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991.
Gehrels N Sarazin CL O'Brien PT Zhang B Barbier L Barthelmy SD Blustin A Burrows DN Cannizzo J Cummings JR Goad M Holland ST Hurkett CP Kennea JA Levan A Markwardt CB Mason KO Meszaros P Page M Palmer DM Rol E Sakamoto T Willingale R Angelini L Beardmore A Boyd PT Breeveld A Campana S Chester MM Chincarini G Cominsky LR Cusumano G de Pasquale M Fenimore EE Giommi P Gronwall C Grupe D Hill JE Hinshaw D Hjorth J Hullinger D Hurley KC Klose S Kobayashi S Kouveliotou C Krimm HA Mangano V 《Nature》2005,437(7060):851-854
Gamma-ray bursts (GRBs) come in two classes: long (> 2 s), soft-spectrum bursts and short, hard events. Most progress has been made on understanding the long GRBs, which are typically observed at high redshift (z approximately 1) and found in subluminous star-forming host galaxies. They are likely to be produced in core-collapse explosions of massive stars. In contrast, no short GRB had been accurately (< 10') and rapidly (minutes) located. Here we report the detection of the X-ray afterglow from--and the localization of--the short burst GRB 050509B. Its position on the sky is near a luminous, non-star-forming elliptical galaxy at a redshift of 0.225, which is the location one would expect if the origin of this GRB is through the merger of neutron-star or black-hole binaries. The X-ray afterglow was weak and faded below the detection limit within a few hours; no optical afterglow was detected to stringent limits, explaining the past difficulty in localizing short GRBs. 相似文献
992.
Hjorth J Watson D Fynbo JP Price PA Jensen BL Jørgensen UG Kubas D Gorosabel J Jakobsson P Sollerman J Pedersen K Kouveliotou C 《Nature》2005,437(7060):859-861
It has long been known that there are two classes of gamma-ray bursts (GRBs), mainly distinguished by their durations. The breakthrough in our understanding of long-duration GRBs (those lasting more than approximately 2 s), which ultimately linked them with energetic type Ic supernovae, came from the discovery of their long-lived X-ray and optical 'afterglows', when precise and rapid localizations of the sources could finally be obtained. X-ray localizations have recently become available for short (duration <2 s) GRBs, which have evaded optical detection for more than 30 years. Here we report the first discovery of transient optical emission (R-band magnitude approximately 23) associated with a short burst: GRB 050709. The optical afterglow was localized with subarcsecond accuracy, and lies in the outskirts of a blue dwarf galaxy. The optical and X-ray afterglow properties 34 h after the GRB are reminiscent of the afterglows of long GRBs, which are attributable to synchrotron emission from ultrarelativistic ejecta. We did not, however, detect a supernova, as found in most nearby long GRB afterglows, which suggests a different origin for the short GRBs. 相似文献
993.
Europe-wide reduction in primary productivity caused by the heat and drought in 2003 总被引:22,自引:0,他引:22
Ciais P Reichstein M Viovy N Granier A Ogée J Allard V Aubinet M Buchmann N Bernhofer C Carrara A Chevallier F De Noblet N Friend AD Friedlingstein P Grünwald T Heinesch B Keronen P Knohl A Krinner G Loustau D Manca G Matteucci G Miglietta F Ourcival JM Papale D Pilegaard K Rambal S Seufert G Soussana JF Sanz MJ Schulze ED Vesala T Valentini R 《Nature》2005,437(7058):529-533
Future climate warming is expected to enhance plant growth in temperate ecosystems and to increase carbon sequestration. But although severe regional heatwaves may become more frequent in a changing climate, their impact on terrestrial carbon cycling is unclear. Here we report measurements of ecosystem carbon dioxide fluxes, remotely sensed radiation absorbed by plants, and country-level crop yields taken during the European heatwave in 2003. We use a terrestrial biosphere simulation model to assess continental-scale changes in primary productivity during 2003, and their consequences for the net carbon balance. We estimate a 30 per cent reduction in gross primary productivity over Europe, which resulted in a strong anomalous net source of carbon dioxide (0.5 Pg C yr(-1)) to the atmosphere and reversed the effect of four years of net ecosystem carbon sequestration. Our results suggest that productivity reduction in eastern and western Europe can be explained by rainfall deficit and extreme summer heat, respectively. We also find that ecosystem respiration decreased together with gross primary productivity, rather than accelerating with the temperature rise. Model results, corroborated by historical records of crop yields, suggest that such a reduction in Europe's primary productivity is unprecedented during the last century. An increase in future drought events could turn temperate ecosystems into carbon sources, contributing to positive carbon-climate feedbacks already anticipated in the tropics and at high latitudes. 相似文献
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Recent convergence between India and Eurasia is commonly assumed to be accommodated mainly along a single fault--the Main Himalayan Thrust (MHT)--which reaches the surface in the Siwalik Hills of southern Nepal. Although this model is consistent with geodetic, geomorphic and microseismic data, an alternative model incorporating slip on more northerly surface faults has been proposed to be consistent with these data as well. Here we present in situ cosmogenic 10Be data indicating a fourfold increase in millennial timescale erosion rates occurring over a distance of less than 2 km in central Nepal, delineating for the first time an active thrust fault nearly 100 km north of the surface expression of the MHT. These data challenge the view that rock uplift gradients in central Nepal reflect only passive transport over a ramp in the MHT. Instead, when combined with previously reported 40Ar-39Ar data, our results indicate persistent exhumation above deep-seated, surface-breaking structures at the foot of the high Himalaya. These results suggest that strong dynamic interactions between climate, erosion and tectonics have maintained a locus of active deformation well to the north of the Himalayan deformation front. 相似文献
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养羊业在国营农场是附属部门。我们繁育哈萨克细毛羊品种。现在的数量达到2.5万只并且控制稳定在这个水平。剪毛量按全群平均去年是4.2公斤。近五年国营农场达到了好而稳定的产羔指标。按群平均1975—1976年,从每100只母羊获得了107只羔羊,而1977—1979年获得了110只羔羊。我们比较好的放牧员大大超过了这些 相似文献