Cohesive Properties of Highly Magnetized Neutron Star Surfaces Zach Medin July 19, 2006

Outline Cohesive properties (cohesive energy, work function, zero-pressure density) are fundamental quantities characterizing NS surfaces; they determine whether a “vacuum gap” accelerator can form the character of thermal emission from NS

Polar Gap Model of Pulsar Radio Emission Acceleration of charged particles across gap leads to coherent radio emission If no gap forms, particle acceleration can occur through space-charge- limited flow (e.g., Arons- Scharleman 1979; Muslimov-Tsygan 1992)

Condensed NS Surface and Thermal Emission from NSs Perfect BB spectra in some NSs (e.g., 1856; see Burwitz et al. 2003) Could this arise from condensed NS surface emission (van Adelsberg et al. 2005)?

Calculation of NS Cohesive Properties Our calculation improves on those of previous works (e.g., Jones 1986 and Neuhauser et al. 1987) in several ways: accurate treatment of high-B exchange-correlation effects better treatment of the electron band structure wider range of B considers small molecules, infinite chains, and 3D condensed matter

Application: High-B Radio Pulsars vs. Magnetars Magnetars (AXPs and SGRs): NSs powered by B field dissipation Inferred to have B= G No “pulsar-like” radio emission (but see Camilo et al. 2006) High-B Radio Pulsars Recent observations found several high-B radio pulsars (e.g., McLaughlin-Kaspi 2003) Overlap of magnetars and radio pulsars in the P- diagram

Application: High-B Radio Pulsars vs. Magnetars, Part II Why is there no radio emission from quiescent magnetars? One possibility: particle emission due to twisted magnetic fields overwhelms acceleration region Another possibility: vacuum gap forms in high-B pulsars (T 5 x 10 6 K)

Gap Formation in High-B NSs Potential barrier: E s +I n -nW At high fields, the critical temperature lies between the temperatures observed for magnetars and radio pulsars Gap will form if thermal emission of ions from surface is large enough to replace charges lost in the (+) open field region