The "Harshacharita" is a historical biography of Emperor Harsha, who belonged to the Vardhana dynasty and ruled the Indian subcontinent in the 7th century CE. It primarily focuses on the life and achievements of Harsha and does not provide direct information about the Maurya Empire, which existed much earlier.

On the other hand:

Sculpture: Sculptures from the Mauryan period, such as the famous Ashoka Pillars and the Sarnath Lion Capital, serve as valuable sources for understanding the art, culture, and socio-political aspects of the Maurya Empire.

The account of Megasthenes: Megasthenes was a Greek ambassador to the court of Chandragupta Maurya and his account, known as the "Indika," provides insights into the Mauryan administration, society, and geography.

Arthashastra: Traditionally attributed to Chanakya (Kautilya), the "Arthashastra" is an ancient treatise on statecraft, military strategy, and economic policy. It offers valuable information about the governance and administration of the Maurya Empire under Chandragupta Maurya.

So, the correct option is [4].