Probing the Warm Intergalactic Medium through Absorption against Gamma-Ray Burst X-Ray Afterglows
Abstract
Gamma-ray burst (GRB) afterglows close to their peak intensity are among the brightest X-ray sources in the sky. Despite their fast power-law-like decay, when fluxes are integrated from minutes up to hours after the GRB event, the corresponding number counts (logN-logF relation) far exceed those of any other high-redshift (z>0.5) source, the flux of which is integrated over the same time interval. We discuss how to use X-ray afterglows of GRBs as distant beacons to probe the warm (105 K<T<107 K) intergalactic matter in filaments and outskirts of clusters of galaxies by means of absorption features, the ``X-ray forest.'' According to current cosmological scenarios, this matter may comprise 30%-40% of the baryons in the universe at z<1. Present-generation X-ray spectrometers such as those on Chandra and XMM-Newton can detect it along most GRBs' lines of sight, provided afterglows are observed soon enough (within hours) after the burst. A dedicated medium-sized X-ray telescope (effective area <~0.1 m2) with pointing capabilities similar to that of Swift (minutes) and high spectral resolution (E/ΔE>~300) would be very well suited to exploit the new diagnostic and study the physical conditions in the universe at the critical moment when structure is being formed.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 2000
- DOI:
- 10.1086/317286
- arXiv:
- arXiv:astro-ph/0009292
- Bibcode:
- 2000ApJ...544L...7F
- Keywords:
-
- Cosmology: Observations;
- Gamma Rays: Bursts;
- Cosmology: Large-Scale Structure of Universe;
- Astrophysics
- E-Print:
- ApJ Letters in press