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Post Info TOPIC: GRB050904


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GRB 050904
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Title: Is GRB 050904 at z=6.3 absorbed by dust?
Authors: G. Stratta, S. Gallerani, R. Maiolino

Claim of dust extinction for this GRB has been debated in the past. We suggest that the discrepant results occur primarily because most of previous studies have not simultaneously investigated the X-ray to near-IR spectral energy distribution of this GRB. The difficulty with this burst is that the X-ray afterglow is dominated by strong flares at early times and is poorly monitored at late times. In addition, the Z band photometry, which is the most sensitive to dust extinction, has been found to be affected by strong systematics. In this paper we carefully re-analyse the Swift/XRT afterglow observations of this GRB, using extensive past studies of X-ray flare properties when computing the X-ray afterglow flux level and exploiting the recent reanalysis of the optical (UV rest frame) data of the same GRB. We extract the X-ray to optical/near-IR afterglow SED for the three epochs where the best spectral coverage is available: 0.47, 1.25, and 3.4 days after the trigger. A spectral power-law model has been fitted to the extracted SEDs. We discuss that no spectral breaks or chromatic temporal breaks are expected in the epochs of interest. To fit any UV rest-frame dust absorption, we tested the Small Magellanic Cloud (SMC) extinction curve, the mean extinction curve (MEC) found for a sample of QSO at z>4 and its corresponding attenuation curve, as well as a starburst attenuation curve, and the extinction curve consistent with a supernova dust origin (SN-type). The SMC extinction curve and the SN-type one provide good fit to the data at all epochs, with an average amount of dust absorption at \lambda_{rest} = 3000 \AA of A_{3000} = 0.250.07 mag. These results indicate that the primeval galaxy at z = 6.3 hosting this GRB has already enriched its ISM with dust.

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RE: GRB050904
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Title: Swift observations of GRB050904: the most distant cosmic explosion ever observed
Authors: G. Cusumano, V. Mangano, G. Chincarini, A. Panaitescu, D.N. Burrows, V. La Parola, T. Sakamoto, S. Campana, T. Mineo, G. Tagliaferri, L. Angelini, S.D. Barthelemy, A.P. Beardmore, P.T. Boyd, L. Cominsky, C. Gronwall, E.E. Fenimore, N. Gehrels, P. Giommi, M. Goad, K. Hurley, S. Immler, J.A. Kennea, K.O. Mason, F. Marshall, P. Meszaros, J.A. Nousek, J.P. Osborne, D.M. Palmer, P.W.A. Roming, A. Wells, N.E. White, B. Zhang
(revised v2)

Swift discovered the high redshift (z=6.29) GRB050904 with the Burst Alert Telescope (BAT) and began observing with its narrow field instruments 161 s after the burst onset. This gamma-ray burst is the most distant cosmic explosion ever observed.

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Posts: 131433
Date:
Swift observations of GRB050904
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Title: Swift observations of GRB050904: the most distant cosmic explosion ever observed
Authors: G. Cusumano, V. Mangano, G. Chincarini, A. Panaitescu, D.N. Burrows, V. La Parola, T. Sakamoto, S. Campana, T. Mineo, G. Tagliaferri, L. Angelini, S.D. Barthelemy, A.P. Beardmore, P.T. Boyd, L. Cominsky, C. Gronwall, E.E. Fenimore, N. Gehrels, P. Giommi, M. Goad, K. Hurley, S. Immler, J.A. Kennea, K.O. Mason, F. Marshall, P. Meszaros, J.A. Nousek, J.P. Osborne, D.M. Palmer, P.W.A. Roming, A. Wells, N.E. White, B. Zhang

Swift discovered the high redshift (z=6.29) GRB050904 with the Burst Alert Telescope (BAT) and began observing with its narrow field instruments 161 s after the burst onset. This gamma-ray burst is the most distant cosmic explosion ever observed. Because of its high redshift, the X-ray Telescope (XRT) and BAT simultaneous observations provide 4 orders of magnitude of spectral coverage (0.2-150 keV; 1.4-1090 keV in the source rest frame) at a very early source-frame time (22 s). GRB050904 was a long, multi-peaked, bright GRB with strong variability during its entire evolution. The light curve observed by the XRT is characterised by the presence of a long flaring activity lasting up to 1-2 hours after the burst onset in the burst rest frame, with no evidence of a smooth power-law decay following the prompt emission as seen in other GRBs. However, the BAT tail extrapolated to the XRT band joins the XRT early light curve and the overall behaviour resembles that of a very long GRB prompt. The spectral energy distribution softens with time, with the photon index decreasing from -1.2 during the BAT observation to -1.9 at the end of the XRT observation. The dips of the late X-ray flares may be consistent with an underlying X-ray emission arising from the forward shock and with the properties of the optical afterglow reported by Tagliaferri et al. (2005b). We interpret the BAT and XRT data as a single continuous observation of the prompt emission from a very long GRB. The peculiarities observed in GRB050904 could be due to its origin within one of the first star-forming regions in the Universe; very low metallicities of the progenitor at these epochs may provide an explanation.

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RE: GRB050904
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Universe Re-Ionised 900 Million Years after Birth

Observations by the Subaru telescope of the most distant known gamma-ray bust show that most hydrogen between the galaxies had become ionised 900 million years after the Big Bang. This study by researchers from Kyoto University, Tokyo Institute of Technology, and the National Astronomical Observatory of Japan dates the formation of the first generations of stars and galaxies to an ever precise time than previous studies, and demonstrates the power of gamma-ray bursts to illuminate the early universe.

Fourteen billion years ago the universe came into existence as a fiery furnace of energy and matter. As it expanded, it cooled. After 300 thousand years it reached a temperature of about 3000 degrees, allowing atomic nuclei and electrons to combine and form electrically neutral atoms. After that, gravity brought matter together to form the stars and galaxies we know today.
However, we also know from previous studies of quasars, energetic beacons from the early universe, that most of the sparse matter in between galaxies is now ionised - split back into nuclei and elections. How and when this happened is one of the central questions of modern astronomy because the re-ionisation of the universe and the early genealogy of stars and galaxies are closely linked. Ultra- violet radiation from the first generations of stars is one of the strongest candidates for cause of the re-ionisation.
In recent years, astronomers have learned that gamma-ray bursts can be even better beacons than quasars for illuminating the process of the re-ionisation of the universe. Quasars shine from the release of gravitational energy as matter falls into a black hole. When observing quasars, it is difficult to disentangle the quasar, the quasar's effect on its immediate environment, and the environment in the vastness between the quasar and Earth. Gamma-ray bursts are now known to originate from extremely energetic versions of a supernova, the death throws of a massive star. These events do not disturb their immediate environment, so extracting information about the gas between the galaxies is much easier.

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On September 4, 2005, the Swift Gamma-Ray Burst Mission detected a gamma-ray burst, GRB 050904, that had occurred 900 million years after the birth of the universe. Japanese researchers using the Subaru telescope were able to catch a high-resolution spectrum of the visible light after-glow of the burst. A detailed analysis of this spectrum has revealed that at the time of the burst, more than 80% of the hydrogen between galaxies was already ionised.

"Our technology to observe gamma-ray bursts is really maturing - allowing us to understand earlier times of the universe with ever greater detail. This event demonstrates the power and potential of studying the early universe using gamma-ray bursts. It opens a new frontier of observational cosmology for astronomers worldwide" - Dr. Tomonori Totani.

Now the team awaits the detection of an even more distant gamma-ray burst.

These results will be published in the June 25, 2006 edition of the Publications of the Astronomical Society of Japan.

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Posts: 131433
Date:
GRB 050904
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Today scientists released new findings and an animation that depicts a strange sequence of events in which the explosion of a massive star first settles down but then fires back up several times toward the end.
Astronomers speculate that the black hole did not form instantly, as theory predicts, but that it was a prolonged process.
The gamma-ray burst , named GRB 050904, lasted more than 8 minutes ad originated 12.8 billion light-years away, when the Universe was just 890 million years old.
The burst of high-energy radiation was followed by afterglows in visible light and other wavelengths on the electromagnetic spectrum. It was detected by astronomers in the United States, Japan and Italy last September using NASA's Swift satellite.

"This means that not only did stars form in this short period of time after the Big Bang, but also that enough time had elapsed for them to evolve and collapse into black holes" - Giancarlo Cusumano, of the National Institute for Astrophysics in Palermo, Italy.

Astronomers know very little about the stars that formed back then, other than that they were made almost entirely of hydrogen and helium and a trace of lithium; other, heavier elements formed only when the first stars exploded. However, astronomers did find heavier elements in the spectra of GRB 050904.
Also, the flaring of GRB 050904 is something unusual, and not seen in closer bursts. That means the earliest black holes might have formed differently than those being born today. The difference could be because the first stars were more massive, or perhaps it's just because the cosmic environment was different then.

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Posts: 131433
Date:
Furthest GRBs
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Title: Detection of a huge explosion in the early Universe
Authors: G. Cusumano, V. Mangano, G. Chincarini, A. Panaitescu, D.N. Burows, V. La Parola, T. Sakamoto, S. Campana, T. Mineo, G. Tagliaferri, L. Angelini, S.D. Barthelemy, A.P. Beardmore, P.T. Boyd, L. Cominsky, C. Gronwall, E.E. Fenimore, N. Gehrels, P. Giommi, M. Goad, K. Hurley, J.A. Kennea, K.O. Mason, F. Marshall, P. Meszaros, J.A. Nousek, J.P. Osborne, D.M. Palmer, P.W.A. Roming, A. Wells, N.E. White, B. Zhang

Gamma-ray Bursts (GRBs) are bright flashes of high energy photons that can last from about 10 milliseconds to 10 minutes. Their origin and nature have puzzled the scientific community for about 25 years until 1997, when the first X-ray afterglows of long (greater than 2 seconds duration) bursts were detected and the first optical and radio counterparts were found.
These measurements established that long GRBs are typically at high redshift (z 1.6) and are in sub-luminous star-forming host galaxies. They are likely produced in core-collapse explosions of a class of massive stars that give rise to highly relativistic jets (collapsar model).
Internal inhomogeneities in the velocity field of the relativistic expanding flow lead to collisions between fast moving and slow moving fluid shells and to the formation of internal shock waves. These shocks are believed to produce the observed prompt emission in the form of irregularly shaped and spaced pulses of gamma-rays, each pulse corresponding to a distinct internal collision.

The expansion of the jet outward into the circumstellar medium is believed to give rise to "external" shocks, responsible for producing the smoothly fading afterglow emission seen in the X-ray, optical and radio bands.
Here researchers report on the gamma-ray and x-ray observation of the most distant gamma-ray burst ever observed: its redshift of 6.29 translates to a distance of 13 billion light-years from Earth, corresponding to a time when the Universe was just 700 million to 750 million years old.
The discovery of a gamma-ray burst at such a large redshift implies the presence of massive stars only 700 million years after the Big Bang. The very high redshift bursts represent a good way to study the re-ionization era soon after the Universe came out of the Dark Ages.

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Posts: 131433
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RE: GRB050904
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Nobuyaki Kawai from the Tokyo Institute of Technology led a team that used the 8.2-meter Subaru telescope to measure a precise distance to the explosion: 12.8 billion light-years. This is the most distant explosion astronomers have ever seen. There are less than fifty other known objects at such a great distance from Earth, and the farthest is only a mere 50 million light-years (or 0.4%) more distant. Most of these are too faint for all but the largest of telescopes, so astronomers are excited by the relatively bright explosion.


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"This explosion occurred at the edge of the known Universe. One day soon, gamma-ray bursts will let us see further than ever before" - Nobuyaki Kawai.

The Subaru telescope, Japan's largest optical-infrared telescope, is operated by the National Astronomical Observatory of Japan (NAOJ).
The MAGNUM telescope, run by the University of Tokyo and other Japanese universities, is a 2-meter telescope on Haleakala dedicated to observing galaxies harbouring black holes. The 3.5-meter Infrared Telescope Facility is operated for NASA by the UH Institute for Astronomy.

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"This is uncharted territory. This burst smashes the old distance record by 500 million light-years. We are finally starting to see the remnants of some of the oldest objects in the universe" - Daniel Reichart, University of North Carolina.

The previous most distant gamma-ray burst had a redshift of 4.5.

source

This burst was also very long, lasting more than 200 seconds, whereas most bursts last only about 10 seconds. The detection of this burst confirms that massive stars mingled with the oldest quasars.



Only one quasar has been discovered at a greater distance. Quasars are super-massive black holes containing the mass of billions of stars. This burst comes from a lone star. Scientists say it is puzzling how a single star could have generated so much energy as to be seen across the entire Universe. The science team has not yet determined the nature of the exploded star. A detailed analysis is forthcoming.



The most distant explosion ever detected occurred deep in the constellation Pisces.


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Spectral Energy distribution of GBR 050904.



Credit: VLT/ESO


-- Edited by Blobrana at 19:18, 2005-09-12

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Near-infrared image of GBR 050904.



Credit: VLT/ESO

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