Einstein in his book: Relativity: The Special and General Theory. http://www.ibiblio.org/ebooks/Einstein/Einstein_Relativity.pdf [edit] on page 56, I believe] writes, "the expression for energy" in the form $\frac{mc^2 +E_0}{\sqrt{ 1-v^2/c^2}}$, where $m$ is the rest mass and $mc^2$ the energy of the rest mass. $E_0$ is the energy added to the body (by adding photons, for instance). Then the rest mass energy, $mc^2$, and added energy, $E_0$, is divided by $\sqrt {1-v^2/c^2}$ to account for the energy of the velocity. And that, I think, produces gravity. That is my expectation. Am I right?

I am no expert on this. I welcome criticism of this post. I think this energy is what is said to curve spacetime or create gravity.

Relativistic mass, is calculated as $\frac{M_{(rest)}}{\sqrt {1-v^2/c^2}}$

I think that relativistic mass is gravitational, as is "absorbed energy".