GRB 990123
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Optical afterglow of gamma ray burst GRB-990123 (the bright |
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| Observation data: J2000 epoch | |
|---|---|
| Constellation: | |
| Right ascension: | 15h 25m 29.0s[1] |
| Declination: | +44° 45′ 30″[1] |
| Redshift: | 1.6 |
| Distance: | 9 Gly (2.8 Gpc) |
| Type: | SAX/WFC[1] |
| Apparent dimensions (V): | |
| Apparent magnitude (V): | 20.6R[1] |
| Notable features: | |
| Other designations | |
| See also: Galaxy, List of galaxies | |
GRB 990123 is a gamma-ray burst that occurred on January 23, 1999 (hence the designation). It was found early enough that the optical afterglow was detected.
Astronomers first managed to obtain a visible-light image of a GRB as it occurred on January 23, 1999, using the ROTSE-1 telescope, sited in Los Alamos, New Mexico. ROTSE-1 consists of an array of four commercial 200 millimeter telephoto lenses, focused on CCD electronic imaging arrays and mounted on an automated platform.
While 200 millimeter lenses are modest even by the standards of amateur astronomy, ROTSE-1 has a wide field of view and can be quickly repositioned to scan any part of the visible sky. ROTSE-1 is operated by a team under Dr. Carl Akerlof of the University of Michigan.
In the dark hours of the morning of January 23, 1999, the Compton satellite recorded a gamma-ray burst that lasted for about a minute and a half. There was a peak of gamma and X-ray emission 25 seconds after the event was first detected, followed by a somewhat smaller peak 40 seconds after the beginning of the event. The emission then fizzled out in a series of small peaks over the next 50 seconds, and eight minutes after the event had faded to a hundredth of its maximum brightness. The burst was so strong that it ranked in the top 2% of all bursts detected.
Compton reported the burst to its ground control facility at NASA Goddard Space Flight Center in Maryland the moment it began, and Goddard immediately sent the data out over the "Gamma Ray Burst Coordinates Network (GCN)". While Compton, as mentioned, cannot provide precise locations of bursts, the location was good enough for the wide-field ROTSE-1. The camera array automatically focused on the region of the sky and obtained an image of the burst 22 seconds after it was detected by Compton, with subsequent images obtained every 25 seconds after that.
ROTSE-1 can image cosmic objects as faint as magnitude 16, and GRB hunters had expected the visible component of a GRB to be very faint. Instead, the visible component reached magnitude 9. It was so bright that it could have been seen by an amateur astronomer with good binoculars. The object that produced it increased in brightness by a factor of 4,000 in less than a minute.
The news of ROTSE-1's accomplishment didn't make it out on the networks until later in the day, and in the meantime other observatories were focusing on the event, by then designated "GRB 990123".
The BeppoSAX satellite had also seen the burst, and pinned down its location to within a few arcminutes. This data was sent out, and four hours after the burst the area was imaged with the 1.52 meter (60 inch) Schmidt camera at Palomar Mountain in California. The image revealed a magnitude 18 optical transient that wasn't on archive images of the same area.
The next night, the fading object, by now down to magnitude 20, was imaged by the Keck telescope, and the 2.6 meter Nordic Optical Telescope in the Canary Islands. The observations revealed absorption lines with a redshift of 1.6, implying a distance of 9 billion light-years.
The Hubble Space Telescope performed observations on the location of GRB 990123, sixteen days after the event. It had faded by more than a factor of three million in that time. The Hubble was able to pick up the traces of a faint galaxy, whose blue color suggested it was forming new stars at a rapid rate.
[edit] References
- Castro-Tirado AJ, Zapatero-Osorio MR, Caon N, Cairos LM, Hjorth J, Pedersen H, Andersen MI, Gorosabel J, Bartolini C, Guarnieri A, Piccioni A, Frontera F, Masetti N, Palazzi E, Pian E, Greiner J, Hudec R, Sagar R, Pandey AK, Mohan V V, Yadav RK, Nilakshi, Bjornsson G, Jakobsson P, Burud I I, et al. (1999). "Decay of the GRB 990123 optical afterglow: implications for the fireball model". Science 283 (5410): 2069-73. PMID 0010092226.
- Hjorth J, Bjornsson G, Andersen MI, Caon N, Cairos LM, Castro-Tirado AJ, Osorio MR, Pedersen H, Costa E (1999). "Polarimetric constraints on the optical afterglow emission from GRB 990123". Science 283 (5410): 2073-5. PMID 0010092227.
- Andersen MI, Castro-Tirado AJ, Hjorth J, Moller P, Pedersen H, Caon N, Cairos LM, Korhonen H, Osorio MR, Perez E, Frontera F (1999). "Spectroscopic limits on the distance and energy release of GRB 990123". Science 283 (5410): 2075-7. PMID 0010092228.
- ^ a b c d NASA/IPAC Extragalactic Database. Results for GRB 990123. Retrieved on November 25, 2006.
