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Ulrich Elkmann Offline

Beiträge: 13.550

14.10.2022 19:03
GRB Antworten

Gamma Ray Burster/Gammastrahlenausbruch.

Bright ‘nearby’ gamma-ray burst dazzles astronomers
14 Oct 2022

Several orbiting space telescopes scanning the skies for powerful cosmic explosions have spotted one of the brightest gamma-ray bursts ever detected. Initial evidence suggests that the blast of high-energy radiation occurred when an extremely massive star collapsed – a process that results in an immense flood of gamma-rays and X-rays. Astronomers have been racing to follow-up the discovery with one researcher suggesting it will become the “best studied gamma-ray burst in history”.

The first reports of the explosion, catalogued as GRB 221009A, came from the Neil Gehrels Swift observatory and the Fermi Gamma-ray Space Telescope, which both monitor the universe at gamma-ray and X-ray wavelengths. Their systems noticed a bright source appear in the constellation Sagitta on 9 October. The blast was also picked up by the European Space Agency’s Solar Orbiter mission and since then numerous other observatories – including those looking at visible wavelengths – have scrutinized the fading fireball from the event, which is known as the “afterglow”.

One of the most striking aspects about GRB 221009A is its proximity. The blast appears to have happened in a galaxy about two billion light years away, which is considerably closer than an “average” gamma-ray burst event that may lie some 10 billion light years away. Leicester University astronomer Kim Page, who works on NASA’s Swift mission, says that such closeness had “a big part to play” in why this burst appeared so bright.

While initial analyses are still ongoing, astronomers are already marvelling at some of the early observations. X-ray imagery from the Swift observatory shows prominent, glowing rings around the location of GRB 221009A. These features are not physically part of the blast but “light echoes” that are caused when X-ray radiation streaming towards us from the event scatters off microscopic grains suspended within dust clouds inside our own galaxy.

“This is by far the best set of rings seen around a gamma-ray burst, thanks partly to its brightness in X-rays and its closeness to the Galactic plane,” explains Leicester astronomer Andrew Beardmore, who works on the Swift mission.

Beardmore says analysis of the rings will allow scientists to investigate the nature of the interstellar dust grains and even probe the locations of the Milky Way dust clouds where they reside. “Because [the rings] are so bright, the distance to the dust-layers responsible for [them] will likely be known with great precision. This makes it quite a unique measurement,” he adds.

"At 2022-10-09 13:16:59.000 UT on 9 October 2022, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 221009A (trigger 687014224 / 221009553).

This event, if it is a GRB, it is the brightest among the GBM detected GRBs. If it is not a GRB then it is a rare transient event. Follow-up across all wavelengths is encouraged.

The on-ground calculated location, using the GBM trigger data, is RA = 290.4, DEC = 22.3 (J2000 degrees, equivalent to 19 h 22 m, 22 d 15 '), with a statistical uncertainty of 1 degrees (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a core-plus-tail model, with 90% of GRBs having a 3.7 deg error and a small tail suffering a larger than 10 deg systematic error. [Connaughton et al. 2015, ApJS, 216, 32] ).

This location is consistent with the Swift J1913.1+1946 localization (Dichiara et al. GCN 32632) though it precedes the Swift trigger by an hour.

The angle from the Fermi LAT boresight at the GBM trigger time is 76 degrees.

The GBM light curve consists of an initial ~10 s long pulse, followed by an extraordinarily bright episode at ~180 s after the trigger time, lasting at least 100 seconds.

Y.-D. Hu, V. Casanova, E. Fernandez-Garcia, M. A. Castro Tirado, M.D. Caballero-Garcia, I. Olivares, I. Perez-Garcia and R. Sanchez-Ramirez and A. J. Castro-Tirado (IAA-CSIC), C. Perez del Pulgar and A. Castellon (Univ. de Malaga), R. Fernandez-Munoz (IHSM/UMA-CSIC) and M. Jelinek (ASU-CAS), on behalf of a larger collaboration, report:

The 60cm BOOTES-2/TELMA robotic telescope at IHSM La Mayora (UMA-CSIC) in Algarrobo Costa (Malaga, Spain) responded to the extraordinarily bright GRB 221009A detected by Swift, Fermi, MAXI/GSC, INTEGRAL (SPI-ACS), Konus-Wind, and the IPN (Dichiara et al. GCNC 32632, Veres et al. GCNC 32636, Bissaldi et al. GCNC 32637, Svinkin et al. GCNC 32641, Negoro et al. ATEL 15651). A number of images (60s exposures in clear filter) were taken starting at 18:23 UT on 9 Oct (~ 4.2 hours after trigger). Due to passing clouds, the optical afterglow was only detected in frames around 18:44 UT with 16.21+/-0.11 mag.

Later on, we triggered the 0.9m telescope of the Observatiorio Sierra Nevada (OSN) near Granada, Spain. Observations started on 9 Oct 18:45 UT (~ 4.6 hours after trigger) in BVRI-bands (90 s exposures each). The optical afterglow is clearly detected with R=16.57+-0.02 mag on the first R-band image (gathered at 18:49 UT).

These detections are consistent with the ones reported by Lipunov et al. (GCNC 32634), Perley et al. (GCNC 32638) and Broens et al. (GCNC 32640). Further observations are ongoing.

"GCNC" ist der "Circular" des Gamma-ray Coordinates Network.


Will Gater @willgater
Last Sunday astronomers spotted one of the brightest gamma-ray bursts ever detected.
I've been speaking to scientists leading early analysis of the event, which one researcher told me will become the "best-studied GRB in history."
@PhysicsWorld story + 🧵

2/ What's a gamma-ray burst?💥 In this case, it's the cataclysmic explosion that occurs when an extremely massive star collapses during its death.
This star would've been much more massive than those that create regular supernovae – we're talking several *10s* of solar masses.

3/ This violent detonation causes a flood of high-energy radiation – including X-rays and gamma-rays – to stream out from the blast. And that's what orbiting observatories caught sight of on the afternoon of 9 October.

4/ You can read why this event is unusual in the Physics World piece, but I want to concentrate here on one really neat aspect of it.
That's the amazing set of rings that have appeared around the gamma-ray burst (seen in this image captured by the orbiting Swift telescope).

5/ Those rings are *not* physically associated with the gamma-ray burst explosion itself. So what's going on?
Although GRB 221009A occurred in a galaxy 2 billion light years away, the answer actually lies in our own Milky Way.

6/ They are in fact light 'echoes' from the blast formed when X-rays from the GRB stream through the Milky Way & scatter off dust grains in nebulae within our galaxy.
The GRB is in Sagitta & this is what that part of sky looks like. Look at all those silhouetted dust clouds!

7/ Those rings aren't just interesting to look at. They give astronomers an extraordinary glimpse at the dust within our Milky Way.
Andrea Tiengo, a researcher at @IussPavia who I interviewed for the piece, likened it to having a "medical scanner" for the galaxy.

8/ The size of the glowing rings and how they change in the coming days will tell astronomers about the make-up of the dust grains in these extremely distant Milky Way dust clouds.

9/ And according to Andrew Beardmore, a Swift scientist at @uniofleicester, who’s been working on studying these rings, it "may even be possible to associate some of the regions where the dust layers are with a specific structure in the Galaxy such as a spiral arm.”

10/ So one of the coolest things to come out of this bright & 'nearby' gamma-ray burst is that it'll actually allow us to learn more about our own galaxy.
3:24 PM · Oct 14, 2022·Twitter Web App

"Les hommes seront toujours fous; et ceux qui croient les guérir sont les plus fous de la bande." - Voltaire


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