اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدLocal starburst conditions and formation of GRB 980425 / SN 1998bw within a collisional ring
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We present the first spatially resolved study of molecular gas in the vicinity of a Gamma Ray Burst, using CO(2-1) emission line observations with the Atacama Large Millimetre Array (ALMA) at ~50 pc scales. The host galaxy of GRB 980425 contains a ring of high column density HI gas which is likely to have formed due to a collision between the GRB host and its companion galaxy, within which the GRB is located. We detect eleven molecular gas clumps in the galaxy, seven of which are within the gas ring. The clump closest to the GRB position is at a projected separation of ~280 pc. Although it is plausible that the GRB progenitor was ejected from clusters formed in this clump, we argue that the in situ formation of the GRB progenitor is the most likely scenario. We measure the molecular gas masses of the clumps and find them to be sufficient for forming massive star clusters. The molecular gas depletion times of the clumps show a variation of ~2 dex, comparable with the large variation in depletion times found in starburst galaxies in the nearby Universe. This demonstrates the presence of starburst modes of star formation on local scales in the galaxy, even while the galaxy as a whole cannot be categorised as a starburst based on its global properties. Our findings suggest that the progenitor of GRB 9802425 was originated in a young massive star cluster formed in the starburst mode of star formation.
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We report Giant Metrewave Radio Telescope (GMRT) , Very Large Telescope (VLT) and Spitzer Space Telescope observations of ESO 184$-$G82, the host galaxy of GRB 980425/SN 1998bw, that yield evidence of a companion dwarf galaxy at a projected distance
of 13 kpc. The companion, hereafter GALJ193510-524947, is a gas-rich, star-forming galaxy with a star formation rate of $rm0.004,M_{odot}, yr^{-1}$, a gas mass of $10^{7.1pm0.1} M_{odot}$, and a stellar mass of $10^{7.0pm0.3} M_{odot}$. The interaction between ESO 184$-$G82 and GALJ193510-524947 is evident from the extended gaseous structure between the two galaxies in the GMRT HI 21 cm map. We find a ring of high column density HI gas, passing through the actively star forming regions of ESO 184$-$G82 and the GRB location. This ring lends support to the picture in which ESO 184$-$G82 is interacting with GALJ193510-524947. The massive stars in GALJ193510-524947 have similar ages to those in star-forming regions in ESO 184$-$G82, also suggesting that the interaction may have triggered star formation in both galaxies. The gas and star formation properties of ESO 184$-$G82 favour a head-on collision with GALJ193510-524947 rather than a classical tidal interaction. We perform state-of-the art simulations of dwarf--dwarf mergers and confirm that the observed properties of ESO 184$-$G82 can be reproduced by collision with a small companion galaxy. This is a very clear case of interaction in a gamma ray burst host galaxy, and of interaction-driven star formation giving rise to a gamma ray burst in a dense environment.
We calculate radio-to-X-ray light curves for afterglows caused by non-thermal emission from a highly relativistic blast wave, which is inferred from the gamma-ray flux detected in GRB 980425 and from the very bright radio emission detected in SN 1998
bw. We find that the observed gamma-ray and radio light curves are roughly reproduced by the synchrotron emission from a relativistic fireball. The optical flux predicted for the non-thermal emission is well below that of the thermal emission observed for SN 1998bw so that it will not be seen at least for a few years. The model predicts the X-ray flux just above the detection limit of BeppoSAX for the epoch when it was pointed to the field of GRB980425. Therefore, the nondetection of X-ray and optical afterglows is consistent with the model. The models presented here are consistent with the physical association between SN 1998bw and GRB980425, and lend further support to the idea that this object might correspond to an event similar to the ``hypernova or ``collapsar -- events in which the collapse of a massive star forms a rotating black hole surrounded by a disk of the remnant stellar mantle.
We have recently suggested that gas accretion can be studied using host galaxies of gamma-ray bursts (GRBs). We obtained the first ever far-infrared (FIR) line observations of a GRB host, namely Herschel/PACS resolved [CII] 158 um and [OI] 63 um spec
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Giant molecular clouds (GMCs) are the primary reservoirs of cold, star-forming molecular gas in the Milky Way and similar galaxies, and thus any understanding of star formation must encompass a model for GMC formation, evolution, and destruction. The
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