What is this absorption called?

Whatever you doing – you are doing it too hard/wrong. This is not a state but sounds like suppression. Try to use understanding rather focusing/concentration as it’s not right for sure.

Tien wrote: “Recently, while I contemplate on Dhamma or a relate subject, even in crowded place (while in the bus, on the side of a street, in waiting room, …), I have no awareness of 5 physical senses at all, totally absorb in the thinking for as long as 30 minutes. Then after I’ve done with my contemplation or a sudden sound happens, my awareness of the senses re-emerged..” and “I know it not yet first jhana..”

It is POSSIBLE that it could be a Sotapanna (or higher) phala samapatti.

It is not necessary to be in a jhana to have an experience like that. In fact, at least in the lower jhanas, one can hear external noises, etc while in the jhana. It is only in jhana samapatti (for lower jhanas) that it is guaranteed that one cannot hear, see, etc.

There is a sutta which describes an event where the Buddha was in Arahant phala samapatti (not a jhana or a jhana samapatti), and did not hear thunder and lightning that killed a couple of people close-by. If someone knows the sutta, please post it.

Also see, “Nirōdha Samāpatti, Phala Samāpatti, Jhāna, and Jhāna Samāpatti“.

/suttacentral.net/dn16/en/sujato; 25.On Pukkusa the Malla; some way down ,starting with the para: ‘This one time, Pukkusa, I was staying near Ātumā in a threshing-hut.’…..

However, I did not persist long enough reading the rest of the sutta to come across the particular term: ‘Arahant phala samapatti’, if the term is to be found there at all.

After thinking about it more, I think what Tien has described could also be upacāra samādhi.

Unlike jhānās (which are limited in number), samādhi can be many varieties. There can even be miccā samādhi.
– When one gets fully absorbed in an ārammana (topic), one may not hear, see, etc.
– A simple example is when one is fully absorbed in reading a book, one may not hear, see, etc.

This is discussed in, “What is Samadhi? – Three Kinds of Mindfulness“.

Magga phala and jhāna are two different things. I think Chrisitian is talking about jhanas. It is not necessary to get to jhana to attain magga phala. We all have attained jhana in previous lives.
– It is easy to attain jhana for those who had cultivated them in recent previous lives or were born in brahma realms in recent previous lives.
– One can attain magga phala without jhana (via upacara samadhi).
– One who has anaraiya jhana does not have a magga phala.
– One with magga phala may or may not be able to get to a jhana easily.
More details at: “Samādhi, Jhāna (Dhyāna), Magga Phala“.

Thanks to y not for the reference.