The gravitational-wave signal GW150914 was first identified on Sept 14 2015 by searches for short-duration gravitational-wave transients .
These searches identify time-correlated transients in multiple detectors with minimal assumptions about the signal morphology , allowing them to be sensitive to gravitational waves emitted by a wide range of sources including binary black-hole mergers .
Over the observational period from September 12th to October 20th 2015 , these transient searches were sensitive to binary black-hole mergers similar to GW150914 to an average distance of \sim 600 Mpc .
In this paper , we describe the analyses that first detected GW150914 as well as the parameter estimation and waveform reconstruction techniques that initially identified GW150914 as the merger of two black holes .
We find that the reconstructed waveform is consistent with the signal from a binary black-hole merger with a chirp mass of \sim 30 ~ { } \mathrm { M } _ { \odot } and a total mass before merger of \sim 70 ~ { } \mathrm { M } _ { \odot } in the detector frame .