Nikon 1 aw1 Reference Manual page 70

Choose a shutter speed of "Bulb".
2
Press 2 to highlight shutter speed and
press the W button to select "Bulb".
z
3 Open the shutter.
After focusing, press the shutter-release button all the way
down. Keep the shutter-release button pressed until the
exposure is complete.
Close the shutter.
4
Take your finger off the shutter-release button.
Shooting ends automatically after about two minutes. Note that
some time may be required to record long exposures.
45
W button