When can we expect a possible response?
Any response probably would be forthcoming in at least 25 years due to the distance the message has to travel between Earth and GJ273b. 
The exoplanet was chosen because of its visibility from Earth's northern hemisphere, even if it is not the closest potentially inhabited exoplanet to Earth. That distinction belongs to Proxima b, which is just 4 light-years away. 
Earlier this week, scientists discovered a new exoplanet, Ross 128 b, that is 11 light-years away from Earth. It orbits a very quiet red-dwarf star, meaning it does not have to deal with issues such as deadly ultraviolet or X-ray radiation and could also be home to life.
One light-year is approximately 5.88 trillion miles.
Sonar calling GJ273b is not the first message sent to space. The first was the Arecibo message, sent in 1974. The Arecibo message is expected to take 25,000 light-years to reach its target of the M13 star cluster.
While hopeful of receiving a response, Vakoch says we may never hear anything from another intelligent civilization. 
"Practically speaking, if we get a signal from Luyten's Star, it will mean the Milky Way is teeming with life. It's certainly possible," Vakoch said. "It seems more likely that we'll need to target not just one star, but hundreds, thousands, or even millions before we get a reply back."