Can I do penance (prayaschitt) for evil thoughts (ashubh vichaar) through repentance (paschatap) only, or does it require fasting (tapsya)

Sometimes I get bad thoughts in my mind, but on realising my mistake, I immediately repent for my bad thoughts with Dev, Guru and Dharma as witnesses. Can I do penance (prayaschitt) for evil thoughts (ashubh vichaar) through repentance (paschatap) only, o