Models of hydrostatic atmospheres of magnetars at high luminosities Thijs van Putten1 Anna Watts1, Caroline D’Angelo1, Matthew Baring2, Chryssa Kouveliotou3 1University of Amsterdam, 2Rice University, 3NASA/Marshall Space Flight Center arXiv:1208.4212 October 30 2012, Fermi Symposium, Monterey image © Don Dixon Magnetars ✤ Neutron stars with inferred dipole magnetic field B ~ 1013-1016 G. ✤ Exhibit pulses (X-ray & radio), soft gamma ray bursts (~1040 erg s-1) and giant flares (~1044 erg s-1). image © NASA Magnetar atmosphere models Thijs van Putten October 30 2012 Magnetar model ✤ What is the equation of state? ✤ How and where is the emission created? ✤ What is the magnetic field configuration? Thompson & Duncan (1995) Magnetar atmosphere models Thijs van Putten October 30 2012 A peculiar magnetar burst Fermi GBM light curve of August 2008 burst from SGR 0501+4516. Light curve and black body fits of X2127 (Smale 2001) Magnetar atmosphere models Thijs van Putten October 30 2012 Photospheric Radius Expansion in magnetars? ✤ PRE in magnetars seems qualitatively possible (Watts et al. 2010) if magnetars have: ✤ Emission from optically thick region ✤ A critical luminosity ✤ Photosphere cooling with expansion ✤ Opacity increasing with radius Fermi GBM light curve of August 2008 burst from SGR 0501+4516. ✤ Observing it would constrain EoS, B and the emission location. Magnetar atmosphere models Thijs van Putten October 30 2012 Nonmagnetic models 0.9999 ✤ PRE requires sequence of extended stable atmospheres. ✤ Nonmagnetic models made by 0.9998 Paczynski & Anderson (1986). Luminosity / Eddington luminosity 0.0002 0.1 1 10 100 Atmosphere height (km) ✤ Stable nonmagnetic atmospheres exist up to r = 200 km. dP GM L r 0.0001 ⇢ 2 1 dr ' r ! Lcr ' Gas pressure / total 0.1 1 10 100 Atmosphere height (km) Magnetar atmosphere models Thijs van Putten October 30 2012 We find: No hydrostatic magnetar atmospheres with photospheric height > 10 m. Nonmagnetic case Our result Magnetar atmosphere models Thijs van Putten October 30 2012 Magnetar atmosphere models Thijs van Putten October 30 2012 Opacity in a super strong magnetic field BRIEF ARTICLE THE AUTHOR 0 Thomson scattering -2 ✤ Two photon polarizations: O-mode ] -1 g -4 (E∥B) and E-mode (E⊥B) 2 -6 10 keV -8 log Opacity [cm σO σTh 1 keV ' -10 2 2 ! T 0.1 keV -12 σE σTh 2 2 ' !C / B 11 12 13 14 15 16 log Magnetic field strength [G] E-mode Rosseland mean electron scattering opacity Magnetar atmosphere models Thijs van Putten October 30 2012 1 Atmosphere models E O 5 / P g 4 T 2 3 / B2 2 T 1 Lcr − ] ; log T [keV] P / -3 1 [g cm 0 L/Lcr =1 6 Pg / P log -1 0.01 0.1 1 10 Atmosphere height [m] Magnetar atmosphere models Thijs van Putten October 30 2012 Conclusions ✤ Hydrostatic extended magnetar atmospheres do not exist in open field line regions. ✤ Photospheric Radius Expansion cannot occur in magnetars. ✤ Spectral models of magnetar bursts considering two distinct components attributed to the E- and O-mode photospheres may have to be reconsidered. ✤ Future work: what does happen when L reaches Lcr in a magnetar atmosphere? Magnetar atmosphere models Thijs van Putten October 30 2012.