Zou 2007 伽玛暴的高辐射效率

主要内容:
用ApJ上050904相同的模型，假设后面喷出的所有sub－shell都相同，可以计算辐射效率，得到的效率可以很高。

精彩摘抄:


文章信息:
High Efficiency of Gamma-Ray Bursts Revisited

Authors: Y. C. Zou, Z. G. Dai

(Submitted on 7 Mar 2007)

Abstract: Using the conservation of energy and momentum during collisions of any two shells, we consider the efficiency of gamma-ray bursts by assuming that the ejecta from the central engine are equally massive and have the same Lorentz factors. We calculate the efficiency and the final Lorentz factor of the merged whole shell for different initial diversities of Lorentz factors and for different microscopic radiative efficiency. As a result, a common high efficiency in the range of 0.1 to 0.9 is considerable, and a very high value near 100% is also reachable if the diversity of the Lorentz factors is large enough.

Comments:

12 pages, 6 figures, accepted by JASR

Subjects:

Astrophysics (astro-ph)

Cite as:

arXiv:astro-ph/0703136v1

Belczynski 2007 短暴的黑洞双星演化和引力波辐射

主要内容:


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文章信息:
Black Hole Spin Evolution: Implications for Short-hard Gamma Ray Bursts and Gravitational Wave Detection

Authors: Krzysztof Belczynski, Ronald E. Taam, Emmanouela Rantsiou, Marc van der Sluys

(Submitted on 6 Mar 2007)

Abstract: The evolution of the spin and tilt of black holes in compact black hole - neutron star and black hole - black hole binary systems is investigated via the population synthesis method. Based on recent results on accretion at super Eddington rates in slim disk models, estimates of natal kicks, and the results regarding fallback in supernova models, we obtain the black hole spin and misalignment. It is found that the spin parameter, a_spin, is less than 0.5 for initially non rotating black holes and the tilt, i_tilt, is less than 40 deg for 50% of the systems in black hole - neutron star binaries. Upon comparison with the results of black hole - neutron star merger calculations we estimate that only a small fraction (~0.02) of these systems can potentially produce a short-hard gamma ray burst. Only for high initial black hole spin parameters (a_spin>0.6) can this fraction be significant (~0.35). For the majority of black holes in black hole - neutron star systems the spin magnitude is increased to a_spin>0.1 and the degree of spin misalignment (i_tilt ~ 40 deg) is sufficiently high that the predicted gravitational radiation signal significantly differs from that for non rotating black holes. However, due to the (i) insensitivity of signal detection techniques to the black hole spin and the (ii) predicted overall low contribution of black hole binaries to the signal we find that the detection of gravitational waves are not greatly inhibited by current searches with non spinning templates. It is pointed out that the detection of a black hole - black hole binary inspiral system with LIGO or VIRGO may provide a direct measurement of the initial spin of a black hole.

Comments:

19 pages, 3 tables, 10 figures: submitted to ApJ

Subjects:

Astrophysics (astro-ph)

Cite as:

arXiv:astro-ph/0703131v1

Nakar 2007 短暴观测的理论暗示

主要内容:


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文章信息:
Some Theoretical Implications of Short-Hard Gamma-Ray Burst observations

Authors: Ehud Nakar

(Submitted on 7 Mar 2007)

Abstract: Short-hard and long-soft gamma-ray bursts (GRBs) are two distinct phenomena, but their prompt and afterglow emission show many similarities. This suggests that two different progenitor systems lead to similar physical processes and that the prompt and afterglow observations of short-hard GRBs (SHBs) can be examined using models of long GRBs. Here, I discuss three conclusions that can be drawn from SHB observations. I show that the lower limit on the Lorentz factor of SHBs is typically ``only'' 10-50, significantly lower than that of long GRBs. SHBs with observed X-ray afterglow after 1 day are found to be roughly as efficient as long GRBs in converting the outflow energy into prompt gamma-rays. Finally, I examine the origin of SHBs with X-ray dark afterglows and find that the most plausible explanation is that these SHBs exploded in extremely low density environment ($n \lesssim 10^{-5} cm^{-3}$)

Comments:

9 pages, 2 figures; Proceedings of the 36th COSPAR Scientific Assembly, 2006, Beijing, China. Advances in Space Research in press

Subjects:

Astrophysics (astro-ph)

Cite as:

arXiv:astro-ph/0703129v1

Mazzali 2007 SN 2006aj的晚期谱观测

主要内容:


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文章信息:
Keck and ESO-VLT View of the Symmetry of the Ejecta of the XRF/SN 2006aj

Authors: Paolo A. Mazzali, Ryan J. Foley, Jinsong Deng, Ferdinando Patat, Elena Pian, Dietrich Baade, Joshua S. Bloom, Alexei V. Filippenko, Daniel A. Perley, Stefano Valenti, Lifan Wang, Koji Kawabata, Keiichi Maeda, Ken-ichi Nomoto

(Submitted on 6 Mar 2007)

Abstract: Nebular-phase spectra of SN 2006aj, which was discovered in coincidence with X-ray flash 060218, were obtained with Keck in 2006 July and the Very Large Telescope in 2006 September. At the latter epoch spectropolarimetry was also attempted, yielding an upper limit of ~ 2% for the polarization. The spectra show strong emission lines of [OI] and MgI], as expected from a Type Ic supernova, but weak CaII lines. The [FeII] lines that were strong in the spectra of SN 1998bw are much weaker in SN 2006aj, consistent with the lower luminosity of this SN. The outer velocity of the line-emitting ejecta is ~ 8000 km/s in July and ~ 7400 km/s in September, consistent with the relatively low kinetic energy of expansion of SN 2006aj. All emission lines have similar width, and the profiles are symmetric, indicating that no major asymmetries are present in the ejecta at the velocities sampled by the nebular lines (v <>

Comments:

20 pages, 6 figures. Accepted for publication in the Astrophysical Journal

Subjects:

Astrophysics (astro-ph)

Cite as:

arXiv:astro-ph/0703109v1

Maeda SN 2006aj的晚期辐射谱的观测

主要内容:
在200多天后的观测发现O和Ni的发射线，暗示这个Ic型超新星产生了一个中子星。

精彩摘抄:


文章信息:
SN 2006aj Associated with XRF 060218 At Late Phases: Nucleosynthesis-Signature of A Neutron Star-Driven Explosion

Authors: Keiichi Maeda, Koji Kawabata, Masaomi Tanaka, Ken'ichi Nomoto, Nozomu Tominaga, Takashi Hattori, Takeo Minezaki, Takami Kuroda, Tomoharu Suzuki, Jinsong Deng, Paolo A. Mazzali, Elena Pian

Abstract: Optical spectroscopy and photometry of SN 2006aj have been performed with the Subaru telescope at t > 200 days after GRB060218, the X-ray Flash with which it was associated. Strong nebular emission-lines with an expansion velocity of v ~ 7,300 km/s were detected. The peaked but relatively broad [OI]6300,6363 suggests the existence of ~ 2 Msun of materials in which ~1.3 Msun is oxygen. The core might be produced by a mildly asymmetric explosion. The spectra are unique among SNe Ic in (1) the absence of [CaII]7291,7324 emission, and (2) a strong emission feature at ~ 7400A, which requires ~ 0.05 Msun of newly-synthesized 58Ni. Such a large amount of stable neutron-rich Ni strongly indicates the formation of a neutron star. The progenitor and the explosion energy are constrained to 18 Msun

Comments:

Accepted for Publication in the Astrophysical Journal Letters (2007, ApJ, 658, L5). 8 pages, including 1 table and 3 figures. Typos corrected

Subjects:

Astrophysics (astro-ph)

Cite as:

arXiv:astro-ph/0703107v2

Arimoto 2007 XRF 040916的HETE－2的观测

主要内容:


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文章信息:

HETE-2 Observations of the X-Ray Flash XRF 040916

Authors: Makoto Arimoto, Nobuyuki Kawai, Atsumasa Yoshida, Toru Tamagawa, Yuji Shirasaki, Motoko Suzuki, Masaru Matsuoka, Jun'ichi Kotoku, Rie Sato, Takashi Shimokawabe, Nicolas Vasquez Pazmino, Takuto Ishimura, Yujin Nakagawa, Nobuyuki Ishikawa, Akina Kobayashi, Satoshi Sugita, Ichiro Takahashi, Makoto Kuwahara, Makoto Yamauchi, Kunio Takagishi, Isamu Hatsukade, Jean-Luc Atteia, Alexandre Pelangeon, Roland Vanderspek, Carlo Graziani, Gregory Prigozhin, Joel Villasenor, J. Garrett Jernigan, Geoffrey B. Crew, Kevin Hurley, Takanori Sakamoto, George R. Ricker, Stanford E. Woosley, Nat Butler, Al Levine, John P. Doty, Timothy Q. Donaghy, Donald Q. Lamb, Edward E. Fenimore, Mark Galassi, Michel Boer, Jean-Pascal Dezalay, Jean-Francios Olive, Joao Braga, Ravi Manchanda, Graziella Pizzichini

(Submitted on 2 Mar 2007 (v1), last revised 7 Mar 2007 (this version, v2))

Abstract: A long X-ray flash was detected and localized by the instruments aboard the High Energy Transient Explorer II (HETE-2) at 00:03:30 UT on 2004 September 16. The position was reported to the GRB Coordinates Network (GCN) approximately 2 hours after the burst. This burst consists of two peaks separated by 200 s, with durations of 110 s and 60 s. We have analyzed the energy spectra of the 1st and 2nd peaks observed with the Wide Field X-Ray Monitor (WXM) and the French Gamma Telescope (FREGATE). We discuss the origin of the 2nd peak in terms of flux variabilities and timescales. We find that it is most likely part of the prompt emission, and is explained by the long-acting engine model. This feature is similar to some bright X-ray flares detected in the early afterglow phase of bursts observed by the Swift satellite.

Comments:

9 pages, 4 figures, Accepted for publication in PASJ

Subjects:

Astrophysics (astro-ph)

Cite as:

arXiv:astro-ph/0703045v2

Shao 2007 尘埃散射作为X射线余辉的来源

主要内容:
一部分伽玛暴的X射线余辉来自于暴本身的辐射被尘埃散射的结果。

精彩摘抄:


文章信息:
Behavior of X-Ray Dust Scattering and Implications for X-Ray Afterglows of Gamma-Ray Bursts

Authors: L. Shao, Z. G. Dai (NJU)

(Submitted on 1 Mar 2007 (v1), last revised 30 Mar 2007 (this version, v2))

Abstract: The afterglows of gamma-ray bursts (GRBs) have commonly been assumed to be due to shocks sweeping up the circum-stellar medium. However, most GRBs have been found in dense star-forming regions where a significant fraction of the prompt X-ray emission can be scattered by dust grains. Here we revisit the behavior of dust scattering of X-rays in GRBs. We find that the features of some X-ray afterglows from minutes to days after the gamma-ray triggers are consistent with the scattering of prompt X-ray emission from GRBs off host dust grains. This implies that some of the observed X-ray afterglows (especially those without sharp rising and decaying flares) could be understood with a dust-scattering--driven emission model.

Comments:

ApJ, in press

Subjects:

Astrophysics (astro-ph)

Cite as:

arXiv:astro-ph/0703009v2

天文学网上教学资源

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网上课程

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Contact: lixd@nju.edu.cn 2006-10

宇宙是一个大黑洞？

好像有地方说宇宙本身可能就是一个黑洞，什么意思？
是说现在的宇宙就是？也就是说黑洞里不是奇点，而是可以存在像咱们这样的物体；
还是说宇宙过一段时间收缩，最终会形成一个黑洞。
如果是后者就没什么意思了。

天文学基础网上课程地址

from http://astronomy.nju.edu.cn/~lixd/wrat/astronomy.htm

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