Liu 2007 NDAF as central engine for X-ray flares

主要内容:


精彩摘抄:


文章信息:
Constraints on the Mass Accretion Rate of Neutrino-Cooled Disks in Gamma-Ray Bursts

Authors: Tong Liu, Wei-Min Gu, Li Xue, Shan-Shan Weng, Ju-Fu Lu

(Submitted on 26 Dec 2007)

Abstract: We present a unified description of all the three known classes of optically thick accretion disks around black holes, namely Shakura-Sunyaev disks, slim disks, and neutrino-dominated accretion flows (NDAFs). It is found that NDAFs have both a maximal and a minimal possible mass accretion rate at their each radius. This may be suggestive of an interpretation for the origin of X-ray flares observed in gamma-ray bursts.

Comments:	13 pages, 3 figures, accepted by ApJ
Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0712.4107v1 [astro-ph]

Ofek 2007 GRB 070201: A possible Soft Gamma Ray Repeater in M31

主要内容:
Their main idea can be well described by the title.

精彩摘抄:


文章信息:

arXiv:0712.3585 [ps, pdf, other]

Title: GRB 070201: A possible Soft Gamma Ray Repeater in M31

Authors: E. O. Ofek, M. Muno, R. Quimby, S. R. Kulkarni, H. Stiele, W. Pietsch, E. Nakar, A. Gal-Yam, A. Rau, P. B. Cameron, S. B. Cenko, M. M. Kasliwal, D. B. Fox, P. Chandra, A. K. H. Kong, R. Barnard

Comments: 7 pages, submitted to ApJ (Fig. 2 resolution reduced)

Subjects: Astrophysics (astro-ph)

The gamma-ray burst (GRB) 070201 was a bright short-duration hard-spectrum GRB detected by the Inter-Planetary Network (IPN). Its error quadrilateral, which has an area of 0.124 sq. deg, intersects some prominent spiral arms of the nearby M31 (Andromeda) galaxy. Given the properties of this GRB, along with the fact that LIGO data argues against a compact binary merger origin in M31, this GRB is an excellent candidate for an extragalactic Soft Gamma-ray Repeater (SGR) giant flare, with energy of 1.4x10^45 erg. Analysis of ROTSE-IIIb visible light observations of M31, taken 10.6 hours after the burst and covering 42% of the GRB error region, did not reveal any optical transient down to a limiting magnitude of 17.1. We inspected archival and proprietary XMM-Newton X-ray observations of the intersection of the GRB error quadrilateral and M31, obtained about four weeks prior to the outburst, in order to look for periodic variable X-ray sources. No SGR or Anomalous X-ray Pulsar (AXP) candidates (periods in range 1 to 20 s) were detected. We discuss the possibility of detecting extragalactic SGRs/AXPs by identifying their periodic X-ray light curves. Our simulations suggest that the probability of detecting the periodic X-ray signal of one of the known Galactic SGRs/AXPs, if placed in M31, is about 10% (50%), using 50 ks (2 Ms) XMM-Newton exposures.

Belczynski 2007 binary twin acts in the progenitor of short bursts

主要内容:
Prompt Twins may be a good part as the binary NS as short bursts progenitor, where twins are the binaries with almost equal mass stars, q = M2/M1 > 0.95

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文章信息:

arXiv:0712.3309 [ps, pdf, other]

Title: Short-Hard Gamma-Ray Bursts in Young Host Galaxies: the Effect of Prompt Twins

Authors: Krzysztof Belczynski, K.Z. Stanek, Chris L. Fryer

Comments: 12 pages, 1 table, 4 figures (submitted to ApJ)

Subjects: Astrophysics (astro-ph)

We investigate the effect of including a significant ``binary twin'' population (binaries with almost equal mass stars, q = M2/M1 > 0.95) for the production of double compact objects and some resulting consequences, including LIGO inspiral rate and some properties of short-hard gamma-ray bursts. We employ very optimistic assumptions on the twin fraction (50%) among all binaries, and therefore our calculations place an upper limits on the influence of twins on double compact object populations. We show that for LIGO the effect of including twins is relatively minor: although the merger rates does indeed increase when twins are considered, the rate increase is fairly small (1.5). Also, chirp mass distribution for double compact objects formed with or without twins are almost indistinguishable. If double compact object are short-hard GRB progenitors, including twins in population synthesis calculations does not alter significantly the earlier rate predictions for the event rate. However, for one channel of binary evolution, introducing twins more than doubles the rate of ``very prompt'' NS-NS mergers (time to merger less than 1 Myr) compared to models with the ``flat'' q distribution. In that case, 70% of all NS-NS binaries merge within 100 Myr after their formation, indicating a possibility of a very significant population of ``prompt'' short-hard gamma-ray bursts, associated with star forming galaxies. We also point out that, independent of assumptions, fraction of such prompt neutron star mergers is always high, 35--70%. We note that recent observations (e.g., Berger et al.) indicate that fraction of short-hard GRBs found in young hosts is at least 40% and possibly even 80%.

Kann 2007 Swift Optical afterglows

主要内容:
Data gathering.

精彩摘抄:
Some energetics
Light curves
E_iso,bol distribution

文章信息: The Afterglows of Swift-era Gamma-Ray Bursts. I. Comparing pre-Swift and Swift era Long/Soft (Type II) GRB Optical Afterglows

Authors: D. A. Kann, S. Klose, B. Zhang, D. Malesani, E. Nakar, A. C. Wilson, N. R. Butler, L. A. Antonelli, G. Chincarini, B. E. Cobb, S. Covino, P. D'Avanzo, V. D'Elia, M. Della Valle, P. Ferrero, D. Fugazza, J. Gorosabel, G. L. Israel, F. Mannucci, S. Piranomonte, S. Schulze, L. Stella, G. Tagliaferri, K. Wiersema

(Submitted on 13 Dec 2007)

Abstract: We have gathered optical photometry data on a large sample of Swift-era gamma-ray burst (GRB) afterglows. We analyzed their light curves and derive spectral energy distributions for the sample with the best data quality, allowing us to derive the host galaxy extinction. We transform the afterglow light curves into an extinction-corrected $z=1$ system and compare their luminosities with a sample of pre-Swift afterglows. We find that the luminosity distribution of the two afterglow samples are very similar, and that a fainter sample can be explained by a moderate amount of line-of-sight host extinction. We derive bolometric isotropic energies for all GRBs in our sample, and find only a tentative correlation between the prompt energy release and the optical afterglow luminosity. Furthermore, we propose the existence of an upper ceiling on afterglow luminosities and study the luminosity distribution at early times, which was not accessible before the advent of the Swift satellite. Finally, we postulate the existence of an intermediate class of long GRBs which lie between the typical high-luminosity, high-redshift events described in the rest of the paper and nearby low-luminosity events associated with spectroscopic SNe in terms of energetics and redshift distribution.

Comments:	Submitted to ApJ; 65 pages in referee format; 20 pages main text, 12 pages Appendix, 20 pages references, 4 tables, 8 figures)
Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0712.2186v1 [astro-ph]

Ziaeepour 2007 GRB 060607A Asynchronous Early $X$-ray and Optical Emissions

主要内容:
Observational data for GRB 060607A. X-ray and Optical didn't break at the same time, so not a jet break. X-ray is typical four segment "swift profile".

精彩摘抄:
X-ray light curve

文章信息:

arXiv:0712.3269 [ps, pdf, other]

Title: GRB 060607A: A GRB with Bright Asynchronous Early $X$-ray and Optical Emissions

Authors: Houri Ziaeepour, Stephen T. Holland, Patricia T. Boyd, Kim L. Page, Samantha Oates, Craig B. Markwardt, Peter Meszaros, Neil Gehrels, Francis E. Marshall, Jay Cummings, Mike Goad

Comments: 17 pages; 9 figures; Accepted for publication in MNRAS

Subjects: Astrophysics (astro-ph)

The early optical emission of the moderately high redshift ($z=3.08$) GRB 060607A shows a remarkable broad and strong peak with a rapid rise and a relatively slow power-law decay. It is not coincident with the strong early-time flares seen in the X-ray and gamma-ray energy bands. There is weak evidence for variability superposed on this dominant component in several optical bands that can be related to flares in high energy bands. While for a small number of GRBs, well-sampled optical flares have been observed simultaneously with X-ray and gamma ray pulses, GRB 060607A is one of the few cases where the early optical emission shows no significant evidence for correlation with the prompt emission. In this work we first report in detail the broad band observations of this burst by Swift. Then by applying a simple model for the dynamics and the synchrotron radiation of a relativistic shock, we show that the dominant component of the early emissions in optical wavelengths has the same origin as the tail emission produced after the main gamma ray activity. The most plausible explanation for the peak in the optical light curve seems to be the cooling of the prompt after the main collisions, shifting the characteristic synchrotron frequency to the optical bands. It seems that the cooling process requires a steepening of the electron energy distribution and/or a break in this distribution at high energies. The sharp break in the X-ray light curve at few thousands of seconds after the trigger, is not observed in the IR/optical/UV bands, and therefore can not be a jet break. Either the X-ray break is due to a change in the spectrum of the accelerated electrons or the lack of an optical break is due to the presence of a related delayed response component (Abbreviated).

Cenko 2007 GRB 070125 long burst not very in a galaxy

主要内容:
The difference of this burst is its host galaxy: none, or maybe have both. More accurate may be collision of the two galaxies.

精彩摘抄:
Two circles point to the same region, in different time. From the right (cross), it may be in the collision of two galaxies B1 and B2.

文章信息:

arXiv:0712.2828 [ps, pdf, other]

Title: GRB070125: The First Long-Duration Gamma-Ray Burst in a Halo Environment

Authors: S. B. Cenko, D. B. Fox, B. E. Penprase, A. Cucchiara, P. A. Price, E. Berger, S. R. Kulkarni, F. A. Harrison, A. Gal-Yam, E. O. Ofek, A. Rau, P. Chandra, D. A. Frail, M. K. Kasliwal, B. P. Schmidt, A. M. Soderberg, P. B. Cameron, K. C. Roth

Comments: 8 pages, accepted in ApJ

Subjects: Astrophysics (astro-ph)

We present the discovery and high signal-to-noise spectroscopic observations of the optical afterglow of the long-duration gamma-ray burst GRB070125. Unlike all previously observed long-duration afterglows in the redshift range 0.5 <> 1.0 A) absorption features in the wavelength range 4000 - 10000 A. The sole significant feature is a weak doublet we identify as Mg II 2796 (W = 0.18 +/- 0.02 A), 2803 (W = 0.08 +/- 0.01) at z = 1.5477 +/- 0.0001. The low observed Mg II and inferred H I column densities are typically observed in galactic halos, far away from the bulk of massive star formation. Deep ground-based imaging reveals no host directly underneath the afterglow to a limit of R > 25.4 mag. Either of the two nearest blue galaxies could host GRB070125; the large offset (d >= 27 kpc) would naturally explain the low column density. To remain consistent with the large local (i.e. parsec scale) circum-burst density inferred from broadband afterglow observations, we speculate GRB070125 may have occurred far away from the disk of its host in a compact star-forming cluster. Such distant stellar clusters, typically formed by dynamical galaxy interactions, have been observed in the nearby universe, and should be more prevalent at z>1 where galaxy mergers occur more frequently.

Metcalfe 2007 The Production Rate and Employment of Ph.D. Astronomers

主要内容:
没怎么看懂，不过知道了他的结论：每个天文的新博士需要做两三站博后才能找到工作。（可能只指美国，还有他可能没计算上转行的。）

徐栋，你偷看我博客不发言。鄙视你！

精彩摘抄:


文章信息:

arXiv:0712.2820 [ps, pdf, other]

Title: The Production Rate and Employment of Ph.D. Astronomers

Authors: Travis S. Metcalfe (NCAR)

Comments: 5 pages, 4 figures, 2 tables, PASP

Subjects: Astrophysics (astro-ph)

In an effort to promote self-regulation of the astronomy job market, I examine the supply of, and demand for, astronomers over time. On the supply side, I document the production rate of Ph.D. astronomers from 1970 to 2006 using the UMI Dissertation Abstracts database, along with data from other independent sources. I compare the long-term trends in Ph.D. production with federal astronomy research funding over the same time period, and I demonstrate that additional funding is correlated with higher subsequent Ph.D. production. On the demand side, I monitor the changing patterns of employment using statistics about the number and types of jobs advertised in the AAS Job Register from 1984 to 2006. Finally, I assess the sustainability of the job market by normalizing this demand by the annual Ph.D. production. The most recent data suggest that there are now annual advertisements for about one postdoctoral job, half a faculty job, and half a research/support position for every new domestic Ph.D. recipient in astronomy and astrophysics. The average new astronomer might expect to hold up to 3 jobs before finding a steady position.

Ellis 2007 Erratum (astro-ph/0510172): on Lorentz Violation

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文章信息:

arXiv:0712.2781 [ps, pdf, other]

Title: Erratum Robust Limits on Lorentz Violation from Gamma-Ray Bursts

Authors: John Ellis, N.E. Mavromatos, D.V. Nanopoulos, A.S. Sakharov, E.K.G. Sarkisyan

Comments: four pages latex, two eps figures, uses special macros

Subjects: Astrophysics (astro-ph)

We correct the fitting formula used in refs. [1,2] to obtain a robust limit on a violation of Lorentz invariance that depends linearly on the photon energy. The correction leads to a slight increase of the limit on the scale of the violation, to M > 1.4 x 10^{16} GeV.

Li 2007 Determining the Dust Extinction of Gamma-ray Burst Host Galaxies

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文章信息:

arXiv:0712.2622 [ps, pdf, other]

Title: Determining the Dust Extinction of Gamma-ray Burst Host Galaxies: A Direct Method Based on Optical and X-ray Photometry

Authors: Yuan Li, Aigen Li, Daming Wei

Comments: 14 pages, 2 figures, accepted for publication in ApJ

Subjects: Astrophysics (astro-ph)

The dust extinction of gamma-ray bursts (GRBs) host galaxies, containing important clues to the nature of GRB progenitors and crucial for dereddening, is still poorly known. Here we propose a straightforward method to determine the extinction of GRB host galaxies by comparing the observed optical spectra to the intrinsic ones extrapolated from the X-ray spectra. The rationale for this method is from the standard fireball model: if the optical flux decay index equals to that of the X-ray flux, then there is no break frequency between the optical and X-ray bands, therefore we can derive the intrinsic optical flux from the X-ray spectra. We apply this method to three GRBs of which the optical and X-ray fluxes have the same decay indices and another one with inferred cooling break frequency, and obtain the rest-frame extinction curves of their host galaxies. The derived extinction curves are gray and do not resemble any extinction curves of local galaxies (e.g. the Milk Way, the Small/Large Magellanic Clouds, or nearby starburst galaxies). The amount of extinction is rather large (with visual extinction $A_V$ $\sim$ 1.6--3.4$\magni$). We model the derived extinction curves in terms of the silicate-graphite interstellar grain model. As expected from the ``gray'' nature of the derived extinction curve, the dust size distribution is skewed to large grains. We determine, for the first time, the local dust-to-gas ratios of GRB host galaxies using the model-derived dust parameters and the hydrogen column densities determined from X-ray absorptions.

Dai 2007 Go Long, Go Deep: Finding Optical Jet Breaks

主要内容:
They observed six bursts' optical late faint afterglows by LBT. And said the jet break is still their, but late.

精彩摘抄:


文章信息:

arXiv:0712.2239 [ps, pdf, other]

Title: Go Long, Go Deep: Finding Optical Jet Breaks for Swift-Era GRBs with the LBT

Authors: X. Dai, P. M. Garnavich, J. L. Prieto, K. Z. Stanek, C. S. Kochanek, J. Bechtold, N. Bouche, P. Buschkamp, E. Diolaiti, X. Fan, E. Giallongo, R. Gredel, J. M. Hill, L. Jiang, C. McClellend, P. Milne, F. Pedichini, R. W. Pogge, R. Ragazzoni, J. Rhoads, R. Smareglia, D. Thompson, R. M. Wagner

Comments: submitted to ApJ Letters, 16 pages, 3 figures

Subjects: Astrophysics (astro-ph)

Using the 8.4m Large Binocular Telescope, we observed six GRB afterglows from 2.8 hours to 30.8 days after the burst triggers to systematically probe the late time behaviors of afterglows including jet breaks, flares, and supernova bumps. We detected five afterglows with Sloan r' magnitudes ranging from 23.0--26.3 mag. The depth of our observations allows us to extend the temporal baseline for measuring jet breaks by another decade in time scale. We detected two jet breaks and a third candidate, all of which are not detectable without deep, late time optical observations. In the other three cases, we do not detect the jet breaks either because of contamination from the host galaxy light, the presence of a supernova bump, or the intrinsic faintness of the optical afterglow. This suggests that the basic picture that GRBs are collimated is still valid and that the apparent lack of Swift jet breaks is due to poorly sampled afterglow light curves, particularly at late times.

Staff 2007 quark star as GRB central object

主要内容:

They have done something similar as " quark nova for GRB early X-ray afterglow".

精彩摘抄:


文章信息:

arXiv:0712.1841 [ps, pdf, other]

Title: A three stage model for the inner engine of GRBs: Prompt emission and early afterglow

Authors: Jan Staff, Brian Niebergal, Rachid Ouyed

Comments: 4 pages, to appear in the proceedings of the HEPRO conference, September 24-28, 2007, Dublin, Ireland

Subjects: Astrophysics (astro-ph)

We describe a model within the ``Quark-nova'' scenario to interpret the recent observations of early X-ray afterglows of long Gamma-Ray Bursts (GRB) with the Swift satellite. This is a three-stage model within the context of a core-collapse supernova. STAGE 1 is an accreting (proto-) neutron star leading to a possible delay between the core collapse and the GRB. STAGE 2 is accretion onto a quark-star, launching an ultrarelativistic jet generating the prompt GRB. This jet also creates the afterglow as the jet interacts with the surrounding medium creating an external shock. Slower shells ejected from the quark star (during accretion), can re-energize the external shock leading to a flatter segment in the X-ray afterglow. STAGE 3, which occurs only if the quark-star collapses to form a black-hole, consists of an accreting black-hole. The jet launched in this accretion process interacts with the preceding quark star jet, and could generate the flaring activity frequently seen in early X-ray afterglows. Alternatively, a STAGE 2b can occur in our model if the quark star does not collapse to a black hole. The quark star in this case can then spin down due to magnetic braking, and the spin down energy may lead to flattening in the X-ray afterglow as well. This model seems to account for both the energies and the timescales of GRBs, in addition to the newly discovered early X-ray afterglow features.

Panaitescu 2007 GeV emission from Gamma-Ray Burst afterglows

主要内容:
Considering 4 mechanism for High energy emission for GLAST:
1. curvature effect of prompt emission;
2. spectral extension of X-ray (-p/2);
3. SSC of normal afterglow;
4. Bulk-scattering of GRB emission.

精彩摘抄:


文章信息:
arXiv:0712.1536 [ps, pdf, other]

Title: GeV emission from Gamma-Ray Burst afterglows

Authors: A. Panaitescu

Comments: 7 pages (too long to be reviewed in only 6 weeks)

Subjects: Astrophysics (astro-ph)

We calculate the GeV afterglow emission expected from a few mechanisms related to GRBs and their afterglows. Given the brightness of the early X-ray afterglow emission measured by Swift/XRT, GLAST/LAT should detect the self-Compton emission from the forward-shock driven by the GRB ejecta into the circumburst medium. Novel features discovered by Swift in X-ray afterglows (plateaus and chromatic light-curve breaks) indicate the existence of a pair-enriched, relativistic outflow located behind the forward shock. Bulk and inverse-Compton upscattering of the prompt GRB emission by such outflows provide another source of GeV afterglow emission detectable by LAT. The large-angle burst emission and synchrotron forward-shock emission are, most likely, too dim at high photon energy to be observed by LAT. The spectral slope of the high-energy afterglow emission and its decay rate (if it can be measured) allow the identification of the mechanism producing the GeV transient emission following GRBs

Dado 2007 'Jet breaks' and 'missing breaks' in the X-Ray afterglow of Gamma Ray Bursts

主要内容:
Still using their "canon ball" model. But contain many data (from other references).

A useful information: more energetic, t_b smaller. Is that right? If yes, which will means, in fireball model, with standard reservoir, more energetic (E_iso) means larger jet angle, and then larger t_b.

精彩摘抄:


文章信息:

arXiv:0712.1527 [ps, pdf, other]

Title: 'Jet breaks' and 'missing breaks' in the X-Ray afterglow of Gamma Ray Bursts

Authors: Shlomo Dado, Arnon Dar, A. De Rujula

Comments: 33 pages, 9 multiple figures

Subjects: Astrophysics (astro-ph)

The X-ray afterglows (AGs) of Gamma-Ray Bursts (GRBs) and X-Ray Flashes (XRFs) have, after the fast decline phase of their prompt emission, a temporal behaviour varying between two extremes. A large fraction of these AGs has a 'canonical' light curve which, after an initial shallow-decay 'plateau' phase, 'breaks smoothly' into a fast power-law decline. Very energetic GRBs, contrariwise, appear not to have a 'break', their AG declines like a power-law from the start of the observations. Breaks and 'missing breaks' are intimately related to the geometry and deceleration of the jets responsible for GRBs. In the frame of the 'cannonball' (CB) model of GRBs and XRFs, we analyze the cited extreme behaviours (canonical and pure power-law) and intermediate cases spanning the observed range of X-ray AG shapes. We show that the entire panoply of X-ray light-curve shapes --measured with Swift and other satellites-- are as anticipated, on very limpid grounds, by the CB model. We test the expected correlations between the AG's shape and the peak- and isotropic energies of the prompt radiation, strengthening a simple conclusion of the analysis of AG shapes: in energetic GRBs the break is not truly 'missing', it is hidden under the tail of the prompt emission, or it occurs too early to be recorded. We also verify that the spectral index of the unabsorbed AGs and the temporal index of their late power-law decline differ by half a unit, as predicted.

Mazets 2007 GRB 070201 maybe a giant flare of SGR

主要内容:
If take GRB 070201 occur in M31, it is very like a giant flare of a certain soft gamma-ray repeater.

精彩摘抄:


文章信息:

arXiv:0712.1502 [ps, pdf, other]

Title: A Giant Flare from a Soft Gamma Repeater in the Andromeda Galaxy, M31

Authors: E.P. Mazets, R.L. Aptekar, T.L. Cline, D.D. Frederiks, J.O. Goldsten, S.V. Golenetskii, K. Hurley, A. von Kienlin, V.D. Pal'shin

Comments: 15 pages, 5 figures, submitted to ApJ

Subjects: Astrophysics (astro-ph)

The light curve, energy spectra, energetics, and IPN localization of an exceedingly intense short duration hard spectrum burst, GRB 070201, obtained from Konus-Wind, INTEGRAL (SPI-ACS), and MESSENGER data are presented. The total fluence of the burst and the peak flux are $S = 2.00_{-0.26}^{+0.10} \times 10^{-5}$ erg cm$^{-2}$ and $F_{max} = 1.61_{-0.50}^{+0.29} \times 10^{-3}$ erg cm$^{-2}$ s$^{-1}$. The IPN error box has an area of 446 square arcminutes and covers the peripheral part of the M31 galaxy. Assuming that the source of the burst is indeed in M31 at a distance of 0.78 Mpc, the measured values of the fluence $S$ and maximum flux $F_{max}$ correspond to a total energy of $Q = 1.5 \times 10^{45}$ erg, and a maximum luminosity $L = 1.2 \times 10^{47}$ erg s$^{-1}$. These data are in good agreement with the corresponding characteristics of the previously observed giant flares from other soft gamma repeaters. The evidence for the identification of this event as a giant flare from a soft gamma repeater in the M31 galaxy is presented.

Margutti 2007 spectrum of GRB 060904B

主要内容:
Maybe a Nickel line.

精彩摘抄:


文章信息:

arXiv:0712.1412 [ps, pdf, other]

Title: Anomalous X-Ray emission in GRB060904B: a Nickel line?

Authors: R. Margutti, A. Moretti, F. Pasotti, S. Campana, G. Chincarini, S. Covino, C. Guidorzi, P. Romano, G. Tagliaferri

Comments: Accepted by A&A

Subjects: Astrophysics (astro-ph)

The detection of an extra component in GRB060904B X-ray spectra in addition to the standard single power-law behaviour has recently been reported in the literature. This component can be fit with different models; in particular the addition of a spectral line provides the best representation.In this paper we investigate the physical properties that the surrounding medium must have in order to produce a spectral feature that can explain the detected emission. We analyse and discuss how and if the detected spectral excess fits in different theoretical models developed to explain the nature of line emission during the afterglow phase of Gamma-Ray Bursts (GRBs). Trasmission and reflection models have been considered. Given the high value (>>1) of the Thomson optical depth, the emission is likely to arise in a reflection scenario. Within reflection models, the external reflection geometry fails to predict the observed luminosity. On the contrary, the detected feature can be explained in a funnel scenario with typical opening angle theta of 5 degrees, Nickel mass of the order of 0.1 M_o and T=10^6 K. For theta=20 degrees, assuming the reprocessing material to be the SN shell, the detected emission implies a Nickel mass of 0.4 M_o at T=10^7 K and a metallicity 10 times the solar value. If the giant X-ray flare that dominates the early XRT light curve is identified with the ionizing source, the SN expansion began 3000 s before the GRB event.

Metzger 2007 Short GRB from Proto-Magnetar spin-down

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文章信息:

arXiv:0712.1233 [ps, pdf, other]

Title: Short Duration Gamma-Ray Bursts with Extended Emission from Proto-Magnetar Spin-Down

Authors: B.D. Metzger, E. Quataert, T.A. Thompson

Comments: 5 pages, 2 figures; submitted to MNRAS Letters

Subjects: Astrophysics (astro-ph)

Evidence is growing for a class of gamma-ray bursts (GRBs) characterized by an initial ~0.1-1 s spike of hard radiation followed, after a ~10 s lull in emission, by a softer period of extended emission lasting ~10-100 s. In a few well-studied cases, these ``short GRBs with extended emission'' show no evidence for a bright associated supernova (SN). We propose that these events are produced by the formation and early evolution of a highly magnetized, rapidly rotating neutron star (a ``proto-magnetar'') which is formed from the accretion-induced collapse (AIC) of a white dwarf (WD), the merger and collapse of a WD-WD binary, or, perhaps, the merger of a double neutron star binary. The initial emission spike is powered by accretion onto the proto-magnetar from a small disk that is formed during the AIC or merger event. The extended emission is produced by a relativistic wind that extracts the rotational energy of the proto-magnetar on a timescale ~10-100 s. The ~10 s delay between the prompt and extended emission is the time required for the newly-formed proto-magnetar to cool sufficiently that the neutrino-heated wind from its surface becomes ultra-relativistic. Because a proto-magnetar ejects little or no Ni56 (<>

Belczynski 2007 Constrain the NS-NS merger model

主要内容:
Using their startrack code, the result is: if the mass of NS is greater 2.5 M_sun, can't produce short GRB.

精彩摘抄:


文章信息:

arXiv:0712.1036 [ps, pdf, other]

Title: The lowest-mass stellar black holes: catastrophic death of neutron stars in gamma-ray bursts

Authors: K. Belczynski, R. O'Shaughnessy, V. Kalogera, F. Rasio, R. Taam, T. Bulik

Comments: 4 pages, submitted to Science

Subjects: Astrophysics (astro-ph)

Mergers of double neutron stars are considered the most likely progenitors for short gamma-ray bursts. Indeed such a merger can produce a black hole with a transient accreting torus of nuclear matter and the conversion of the torus mass-energy to radiation can power a gamma-ray burst. Using available binary pulsar observations supported by our extensive evolutionary calculations of double neutron star formation, we demonstrate that the fraction of mergers that can form a black hole -- torus system depends very sensitively on the (largely unknown) maximum neutron star mass. We show that the available observations and models put a very stringent constraint on this maximum mass under the assumption that a majority of short gamma-ray bursts originate in double neutron star mergers. Specifically, we find that the maximum neutron star mass must be within 2--2.5 Msun. Moreover, a single unambiguous measurement of a neutron star mass above 2.5 Msun would exclude double neutron star mergers as short gamma-ray burst progenitors.

Biesiada 2007 Gravitational lensing time delays as a tool for testing Lorentz Invariance Violation

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文章信息:

arXiv:0712.0941 [ps, pdf, other]

Title: Gravitational lensing time delays as a tool for testing Lorentz Invariance Violation

Authors: Marek Biesiada, Aleksandra Piórkowska

Comments: 11 pages, submitted to JCAP

Subjects: Astrophysics (astro-ph)

Despite the fact that quantum gravity theory still remains elusive, it is generally expected that it will bring the picture of a space-time foam at short distances leading to Lorenz Invariance Violation (LIV) manifested e.g. by energy dependent modification of standard relativistic dispersion relation. One direction of research, pursued intensively is to measure energy dependent time of arrival delays in photons emitted by astrophysical sources located at cosmological distances. This is tempered however by our ignorance of either intrinsic delay (at source frame) in different energy channels or as recently shown, the correct model of the background cosmology.
In this paper we propose a new test based on gravitational lensing. Monitoring time delays between images performed in different energy channels (e.g. optical - low energy and TeV photons) may reveal extra delays due to distorted dispersion relation typical in LIV theories - a test which is free from the systematics inherent in other settings.

Biesiada 2007 Infulence of cosmoligical models on QG limitation

主要内容:
Considering the cosmological effect, then study the quantum gravity limitation by means of GRB neutrinos.

精彩摘抄:


文章信息:

arXiv:0712.0937 [ps, pdf, other]

Title: GRB neutrinos, Lorenz Invariance Violation and the influence of background cosmology

Authors: Marek Biesiada, Aleksandra Piórkowska

Comments: Accepted for publication in JCAP. 10 pages, 3 figures

Journal-ref: JCAP05(2007)011

Subjects: Astrophysics (astro-ph)

Modern ideas in quantum gravity predict the possibility of Lorenz Invariance Violation (LIV) manifested e.g. by energy dependent modification of standard relativistic dispersion relation. In a recent paper Jacob and Piran proposed that time of flight delays in high energy neutrinos emitted by gamma ray bursts (GRBs) located at cosmological distances can become a valuable tool for setting limits on LIV theories. However, current advances in observational cosmology suggest that our Universe is dominated by dark energy with relatively little guidance on its nature thus leading to several cosmological scenarios compatible with observations.
In this paper we raise the issue of how important, in the context of testing LIV theories, is our knowledge of background cosmological model. Specifically we calculate expected time lags for high-energy (100 TeV) neutrinos in different cosmological models. Out of many particular models of dark energy we focus on five: $\Lambda$CDM, quintessence, quintessence with time varying equation of state, brane-world and generalized Chaplygin gas model as representative for various competing approaches. The result is that uncertainty introduced by our ignorance concerning the right phenomenological model describing dark energy dominated universe is considerable and may obscure bounds derived from studying time delays from cosmological sources.

van Eijndhoven 2007 Method to identify GRB Netrutrinos from the background

主要内容:


精彩摘抄:


文章信息:

arXiv:0712.0924 [pdf, other]

Title: GRB neutrino detection via time profile stacking

Authors: Nick van Eijndhoven

Comments: 4 pages, 5 figures. Talk presented at ICRC07, Merida, Mexico

Subjects: Astrophysics (astro-ph)

A method is presented for the identification of high-energy neutrinos from gamma ray bursts by means of a large-scale neutrino telescope. The procedure makes use of a time profile stacking technique of observed neutrino induced signals in correlation with satellite observations. By selecting a rather wide time window, a possible difference between the arrival times of the gamma and neutrino signals may also be identified. This might provide insight in the particle production processes at the source. By means of a toy model it will be demonstrated that a statistically significant signal can be obtained with a km$^{3}$-scale neutrino telescope on a sample of 500 gamma ray bursts for a signal rate as low as 1 detectable neutrino for 3% of the bursts.

Dainotti 2007 GRB 060218 and binary model

主要内容:
Observation summarized first, then pointed out that: collapse of NS in a binary system can give this low energetic thing.

精彩摘抄:


文章信息:

arXiv:0712.0567 [ps, pdf, other]

Title: GRB 060218 and the binaries as progenitors of GRB-SN systems

Authors: Maria Giovanna Dainotti, Maria Grazia Bernardini, Carlo Luciano Bianco, Letizia Caito, Roberto Guida, Remo Ruffini

Comments: 6 pages, 3 figures, in the Proceedings of the "4th Italian-Sino Workshop on Relativistic Astrophysics", held in Pescara, Italy, July 20-28, 2007, C.L. Bianco, S.-S. Xue, Editors

Journal-ref: AIP Conf.Proc. 966 (2007) 25-30

Subjects: Astrophysics (astro-ph)

(shortened) We study the Gamma-Ray Burst (GRB) 060218: a particularly close source at z=0.033 with an extremely long duration, namely T_{90} ~ 2000 s, related to SN 2006aj. [...] I present the fitting time consuming procedure. In order to show its sensitivity I also present two examples of fits with the same value of B and different value of E_{e^\pm}^{tot}. We fit the X- and \gamma-ray observations by Swift of GRB 060218 in the 0.1-150 keV energy band during the entire time of observations from 0 all the way to 10^6 s within a unified theoretical model. The free parameters of our theory are only three, namely the total energy E_{e\pm}^{tot} of the e^\pm plasma, its baryon loading B \equiv M_Bc^2/E_{e\pm}^{tot}, as well as the CircumBurst Medium (CBM) distribution. We justify the extremely long duration of this GRB by a total energy E_{e\pm}^{tot} = 2.32\times 10^{50} erg, a very high value of the baryon loading B=1.0\times 10^{-2} and the effective CircumBurst Medium (CBM) density which shows a radial dependence n_{cbm} \propto r^{-\alpha} with 1.0 \leq \alpha \leq 1.7 and monotonically decreases from 1 to $10^{-6}$ particles/cm$^3$. We recall that this value of the $B$ parameter is the highest among the sources we have analyzed and it is very close to its absolute upper limit expected. [...] We also think that the smallest possible black hole, formed by the gravitational collapse of a neutron star in a binary system, is consistent with the especially low energetics of the class of GRBs associated with SNe Ib/c.

Bernardini 2007 GRB 970228 doesn't fulfill Amati relation

主要内容:


精彩摘抄:


文章信息:

arXiv:0712.0550 [ps, pdf, other]

Title: GRB970228 and the class of GRBs with an initial spikelike emission: do they follow the Amati relation?

Authors: Maria Grazia Bernardini, Carlo Luciano Bianco, Letizia Caito, Maria Giovanna Dainotti, Roberto Guida, Remo Ruffini

Comments: 5 pages, 3 figures, in the Proceedings of the "4th Italian-Sino Workshop on Relativistic Astrophysics", held in Pescara, Italy, July 20-28, 2007, C.L. Bianco, S.-S. Xue, Editors

Journal-ref: AIP Conf.Proc. 966 (2007) 7-11

Subjects: Astrophysics (astro-ph)

On the basis of the recent understanding of GRB050315 and GRB060218, we return to GRB970228, the first Gamma-Ray Burst (GRB) with detected afterglow. We proposed it as the prototype for a new class of GRBs with "an occasional softer extended emission lasting tenths of seconds after an initial spikelike emission". Detailed theoretical computation of the GRB970228 light curves in selected energy bands for the prompt emission are presented and compared with observational BeppoSAX data. From our analysis we conclude that GRB970228 and likely the ones of the above mentioned new class of GRBs are "canonical GRBs" have only one peculiarity: they exploded in a galactic environment, possibly the halo, with a very low value of CBM density. Here we investigate how GRB970228 unveils another peculiarity of this class of GRBs: they do not fulfill the "Amati relation". We provide a theoretical explanation within the fireshell model for the apparent absence of such correlation for the GRBs belonging to this new class.

gamma ray satellite AGILE by Italy

主要内容:
AGILE (Astro-rivelatore Gamma a Immagini LEggero), energy band 30 MeV–50 GeV and 10–40keV. Launched on April 23, 2007.

Contain three instrument: GRID, MC, and Super-AGILE. Gamma-Ray Imaging Detector (GRID) is sensitive in the energy range 30 MeV–50 GeV. And X-ray range (10-40 keV), the Super-AGILE detector. Mini-Calorimeter (MC) 0.25–200 MeV.

Scientific goal:

For Gamma-Ray Bursts :
(1) Expected detection rate above 50 MeV: 5-10 events/year
(2) Study of the initial impulsive phase (GRID deadtime < 200 \mu s)
(3) Broad-band spectral information (10 keV –30 GeV)
(4) Super-AGILE imaging ( 1'-2' for intense GRBs)
(5) Super-AGILE study of gamma-ray vs. hard X-ray emission
(6) Search for sub-millisecond GRB pulses
(7) Rapid communication of GRB coordinates and quicklook results
url:
http://agile.rm.iasf.cnr.it/doc/a-science-27.pdf

精彩摘抄:
Comparing with EGRET in CGRO (BATSE is also on this satellite)





sensitivity with 10^6 s.
sensitivity

The missions.

文章信息:

Del Monte 2007 first burst (070724B) detected by Super AGILE

主要内容:
Trigger by SuperAGILE on AGILE. Gave the coordinate 19 hours later, then, Swift XRT observed the X-ray afterglow. No signal on radio, optical and high energy observations. Upper limit: 350 keV – 2.8 MeV, 4 × 10^−6 erg cm^−2; above 100MeV, 0.02 ph cm^−2. While EGRET (NOT the upper limit): ~ 0.039 ph cm^−2 for GRB 930131 and ~ 0.015 ph cm^−2 for GRB 940217.

精彩摘抄:


文章信息:

arXiv:0712.0500 [ps, pdf, other]

Title: GRB 070724B: the first Gamma Ray Burst localized by SuperAGILE and its Swift X-ray Afterglow

Authors: E. Del Monte, M. Feroci, L. Pacciani, Y. Evangelista, I. Donnarumma, P. Soffitta, E. Costa, I. Lapshov, F. Lazzarotto, M. Rapisarda, A. Argan, G. Barbiellini, M. Basset, A. Bulgarelli, P. Caraveo, A. Chen, G. Di Cocco, L. Foggetta, F. Fuschino, M. Galli, F. Gianotti, A. Giuliani, C. Labanti, P. Lipari, F. Longo, M. Marisaldi, F. Mauri, S. Mereghetti, A. Morselli, A. Pellizzoni, F. Perotti, P. Picozza, M. Prest, G. Pucella, M. Tavani, M. Trifoglio, A. Trois, E. Vallazza, S. Vercellone, V. Vittorini, A. Zambra, P. Romano, D. N. Burrows, G. Chincarini, N. Gehrels, V. La Parola, P. T.O'Brien, J. P. Osborne, B. Preger, C. Pittori, L. A. Antonelli, F. Verrecchia, P. Giommi, L. Salotti

Comments: 7 pages, 4 figures (of which 2 in color), contains online material. Accepted for publication by Astronomy & Astrophysics Letters

Subjects: Astrophysics (astro-ph)

GRB 070724B is the first Gamma Ray Burst localized by SuperAGILE, the hard X-ray monitor aboard the AGILE satellite. The coordinates of the event were published $\sim 19$ hours after the trigger. The Swift X-Ray Telescope pointed at the SuperAGILE location and detected the X-ray afterglow inside the SuperAGILE error circle. The AGILE gamma-ray Tracker and Minicalorimeter did not detect any significant gamma ray emission associated with GRB 070724B in the MeV and GeV range, neither prompt nor delayed. Searches of the optical afterglow were performed by the Swift UVOT and the Palomar automated 60-inch telescopes without any significant detection. Similarly the Very Large Array did not detect a radio afterglow. This is the first GRB event with a firm upper limit in the 100 MeV -- 30 GeV energy range, associated with an X-ray afterglow.

Bianco 2007 The "fireshell" model and the "canonical" GRB scenario

主要内容:
precursor is their GRB, and GRB is their afterglow. (It was appeared before.)

精彩摘抄:


文章信息:

arXiv:0712.0495 [ps, pdf, other]

Title: The "fireshell" model and the "canonical" GRB scenario

Authors: Carlo Luciano Bianco, Maria Grazia Bernardini, Letizia Caito, Maria Giovanna Dainotti, Roberto Guida, Remo Ruffini

Comments: 4 pages, 5 figures, in the Proceedings of the "4th Italian-Sino Workshop on Relativistic Astrophysics", held in Pescara, Italy, July 20-28, 2007, C.L. Bianco, S.-S. Xue, Editors

Journal-ref: AIP Conf.Proc. 966 (2007) 12-15

Subjects: Astrophysics (astro-ph)

In the "fireshell" model we define a "canonical GRB" light curve with two sharply different components: the Proper-GRB (P-GRB), emitted when the optically thick fireshell of electron-positron plasma originating the phenomenon reaches transparency, and the afterglow, emitted due to the collision between the remaining optically thin fireshell and the CircumBurst Medium (CBM). We outline our "canonical GRB" scenario, originating from the gravitational collapse to a black hole, with a special emphasis on the discrimination between "genuine" and "fake" short GRBs.

Kelly 2007 Long GRBs and SNe Ic have similar galactic environment

主要内容:
Using SDSS data, they found long GRBs and SNe distribute in the same region of galaxies: the brightest region.

精彩摘抄:


文章信息:

arXiv:0712.0430 [ps, pdf, other]

Title: Long Gamma-Ray Bursts and Type Ic Core Collapse Supernovae Have Similar Environments

Authors: P. L. Kelly (1 and 2), R. P. Kirshner (2), M. Pahre (2) ((1) Stanford University, (2) CfA)

Comments: 11 pages, 4 figures, 2 tables

Subjects: Astrophysics (astro-ph)

When the afterglow fades at the site of a long-duration gamma-ray burst (LGRB), Type Ic supernovae (SN Ic) are the only type of core collapse supernova observed. Recent work found that a sample of LGRB had different environments from a collection of core-collapse supernovae identified in a high-redshift sample from colors and light curves. LGRB were in the brightest regions of their hosts, but the core-collapse sample followed the overall distribution of the galaxy light. Here we examine 263 fully spectroscopically-typed supernovae found in nearby (z <>

Zhang 2007 Hyperaccretion on Netron stars

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文章信息:

arXiv:0712.0423 [ps, pdf, other]

Title: Hyperaccretion Disks around Neutron Stars

Authors: Dong Zhang, Z. G. Dai (NJU)

Comments: 33 pages including 7 figures

Subjects: Astrophysics (astro-ph)

It is usually proposed that hyperaccretion disks surrounding stellar-mass black holes at an accretion rate of a fraction of one solar mass per second, which are produced during the mergers of double compact stars or the collapses of massive stars, are central engines of gamma-ray bursts (GRBs). In some origin/afterglow models, however, newborn compact objects are invoked to be neutron stars rather than black holes. Thus, hyperaccretion disks around neutron stars seem to exist in some GRBs. Such disks may also occur in type-II supernovae. In this paper we study the structure of a hyperaccretion disk around a neutron star. We consider a steady-state disk model and divide the disk into two regions, called inner and outer disks. The inner disk satisfies an adiabatic self-similar structure and the outer disk is similar to the outer region of a hyperaccretion disk around a black hole. By using analytical and numerical methods, we explore the size of the inner disk, the radial distributions of the density, temperature and pressure of the whole disk, the mechanisms of energy heating and cooling, and the efficiency of neutrino cooling. We find that, compared with a black-hole disk, the hyperaccretion disk around a neutron star can cool more efficiently and produce a much higher neutrino luminosity.

Alexander 2007 Local void for acceleration vs. Dark Energy

主要内容:


精彩摘抄:
if we happen to be living in the middle of a large underdense region, then we will observe an ``apparent acceleration''

文章信息:

arXiv:0712.0370 [ps, pdf, other]

Title: Local Void vs Dark Energy: Confrontation with WMAP and Type Ia Supernovae

Authors: Stephon Alexander, Tirthabir Biswas, Alessio Notari, Deepak Vaid

Comments: 26 pages, 11 figures

Subjects: Astrophysics (astro-ph)

It is now a known fact that if we happen to be living in the middle of a large underdense region, then we will observe an ``apparent acceleration'', even when any form of dark energy is absent. In this paper, we present a ``Minimal Void'' scenario, i.e. a ``void'' with minimal underdensity contrast (of about -0.4) and radius (~ 200-250 Mpc/h) that can, not only be consistent with the supernovae data, but also with the 3-yr WMAP data. We also discuss consistency of our model with various other measurements such as Big Bang Nucleosynthesis, Baryon Acoustic Oscillations and local measurements of the Hubble parameter. We also point out possible other observable signatures.

van Marle 2007 rapid rotating progenitor enviroment

主要内容:


精彩摘抄:
we find a strong deviation of the circumstellar density profile in the polar direction from the 1/R^2 density profile normally associated with stellar winds close to the star.

Solid: mass density; dashed: energy density

文章信息:

arXiv:0711.4807 [ps, pdf, other]

Title: The circumstellar medium around a rapidly rotating, chemically homogeneously evolving, possible gamma-ray burst progenitor

Authors: Allard Jan van Marle, Norbert Langer, Sung-Chul Yoon, Guillermo Garcia-Segura

Comments: accepted by Astronomy & Astrophysics

Subjects: Astrophysics (astro-ph)

Rapidly rotating, chemically homogeneously evolving massive stars are considered to be progenitors of long gamma-ray bursts. We present numerical simulations of the evolution of the circumstellar medium around a rapidly rotating 20 Msol star at a metallicity of Z=0.001. Its rotation is fast enough to produce quasi-chemically homogeneous evolution. While conventionally, a star of 20 Msol would not evolve into a Wolf-Rayet stage, the considered model evolves from the main sequence directly to the helium main sequence. We use the time-dependent wind parameters, such as mass loss rate, wind velocity and rotation-induced wind anisotropy from the evolution model as input for a 2D hydrodynamical simulation. While the outer edge of the pressure-driven circumstellar bubble is spherical, the circumstellar medium close to the star shows strong non-spherical features during and after the periods of near-critical rotation. We conclude that the circumstellar medium around rapidly rotating massive stars differs considerably from the surrounding material of non-rotating stars of similar mass. Multiple blue-shifted high velocity absorption components in gamma-ray burst afterglow spectra are predicted. As a consequence of near critical rotation and short stellar evolution time scales during the last few thousand years of the star's life, we find a strong deviation of the circumstellar density profile in the polar direction from the 1/R^2 density profile normally associated with stellar winds close to the star.