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Models of Hydrostatic Magnetar Atmospheres at High Luminosities

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Models of Hydrostatic Magnetar Atmospheres at High Luminosities 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.
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