  In 2016, IceCube initiated a system of public real-time alerts that are
typically issued within one minute, following the detection of a neutrino
candidate event that is likely to be of astrophysical origin. The goal of these
alerts is to enable multi-messenger observations that may identify the neutrino
source. Through January 31, 2019, a total of 20 public alerts have been issued,
with many of them receiving follow-up observations across multiple wavelength
bands. One alert in particular, IceCube-170922A, was found to be associated
with a flaring gamma-ray blazar, TXS 0506+056. This was the first >3 sigma
association of a high-energy neutrino with an electromagnetic counterpart. In
2019, the IceCube collaboration is introducing a new set of neutrino candidate
selections that expand the alert program. These new selections provide two
alert channels. A "Gold" channel will issue alerts for neutrino candidates at
least 50% likely to be of astrophysical origin and is expected to deliver
$\sim$10 alerts per year. Additionally a more frequent "Bronze" channel will
provide $\sim$20 alerts per year for neutrino candidates that are between 30%
and 50% likely to be of astrophysical origin. We present the neutrino event
selections used to generate these alerts, the expected alert rates, and a
description of the alert message.
