My progress so far:
The signal source turned out to be Artemis' grave. Artemis' consciousness seemed to be still remaining in a form of hologram, but I couldn't talk with her effectively. I went to a long-range communication tower to contact Apollo, but I couldn't. Instead I was connected with an entity named Null via manual override. Null gave me blueprints of Mind Arc and Soul Engine. According to Null, I might be able to revive Artemis with them. (log #16)
Before starting to gather materials needed for crafting Mind Arc, I decided to check out the source of distress signal I previously picked up. It turned out to be a settlement on planet Nucaselis L12 in Onbets-Arg system. I took out the Sentinels and then pirate starships attacking the settlement. I was offered to be the overseer of the town, but chose not to take the seat because of harsh natural environment. After a few going back and forth, I gathered all the material and components needed and crafted the Mind Arc. I'm going to contact Artemis again and see what this Mind Ark can do to help her. (log #17)
I contacted Artemis via Holo-Terminus on planet Jodice G20 in Konaka system. Activation of the Mind Arc didn't revive her. Instead, her consciousness was dumped to the Arc. Null told me that I could get help from my friends at the Space Anomaly station. So I visited the station and showed the Arc to Nada and Polo. It turned out they had a star system simulator. I was offered to upload Artemis consciousness to the simulator so that she could kind of live within the simulation, forever trapped in a lesser version of reality. After a long consideration, I decided let her die. The Arc was opened without uploading, and her consciousness faded away. (log #18)
I told Polo and Nada about my choice to let Artemis die. They told me I did the right thing, and Artemis would be at peace.
I left the Space Anomaly station and went out to the space. Apollo contacted me. I told him what happened so far, of encounter with Atlas, of encounter with the First Traveler, and death of Artemis. Apollo also supported my choice about Artemis. I'm not entirely sure of what I did, but what's done is done.
Apollo wanted to investigate Atlas and the Sentinels further. He suggested we meet and join forces. To tell him where I was, I needed to find monolith and get the glyphs for this star system. With the glyphs, Apollo could calibrate a portal and teleport to this system.
Using my starship's scanner, I detected a monolith on planet Jodice G20. I landed nearby and accessed the monolith. Location of nearby portal was revealed. It was on the same planet, and not far from here.
I flew to the portal and obtained the glyphs. To send the glyphs to Apollo, I needed to find a Holo-Terminus. Luckily, I found one not far from the portal.
I activated Holo-Terminus and tuned signal to Apollo. He was more than willing to come across the galaxy and join me. I gave the glyphs to Apollo.
Right after I terminated communication with Apollo, I was contacted by Null. Null was thinking something huge is happening in the galaxy, and requested my help with its investigation. Null's appearance could immediately invoke Sentinel aggression, so I was better suited for poking around.
Null wanted me to check out an observatory nearby. I was supposed to visit this observatory and get the coordinate of a crashed freighter which might hold information of Null's interest. I decided to go along with Null's plan.
I flew to the observatory, and accessed the terminal inside. According to the observatory's log, this outpost was stationed by a Gek specialist. This Gek found starship wrecks whose logs spoke of star systems that didn't exist and events that could have never happened. One day, the Gek went out to investigate a Korvax freighter crash site and never returned.
I extracted the coordinate of the freighter crash site. It's on the planet Aputon Sigma. I'm going to check out the crashed freighter.