GRB 060614
Encyclopedia
GRB 060614 was a remarkable gamma-ray burst (GRB) detected by the Swift
satellite on June 14, 2006 with puzzling properties, which challenge current progenitor models.
In particular, the lack of any bright supernova (SN) down to very strict limits and the vanishing spectral lags during the whole burst are typical of short GRBs, strikingly at odds with the long (102s) duration of this event and its origin in a galaxy 1.6 billion light years away in the constellation
Indus
.
As of December 2006, more than a dozen telescopes, including the Hubble Space Telescope
and large ground-based observatories, have studied the burst.
Gamma-ray bursts represent the most powerful known explosions in the universe. Yet they are random and fleeting, never appearing twice. Scientists have only recently begun to understand their nature.
Such bursts typically fall into one of two categories, long or short. The long bursts last more than two seconds and appear to be from the core collapse of massive stars forming a black hole. Most of these bursts come from the edge of the visible universe. The short bursts, which are under two seconds and often last just a few milliseconds, appear to be the merger of two neutron star
s or a neutron star with a black hole
, which subsequently creates a new or bigger black hole.
The hybrid burst, called GRB 060614, after the date it was detected, originated from within a galaxy 1.6 billion light years away in the southern constellation Indus. The burst lasted for 102 seconds, placing it soundly in long-burst territory. But the burst lacked the hallmark of a supernova
, or star explosion, commonly seen shortly after long bursts. Also, the burst's host galaxy has a low star-formation rate with few massive stars that could produce supernovae and long gamma-ray bursts. "This was close enough to detect a supernova if it existed," said Avishay Gal-Yam of Caltech, Pasadena, Calif., lead author on another Nature
report. "Even Hubble didn't see anything."
Certain properties of the burst concerning its brightness and the arrival time of photons of various energies, called the lag-luminosity relationship, suggest that burst behaved more like a short burst (from a merger) than a long burst. Yet no theoretical model of mergers can support a sustained release of gamma-ray energy for 102 seconds. "This is brand new territory; we have no theories to guide us," said Gehrels. However, long GRBs from rapidly rotating black holes feature a viscous time-scale of tens of seconds of spin-down against high-density turbulent matter. As a candidate inner engine of long GRBs in mergers and collapsars alike, it can account naturally for long GRBs with and without supernovae and a diversity in X-ray afterglows representing different host environments, whose signatures in gravitational-waves fall within the bandwidth of sensitivity of LIGO-Virgo
The burst is perhaps not unprecedented. Archived data from the Compton Gamma Ray Observatory
in the 1990s possibly reveal other hybrid "long-short" bursts, but no follow-up observations are available to confirm this. Johan Fynbo of the Niels Bohr Institute in Copenhagen, also lead author on a Nature report, suggests that a burst from May of this year was also long, but had no associated supernova.
Scientists remain divided on whether this was a long-short burst from a merger or a long burst from a star explosion with no supernova. Most conclude, however, that some new process must be at play – either the model of mergers creating second-long bursts needs a major overhaul, or the progenitor star from an explosion is intrinsically different from the kind that make supernovae.
"We siphoned out all the information we could from GRB 060614," said Massimo Della Valle of the Osservatorio Astrofisico di Arcetri in Firenze, Italy, another lead author on a Nature report. "All we can do now is wait for the next nearby hybrid burst."
Swift Gamma-Ray Burst Mission
The Swift Gamma-Ray Burst Mission consists of a robotic spacecraft called Swift, which was launched into orbit on 20 November 2004, 17:16:00 UTC on a Delta II 7320-10C expendable launch vehicle. Swift is managed by the NASA Goddard Space Flight Center, and was developed by an international...
satellite on June 14, 2006 with puzzling properties, which challenge current progenitor models.
In particular, the lack of any bright supernova (SN) down to very strict limits and the vanishing spectral lags during the whole burst are typical of short GRBs, strikingly at odds with the long (102s) duration of this event and its origin in a galaxy 1.6 billion light years away in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Indus
Indus (constellation)
Indus is a constellation in the southern sky. Created in the sixteenth century, it represents an Indian, a word that could refer at the time to any native of Asia or the Americas.-Notable features:...
.
As of December 2006, more than a dozen telescopes, including the Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
and large ground-based observatories, have studied the burst.
Gamma-ray bursts represent the most powerful known explosions in the universe. Yet they are random and fleeting, never appearing twice. Scientists have only recently begun to understand their nature.
Such bursts typically fall into one of two categories, long or short. The long bursts last more than two seconds and appear to be from the core collapse of massive stars forming a black hole. Most of these bursts come from the edge of the visible universe. The short bursts, which are under two seconds and often last just a few milliseconds, appear to be the merger of two neutron star
Neutron star
A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...
s or a neutron star with a black hole
Black hole
A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...
, which subsequently creates a new or bigger black hole.
The hybrid burst, called GRB 060614, after the date it was detected, originated from within a galaxy 1.6 billion light years away in the southern constellation Indus. The burst lasted for 102 seconds, placing it soundly in long-burst territory. But the burst lacked the hallmark of a supernova
Supernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...
, or star explosion, commonly seen shortly after long bursts. Also, the burst's host galaxy has a low star-formation rate with few massive stars that could produce supernovae and long gamma-ray bursts. "This was close enough to detect a supernova if it existed," said Avishay Gal-Yam of Caltech, Pasadena, Calif., lead author on another Nature
Nature (journal)
Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...
report. "Even Hubble didn't see anything."
Certain properties of the burst concerning its brightness and the arrival time of photons of various energies, called the lag-luminosity relationship, suggest that burst behaved more like a short burst (from a merger) than a long burst. Yet no theoretical model of mergers can support a sustained release of gamma-ray energy for 102 seconds. "This is brand new territory; we have no theories to guide us," said Gehrels. However, long GRBs from rapidly rotating black holes feature a viscous time-scale of tens of seconds of spin-down against high-density turbulent matter. As a candidate inner engine of long GRBs in mergers and collapsars alike, it can account naturally for long GRBs with and without supernovae and a diversity in X-ray afterglows representing different host environments, whose signatures in gravitational-waves fall within the bandwidth of sensitivity of LIGO-Virgo
The burst is perhaps not unprecedented. Archived data from the Compton Gamma Ray Observatory
Compton Gamma Ray Observatory
The Compton Gamma Ray Observatory was a space observatory detecting light from 20 KeV to 30 GeV in Earth orbit from 1991 to 2000. It featured four main telescopes in one spacecraft covering x-rays and gamma-rays, including various specialized sub-instruments and detectors...
in the 1990s possibly reveal other hybrid "long-short" bursts, but no follow-up observations are available to confirm this. Johan Fynbo of the Niels Bohr Institute in Copenhagen, also lead author on a Nature report, suggests that a burst from May of this year was also long, but had no associated supernova.
Scientists remain divided on whether this was a long-short burst from a merger or a long burst from a star explosion with no supernova. Most conclude, however, that some new process must be at play – either the model of mergers creating second-long bursts needs a major overhaul, or the progenitor star from an explosion is intrinsically different from the kind that make supernovae.
"We siphoned out all the information we could from GRB 060614," said Massimo Della Valle of the Osservatorio Astrofisico di Arcetri in Firenze, Italy, another lead author on a Nature report. "All we can do now is wait for the next nearby hybrid burst."
External links
- http://www.nasa.gov/home/hqnews/2006/dec/HQ_06373_Hybrid_Burst.html
- Simbad