On the GBM event seen 0.4 sec after GW 150914

In view of the recent report by Connaughton we analyse continuous TTE data of Fermi-GBM around the time of the gravitational wave event GW 150914. We find that after proper accounting for low count statistics, the GBM transient event at 0.4 s after GW 150914 is likely not due to an astrophysical source, but consistent with a background fluctuation, removing the tension between the INTEGRAL/ACS non-detection and GBM. Additionally, reanalysis of other short GRBs shows that without proper statistical modeling the fluence of faint events is over-predicted, as verified for some joint GBM-ACS detections of short GRBs. We detail the statistical procedure to correct these biases. As a result, faint short GRBs, verified by ACS detections, with significances in the broad-band light curve even smaller than that of the GBM-GW150914 event are recovered as proper non-zero source, while the GBM-GW150914 event is consistent with zero fluence.
Comment: 13 pages, 12 figures, ApJL (acc.); subm. 2016 March 10, Apr 21 (1st rev.), May 13 (2nd rev), Jun 1 (3rd rev), and editorial changes by Jun 2 (4th rev), Jun 8 (5th rev): Our manuscript refers exclusively to arXiv:1602.03920.v3 since we had no prior access to arXiv:1602.03920.v4/5 (2016 May 31). Note that JG and HFY are not co-authors on arXiv:1602.03920.v4/5