk created during the supernova event Michel & Dessler, 1981, ApJ, 251, 654, Pulsar Disk System Michel, Nature, 1988, 333, 644, Neutron star disk formation from supernova fall-back and possible observational consequences continually fed from the ISM e.g. Popov, Colpi, Treves, Turolla, Lipunov, & Prokhorov, 2000, ApJ, 530, 896 pulsar planetary system first discovered in 1992 - and to date the lowest mass planet Wolszczan, A.; Frail, D. A., 1992, Nature, 355, 145 22/02/2019

Some more background - Spin History But n=2.4 - PSR B0540-69 1.4 - Vela 2.51 - Crab 2.91 PSR J1119-6127 2.837 PSR B1509-58 Additional torque from a fall-back disk Menou, Perna & Hernquist, ApJ, L63, 554 (2001) Mass in flow ~ 10-6 M☉ / year for the Crab But requires limitations on the radial extent of the disk to avoid optical detection An additional source of torque for Vela? Possibly a fall-back/debris disk? 22/02/2019

UltraCam observations - Dhillon et al, MNRAS, 363, 609, 2005 First observation of a neutron star disk - AXP- 4U 0142+61 unpulsed Wang et al, 2006, Nature, 440, 772 Pulsed Figure 3. Energy distribution for 4U 0142+61. At low frequencies (1014–1015 Hz), the points marked V, R, and I indicate the observed V, R, and I-band fluxes. The vertical error bars reflect the uncer- tainties, while the horizontal ones indicate the filter bandwidths. The set of points above the mea- surements indicate dereddened fluxes for AV = 5.4, as inferred from the X-ray column density.10,11 The errors include a 3% uncertainty in the reddening correction.9 At high frequencies (1017–1018 Hz), the crosses show the incident X-ray spectrum as inferred from ASCA measurements.10 The diamonds show the spectrum after correction for interstellar absorption, and the two thick dashed curves show the two components used in the fit10: a power law of the form F = 103(h /1 keV)−2.67 μJy and a black body with T = 4.4 Å~ 106 K and R = 12d5 km. The latter component is extrapolated to lower frequencies to show it cannot reproduce the optical fluxes. Drawn in thin solid lines are models for the optical emission. The curve marked disk is for an accretion disk that has inner radius equal to the corotation radius Rco = (GMP2/4 2)1/3 = 0.010R⊙ (for M = 1.4M⊙, P = 8.7 s), outer radius of 1014 cm, and inclination of 60 degrees. Both irradiation and viscous heating are taken into account13; the former dominates in the optical and the latter causes the bump in the ultra-violet. The calculation is for d = 5 kpc, but since the disk luminosity scales almost linearly with the X-ray luminosity, the result is not sensitive to distance. The optical fluxes expected in the accretion model are greatly in excess of those observed. Only for a truncated disk with a small outer disk radius, rout ∼ < 0.1d10/11 5 (f/0.25)−2/11 R⊙, can the observed fluxes be reproduced, as is shown by the dashed curve. The thin solid curves marked BB, H, and He are black body, pure hydrogen and pure helium white dwarf model atmospheres for T = 4 Å~ 105 K. The normalization to the optical data implies R = 0.011d5, 0.017d5 and 0.015d5 R⊙, respectively. None of the spectra can reproduce the X-ray emission. Pulsars are rotating, magnetized neutron stars that are born in supernova explosions following the collapse of the cores of massive stars. If some of the explosion ejecta fails to escape, it may fall back onto the neutron star or it may possess sufficient angular momentum to form a disk. Such `fallback' is both a general prediction of current supernova models and, if the material pushes the neutron star over its stability limit, a possible mode of black hole formation. Fallback disks could dramatically affect the early evolution of pulsars, yet there are few observational constraints on whether significant fallback occurs or even the actual existence of such disks. Here we report the discovery of mid-infrared emission from a cool disk around an isolated young X-ray pulsar. The disk does not power the pulsar's X-ray emission but is passively illuminated by these X-rays. The estimated mass of the disk is of the order of 10 Earth masses, and its lifetime (>= 106years) significantly exceeds the spin-down age of the pulsar, supporting a supernova fallback origin. The disk resembles protoplanetary disks seen around ordinary young stars, suggesting the possibility of planet formation around young neutron stars. UltraCam observations - Dhillon et al, MNRAS, 363, 609, 2005 22/02/2019

Other evidence for debris disks? Shibanov, Y. A, et al, 2006, A&A, 448, 313

Perna, Hernquist & Narayan, 2000, ApJ, 54, 344 Not a new idea ... Perna, Hernquist & Narayan, 2000, ApJ, 54, 344

Spitzer - NICMOS - Subaru Image PSR B0656+15 Spitzer 3.6μm Spitzer 5.8μm Subaru B NICMOS 160W Subaru -Shibanov et al., A&A, 448, 313 (2006) Nicmos - Koptsevich et al, A&A., 370, 1004 (2001) Spitzer - Spitzer archive. 22/02/2019

Predicted Debris Disk Fluxes for Normal Pulsars Predicted Debris Disk Fluxes for Normal Pulsars rinner= light cylinder radius router=1R Geminga parallax 2007Ap&SS.308..225 Faherty, Jacqueline; Walter, Frederick M.; Anderson, Jay 1055 distance 2002ApJ...564..369H Gamma-Ray Emission from an Outer Gap Accelerator: Constraints on Magnetospheric Current, Magnetic Inclination, and Distance for PSR B1055-52 Hirotani, Kouichi; Shibata, Shinpei

Rotating RAdio Transients - RRATs Transient phenomena - Debris Disk hints? Rotating RAdio Transients - RRATs To date ~10 pulsars show transient behaviour McLaughlin et al, Nature, 2006, 439, 817 At least one with an X-ray counterpart Reynolds et al, 2006, ApJ, 639, L71 Accreting material triggering magneto-spheric activity? Li, 2006, ApJ, 646, L139, also PSR B1931+24 Authors: Li, Xiang-Dong Affiliation: AA(Department of Astronomy, Nanjing University, Nanjing 210093, China; lixd@nju.edu.cn) Publication: The Astrophysical Journal, Volume 646, Issue 2, pp. L139-L142. (ApJ Homepage) Publication Date: 08/2006 22/02/2019

Other stochastic emitters - Giant Radio Pulse[GRPs] Pulsars A few pulsars emit GRPs where the randomly occurring pulses have a flux many thousand times greater than the normal 22/02/2019

Ground based AO Observations arXiv:0712.4171v2 Possible interpretations X-ray heated fossil debris disk Viscously heated disk 22/02/2019

Summary - why near IR observations are important At least one young neutron star, 4U 0142+61, has been observed to have a debris-disk, but how many others do? how long does a disk last? are such disks suitable for planet formation? disks or rings? How many young ‘normal’ pulsars have associated debris disks? t < 100,000 years Vela, Crab ...... middle aged pulsars - PSR B0656+14, Geminga, Can debris disks explain Stochastic pulsar behaviour? Spin evolution and birth spin period? 22/02/2019

Summary - Why SM4 will be important ACS Visible polarisation WFC3 NIR imaging for 0.1μJy fluxes NICMOS NIR imaging and polarimetry compare LONG and SHORT polarisation fluxes Observations at 2 microns Need multi-wavelength studies X-Ray - IR variability for AXP disks WFC3 and ground based adaptive optic observations [ELTs] 22/02/2019