Copy another field with nanoseconds to elasticsearch/kibana @timestamp field

Elastic Stack Elasticsearch
4

Hi @Christian,
I have set the date field format to nanoseconds.

For e.g:
Initial values for:
@timestamp: Mar 9, 2020 @ 00:58:55.528000000
event_timestamp: 2020-03-09 04:58:54.497305256 +0000

After 1st, 2nd and 3rd above are applied, I see
@timestamp: Mar 9, 2020 @ 00:58:54.497000000
ls_timestamp: 2020-03-09T04:58:55.528Z

The issue I see is @timestamp is not showing all the nanoseconds as in event_timestamp.
and ls_timestamp is showing in UTC even though my original @timestamp is in EST.

Filter used:
mutate
{
add_field => ["ls_timestamp", "%{@timestamp}"]
}
date {
match => ["event_timestamp" ,"yyyy-MM-dd HH:mm:ss.SSSSSSSSS Z"]
target => "@timestamp"
timezone => "UTC"
}