Foreigners are planning to stay in a longer duration in Indonesia for purposes such as doing Research, may choose this type of visa: Limited Stay Visa.
To obtain this type of visa, your guarantor in Indonesia need to apply in the Directorate General of Immigration in Jakarta, Indonesia. Once the visa is approved, the Directorate General of Immigration in Jakarta will send authorization letter that enables Indonesian embassy or Consulates to grant you the visa.
This type of visa is divided into several indexes that each visa index have different requirements http://www.imigrasi.go.id/index.php/en/public-services/limited-stay-visa#requirements
Requirements for Limited Stay Visa for Research, index 315: application and guarantee letter, passport copy, bank account copy, recommendation from Indonesian research institutions such as LIPI, Ristek.
Check the complete procedures here Research Permit Procedures