Dust extinction properties of a sample of bright X-rays afterglows

Details Dust extinction properties of a sample of bright X-rays afterglows Dust extinction properties of a sample of bright X-rays afterglows

Jul 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005ncimc..28..693s&link_type=abstract

Il Nuovo Cimento C, vol. 28, Issue 4, p.693

Computer Science

1

Scientific paper

We have studied a sample of four bright X-rays afterglows of Gamma-ray Bursts (GRBs) for which the optical spectral energy distributions (SEDs), not corrected for extra-galactic dust extinction, have spectral index consistent with the X-rays spectral index, but with fluxes significantly below the X-rays extrapolation assuming a simple power law spectral model. A simple power law model is suggested by the spectral and temporal indices of these afterglows as already noted in previous works, although a spectral break between the X-rays and the optical band cannot be excluded but in one case. Previous works invoked a non standard extinction law to recover the observed spectral “mismatch”; alternatively, the same electron population may have produced the observed NIR-optical emission via synchrotron radiation and the X-rays via Inverse Compton scattering. We have investigated on the non-standard extinction hypothesis, since high redshift environments can be in principle very different from standard (local) interstellar media and GRB circumburst environment may well be modified by the burst itself. Although the uncertainty on the underlying spectral model prevented us to reach firm conclusions, we found that an extinction curve weakly dependent on the wavelenght makes the optical SED consistent with the X-rays flux extrapolation assuming a simple power law model and provides at the same time rest frame visual extinction values nicely in agreement with the equivalent hydrogen column densities measured from X-rays analysis. An extinction law weakly dependent on the wavelenght can be provided by dust grains destruction due to the intense X-rays and UV fluxes from the burst itself or by small dust grains coagulation into larger ones. The large sample of optical-to-X-rays spectrally monitored afterglows provided by Swift will address our findings.

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