1999 August 1, Erik Pema Kunsang, Marcia Binder Schmidt, Tulku Urgyen Rinpoche, As it is, volume 1, Rangjung Yeshe Publications, →ISBN, page 25:
Tulku Urgyen Rinpoche passed away quite suddenly, but after he died he remained in tukdam for quite a while, longer than the sun was in the sky that day.
The signs of tukdam are that the heart remains warm, rigor mortis does not set in, and the body does not begin to deteriorate.
2012 April 16, Lama Kunsang, Lama Pemo, Marie Aubele, History of the Karmapas: The Odyssey of the Tibetan Masters with the Black Crown, Shambhala Publications, →ISBN, page 42:
At noon, after his breathing had stopped, he manifested the state of tukdam, the ultimate meditation at the moment of death.