Phy Spring20051 Rp-process Nuclosynthesis in Type I X-ray Bursts A.M. Amthor Church of Christ, Kingdom of Heaven National Superconducting Cyclotron Laboratory, Michigan State University Department of Physics and Astronomy, Michigan State University

AMA Phy Spring20052 Outline Quick Review of X-ray bursts Delineation of burst types by total accretion rate Method of breakout to start the rp-process in a mixed H/He burst Observations – compared to expectations Simulations

AMA Phy Spring20053 X-ray burst basics – mostly review Accretion – of matter from companion star Accumulation – of matter on the NS surface Ignition – near the base of the accreted column Explosion – runaway fusion chain reactions through the  p and rp-process Burst flux Persistent flux Interesting quantities are: - the total mass accretion rate - the specific accretion rate - the ratio of persistent flux to burst flux - the recurrence time Also the burst duration and regularity Bursts happen for :

AMA Phy Spring20054 Burst types (Assuming accreted material with ) For we have which allows unstable CNO H burning.For we have for which the HCNO cycle leads to stable H burning. Burst So for and the burst ignition will be by unstable 3  Burst Pure He BurstMixed H/He Burst

AMA Phy Spring20055 Breakout to Rp-process (H/He burst) Significant boundaries in temperature vs. density for the development of the rp-process 3  flow Hot CNO cycle below curve a) Beyond curve a) is dominant Beyond curve b) is dominant Beyond curve a) is dominant By curve d) dominates the flow, then avoiding all decays up to that point Beyond curve c) the rp-process rate is limited by decays not by Schatz, Phy 983 notes spring 2003.

AMA Phy Spring20056 Observations Line for Extended study of GS Measures total accretion rate Increased total accretion rate for the same type of burst Reduced time to build to critical column depth & Increased temperature in accreted layer from gravitational energy release Reduced recurrence time

AMA Phy Spring20057 ms Oscillations Strohmayer, T. E. and L. Bildsten, Compact Stellar X-ray sources, astro-ph/ (2003). From the neutron star binary 4U Oscillations likely caused by asymmetric burst ignition. Frequencies closely related to the neutron star rotation frequencies. Frequency drift possibly caused by expansion of the burning envelope during the burst. Contraction recouples the envelope to the surface resulting in spin up approaching NS’s rotation frequency. Spin up – Spin down ? Burst rise – Burst tail ?

AMA Phy Spring20058 Unexplained observations LMXB with accretion rates consistent with steady bursting which show few or no bursts Transition between bursting regimes at total accretion rates not consistent with theory Large frequency drifts in oscillations

AMA Phy Spring20059 Simulations van Wormer et al. ApJ. 432:326 (1994) Truncated Network  1-Zone Model  Constant temperature  Constant density  Limited reaction network Reaction Network Calculations Given adequate hydrogen and slow cooling, burning would continue to a closed cycle in Sn, Sb, and Te.

AMA Phy Spring Newer model calculations  Multi-Zone/1d-Model  Variable temperature  Variable density  1300 isotopes in adaptive network  Convective and semiconvective mixing and energy transport  Compositional inertia in burst trains Still assumes spherical symmetry!

AMA Phy Spring Thank you – any questions? ?