vaiśampāyana-śiṣyāḥ — the disciples of Vaiśampāyana; vai — indeed; caraka — named the Carakas; adhvaryavaḥ — authorities of the Atharva Veda; abhavan — became; yat — because; ceruḥ — they executed; brahma-hatyā — due to the killing of a brāhmaṇa; aṁhaḥ — of the sin; kṣapaṇam — the expiation; sva-guroḥ — for their own guru; vratam — the vow.