George's Random Astronomical Object

Object 77: GRB 980326

Podcast release date: 07 November 2022

Right ascension: 08:36:34.8

Declination: -18:51:24

Epoch: J2000

Constellation: Pyxis

Corresponding Earth location: A part of the desert in the Northern Territory of Australia near the border with Western Australia

The object GRB 980326 lies within the constellation Pyxis, which is yet another lame constellation invented in the 18th century by the French astronomer Nicolas Louis de Lacaille to fill a relatively blank part of sky [1]. It used to be part of a much larger and brighter but more complicated constellation named Argo Navis after the ship used by Jason in the quest for the Golden Fleece, but for some reason, when that constellation was broken up into several smaller ones, Lacaille and other 18th century astronomers thought that Pyxis deserved to be its own constellation even though the stars are hardly visible without a telescope. It's supposed to depict a compass, like the one that is used for natuical navigation, but of course, the stars don't look like a compass or like much of anything else. They could have called it the unicorn constellation or the lizard constellation except that other patches of faint stars in the sky have already been named after these animals.

Anyway, back to GRB 980326. This is a gamma ray burst. Gamma ray busrts are brief flashes of gamma rays that typically last from a fraction of a second to a few minutes, although they can be longer. I've actually discussed gamma ray bursts in episodes 18, 34, and 51, so you could go check out those episodes if you want more or different information about these objects.

If you break down the name for GRB 980326, the letters stand for the words "gamma ray burst", and the numbers give the year, month, and day of the discovery of this gamma ray burst, which was March 26th, 1998 [2]. So, in this episode, we will be flashing back to the 1990s, a time of unimaginable peace and prosperity, but before that, we are going to make a stop in the more tumultuous 1960s.

The discovery of gamma ray bursts in this decade was directly connected to other events surrounding the Cold War. In the 1960s, the United States launched spy satellites that were originally searching for gamma rays from nuclear bomb tests in the Soviet Union, but they instead found gamma rays coming from the opposite direction [3, 4]. While this was a little bit of a disappointment for intelligence agencies, it was quite exciting for the astronomers who got access to the data from these satellites. This was the point in time when these events were named gamma ray bursts.

Not much of anything happened for a couple of decades after this, but then, in 1991, the Soviet Union collapsed, Nirvana released the album Nevermind, and NASA launched the Compton Gamma Ray Observatory, which was the first space observatory dedicated to finding gamma ray bursts [4]. It found over 2000 of them [5]. However, aside from establishing that gamma ray bursts seem to be evenly distributed across the sky, astronomers still did not know what was going on with these objects [4]. The Compton Gamma Ray Observatory did not provide detailed enough positional information for astronomers to associate the gamma ray bursts with any other astronomical objects. The seemingly random, uniform distribution of these gamma ray bursts implied that they weren't related to the planets in the Solar System, which lie within a plane, or the disk of the Milky Way, which is another plane, or nearby galaxies, which tend to be clustered in a few places like the constellations Virgo and Fornax. This left two plausible options. First, the gamma ray bursts could be distributed within the spherical halo of our galaxy [6]. Second, the gamma ray bursts could be located in very distant galaxies. Either of these scenarios would have made the gamma ray bursts look uniformly distributed in the sky as seen from Earth, but it was not clear which scenario was correct.

Flash forward to 1996 and the Chicago Bulls, led by Michael Jordan, won yet another NBA championship, the Spice Girls released Wannabe, and the BeppoSAX satellite was launched into space [7, 8]. This satellite was constructed by a collaboration between the Italian Space Agency and the Netherlands. The "Beppo" part of the name refers to the Italian physicist Guiseppe Occhialini, who went by the nickname "Beppo", while the SAX part was an abbreviation that, when translated into English, stood for "Satellite for X-ray Astronomy". While this satellite was designed for X-ray observations, it also had an instrument called the Gamma-Ray Burst Monitor that turned out to be very effective at detecting gamma ray bursts. When this gamma ray detector was used in conjunction with the X-ray detector on BeppoSAX, the satellite could pinpoint the locations of gamma ray bursts much more accurately than the Compton Gamma Ray Observatory.

This now brings us to the part of the story involving GRB 980326. One of the first major discoveries from BeppoSAX was that gamma ray bursts have an X-ray afterglow [9], and the object that was involved in this discovery was not GRB 980326. It was a completely different gamma ray burst. After this, though, another gamma ray burst found by BeppoSAX was seen to be very redshifted, which was a sign that it was in a very distant galaxy that, because of the expansion of the universe, appeared to be moving very quickly away from the Earth [10, 11]. That gamma ray burst was also not GRB 980326 but instead a completely different gamma ray burst. After this, BeppoSAX discovered for the first time a gamma ray burst associated with visible light emission from what looked like a supernova in a very distant galaxy. That gamma ray burst was indeed GRB 980326 [12].

Yes, GRB 980326 has the important distinction of being the first gamma ray burst where astronomers could actually identify what phenomenon was creating the gamma rays. This was really important because, before this gamma ray burst, people had no idea what astrophyical phenomena created these events. They only knew that they came from very far away galaxies. With the association of GRB 980326 with a supernova, astronomers could now model how the gamma rays are produced in these explosions and thus learned more about the physics of supernovae.

So, at this point, the people who did this analysis thought that they could throw away all of those other theories about how gamma ray bursts are created. After all, this and subsequent observations of gamma ray bursts associated with supernovae were very convincing. However, a subset of gamma ray bursts turned out to be not associated with supernovae, which meant that someone needed to go fish one of those discarded theories out of the garbage. It turned out that supernovae are the general explanation for how gamma ray bursts longer than 2 seconds are created. The favored theory for shorter gamma ray bursts is that most of them are created when two ultra-dense objects, like two neutron stars, two black holes, or a neutron star and a black hole merge together [13]. Nonetheless, even if GRB 980326 did not provide the final answer for the origin of where gamma ray bursts come from, it was still extremely important in advancing the research on these objects.

References

[1] Constellation Guide, Pyxis Constellation, 2021

[2] Celidonio, G. et al., GRB 980326, 1998, International Astronomical Union Circular, 6851, 1

[3] Klebesadel, Ray W. et al., Observations of Gamma-Ray Bursts of Cosmic Origin, 1973, Astrophysical Journal Letters, 182, L85

[4] Robson, Colin, What are Gamma-Ray Bursts and how Did we Discover Them?, 2013, Futurism

[5] Paciesas, William S., The BATSE Gamma-Ray Burst Legacy, 2004, Baltic Astronomy, 13, 187

[6] Podsiadlowski, Philipp et al., Gamma-ray bursts and the structure of the Galactic halo, 1995, Monthly Notices of the Royal Astronomical Society, 273, 755

[7] Boella, G. et al., BeppoSAX, the wide band mission for X-ray astronomy, 1997, Astronomy & Astrophysics Supplements, 122, 299

[8] Robson, Colin, The Study of Gamma Ray Bursts (part II), 2013, Futurism

[9] Costa, E. et al., Discovery of an X-ray afterglow associated with the gamma-ray burst of 28 February 1997, 1997, Nature, 387, 783

[10] Djorgovski, S. G. et al., The optical counterpart to the gamma-ray burst GRB970508, 1997, Nature, 387, 876

[11] Metzger, M. R. et al., Spectral constraints on the redshift of the optical counterpart to the gamma-ray burst of 8 May 1997, 1997, Nature, 387, 878

[12] Bloom, J. S. et al., The unusual afterglow of the gamma-ray burst of 26 March 1998 as evidence for a supernova connection, 1999, Nature, 401, 453

[13] Berger, Edo, Short-Duration Gamma-Ray Bursts, 2014, Annual Reviews of Astronomy and Astrophysics, 52, 43

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Last update: 9 July 2022