看图说话 行星, 恒星, 星系

Gardner 2009 用伽玛暴限制暗物质

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(原理不懂)

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Title:		Dark Matter Constraints from a Cosmic Index of Refraction
Authors:		Gardner, S.; Latimer, D.
Publication:		eprint arXiv:0904.1612
Publication Date:		04/2009
Origin:		ARXIV
Keywords:		High Energy Physics - Phenomenology, Astrophysics - Cosmology and Extragalactic Astrophysics, Nuclear Theory
Comment:		9 pages, LaTeX, 1 figure
Bibliographic Code:		2009arXiv0904.1612G

Abstract

The dark-matter candidates of particle physics invariably possess electromagnetic interactions, if only via quantum fluctuations. Taken en masse, dark matter can thus engender an index of refraction which deviates from its vacuum value. Its presence is signaled through frequency-dependent effects: the real part yields dispersive effects in propagation, and the imaginary part yields such in attenuation. We discuss theoretical constraints on the expansion of the index of refraction with frequency, the physical interpretation of the terms, and the particular observations needed to isolate its coefficients. This, with the advent of new opportunities to view gamma-ray bursts at cosmological distance scales, gives us a new probe of dark matter. As a first application we use the time delay determined from radio afterglow observations of gamma-ray bursts to limit the charge-to-mass ratio of dark matter to |\epsilon/M|<> Bibtex entry for this abstract Preferred format for this abstract (see Preferences)

Shahmoradi 2009 The Possible Impact of GRB Detector Thresholds on Cosmological Standard Candles

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Title:
The Possible Impact of GRB Detector Thresholds on Cosmological Standard Candles
Authors:
Shahmoradi, A.; Nemiroff, R. J.
Publication:
eprint arXiv:0904.1464
Publication Date:
04/2009
Origin:
ARXIV
Keywords:
Astrophysics - High Energy Astrophysical Phenomena
Bibliographic Code:
2009arXiv0904.1464S
AbstractGRB satellites are relatively inefficient detectors of dim hard bursts because they trigger on photon counts, which are number-biased against hard photons. Therefore, for example, given two bursts of identical peak luminosity near the detection threshold, a dim soft burst will be preferentially detected over a dim hard burst. This detector bias can create an apparent correlation where increasingly hard GRBs appear increasingly bright. Although such correlations may be obfuscated by a middle step where GRBs need to be bright enough to have their actual redshifts determined, it is found that the bias is generally pervasive. This result is derived here through simulations convolving a wide variety of possible GRB brightnesses and spectra with the BATSE Large Area Detectors (LAD) detection thresholds. The presented analyses indicate that the rest-frame $\nu F_{\nu}$ spectrum peak energy of long-duration GRBs, $\epi$, is not a good cosmological standard candle. Therefore, the appearance of $\epi$ in seeming correlations such as the Amati ($E_{iso}-\epi$), Ghirlanda ($E_{\gamma}-\epi$), and $L_{iso}-\epi$ relations is statistically real but strongly influenced or wholly created by GRB detector thresholds.
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Nissanke 2009 短暴的引力波辐射

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Title:		Exploring short gamma-ray bursts as gravitational-wave standard sirens
Authors:		Nissanke, Samaya; Hughes, Scott A.; Holz, Daniel E.; Dalal, Neal; Sievers, Jonathan L.
Publication:		eprint arXiv:0904.1017
Publication Date:		04/2009
Origin:		ARXIV
Keywords:		Astrophysics - Cosmology and Extragalactic Astrophysics
Comment:		23 pages, 17 figures. Submitted to ApJ
Bibliographic Code:		2009arXiv0904.1017N

Abstract

Recent observations support the hypothesis that a large fraction of "short-hard" gamma-ray bursts (SHBs) are associated with compact binary inspiral. Since gravitational-wave (GW) measurements of well-localized inspiraling binaries can measure absolute source distances, simultaneous observation of a binary's GWs and SHB would allow us to independently determine both its luminosity distance and redshift. Such a "standard siren" (the GW analog of a standard candle) would provide an excellent probe of the relatively nearby universe's expansion, complementing other standard candles. In this paper, we examine binary measurement using a Markov Chain Monte Carlo technique to build the probability distributions describing measured parameters. We assume that each SHB observation gives both sky position and the time of coalescence, and we take both binary neutron stars and black hole-neutron star coalescences as plausible SHB progenitors. We examine how well parameters (particularly luminosity distance) can be measured from GW observations of these sources by a range of ground-based detector networks. We find that earlier estimates overstate how well distances can be measured, even at fairly large signal-to-noise ratio. The fundamental limitation to determining distance to these sources is the gravitational waveform's degeneracy between luminosity distance and source inclination. Despite this, we find that excellent results can be achieved by measuring a large number of coalescing binaries, especially if the worldwide network consists of many widely separated detectors. Advanced GW detectors will be able to determine the absolute luminosity distance to an accuracy of 10-30% for NS-NS (out to 600 Mpc) and NS-BH binaries (out to 1400 Mpc). (Abridged)

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Dietz 2009 LIGO/Virgo 探测和短暴成协的几率估计

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arXiv:0904.0347 [pdf, other]

Title: Chance Estimations for Detecting Gravitational Waves with LIGO/Virgo Associated with Gamma Ray Bursts

Authors: Alexander Dietz

Comments: 17 pages, 8 figures

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Short Gamma Ray Bursts (SGRB) are believed to originate from the merger of two compact objects. If this scenario is correct, SGRB will be accompanied by the emission of strong gravitational waves, detectable by current or planned GW detectors, such as LIGO and Virgo. No detection of a gravitational wave has been made up to date. In this paper I will use a set of SGRB with observed redshifts to fit a model describing the cumulative number of SGRB as a function of redshift, to determine the rate of such merger events in the nearby universe. These estimations will be used to make probability statements about detecting a gravitational wave associated with a short gamma ray burst during the latest science run of LIGO/Virgo. Chance estimations for the enhanced and advanced detectors will also be made, and a comparison between the rates deduced from this work will be compared to the existing literature.

Rykoff 2009 ROTSE-III and Swift对早期余辉的观测

主要内容:
主要是光学的观测数据. 包括的暴有:
GRB 050319, GRB 050401, GRB 050525a,
GRB 050801, GRB 050922c, GRB 051109a, GRB 060111b, GRB 060605,
GRB 060729, GRB 060904b, GRB 061007, GRB 070611

还包括确定了一些initial LF.

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文章信息:

arXiv:0904.0261 [ps, pdf, other]

Title: Looking Into the Fireball: ROTSE-III and Swift Observations of Early GRB Afterglows

Authors: E. S. Rykoff (UCSB), F. Aharonian (MPIK), C. W. Akerlof (UMich), M. C. B. Ashley (UNSW), S. D. Barthelmy (GSFC), H. A. Flewelling (UMich), N. Gehrels (GSFC), E. Gogus (Sabanci), T. Guver (Arizona), U. Kiziloglu (METU), H. A. Krimm (GSFC, USRA), T. A. McKay (UMich), M. Ozel (Cag), A. Phillips (UNSW), R. M. Quimby (Caltech), G. Rowell (Adelaide), W. Rujopakarn (Steward), B. E. Schaefer (LSU), D. A. Smith (Guilford), W. T. Vestrand (LANL), J. C. Wheeler (UTexas), J. Wren (LANL), F. Yuan (UMich), S. A. Yost (CSB/SJU)

Comments: 31 pages, 5 figures, submitted to ApJ

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We report on a complete set of early optical afterglows of gamma-ray bursts (GRBs) obtained with the ROTSE-III telescope network from March 2005 through June 2007. This set is comprised of 12 afterglows with early optical and Swift/XRT observations, with a median ROTSE-III response time of 45 s after the start of gamma-ray emission (8 s after the GCN notice time). These afterglows span four orders of magnitude in optical luminosity, and the contemporaneous X-ray detections allow multi-wavelength spectral analysis. Excluding X-ray flares, the broadband synchrotron spectra show that the optical and X-ray emission originate in a common region, consistent with predictions of the external forward shock in the fireball model. However, the fireball model is inadequate to predict the temporal decay indices of the early afterglows, even after accounting for possible long-duration continuous energy injection. We find that the optical afterglow is a clean tracer of the forward shock, and we use the peak time of the forward shock to estimate the initial bulk Lorentz factor of the GRB outflow, and find 100 .lt. Gamma_0 .lt. 1000, consistent with expectations.

Adriani 2009 PAMELA对高能正电子电子的观测

主要内容:
正电子数/(正电子数+电子数)的数值在这一阶段开始上升

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Letter

Nature 458, 607-609 (2 April 2009) | doi:10.1038/nature07942; Received 28 October 2008; Accepted 6 February 2009

An anomalous positron abundance in cosmic rays with energies 1.5–100 GeV

O. Adriani^1,2, G. C. Barbarino^3,4, G. A. Bazilevskaya⁵, R. Bellotti^6,7, M. Boezio⁸, E. A. Bogomolov⁹, L. Bonechi^1,2, M. Bongi², V. Bonvicini⁸, S. Bottai², A. Bruno^6,7, F. Cafagna⁷, D. Campana⁴, P. Carlson¹⁰, M. Casolino¹¹, G. Castellini¹², M. P. De Pascale^11,13, G. De Rosa⁴, N. De Simone^11,13, V. Di Felice^11,13, A. M. Galper¹⁴, L. Grishantseva¹⁴, P. Hofverberg¹⁰, S. V. Koldashov¹⁴, S. Y. Krutkov⁹, A. N. Kvashnin⁵, A. Leonov¹⁴, V. Malvezzi¹¹, L. Marcelli¹¹, W. Menn¹⁵, V. V. Mikhailov¹⁴, E. Mocchiutti⁸, S. Orsi^10,11, G. Osteria⁴, P. Papini², M. Pearce¹⁶, P. Picozza^11,13, M. Ricci¹⁷, S. B. Ricciarini², M. Simon¹⁵, R. Sparvoli^11,13, P. Spillantini^1,2, Y. I. Stozhkov⁵, A. Vacchi⁸, E. Vannuccini², G. Vasilyev⁹, S. A. Voronov¹⁴, Y. T. Yurkin¹⁴, G. Zampa⁸, N. Zampa⁸ & V. G. Zverev¹⁴

1. University of Florence, Department of Physics, Via Sansone 1, I-50019 Sesto Fiorentino, Florence, Italy
2. I...

Correspondence to: P. Picozza^11,13 Correspondence and requests for materials should be addressed to P.P. (Email: Piergiorgio.Picozza@roma2.infn.it).

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Antiparticles account for a small fraction of cosmic rays and are known to be produced in interactions between cosmic-ray nuclei and atoms in the interstellar medium¹, which is referred to as a 'secondary source'. Positrons might also originate in objects such as pulsars² and microquasars³ or through dark matter annihilation⁴, which would be 'primary sources'. Previous statistically limited measurements^{5, 6, 7} of the ratio of positron and electron fluxes have been interpreted as evidence for a primary source for the positrons, as has an increase in the total electron+positron flux at energies between 300 and 600 GeV (ref. 8). Here we report a measurement of the positron fraction in the energy range 1.5–100 GeV. We find that the positron fraction increases sharply over much of that range, in a way that appears to be completely inconsistent with secondary sources. We therefore conclude that a primary source, be it an astrophysical object or dark matter annihilation, is necessary.

Nishikawa 2009 3D模拟非磁化的相对论性激波

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Title:		Weibel instability and associated strong fields in a fully 3D simulation of a relativistic shock
Authors:		Nishikawa, K. -I.; Niemiec, J.; Hardee, P. E.; Medvedev, M.; Sol, H.; Mizuno, Y.; Zhang, B.; Pohl, M.; Oka, M.; Hartmann, D. H.
Publication:		eprint arXiv:0904.0096
Publication Date:		04/2009
Origin:		ARXIV
Keywords:		Astrophysics - Earth and Planetary Astrophysics
Comment:		4 pages, 3 figures, submitted to ApJL
Bibliographic Code:		2009arXiv0904.0096N

Abstract

Plasma instabilities (e.g., Buneman, Weibel and other two-stream instabilities) ex- cited in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a new 3-D relativistic particle-in-cell code, we have investigated the particle acceleration and shock structure associated with an unmagnetized relativis- tic electron-positron jet propagating into an unmagnetized electron-positron plasma. The simulation has been performed using a long simulation system in order to study the nonlinear stages of the Weibel instability, the particle acceleration mechanism, and the shock structure. Cold jet electrons are thermalized and slowed while the ambient electrons are swept up to create a partially developed hydrodynamic (HD) like shock structure. In the leading shock, electron density increases by a factor of 3.5 in the simulation frame. Strong electromagnetic fields are generated in the trailing shock and provide an emission site. We discuss the possible implication of our simulation results within the AGN and GRB context.

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Pedbost 2009 哈哈, galaxy zoo on April 1st

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分别是

we apologise for the inconvenience

Caution! Structure formationn in progress

Delays possible for 7 Gyr

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arXiv:0903.5377 [ps, pdf, other]

Title: Galaxy Zoo: an unusual new class of galaxy cluster

Authors: Marven F. Pedbost, Trillean Pomalgu, the Galaxy Zoo team

Comments: 4 pages, 3 figures

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We have identified a new class of galaxy cluster using data from the Galaxy Zoo project. These clusters are rare, and thus have apparently gone unnoticed before, despite their unusual properties. They appear especially anomalous when the morphological properties of their component galaxies are considered. Their identification therefore depends upon the visual inspection of large numbers of galaxies, a feat which has only recently been made possible by Galaxy Zoo, together with the Sloan Digital Sky Survey. We present the basic properties of our cluster sample, and discuss possible formation scenarios and implications for cosmology.

Graham 2009 GRB 051022 此暗暴的宿主星系金属丰度很高

主要内容:
一般来说长暴来自金属丰度低的大质量恒星坍缩. 但这个暴的宿主星系的金属丰度很高. 文章提出是不是有可能暗暴的金属丰度都比较高?

(可是星系金属丰度高并不代表爆发伽玛暴的前身星的金属丰度高啊)

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氧的丰度

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Title:		Unusually High Metallicity Host Of The Dark LGRB 051022
Authors:		Graham, J. F.; Fruchter, A. S.; Kewley, L. J.; Levesque, E. M.; Levan, A. J.; Tanvir, N. R.; Reichart, D. E.; Nysewander, M.
Publication:		eprint arXiv:0903.5544
Publication Date:		03/2009
Origin:		ARXIV
Keywords:		Astrophysics - Cosmology and Extragalactic Astrophysics
Comment:		Conference procedings for The Sixth Huntsville Gamma-Ray Burst Symposium 2008 October 20-23 (3 pages, 2 figures)
Bibliographic Code:		2009arXiv0903.5544G

Abstract

We present spectroscopy of the host of GRB 051022 with GMOS nod and shuffle on Gemini South and NIRSPEC on Keck II. We determine a metallicity for the host of log(O/H)+12 = 8.77 using the R23 method (Kobulnicky & Kewley 2004 scale) making this the highest metallicity long burst host yet observed. The galaxy itself is unusually luminous for a LGRB host with a rest frame B band absolute magnitude -21.5 and has the spectrum of a rapidly star-forming galaxy. Our work raises the question of whether other dark burst hosts will show high metallicities.

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