关于γ射线爆发的3篇译文
本帖最后由 gohomeman1 于 2009-5-3 00:19 编辑http://science.nasa.gov/headlines/y2009/28apr_grbsmash.htm?list1314647
2009.04.28
New Gamma-Ray Burst Smashes Cosmic Distance Record
新发现的γ射线爆发打破了宇宙（最遥远）距离记录
April 28, 2009: NASA's Swift satellite and an international team of astronomers have found a gamma-ray burst from a star that died when the universe was only 630 million years old--less than five percent of its present age. The event, dubbed GRB 090423, is the most distant cosmic explosion ever seen.
2009.4.28：美国航空航天局（NASA）的雨燕卫星和一个国际天文学家团队已经发现了一次早期宇宙中的因恒星死亡产生的γ射线爆发——此时宇宙年龄仅有6.3亿年，还不到现有年龄的5%。这个编号为 GRB 090423的爆发事件，是我们已经观测到的最遥远距离的宇宙爆发事件。
"The incredible distance to this burst exceeded our greatest expectations -- it was a true blast from the past," says Swift lead scientist Neil Gehrels at NASA's Goddard Space Flight Center.
戈达德太空飞行中心，雨燕科学团队领头人Neil Gehrels说：“这次爆发的距离难以置信，超出了我们最大的想象——它是过去真实发生过的爆炸。”
http://science.nasa.gov/headlines/y2009/images/grbsmash/337655main_GRB090423_Swift.jpg
Above: GRB 090423 as seen by NASA's Swift satellite. The image is a composite of data from Swift's UV/Optical and X-Ray telescopes. Credit: NASA/Swift/Stefan Immler
上图：雨燕卫星拍摄的GRB 090423，图片由雨燕的紫外、可见光和X射线望远镜图像合成。（从文字看，与钱德拉卫星应该无关——译注）
The burst occurred at 3:55 a.m. EDT on April 23rd. Swift quickly pinpointed the explosion, allowing telescopes on Earth to target the burst before its afterglow faded away. Astronomers working in Chile and the Canary Islands independently measured the explosion's redshift. It was 8.2, smashing the previous record of 6.7 set by an explosion in September 2008. A redshift of 8.2 corresponds to a distance of 13.035 billion light years.
爆发于美国东部时间4.23凌晨3:55被观测到。雨燕卫星迅速地精确定位了爆发点，使地面望远镜在它的余辉黯淡之前及时转向目标。位于智利和加那利群岛的天文学家各自独立测定了爆发的红移量。它高达8.2，大大打破了2008.9爆发的前记录——6.7。红移量8.2相当于130.35亿光年距离。
"We're seeing the demise of a star -- and probably the birth of a black hole -- in one of the universe's earliest stellar generations," says Derek Fox at Pennsylvania State University.
“我们见证了宇宙最早世代恒星的死亡——也许是一个黑洞的诞生，” Derek Fox在宾西法尼亚州立大学说。
Gamma-ray bursts are the most luminous explosions in the Universe. Most occur when massive stars run out of nuclear fuel. As their cores collapse into a black hole or neutron star, jets of matter punch through the star and blast into space. There, they strike gas previously shed by the star and heat it, which generates short-lived after glows in many wavelengths.
γ射线爆发是宇宙中能量最强的爆炸，大部分发生在大质量恒星耗尽它的核聚变燃料的时候。当它的核心坍缩为中子星甚至黑洞时，喷射的物质流贯穿恒星外层并把它们爆破到太空中。在那里，物质流强烈冲击原先的恒星膨胀外壳并加热它们，产生短暂高能辐射（而此前的恒星辐射各种波长都有）。
For years, astronomers have been hunting for gamma-ray bursts from the earliest generations of stars--and mysteriously failing to find them. The detection of GRB 090423 is an important milestone in the quest to locate bursts in the redshift range 10 to 20. More information: "The Case of the Missing Gamma-ray Bursts."
天文学家搜寻最早期恒星的γ射线爆发多年，但莫名其妙的连续失败。在我们追寻红移量达10~20的爆发源之路上，发现GRB 090423是一个重要的里程牌。更多信息链接：“失踪的γ射线爆发案例”，2008.10.22。（我将在后面给出全文翻译——译注）
PS：由于图片大，逐段编辑很头晕，文章的第2部分移到第2楼。 ——gohomeman1 本帖最后由 gohomeman1 于 2009-5-3 21:48 编辑
2009.04.28
New Gamma-Ray Burst Smashes Cosmic Distance Record
新发现的γ射线爆发打破了宇宙（最遥远）距离记录
http://apod.nasa.gov/apod/image/0904/grb8_gemini_big.jpg
Within three hours of the April 23rd burst, Nial Tanvir at the University of Leicester, U.K., and his colleagues reported detection of an infrared source at the Swift position using the United Kingdom Infrared Telescope on Mauna Kea, Hawaii.
2009.4.23，英国莱斯特大学。仅仅在探测到爆发后数小时，Nial Tanvir和他的同事就报告在雨燕确定的方位，他们使用夏威夷莫纳克亚死火山上的英国红外望远镜发现了一个红外（点）源。
At the same time, Fox led an effort to obtain infrared images of the afterglow using the Gemini North Telescope on Mauna Kea. The source appeared in longer-wavelength images but was absent in an image taken at the shortest wavelength of 1 micron. This "drop out" corresponded to a distance of about 13 billion light-years.
同时，Fox团队使用莫纳克亚山上的大型双子北座望远镜努力获取了它的红外余辉图像。显示为最长波长图像的源头却是最短波长——小于1微米。这个“落差”大约相当于130亿光年的距离。
As Fox spread the word about the record distance, telescopes around the world turned to observe the afterglow before it faded away.
在Fox团队发布他们的发现后，全球望远镜都转去观测它爆发的余辉。
At the Galileo National Telescope on La Palma in the Canary Islands, a team including Guido Chincarini at the University of Milan-Bicocca, Italy, determined that the afterglow's redshift was 8.2. Tanvir's team, gathering nearly simultaneous observations using one of the European Southern Observatory's Very Large Telescopes on Cerro Paranal, Chile, arrived at the same number.
加那利群岛，拉帕尔马的伽利略自然望远镜，包括意大利米兰比可卡大学的 Guido Chincarini团队测定了余辉的红移量——8.2。Tanvir团队，用位于智利帕拉那山顶ESO的VLT阵列中的一台光谱仪近乎同步观测了余辉，获得相同的数据。
"It's an incredible find," Chincarini says. "What makes it even better is that a telescope named for Galileo made this measurement during the year in which we celebrate the 400th anniversary of Galileo's first astronomical use of the telescope."
“这真是不可思议的发现，” Chincarini说。“更妙的是就在庆祝伽利略首次用望远镜观天400周年纪念时，由现在的伽利略望远镜实现了如此发现。”
http://svs.gsfc.nasa.gov/vis/a010000/a010300/a010369/twoComponentJetStream_1280x720_web.png
An artist's concept of a gamma-ray burst in action. Click on the image for animations. Credit: NASA/Swift/Cruz deWilde.
γ射线暴的艺术想象图，具体的视频见下一楼链接。
Editor: Dr. Tony Phillips | Credit: Science@NASA
编辑：托尼.菲利普博士 版权声明：NASA科学频道
more information
更多信息
Mission home page: Swift
雨燕卫星主页：http://www.nasa.gov/mission_pages/swift/main/index.html
Credits: NASA's Goddard Space Flight Center manages Swift. It was built and is being operated in collaboration with Pennsylvania State University, the Los Alamos National Laboratory in New Mexico, and General Dynamics of Gilbert, Ariz., in the United States. International collaborators include the University of Leicester and Mullard Space Sciences Laboratory in the United Kingdom, Brera Observatory and the Italian Space Agency in Italy, and additional partners in Germany and Japan.
版权：NASA的戈达德太空飞行中心负责管理雨燕卫星。后面的各家大学、研究机构表从略。
PS：ESO的VLT阵列，相关详细数据可以参考ESO的主页或wikipedia的相关内容，欧洲南方天文台的甚大望远镜阵列望远镜包括4台8.2米口径反射镜的主镜，综合口径16米，其中2台是高精密光谱仪。——gohomeman1 本帖最后由 gohomeman1 于 2009-5-2 02:27 编辑
本文配套视频下载，
http://www.nasa.gov/mpg/337653main_Gamma_Ray_Burst_Two_Component_Jet_Stream_640x360.mpg6.7MB
http://svs.gsfc.nasa.gov/vis/a010000/a010300/a010369/twoComponentJetStream_1280x720.mov 94MB
本文的信息链接，2008.10.22的另一篇文章
http://science.nasa.gov/headlines/y2008/22oct_missinggrbs.htm
下一楼给出该文的翻译。
PS：我有一点很不理解，130亿光年外的天体怎么不是一个点，居然还有很多细节？雨燕的分辨率怎么也比不上哈勃吧？！地面望远镜也能发现较大的余辉区域，这该不能用爆发强度极其高来解释吧。种种迹象对比起来，到底是红移测定错误还是对象是个大型星系？抑或不能把哈勃定律直接外推到如此大的红移？说不定是天文学家也浮躁，只想出名、报告爆炸性新闻呢。 本帖最后由 gohomeman1 于 2009-5-2 22:47 编辑
http://science.nasa.gov/headlines/y2008/22oct_missinggrbs.htm
The Case of theMissing Gamma-ray Bursts
失踪的γ射线爆发案例
Oct. 22, 2008: Gamma-ray bursts are by far the brightest and most powerful explosions in the Universe, second only to the Big Bang itself. So it might seem a bit surprising that a group of them has gone missing.
2008.10.22：γ爆发是宇宙中极亮和能级极高的爆发，仅次于宇宙创生的原初大爆炸。所以当它们成群失踪时，会产生不大不小的波澜。（本句是意译的——译注）
A single gamma-ray burst (GRB) can easily outshine an entire galaxy containing hundreds of billions of stars. Powerful telescopes can see them from clear across the Universe. And because the deeper you look into space, the farther back in time you see, astronomers should be able to see GRBs from the time when the very first stars were forming after the Big Bang.
单一γ爆发（简称GRB）的光度能轻易超过包含千亿级恒星的整个星系。强力望远镜能够发现它们穿越了整个宇宙时空的闪光。因为你看见的天体越远，你能回溯的时光越久，天文学家观测到极遥远的GRB爆发也就表明他们看见了宇宙大爆炸后极早期的恒星。
Yet they don't. Gamma-ray bursts from that early epoch seem to be missing, and astronomers are wondering where they are.
但一直没能发现极早世代恒星的γ爆发，它们好像都失踪了，天文学家很想知道它们都在哪里？
http://science.nasa.gov/headlines/y2008/images/missinggrbs/firststars.jpg
Above: An artist's concept of the first stars forming after the Big Bang. Credit: NASA.
上图：宇宙大爆炸后首批恒星形成的艺术概念图。版权：NASA
PS：我很怀疑空间的膨胀速度有多快，如此遥远的星光到底表示宇宙在6亿岁时就相当的大还是表明空间膨胀速度非常快，这些星光花了如此长时间才被我们看见。——gohomeman1 本帖最后由 gohomeman1 于 2009-5-4 12:32 编辑
The Case of theMissing Gamma-ray Bursts
失踪的γ射线爆发案例
"This is one of the biggest questions in the gamma-ray business," says astrophysicist Neil Gehrels of the Goddard Space Flight Center. "It's something we're going to be talking a lot about today at the GRB Symposium."
“这是γ射线爆发研究领域的最大问题”，戈达德太空飞行中心的天体物理学家 Neil Gehrels说。“在今天的GRB专题研讨会上，有许多东西值得讨论。”
Gehrels has joined about a hundred of his colleagues from 25 countries for the 6th Huntsville Gamma-ray Burst Symposium underway this week in Huntsville, Alabama. Missing gamma-ray bursts are one of the top mysteries on the agenda.
Gehrels和他的100多位同事参加了本周正在进行的第6届汉茨维尔γ射线爆发专题研讨会，他们来自25个国家，会议在美国阿拉巴马州汉茨维尔市举行。失踪的γ射线爆发是会议议程中的重点之一。
Until recently, experts were grappling with an even more fundamental question about GRBs: what the heck are they? Astronomers had observed these astonishing bursts since the 1960s, but nobody could imagine an event powerful enough to create them.
直到最近，专家们才确定抓住了GRB爆发的根本问题：它们到底是什么？天文学家从20世纪60年代就观测到这种惊人的爆发现象，但没人能够想象出一个足够强大的事件来产生如此强大的能量爆发。
http://science.nasa.gov/headlines/y2008/images/missinggrbs/collapsar_screenshot_med.jpg
The collapsar model of gamma-ray bursts. Click on the image to view a 5 MB animation.
γ射线爆发的黑洞模型。那个5MB动画下载见下一楼。
The answer eventually came from Stan Woosley, a theoretical astrophysicist at the University of California in San Diego. He suggested that when young, supermassive stars with low metal content collapse under their own weight to form black holes, the stars' rotation funnels the explosive energy into two streamlined jets that shoot out from the stars' poles, like the axis of a gyro. We only see the burst if one of these two jets happens to be pointed toward Earth. The concentration of energy into narrow jets is why GRBs that we do observe appear so remarkably bright.
答案最终由理论天体物理学家——圣迭戈市加利福尼亚大学的斯坦.卫斯理给出。他推测，当年轻的、重元素含量很低初代超级巨恒星在它们自身的巨大重力下形成黑洞时，恒星（外层的）旋转动能爆炸般汇集到两股从极区喷射的物质流中，就像一个陀螺轴似的。当喷流恰巧指向地球时，我们才能观测到爆发现象。由于能量集中在狭窄的喷流中，我们观测到的GRB就显得特别的亮。
http://science.nasa.gov/headlines/y2008/images/grboverview/artistsconcept.jpg
A gamma-ray burst heralds the birth of a black hole--an artist's concept.
艺术想象图：γ射线爆发预告了一个黑洞的诞生。
Note: Woosley's"collapsar model" explains the common long gamma-ray burst, explosions lasting 2 seconds or more. The cause of another class of shorter-lived GRBs is still a mystery, but that's another story.
注意： 卫斯理的“黑洞模型”能够解释长于2s的长周期γ射线爆发。至于短周期γ射线爆发的成因还是个谜，但那是另外一个故事了。
PS：我会在更后面的楼中给出这另一个故事的翻译，现在的成因推测貌似极小概率事件——中子星相撞。 ——gohomeman1 5#楼中提到的动画下载链接，5MB。但是我看不懂最后一段，整个恒星的大气层都被吹散了，恒星怎么却突然全部炸掉了，貌似黑洞突然蒸发一般。
http://www.nasa.gov/centers/goddard/mpg/69479main_collapsar.mpg 请问 雨燕的工作原理是什么怎么能迅速捕捉γ源？ 还能锁定区域？ 本帖最后由 gohomeman1 于 2009-5-4 12:02 编辑
继续第2篇文章的翻译。
The Case of theMissing Gamma-ray Bursts
失踪的γ射线爆发案例
The first waves of star formation after the Big Bang should have produced plenty of metal-poor supermassive stars ripe for collapse. If true, GRBs from that epoch should be abundant. So where are they?
宇宙大爆炸后形成的第一波恒星中，会产生很多缺乏重元素的超大质量恒星的崩溃案例（缺乏重元素的恒星的后期演化史与现在的蓝巨星是不同的——译注）。果真如此，那个纪元的GRB爆发应该相当的多，那么它们都在哪里呢？
One possibility is they're not missing at all.
一种可能是它们并没有都失踪。
"Part of the problem is that burst profiles get stretched out by the expansion of the Universe, so it is harder to recognize them as bursts in the first place," explains astrophysicist Lynn Cominsky of Sonoma State University. "The bursts could be happening, but we're not noticing them."
“一个问题是由于宇宙（快速）膨胀，爆发（星体）资料本身移到了可观测范围外，所以很难在爆发的原地发现它们，”加州州立森诺玛大学天体物理学家琳.Cominsky解释道。“爆发式产生了，但我们没注意到它们”。（貌似在说由于宇宙加速膨胀得太快，这些早期光已经看不到了——译注）
Another trouble is the afterglow—the fading debris that tells so much about a burst, including its distance. "Afterglows from the most distant GRBs may be too red shifted to be seen by current generations of telescopes," she notes.
另一个难题是余辉——凋谢的残骸包含距离等太多的爆发信息。“大部分遥远GRB爆发的余辉，由于红移量太大，当代望远镜已经观测不到了”，她补充道。
"Red shift" is how much the wavelength of light is stretched when it travels to us across the expanding Universe. The farther away a thing is, the more its light is stretched, and the greater the red shift. Until recently, the largest red shift ever measured for a GRB was 6.3. Then, last month, Gehrels and colleagues using NASA's Swift satellite found one with a red shift of 6.7 or 12.8 billion light years away. So far, that's the record.
“红移量”表征的是当光波穿越扩张的宇宙时空到达我们时，它波长变长的幅度。越远的光波红移越大。直到最近，测得的最大红移量是6.3。然后上个月，尼尔·格雷斯博士和他的同仁们用NASA的雨燕卫星探测到红移量达6.7或者相当于120亿光年远的γ射线爆发。这个红移是如此的大，创了记录。（原文所说这么远显然有误，因为哈勃超级深空场照片此前已经发现了129亿光年远的星系，那个星系距离应该也是用红移量标定的。——译注）
http://www.nasa.gov/images/content/276425main_farthestgrb3_HI.jpg
This image merges the view through Swift's UltraViolet and OpticalTelescope, which shows bright stars, and its X-ray Telescope, whichcaptures the burst (orange and yellow). Credit: NASA/Swift/Stefan Immler.
本图由雨燕卫星的图像合成，它的紫外和可见光望远镜显示了前景亮星；而它的X线望远镜捕捉到了爆发余辉（橙黄色最亮的部分）。版权：NASA、雨燕卫星、斯蒂芬.Immler。
"Gamma-ray bursts are predicted in the red shift range 10 to 20, but so far no one has seen anything beyond 6.7," says Cominsky.
“按（理论）预测，γ射线爆发的红移可达10~20，但超过6.7以上的红移量由于距离太远，我们看不到任何东西了，”琳.Cominsky说。
The luminous afterglow of such distant bursts would be red shifted all the way into the infrared. "There's a huge effort right now to try to get those infrared observations," Gehrels says, but in the meantime it's difficult to verify whether a candidate 7+ GRB is truly that far away.
如此远距离的余辉之光会一直红移到红外区。“当前该是投入巨大努力去进行这项红外观测的（时候了），”琳.Cominsky说，与此同时要证实一个红移大于7的天体是真的有这么远是相当难的。（韦伯卫星应该能胜任，天文学家自己都怀疑哈勃定律能否外推到这么大的数值。——译注）
As infrared telescopes improve, scientists should eventually be able to measure the distance to GRBs with red shifts greater than 7 — if they exist. And that's a big IF. What if the missing GRBs really are missing?
随着红外望远镜技术的提升，科学家最终总能测定红移量大于7的GRB爆发的距离，如果它们存在的话——这是一个重大假设。如果那些失踪的GRB爆发真的看不见了，那又会怎样？
"That would teach us something very interesting about the Universe," says Gehrels.
“那将会告诉我们一些令人非常感兴趣的宇宙内幕”，尼尔·格雷斯说。
The Sixth Huntsville Gamma-Ray Burst Symposium 2008 is sponsored by NASA's Fermi and Swift Projects and hosted by the Fermi GBM Team based at the Marshall Space Flight Center in Huntsville.
第6届汉斯维尔2008年度γ射线爆发专题研讨会由美国宇航局的费米和雨燕项目组发起，由汉斯维尔市马歇尔太空飞行中心的费米GBM团队主办。（GBM不知道具体名称——译注）
Editor: Dr.Tony Phillips | Credit: Science@NASA
编辑：托尼.菲利普博士 版权声明：NASA科学频道
more information
更多信息
6th Huntsville Gamma-ray Burst Symposium 2008 -- home page
第6届汉斯维尔γ射线爆发专题研讨会主页http://grbhuntsville2008.cspar.uah.edu/
Gamma-ray Bursts: The Mystery Continues (Science@NASA)
γ射线爆发：谜继续…… http://science.nasa.gov/headlines/y2008/16oct_grboverview.htm
Brief Mystery: What are Short Gamma-ray Bursts? (Science@NASA)
谜一般的短暂爆发:何谓短周期γ射线爆发？（后文有翻译）http://science.nasa.gov/headlines/y2008/20oct_briefmystery.htm
The Oddball Hosts of Gamma-ray Bursts (Science@NASA)
奇特的γ射线爆发宿主星系 http://science.nasa.gov/headlines/y2008/21oct_oddballs.htm 请问 雨燕的工作原理是什么怎么能迅速捕捉γ源？ 还能锁定区域？
poweru235 发表于 2009-5-3 00:33 http://www.astronomy.com.cn/bbs/images/common/back.gif
这个我不了解哦，你可以去看看雨燕的主页。
其实我对哈勃的观测方式还有不懂地方呢，它是怎么跟踪拍摄天体的，因为哈勃并没有像航天飞机那样的调整姿态的各个喷口啊！ 本帖最后由 gohomeman1 于 2009-5-3 02:23 编辑
背景资料：
从NASA的资料看，雨燕卫星带有调姿喷口，那么它当然能迅速转向了。至于它的方位探测能力，看看这篇PDF能了解大概了——卫星的整个表面都是射线感应探测器，这样辨别方位完全取决于探测器的灵敏度了。现代科技的进步速度是惊人的，这种探测器能做到多少灵敏度，大家可以查查看。PDF中的数据是：探测器表面积5200cm2，探测单体4mmX4mmX2mm，探测方式：γ光子计数器。
http://swift.gsfc.nasa.gov/docs/swift/about_swift/factsheet.pdf
下一楼将继续翻译第3篇文章。 本帖最后由 gohomeman1 于 2009-5-4 12:04 编辑
http://science.nasa.gov/headlines/y2008/20oct_briefmystery.htm
2008.10.20
A Brief Mystery: What are Short Gamma-ray Bursts?
暂时还是谜：短周期γ射线爆发是什么？
October 20, 2008: For decades it was baffling. Out of the still night sky, astronomers peering through their telescopes would occasionally glimpse quick bursts of high-energy light popping off like flashbulbs at the far side of the universe.
2008.10.20：数十年来，此事真令人困惑：天文学家用他们的望远镜凝望静谧的夜空，有时候会突然看到遥远宇宙中高能爆发的惊鸿一瞥，似闪光灯般的一闪即逝。
These bursts seemed impossibly powerful: to appear so bright from so very far away, they must vastly outshine entire galaxies containing hundreds of billions of stars. These explosions, called gamma ray bursts (GRBs), are by far the brightest and most energetic phenomena in the known universe, second only to the Big Bang itself. Scientists were at a loss to imagine what could possibly cause them.
这些爆发的能级看来不得了的强：如此遥远的地方爆发显现的却如此之强，它们必定比包含上千亿恒星的整个星系的光还亮得多。这种爆炸被称为γ射线爆发（简称GRB），是我们已知宇宙中仅次于宇宙大爆炸的最强、最亮的能量爆发现象。科学家都想不出什么机制能够产生这种爆发。
http://science.nasa.gov/headlines/y2008/images/briefmystery/sgrb_bigstrip.jpg
An artist's concept of a gamma-ray burst. γ射线爆发的艺术概念图
Astronomers now know what the longer-lasting GRBs are: the collapse and explosion of an ultra-massive star to form a black hole at its core, an explanation first proposed by Stan Woosley of the University of California in San Diego. But there’s a second category of GRBs that still remains a mystery.
现在天文学家大概知道长周期GRB爆发成因是什么了：一个超大质量的恒星（比如海山二这样的级别），当它的核心坍缩为黑洞时产生的巨大（喷流）爆发现象，圣迭戈市加利福尼亚大学的斯坦.卫斯理首先提出了这个解释。但是另一类的（短周期）GRB爆发还是个谜。
PS：卫斯理这个模型的问题是，这么遥远的一个恒星的爆发之光怎么会比整个活动星系核喷流（就是类星体啊）的亮度还大？——gohomeman1 本帖最后由 gohomeman1 于 2009-5-4 13:09 编辑
A Brief Mystery: What are Short Gamma-ray Bursts?
暂时还是谜：短周期γ射线爆发是什么？
http://science.nasa.gov/headlines/y2008/images/grboverview/grb_animation.gif
"The short-lived ones are very poorly understood. It's where the frontier is now," says Neil Gehrels, principal investigator for the GRB-detecting Swift satellite at NASA's Goddard Space Flight Center.
“这些瞬间爆发实在难于理解，它们就在我们当前的宇宙观测边界上，”美国宇航局戈达德太空飞行中心雨燕卫星GRB探测项目首席调研员尼尔·格雷斯（博士）说。
Gehrels and other researchers have gathered this week at the Sixth Huntsville Gamma Ray Burst Symposium in Huntsville, Ala., to discuss progress on this and other mysteries surrounding GRBs. Short gamma-ray bursts are a hot topic at today's sessions: agenda.
尼尔·格雷斯和其他搜寻者本周齐聚美国阿拉巴马州汉茨维尔市，出席第6届汉茨维尔γ射线爆发研讨会，讨论围绕GRB的各个谜。短周期γ射线爆发问题是当日议程表的一个顶级议题。链接：http://grbhuntsville2008.cspar.uah.edu/content/programme.html
"We have had good evidence since the 1990s that the short bursts and long bursts were different classes," Gehrels explains. "It had to do with their gamma ray properties." Not only do the short bursts last less than about 2 seconds, the spectrum of light they emit is distinct. Gamma rays from short bursts lean toward the high-energy end of the spectrum, while long GRBs emit lower-energy gamma rays.
尼尔·格雷斯说：“从上个世纪90年代以来，我们已经拥有比较过硬的证据，证明短周期γ射线爆发与长周期爆发属于不同的类型，它有自己的爆发机制。”这不仅是因为短周期爆发持续时间不到2秒，更重要的是两者的光谱截然不同。短周期GRB爆发的光谱趋向于最高能级的
γ射线（波长极短），而长周期GRB则辐射低能级γ射线。（波长靠近X线波段——译注）
The differences were highlighted in 2005 when, for the first time, telescopes caught sight of short GRB afterglows. The fading debris contained no supernova, arguing against the collapse of a massive star. George Ricker of MIT, principal investigator of NASA's HETE (High Energy and Transient Explorer) satellite, famously likened a short burst on July 9, 2005, to "the dog that didn't bark."
当2005年望远镜首次捕捉到短周期GRB的余晖时，这种区别显得格外明显。爆发残骸并不是超新星残骸，显然不是大质量恒星坍缩产生的。2005.7.9，NASA的HETE卫星（高能瞬时爆发勘测卫星 ）首席调研员、麻省理工学院的乔治.雷克对短周期GRB有个著名的比喻：“不叫的狗（最可怕）”。
Ultimately, the cause of short bursts is unknown. But scientists do have some good guesses.
最终，短周期GRB的成因还是不清楚。不过科学家有些不错的猜想。 本帖最后由 gohomeman1 于 2009-5-4 18:50 编辑
A Brief Mystery: What are Short Gamma-ray Bursts?
暂时还是谜：短周期γ射线爆发是什么？
The leading theory is that these bursts are extremely violent collisions between pairs of neutron stars. These stars aren't gassy, wispy giants like other stars — a neutron star is more like an atomic nucleus that's 12 kilometers across. Since the atoms that make up normal, "solid" matter are mostly empty space, a star made almost entirely of tightly packed neutrons is extraordinarily dense: a fingernail's worth of a neutron star would have a mass of more than a trillion kilograms. A neutron star's density and gravity is second only to a black hole. "When you have these two hard stars that run into each other, it's a very rapid fiery explosion. It's kind of like a crash."
当前居首的假说认为，短周期GRB是在一对中子星的猛烈对撞中产生的。中子星不是像其他恒星那样的气态巨星——更像一个直径12英里的原子核。（确切的说，是直径20km左右的一个超级中子，虽然不过只有一个大中型城市的体积，质量超过1.5倍太阳——译注）由原子组成的普通物质，其“实心”的物质内部其实绝大部分都是（真）空的（大家完全可以用太阳系质量集中在太阳来想象原子内部，当然电子与行星有本质区别——译注），而一颗几乎全部由中子构成的恒星却密度极大：指甲大的一块中子星物质的质量达到万亿吨级，中子星的密度、引力仅次于黑洞。“如果有2个这么坚硬的恒星对碰，那就是非常激烈的爆炸，就像汽车高速对撞一样。”
http://science.nasa.gov/headlines/y2008/images/briefmystery/nn_bigstrip.jpg
An artist's concept of a neutron star-neutron star collision. 一对中子星对撞的艺术效果图
So how could scientists know whether this explanation is true?
那么科学家怎么知道这种解释的真伪呢？
One way could be to detect gravitational waves. Before the two neutron stars collide, they would orbit each other as a binary system. Because their fields of gravity are so intense, the stars ought to send waves rippling outward in the fabric of space-time: gravitational waves. As the neutron stars spiral in toward each other, the frequency of those waves would ramp up in a characteristic pattern called a chirp signal.
一种方法是检测引力波。两颗中子星相撞前，它们必然是一对互相绕转的双星系统。由于它们的引力场是如此之强，它们互绕时应当会会时空中散发出一圈圈引力波。当它们以螺旋线逐步靠拢时，引力波的频率特征会逐步增加，称为线性递增调频信号波。
"Scientists are trying to that now," Gehrels says. "It's the ultimate way of verifying the model."
“现在科学家试图检测到引力波，这是证实本模型的最终手段”，格雷斯说。
Scientists at the Huntsville symposium are discussing the progress of gravitational wave detectors such as the Laser Interferometer Gravitational-wave Observatory (LIGO) located in Hanford, Washington, and Livingston, Louisiana. By using lasers to carefully measure the distances between pairs of mirrors at these observatories, LIGO scientists can notice tiny changes in these distances that would occur if subtle gravitational waves were passing through the Earth.
在汉茨维尔市研讨会上，科学家讨论了引力波探测器的进展，比如美国华盛顿州汉福德（原子能研究中心）和路易斯安那州利文斯顿的激光干涉引力波探测仪（LIGO）。LIGO科学家使用激光（干涉）仔细测量观测所两面镜子间的距离，用以探测当难以捉摸的引力波通过地球时引起的镜子距离的极细微变动。
Other possible explanations for short GRBs exist as well, but only hard data from experiments such as LIGO can settle what is the real cause of these mysterious celestial bursts.
短周期GRB的其他解释也有可能成立，但是只有像LIGO这样基于过硬数据的解释才能解决这些天空中谜一般爆发的真正成因是什么。
The Sixth Huntsville Gamma-Ray Burst Symposium 2008 is sponsored byNASA's Fermi and Swift Projects and hosted by the Fermi GBM Team basedat the Marshall Space Flight Center in Huntsville.
第6届汉斯维尔2008年度γ射线爆发专题研讨会由美国宇航局的费米和雨燕项目组发起，由汉茨维尔市马歇尔太空飞行中心的费米GBM团队主办。
Editor: Dr.Tony Phillips | Credit: Science@NASA
编辑：托尼.菲利普 版权声明：NASA科学频道 本文貌似没写得很详细，所谓一对中子星对撞，只能发生在密近双星系统中。由于孤立中子星对撞的概率极低，这种可能只能在两个大质量恒星（但不能太大）组成的密近双星系统中，当它们相继发生超新星爆发并都形成中子星，而且两次爆发都没有把伴星吹走的情形下才有可能。如果两颗伴星够近，在它们两次爆发过程中，恒星外层大气会持续把两颗恒星的核心包在一起，从而使两者距离越来越近。这样最后两者相撞并爆发短周期GRB就非常可能了。当2颗中子星合并时，其质量立刻超过了引力极限而形成了黑洞，这时产生巨大的能量辐射是很正常的。
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