In April, the NASA Fermi Gamma-ray Burst Monitor (GBM) team announced the discovery of a weak gamma-ray burst that may be associated with the recent LIGO discovery of gravitational waves from a black hole merger, an event known as GW150914. The team notes that Fermi observations associated with future LIGO/Virgo gravitational wave detections are needed to reveal whether this weak burst is a plausible counterpart or a chance coincidence. The NASA Fermi team stands behind this finding, which has successfully passed through the scientific review process and is awaiting publication in a special issue of The Astrophysical Journal.
The AntiCoincidence Shield of the European Space Agency’s INTEGRAL spacecraft, however, did not detect the GBM burst, a result that might be incompatible with the Fermi finding, a possibility noted in the discovery paper. In an effort to resolve this apparent discrepancy, three members of the Fermi team who are not authors of the discovery paper undertook an alternate analysis of the spectral properties of the GBM data. These authors conclude that while the signal was consistent with the INTEGRAL data, it was also consistent with a fluctuation of background noise.
To establish the existence and significance of the burst, the authors of the original paper included data from all 14 GBM detectors, a result that is not addressed in the new study. The team also examined spectral information from two GBM detectors in an effort to further understand the nature of the signal. The new study applies a different analysis method to the data from the same two detectors and finds a different spectral shape.
Careful examination and criticism of assumptions, analysis methods and interpretations is a normal part of the scientific process. The Fermi team is committed to open scientific dialogue. The authors of both studies are working together (and with the INTEGRAL team) to explore these differences further.