Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

July 13, 1998

GRB 980703: A Reassuring Redshift
Credit: S. G. Djorgovski, S. R. Kulkarni, (Caltech) et al., Keck Observatory

Explanation: In the old days, just over a year ago, astronomers had little idea of the true distance to gamma-ray bursts. Did these enigmatic explosions occur in our outer Galaxy, or in the outer Universe? Last May, a first telling distance measure was made - GRB 970508 showed an absorption line with a redshift of about 0.8 - indicating that this gamma-ray burst (GRB) was an enormous distance away. Skeptics, however, are not always convinced by an unrepeated measurement. Since then, though, other tantalizing coincidences have occurred: GRB 971214 occurred unusually near a galaxy with the enormous redshift of 3.4, and GRB 980425 occurred unusually near a peculiar low-redshift supernova. Skeptics were intrigued. Now, the potentially definitive implications of the above-pictured optical transient might impress even the cautious. GRB 980703's optical transient shows a well-measured redshift from both an absorption line and an emission line: 0.97. The above negative highlights the uncommon transient source with the label "OT", while letters designate common comparison stars.

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