Biswaraj Palit

Centrum Astronomiczne im. M. Kopernika PAN

Sesja X: Sesja plakatowa

Czwartek 14.09.2023 12:00 – 13:00

abstrakt:
The observed spectra of compact objects are significantly impacted by general relativity. For different chemical compositions, we present new models of hot, non-rotating neutron star (NS) atmospheres. To determine the observable appearance of the NS’s continuum emission, ray tracing computations are carried out for the single space-time configuration. These models combined with ray tracing will be made available as an XSPEC fitting package. We show how strong gravity affects the value of the color-correction factor (the ratio of frequency at which the best-fit spectrum displays the maximum to the peak flux of the black body at the effective temperature of the atmosphere) as determined by the distant observer.
The ATM24 code, which accurately treats the Compton scattering of photons on free electrons in fully relativistic thermal motion, was used to calculate the grid of intensity spectra emanating from the NS surface. Using the GYOTO code and the range of surface gravities from the atmosphere, the emerging specific intensity spectra are then ray-traced over the spacetime of a non-rotating NS to the far-off observer. For a broad grid of models with various chemical compositions, color-correction factors were established for surface gravities ranging from the critical gravity (log g_{crit}) up to 15.00 (cgs) and for effective temperatures in the range 1x 10^7 K to 3 x 10^7 K.
In very bright metal-rich atmospheres, Comptonized spectra at the source rest frame show color-correction factors ranging from 1.4 to 2.0 and even up to 3.0 in pure hydrogen atmospheres. For ray-traced spectra, the color-correction factors ranged from 0.9 to 1.4.
The NS’s surface gravity, brightness, and atmospheric metal abundance all play a significant role in determining the structure of the hot atmosphere in the strong gravity regime. The theoretical color-correction factors of the ray-traced spectra are typically roughly 30% lower than the hardening factors of the source spectra.