Chaitra Purnima (Chitra Paurnami in Tamil) is well known as the date in our Hindu calendar in which Chitragupta, the assistant of Lord Yama, writes down the punya-papa-karmas of all humans.
Another significant event took place on this date in our Sampradaya (Shankaracharya's tradition). Srimad Appayya Dikshitendra, an Incarnation of an amsha of the Lord, who appeared some 500 years ago in Tamil Nadu merged with the deity of Lord Natarajar in Chidambaram. This type of liberation is known as Sayujya-mukti. In this type of mukti the devotee merges into the murti of the Deity he has worshiped.
Sri Sacchidananda Sivabhinava Nrsimha Bharati Swamigal explains this type of mukti in His Vedantic work 'Purushartha-nirnaya' as follows: सायुज्यं सगुणस्य देवतारूपस्य अहंग्रहोपासनां कुर्वतः उपास्यदेवतातादात्म्यम्। TRANSLATION--- The state of becoming one with the Upasya-devata (the deity who is the object of worship) by a (devotee) who performs ahangrahopasana of the form of the God who is associated with attributes. Ahangrahopasana is a form of daharopasana wherein the upasaka worships the Saguna Devata situated within the chambers of his heart (Hridayaakasha).
(Reference: Bhakti Sudha Tarangini" published by Sri Vani Vilas Press, Srirangam; 1913)
Dikshitendra was born to the celebrated Advaita-vidyacharya Rangarajadhvari with the blessing of the same deity of Chidambaram Natarajar into whom He merged at the age of 72. Both His avatara and tirobhava (disappearance from the earthly planet) were from/into the same Lord.
It was on this sacred tithi that He uttered the following one and a half shloka and merged into the Lord's murti as He ascended the steps inside the chit-sabha:
AV Gopalacharya's Translation: ‘This city of Chidambaram is well known for its sacredness. Splendidly modest sons (have been born to me). Some good works have also been written. My years are more than seventy. Longing for pleasure, I have none. I want nothing. Only I am anxious to see my Lord’s place. There flashes in my heart the rising sun of the light of the Lotus-Feet of the Dancer of the Golden Hall’. (REFERENCE: Preface to Yadavabhyudaya Mahakavyam of Swami Vedanta Deshikar with the commentary of Srimad Appayya Dikshitendra; Volume II; Year of Publication: 1909)
Saying this He disappeared. One of His sons, Nilakantha Dikshitar, subjoined His father to complete the remaining half of the second verse as follows: नूनं जरामरणघोरपिशाचकीर्णा संसारमोहरजनी विरतिं प्रयाता॥
AV Gopalacharya's Translation: ‘Certainly the bewildering night of Samsara filled with the fierce demons of births and deaths has come to an end’.