Reason Why Angaraparna Addresses Arjuna As 'tapatya'

Mahabharata Adiparva Chaitrarathaparva section 173 - 177

Pandavas, along with their mother start walking towards Panchala, to obtain Draupadi as their wife. At nightfall they reach the banks of river Ganga. A gandharva king by name Angaraparna (Blazing chariot), was bathing in that river along with his wives and retinue.

Arjuna approaches water to quench thirst, and the gandharva challenges Arjuna for a fight, saying that during nightfall, men are not supposed to enter Ganga.

Arjuna asks Gandharva, why he fought with them, chastised them for entering Ganga, as they are not at fault. Angaraparna replies "Even though you are not at fault, and I know that you are from Kuru race, I also know the knowledge and power of your preceptor Drona, I also know that you five brothers are noble and well learned, and good fighters, yet I censured you.

The reason is , you have completed your studies, yet you have not taken a wife and you have not taken up any mode of life and wandering in forest. Lastly, being of nobility, you dont have a priest who can guide you on the path of virtue, you have not appointed one."

Gandharava addresses Arjuna as 'Tapatya'. Arjuna was curious to know why he is called as Tapatya, as he is son of Kunti and should be called as Kaunteya.

Gandharva king Angaraparna then tells him the story of Tapati, daughter of Surya the sun god.

There was a king named Samvarana, was a just ruler of earth. Once when he was on a hunting expedition, he saw the daughter of Sun god, Tapati, in a dazzling golden light. He immediately falls in love with that damsel and requests her hand. She says, only her father, Surya can determine who has to be her husband. Samvarna then, prays to his chief priest Sage Vashishta, who ascends to the world of light, illuminated by Surya and requests his daughter's hand for Samvarna. Sun god agrees to that and marries off his daughter tapati to Samvarana. They have a illustrious son by name Kuru, on whose name the entire race is known as Kauravas.

On Hearing this story Arjuna wanted to know about Sage Vashishta.

Gandharva then tells about Sage Vashishta , "Vashishta is the foremost among sages. he is the manasa putra (mind-born son) of the creator Brahmaji. His wife is Arundhati. He has fully conquered all the 6 enemies of any person, viz kama (unreasonable desires), krodha (anger), lobha (greed), moha (attachment and delusion), madha (pride) and matsarya (jealousy) .

He is conversant in all Vedas. King Vishwamitra, to spite Vashishta has killed all his sons. Even then Vashishta did not retaliate, and exterminate the race of Kusikas, to which Vishwamitra belongs. Instead he forgave him. He could have brought back his children from the world of death, through his ascetic power. Even that he did not do, as he does not want to interfere in natural order of things. He has helped many Kings, by being their priest, in putting them on the path of virtue. So , O Tapatya, you should also appoint a good priest for you."

Source:

1) http://atmajyoti-prasad-jayakavya.blogspot.com/2010/06/race-of-kuru.html
2) http://atmajyoti-prasad-jayakavya.blogspot.com/2010/06/chakshusi-science-of-illusion.html