The s of the s-Aorist always takes the iṭ augment after añj - rudhādigaṇaḥ (7th Conjugation).,
As आञ्जीत्, आञ्जिष्टाम्, आञ्जिषुः ॥ But अङ्क्ता or अञ्जिता in tenses other than Aorist. The root having an indicatory long ऊ optionally takes इट् 7.2.44,
अज्ञेः सिचि
Adhyāya 7 · Pāda 2 · Rule 71