Bibcode
Stratta, G.; Basa, S.; Butler, N.; Atteia, J. L.; Gendre, B.; Pélangeon, A.; Malacrino, F.; Mellier, Y.; Kann, D. A.; Klose, S.; Zeh, A.; Masetti, N.; Palazzi, E.; Gorosabel, J.; Castro-Tirado, A. J.; de Ugarte Postigo, A.; Jelinek, M.; Cepa, J.; Castañeda, H.; Martínez-Delgado, D.; Boër, M.; Braga, J.; Crew, G.; Donaghy, T. Q.; Dezalay, J.-P.; Doty, J.; Fenimore, E. E.; Galassi, M.; Graziani, C.; Jernigan, J. G.; Kawai, N.; Lamb, D. Q.; Levine, A.; Manchanda, R. K.; Martel, F.; Matsuoka, M.; Nakagawa, Y.; Olive, J.-F.; Pizzichini, G.; Prigozhin, G.; Ricker, G.; Sakamoto, T.; Shirasaki, Y.; Sugita, S.; Suzuki, M.; Takagishi, K.; Tamagawa, T.; Vanderspek, R.; Villasenor, J.; Woosley, S. E.; Yamauchi, M.; Yoshida, A.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 461, Issue 2, January II 2007, pp.485-492
Fecha de publicación:
1
2007
Revista
Número de citas
12
Número de citas referidas
10
Descripción
Context: The origin of X-ray Flashes (XRFs) is still a mystery and
several models have been proposed. To disentangle among these models, an
important observational tool is the measure of the XRF distance scale,
so far available only for a few of them. Aims: In this work, we
present a multi-wavelength study of XRF 040912, aimed at measuring its
distance scale and the intrinsic burst properties. Methods: We
performed a detailed spectral and temporal analysis of both the prompt
and the afterglow emission and we estimated the distance scale of the
likely host galaxy. We then used the currently available sample of XRFs
with known distance to discuss the connection between XRFs and classical
Gamma-ray Bursts (GRBs). Results: We found that the prompt
emission properties unambiguously identify this burst as an XRF, with an
observed peak energy of E_p=17±13 keV and a burst fluence ratio
S2{-30 keV}/S30{-400 keV}>1. A non-fading
optical source with R˜24 mag and with an apparently extended
morphology is spatially consistent with the X-ray afterglow, likely the
host galaxy. XRF 040912 is a very dark burst since no afterglow optical
counterpart is detected down to R>25 mag (3σ limiting
magnitude) at 13.6 h after the burst. The host galaxy spectrum detected
from 3800 Å to 10 000 Å, shows a single emission line at
9552 Å. The lack of any other strong emission lines blue-ward of
the detected one and the absence of the Lyα cut-off down to 3800
Å are consistent with the hypothesis of the [OII] line at redshift
z=1.563±0.001. The intrinsic spectral properties rank this XRF
among the soft GRBs in the E_peak-E_iso diagram. Similar results were
obtained for most XRFs at known redshift. Only XRF 060218 and XRF 020903
represent a good example of instrinsic XRF (i-XRF) and are possibly
associated with a different progenitor population. This scenario may
call for a new definition of XRFs.