Abstract
Long-duration Gamma-ray bursts (GRBs) occur in star-forming regions and have simple synchrotron emission spectra. In a sample study of 41 GRB afterglows 21 require a cooling break between the X-ray and the optical/near-infrared. Excluding one outlier, GRB080210, the average spectral slope change is Δβ = 0:51 with a standard deviation of 0.02 consistent with the prediction of synchrotron model. To understand environmental properties of GRBs, gas-to-dust ratios are compared with the metallicities of GRB afterglows, indicating an anti-correlation between the two values. This anti-correlation is consistent with the Local Group relation. Since GRBs occur in star-forming regions, it was anticipated that there should be significant dust extinction of GRB optical afterglows. The vast majority of GRB extinction curves are featureless-the 2175Å bump so far has been detected in the optical spectra of only four GRBs. Using the Fitzpatrick & Massa (1990) extinction model, the strength of the bump is estimated for 38 GRB afterglows, preferring Small Magellanic Cloud (SMC)-type extinction curve, finding in no significant detection of the 2175Å bump. The comparison of GRB afterglows to the Local Group sightlines suggests that GRB afterglows usually have lower bump strength for a given AV.
| Original language | English |
|---|---|
| Pages (from-to) | 108-112 |
| Number of pages | 5 |
| Journal | Memorie della Societa Astronomica Italiana, Supplementi - Journal of the Italian Astronomical Society, Supplement |
| Volume | 21 |
| Publication status | Published - 1 Jan 2012 |
| Externally published | Yes |
| Event | GRBs as Probes: From the Progenitors Environment to the High - Como, Italy Duration: 16 May 2011 → 20 May 2011 |
Keywords
- Galaxies: high-redshift
- ISM: dust, extinction
- Gamma-ray burst: general