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TOPIC: Gamma-Ray Bursts
Blobrana


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RE: Gamma-Ray Bursts
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If you were unfortunate enough to experience one of the universe's most powerful explosions up close, you would certainly be doomed. But would the blast obliterate you with jets like something from a flamethrower or with cannonball-like projectiles of plasma? We thought we knew the answer, but now the picture is not so clear.
Gamma-ray bursts (GRBs), the most violent explosions in the cosmos, are intense flashes of high-energy radiation. The shorter bursts probably happen when a neutron star collides with another neutron star or a black hole. More protracted bursts release so much energy that only one type of event is thought capable of producing them - the collapse of a massive star's core to form a black hole or neutron star.
The standard picture of longer-lasting GRBs is that magnetic fields steer the matter thrown off by the collapsing star into a pair of jets travelling in opposite ...

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Blobrana


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GRB afterglows
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Title: GRB afterglows in the ELT era
Authors: D. A. Kann, S. Klose

This is a very short conference proceeding based on a poster shown at the ESO workshop "Science with the VLT in the ELT Era". For more information, see "The Afterglows of Swift-era Gamma-Ray Bursts. I. Comparing pre-Swift and Swift era Long/Soft (Type II) GRB Optical Afterglows"  as well as "The Afterglows of Swift-era Gamma-Ray Bursts. II. Short/Hard (Type I) vs. Long/Soft (Type II) Optical Afterglows"

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Blobrana


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RE: Gamma-Ray Bursts
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Title: Bohdan's Impact on Our Understanding of Gamma-ray Bursts
Authors: Tsvi Piran

Bohdan Paczy'nski was one of the pioneers of the cosmological GRB model. His ideas on how GRBs operate and what are their progenitors have dominated the field of GRBs in the hectic nineties during which the distances and the origin of GRBs were revealed. I discuss here Bohdan's contributions in some historical perspective.

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Blobrana


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Millions of faint galaxies are hovering near the edge of our universe, too dim to be detected by most telescopes -- but some huge cosmic explosions and the supersensitive infrared eyes of NASA's Spitzer Space Telescope are bringing many of these muted galaxies to light.
Located approximately 12.5 billion light-years away from Earth, the distant galaxies exist in an era when our universe was just one billion years old. With Spitzer's sensitive infrared eyes, astronomers can finally snap infrared portraits and even "weigh" many of these otherwise invisible galaxies.

"A few billion years after the big bang, 90 percent of the stars being born were occurring in these types of faint galaxies. By identifying this population, we hope to gain insights into the environments where the universe's first stars formed" - Dr. Ranga Ram Chary, of the Spitzer Science Centre, Pasadena, California.

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Blobrana


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GRB060904B
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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

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). Transmission 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 ionising source, the SN expansion began 3000 s before the GRB event.

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Blobrana


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RE: Gamma-Ray Bursts
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Title: A Possible New Distance Indicator -Correlation between the duration and the X-ray luminosity of the shallow decay phase of Gamma Ray Bursts-
Authors: R. Sato, K. Ioka, K. Toma, T. Nakamura, J. Kataoka, N. Kawai, T. Takahashi

We investigated the characteristics of the shallow decay phase in the early Xray afterglows of GRBs observed by Swift X-Ray Telescope (XRT) during the period of January 2005 to December 2006. We found that the intrinsic break time at the shallow-to-normal decay transition in the X-ray light curve Tbrk^0 is moderately well correlated with the isotropic X-ray luminosity in the end of the shallow decay phase (LX,end) as Tbrk^0 =(9.39+/-0.64)*10^3s(LX,end/10^47 ergs/s)^(-0.71+/-0.03), while Tbrk^0 is weakly correlated with the isotropic gamma-ray energy of the prompt emission Egamma,iso. Using Tbrk^0 - LX,end relation we have determined the pseudo redshifts of 33 GRBs. We compared the pseudo redshifts of 11 GRBs with measured redshifts and found the rms error to be 0.17 in log z. From this pseudo redshift, we estimate that ~15% of the Swift GRBs have z > 5. The advantages of this distance indicator is that (1) it requires only X-ray afterglow data while other methods such as Amati and Yonetoku correlations require the peak energy (Ep) of the prompt emission, (2) the redshift is uniquely determined without redshift degeneracies unlike the Amati correlation, and (3) the redshift is estimated in advance of deep follow-ups so that possible high redshift GRBs might be selected for detailed observations.

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Title: A bright millisecond radio burst of extragalactic origin
Authors: D. R. Lorimer, M. Bailes, M. A. McLaughlin, D. J. Narkevic, F. Crawford

Pulsar surveys offer one of the few opportunities to monitor even a small fraction (~0.00001) of the radio sky for impulsive burst-like events with millisecond durations. In analysis of archival survey data, we have discovered a 30-Jy dispersed burst of duration <5 ms located three degrees from the Small Magellanic Cloud. The burst properties argue against a physical association with our Galaxy or the Small Magellanic Cloud. Current models for the free electron content in the Universe imply a distance to the burst of <1 Gpc No further bursts are seen in 90-hr of additional observations, implying that it was a singular event such as a supernova or coalescence of relativistic objects. Hundreds of similar events could occur every day and act as insightful cosmological probes.

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1448887209_fa6b0f8179_o.gif
Position(2000): RA 01h 18m 06s Dec 75°  12 19

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Blobrana


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Computer visualisations of the radio hyperburst

arrow1.gifSwin_media.mov      Suitable for broadcast purposes, [Apple Intermediate Codec, 94mb]

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Blobrana


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Astronomers report seeing an extremely bright, extremely powerful radio burst from far outside of our galaxy. They can't recall seeing anything like it before and they have no idea what caused it.
The story begins in 2001, when astronomers pointed the Parkes radio telescope in Australia at the Small Magellanic Cloud. The cloud is really a galaxy about 200,000 light years away. The astronomers were looking for pulsars, spinning neutron stars that pour out rhythmic bursts of energy.

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Powerful Radio Burst Indicates New Astronomical Phenomenon
Astronomers studying archival data from an Australian radio telescope have discovered a powerful, short-lived burst of radio waves that they say indicates an entirely new type of astronomical phenomenon.

"This burst appears to have originated from the distant Universe and may have been produced by an exotic event such as the collision of two neutron stars or the death throes of an evaporating black hole" - Duncan Lorimer, Assistant Professor of Physics at West Virginia University (WVU) and the National Radio Astronomy Observatory (NRAO).

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