Open AccessAre GRB 980425 and GRB 031203 real outliers or twins of GRB 060218?
Author(s) -
Ghisellini G.,
Ghirlanda G.,
Mereghetti S.,
Bosnjak Z.,
Tavecchio F.,
Firmani C.
Publication year - 2006
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2006.10972.x
Subject(s) - gamma ray burst , physics , astrophysics , spectral properties , astronomy
GRB 980425 and GRB 031203 are apparently two outliers with respect to the correlation between the isotropic equivalent energy E iso emitted in the prompt radiation phase and the peak frequency E peak of the spectrum in a ν F ν representation (the so‐called Amati relation). We discuss if these two bursts are really different from the others or if their location in the E iso – E peak plane is the result of other effects, such as viewing them off‐axis, or through a scattering screen, or a misinterpretation of their spectral properties. The latter case seems particularly interesting after GRB 060218 that, unlike GRB 031203 and GRB 980425, had a prompt emission detected both in hard and soft X‐rays which lasted ∼2800 s. This allowed us to determine its E peak and total emitted energy. Although it shares with GRB 031203 the total energetics, it is not an outlier with respect to the Amati correlation. We then investigate if a hard‐to‐soft spectral evolution in GRB 031203 and GRB 980425, consistent with all the observed properties, can give rise to a time‐integrated spectrum with an E peak consistent with the Amati relation.