For visiting researchers there's 2 types of US visas that can be used, the B-1 or the J-1. Which one applies to you depends on certain criteria (which i'll outline below). If you're eligible for the B-1 visa you can use the ESTA service, provided you're eligible for the visa waiver program and ESTA (i.e. no visits to Iran etc.)
In order to be eligible for the B-1 visa (and by extension VWP and ESTA), your research and speaking must meet the following criteria:
- there is no remuneration from a U.S. source for your research (i.e. no one in the US is paying you for your work)
- the results of the research will not benefit the U.S. institution (i.e. you're doing research for a research project based outside the US)
- you will receive no remuneration from a U.S. source for your speaking engagements, other than expenses incidental to the visit (honorarium fees are allowed providing they meet the criteria outlined below).
If you accept honorarium fees:
- Your speaking activities must last no longer than nine days
at a single institution
- the institution must be a nonprofit research organization
or a governmental research organization, or an
institution of higher education, or a related or
affiliated nonprofit entity
- Your speaking activities are conducted for the benefit of the
institution or entity; and
- you have not accepted such payment or expenses from five
such institutions during the previous six month period.
In your question you state that "collaborator has some funding for this from their home university". Presumably this means that their home university will be befitting from your research in some way. If this is the case then you are not eligible for a B-1 visa (nor VWP/ESTA) and must apply for a J-1 visa instead.