Significance of Rudrakshas:
Maha Deva was tired in tracking the tricky and invincible Demon
Tripurasura, finally pulled out his ‘Ajagava’ dhanush and despatched
the unique Vikaaraal arrow and killed him. The long chase of the
Asura who was fortified with Brahma’s boons tired out Maheswara and
this tedious task ended up with profuse tears from his right eye
signifying Surya Netra and from the streams thus materialised emerged
Rudraksha Trees yielded twenty kinds of yellow seeds, while from his
left eye called Soma Netra came sixteen varieties of white coloured
beads and from the third eye on the forehead called Agni Netra came
black beads.
Source - The book "PURANA SARAAMSHA (Quintessence of Puranas)"
According to this book, the story of Lord Shiva killing Tripurasura using the Ajagava bow is found in Padma Purana, Devi Bhagavatam, Shiva Purana and Skanda Purana.
(Source: Padma Purana, Devi Bhagavata, Siva Purana, Skanda Purana
etc.)
According to Matsya Purana, Agajava was used again by Lord Shiva during the battle that ensued as a result of Chandra abducting Brihaspati's wife Tara.
Quoting from the book "Essence of Matsya Purana":
In course of time, Chandra got infatuated with Devi Tara, the wife
Deva Guru Brihaspati and took her away to his residence despite heavy
protests of Deva Guru, Sadhyagana, Lokapalakas, Marudganas, and even
Bhagavan Shiva himself. Shiva felt highly offended and invoked the
Ekadasha Rudras led by Vamadeva, pulled out his bow called
‘Ajagava’, and accompanied by eighty four Ganas, Ganesha, Kubera
with his shata koti Yakshas, Padma Vetala, three lakh Nagas and twelve
lakh Kinnaras and so on. Chandra on his part too elisted the support
of Nakshatras, Rakshasas, Asuras, Daityas, Shanishwara, Mangala, and
so on.
However, according to the writings of this blog, Ajagava is nothing but the Pinaka bow (and I agree with this view).
Rudra is described as fierce; armed with the mighty bow (pinaka), and
a quiver holding unending array of arrows and missiles which are
terrifyingly swift and penetrating. His fast-flying arrows, ‘brilliant
shafts run about the heaven and the earth’ (RV 7.46.3).
Pinaka the powerful, sturdy bow with a wide span, bending along the course of the Sun , is said to be the symbol of Rudra, the Isana
(Lord); and, his supremacy over all others. In the later texts,
Pinaka is also known as Ajagava, the southern part of the Sun’s path.
(Ajagava is also explained as a bow made of the horns of goats.)
Oh, the devoted to the devotees, always travelling in the chariot,
ever young, fierce like the lion, vanquisher of the enemies, May the
devotees pray to you. May you make us happy. May your armies fight
against the enemies and be merciful towards us. There is none that
matches him in strength. He is the Ishana the Master of the world; he
is the father of worlds (Bhuvanasya pitaram).He commands men and
entrusts tasks. He sets things in motion and makes flow like a river.
He is medhavi, intelligent and the compassionate one. He is praised as
midvah, for his generosity. As he is an auspicious one, he is called
Shiva. (RV: 2-33-7; 6-49-10; 7-46-2)
Note: As per Mahabharata, the king Prithu (from whom the earth got it's name Prithivi) also used to own a bow called Ajagava.
The very mountains used to yield him openings that he might pass
through them. The standard of his car never broke (obstructed by
anything). Once on a time, the tall trees of the forest, the
mountains, the gods, the Asuras, men, the snakes, the seven Rishis,
the Apsaras, and the Pitris, all came to Prithu, seated at his ease,
and addressing him, said, ‘Thou art our Emperor. Thou art our king.
Thou art our protector and Father.
Thou art our Lord. Therefore, O great king, give us boons after our
own hearts, through which we may, for ever, obtain gratification and
joy.’ Unto them Prithu, the son of Vena, said, So be it. Then taking
up his Ajagava bow[117] and some terrible arrows the like of which
existed not, he reflected for a moment.