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GRB 051022及其宿主星系的黑暗性质

The dark nature of GRB 051022 and its host galaxy

A. J. Castro-Tirado, M. Bremer, S. McBreen, J. Gorosabel, S. Guziy, R. M. Gonzalez Delgado, G. Bihain, T. Fakthullin, S. B. Pandey, M. Jelinek, A. de Ugarte Pos… 展开作者

A. J. Castro-Tirado, M. Bremer, S. McBreen, J. Gorosabel, S. Guziy, R. M. Gonzalez Delgado, G. Bihain, T. Fakthullin, S. B. Pandey, M. Jelinek, A. de Ugarte Postigo, V. Sokolov, K. Misra, R. Sagar, P. Bama, A. P. Kamble, G. C. Anupama, J. Licandro, F. J. Aceituno, R. Neri

摘要:

我们目前的多波长(X射线/光学/近红外/毫米)GRB 051022的观测2.5小时和~1.15年后的事件。它是HETE-2探测到的最强烈的伽马射线暴(~ 10^-4 erg cm^-2),附近的GRB 030329除外。光学和近红外观测没有发现余辉,尽管在X射线波长下有很强的余辉。在Plateau de Bure(PdB)的毫米波观测发现了一个源和一个耀斑,证实了这一事件与一个中等亮度(R = 21.5)星系的关联。这个星系的光谱观测显示出强烈的[O II],Hbeta和[O III]发射线,红移为0.809。该星系的光谱能量分布意味着Av(静止坐标系)= 1.0和一个发生在约2500万年前的恒星爆发,在此期间恒星形成速率达到>= 25 Msun/yr。结合空间范围(~ 1“),它表明一个非常明亮(Mv =-21.8)的蓝色紧凑星系,我们也发现了Z Zsun。X射线光谱显示,含有NH的中性气体有相当大的吸收,X射线= 3.47(+0.48/-0.47)x 10^22 cm^-2(静止坐标系)。在z = 0.809的宿主星系中,尘埃的吸收当然不能解释没有检测到光学余辉的原因,除非尘埃与气体的比例与我们星系中看到的有很大的不同(即大的尘埃颗粒)。黑暗GRB 051022的余辉很可能沿着视线被母星系内分子云中一个模糊、致密的恒星形成区所熄灭。这个星系与大多数GRB宿主不同,它比L* 亮3倍。我们还推导出了SFR ~ 50 Msun/yr,并预测该宿主星系将在亚毫米波长处被探测到。

英文摘要:

We present multiwavelength (X-ray/optical/near-infrared/millimetre) observations of GRB 051022 between 2.5 hours and ~1.15 yr after the event. It is the most intense gamma-ray burst (~ 10^-4 erg cm^-2) detected by HETE-2, with the exception of the nearby GRB 030329. Optical and near infrared observations did not detect the afterglow despite a strong afterglow at X-ray wavelengths. Millimetre observations at Plateau de Bure (PdB) detected a source and a flare, confirming the association of this event with a moderately bright (R = 21.5) galaxy. Spectroscopic observations of this galaxy show strong [O II], Hbeta and [O III] emission lines at a redshift of 0.809. The spectral energy distribution of the galaxy implies Av (rest frame) = 1.0 and a starburst occuring ~ 25 Myr ago, during which the star-forming-rate reached >= 25 Msun/yr. In conjunction with the spatial extent (~ 1'') it suggests a very luminous (Mv = - 21.8) blue compact galaxy, for which we also find with Z Zsun. The X-ray spectrum shows evidence of considerable absorption by neutral gas with NH, X-ray = 3.47(+0.48/-0.47) x 10^22 cm^-2 (rest frame). Absorption by dust in the host galaxy at z = 0.809 certainly cannot account for the non-detection of the optical afterglow, unless the dust-to-gas ratio is quite different than that seen in our Galaxy (i.e. large dust grains). It is likely that the afterglow of the dark GRB 051022 was extinguished along the line of sight by an obscured, dense star forming region in a molecular cloud within the parent host galaxy. This galaxy is different from most GRB hosts being brighter than L* by a factor of 3. We have also derived a SFR ~ 50 Msun/yr and predict that this host galaxy will be detected at sub-mm wavelengths.

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