A group of physicists has retracted their preliminary report in the GCN Circular of a massive star-sized explosion after deciding that what they’d really observed was another phenomenon.
Although we could try to explain this, we’d rather leave it up to Giacomo Vianello, an experimental physicist at Stanford University, who was a member of the research team.
Vianello told us:
on March 30th 2014 the Large Area Telescope, orbiting onboard the Fermi NASA spacecraft 560 km above the Earth, detected high-energy gamma-ray emission from a region of the sky close to the position of a Gamma-Ray Burst (GRB 140330A), previously detected and broadly localized by another instrument onboard Fermi (the Gamma-ray Burst Monitor, GBM). GRBs are the largest stellar-class explosions in the universe, releasing in time scale of the minute energies larger than what the Sun will emit in its whole life. Discovered in the sixties, they are now routinely observed (1-3 per week). We therefore issued a circular:
claiming the detection of the GRB. This is a standard procedure. We detect 1-2 GRB per month with the Large Area Telescope.
A few hours later, when we received more data downlinked from Fermi, we realized that what we thought to be the high-energy counterpart of the GRB did not look at all like it. While GRB counterparts decay in luminosity quite fast, this source was steady. Looking back in the data previously collected by Fermi since its launch in 2008 we realized that such source has been active sporadically over the whole mission span, and therefore is unrelated to the GRB (which just happened by chance to go off close by). We then issue a retraction.
Which read thusly:
G. Vianello (Stanford U.), D. Kocevski (NASA/Goddard), J. Racusin (NASA/Goddard), R. Ojha (NASA/GSFC/UMBC/CRESST) <Roopesh.Ojha@gmail.com>, and S. Ciprini (ASDC) report on behalf of the Fermi-LAT team:
The analysis of new data downloaded from Fermi has shown that emission from the proposed high-energy counterpart of GRB 140330A (Vianello et al., GCN 16048; Pittori et al., GCN 16058) has continued up to at least 40 ks after the GBM trigger. This is very unusual for a faint burst such as GRB 140330A. Also, our localization of the LAT excess has improved, and it is now:
R.A., Dec. = 325.40, -64.13 with an error radius of 0.14 (90 % c.l., statistical only),
which is well outside the IPN error box (Hurley et al., GCN 16051).
Moreover, a search in Fermi archival data has shown a variable emission from a source compatible with our position, which was detected in several occasions in 2012 and 2013, and also detected on March 28 and 29, 2014. This source has been tentatively associated with the extra-galactic radio source PKS 2136-642 in the past (ATel #5695; Mauch et al. 2003, MNRAS, 342, 1117).
Therefore, we believe that the high-energy source detected by Fermi and by AGILE (Pittori et al., GCN 16058) is unrelated to GRB 140330A.
Further analysis is ongoing.
Vianello said the circulars are meant as trial balloons for precisely these sorts of observations. They aren’t peer-reviewed, and aren’t even papers:
Instead, they are a fast and easy way to exchange information on localization and characteristics of transient events (mostly GRBs), so that more instruments and observatories can be pointed and look while the transient is still ongoing. Thus, they are by definition preliminary, and all people using them know this very well.