Definition of “hard takeoff” (noun) from Transhumanist Wiki:

The Singularity scenario in which a mind makes the transition from prehuman or human-equivalent intelligence to strong transhumanity or superintelligence over the course of days or hours (Yudkowsky 2001). The high likelihood of a hard takeoff once a roughly human-equivalent AI is created has been argued by the Singularity Institute in Yudkowsky 2003.

Hard takeoff sources and references, which includes hard science fiction novels, academic papers, and a few short articles and interviews:

Blood Music (1985) by Greg Bear
Fire Upon the Deep (1992) by Vernor Vinge
“The Coming Technological Singularity” (1993) by Vernor Vinge
The Metamorphosis of Prime Intellect (1994) by Roger Williams
“Staring into the Singularity” (1996) by Eliezer Yudkowsky
Creating Friendly AI (2001) by Eliezer Yudkowsky
“Wiki Interview with Eliezer” (2002) by Anand
“Impact of the Singularity” (2002) by Eliezer Yudkowsky
“Levels of Organization in General Intelligence” (2002) by Eliezer Yudkowsky
“Ethical Issues in Advanced Artificial Intelligence” by Nick Bostrom
“Relative Advantages of Computer Programs, Minds-in-General, and the Human Brain” (2003) by Michael Anissimov and Anand
“Can We Avoid a Hard Takeoff?” (2005) by Vernor Vinge
“Radical Discontinuity Does Not Follow from Hard Takeoff” (2007) by Michael Anissimov
“Recursive Self-Improvement” (2008) by Eliezer Yudkowsky
“Artificial Intelligence as a Positive and Negative Factor in Global Risk” (2008) by Eliezer Yudkowsky
“The Hanson-Yudkowsky AI Foom Debate” (2008) on Less Wrong wiki
“Brain Emulation and Hard Takeoff” (2008) by Carl Shulman
“Arms Control and Intelligence Explosions” (2009) by Carl Shulman
“Hard Takeoff” (2009) on Less Wrong wiki
“When Software Goes Mental: Why Artificial Minds Mean Fast Endogenous Growth” (2009)
“Thinking About Thinkism” (2009) by Michael Anissimov
“Technological Singularity/Superintelligence/Friendly AI Concerns” (2009) by Michael Anissimov
“The Hard Takeoff Hypothesis” (2010), an abstract by Ben Goertzel
Economic Implications of Software Minds by S. Kaas, S. Rayhawk, A. Salamon and P. Salamon

Critiques

“The Age of Virtuous Machines” (2007) by J. Storrs Hall
“Thinkism” by Kevin Kelly (2008)
“The Hanson-Yudkowsky AI Foom Debate” (2008) on Less Wrong wiki
“How far can an AI jump?” by Katja Grace (2009)
“Is The City-ularity Near?” (2010) by Robin Hanson
“SIA says AI is no big threat” (2010) by Katja Grace

I don’t mean to say that the critiques aren’t important by putting them in a different category, I’m just doing that for easy reference. I’m sure I missed some pages or articles here, so if you have any more, please put them in the comments.