Colleen A. Wilson-Hodge, Michael L. Cherry, Wayne H. Baumgartner, Elif Beklen, P. Narayana Bhat, Michael S. Briggs, Ascension Camero-Arranz, Gary L. Case, Vandi… 展开作者
Colleen A. Wilson-Hodge, Michael L. Cherry, Wayne H. Baumgartner, Elif Beklen, P. Narayana Bhat, Michael S. Briggs, Ascension Camero-Arranz, Gary L. Case, Vandiver Chaplin, Valerie Connaughton, Mark H. Finger, Neil Gehrels, Jochen Greiner, Keith Jahoda, Peter Jenke, R. Marc Kippen, Chryssa Kouveliotou, Hans A. Krimm, Erik Kuulkers, Charles A. Meegan, Lorenzo Natalucci, William S. Paciesas, Robert Preece, James C. Rodi, Nikolai Shaposhnikov, Gerald K. Skinner, Doug Swartz, Andreas von Kienlin, Roland Diehl, Xiao-Ling Zhang
备注：
accepted version 22 pages, 5 figures; published in Astrophysical Journal Letters; 50-100 keV panel added to figure 5, text changes from submitted version
The Crab Nebula is the only hard X-ray source in the sky that is both bright enough and steady enough to be easily used as a standard candle. As a result, it has been used as a normalization standard by most X-ray/gamma ray telescopes. Although small-scale variations in the nebula are well-known, since the start of science operations of the Fermi Gamma-ray Burst Monitor (GBM) in August 2008, a ~ 7% (70 mcrab) decline has been observed in the overall Crab Nebula flux in the 15 - 50 keV band, measured with the Earth occultation technique. This decline is independently confirmed with three other instruments: the Swift Burst Alert Telescope (Swift/BAT), the Rossi X-ray Timing Explorer Proportional Counter Array (RXTE/PCA), and the INTErnational Gamma-Ray Astrophysics Laboratory Imager on Board INTEGRAL (IBIS). A similar decline is also observed in the ~3 - 15 keV data from the RXTE/PCA and INTEGRAL Joint European Monitor (JEM-X) and in the 50 - 100 keV band with GBM and INTEGRAL/IBIS. Observations from 100 to 500 keV with GBM suggest that the decline may be larger at higher energies. The pulsed flux measured with RXTE/PCA since 1999 is consistent with the pulsar spin-down, indicating that the observed changes are nebular. Correlated variations in the Crab Nebula flux on a ~3 year timescale are also seen independently with the PCA, BAT, and IBIS from 2005 to 2008, with a flux minimum in April 2007. As of August 2010, the current flux has declined below the 2007 minimum.
Type II Supernovae: Model Light Curves and Standard Candle Relationships
II型超新星爆炸模型的调查已经进行，以确定它们的光变曲线和光谱如何随它们的质量，金属丰度和爆炸能量而变化。前超新星模型取自最近对太阳金属丰度下大质量恒星演化的调查，并辅以太阳下金属丰度的新计算。爆炸是由一个活塞附近的铁芯的边缘的运动模拟和由此产生的光变曲线和光谱计算使用全多波长辐射输运。公式的开发，描述了大约如何模型观测（光变曲线光度和持续时间）规模与祖质量，爆炸能量，和放射性核合成。与观测数据的比较表明，典型超新星的爆炸能量（用无穷远处的动能来衡量）相差近一个数量级--从0.5到4.0 x 10^51尔格，典型值约为0.9 x 10^51尔格。尽管有很大的变化，模型表现出紧密的光度和膨胀速度之间的关系，类似于以前采用的经验，使SNe IIP标准化蜡烛。这种关系可以用超新星包层中氢复合的简单行为来解释，但是我们发现对祖先金属丰度和质量的敏感性可能导致系统误差。光变曲线光度、持续时间和颜色之间的其他相关性可能使SNe IIP能够仅使用光度数据获得精确到约20%的距离。
The 91T/99aa-like Type Ia Supernova 2019vrq, Part I: Photometry, Spectroscopy, and Spectropolarimetry of a Nearly Standard Candle
Tsinghua University（清华大学）；Florida State University（佛罗里达州立大学）；University of Texas（德克萨斯大学）；European Organisation for Astronomical Research in the Southern Hemisphere (ESO)（欧洲南方天文台）；Texas A&M University（德克萨斯农工大学）；Las Cumbres Observatory（拉西布朗观测站）；University of California, Santa Barbara（加州大学圣塔芭芭拉分校）；University of California, Berkeley（加州大学伯克利分校）
