The Contraband Event started on the 2nd of July and ended on July 9th. In the event, Arc Fence Shards were added as a drop for this timeframe.
Players had a chance to earn Arc Fence Shards, a common item that has a chance of dropping as loot when attacking/retaking a planet.
When the event was on, two event-exclusive bounties were added.
One bounty rewarded the player with 5 Arc Shards, which allowed the player with the Arc Targeting Module, when forged with an Arc Fence Shard and Small Parts, it would create the Arc Annihilator.
After completing the first bounty, another one will be unlocked. This bounty will have the player earning TEN Arc Fence Shards. Completing this bounty will award the player the Arc Tactical Panel, which combined with an Arc Fence Shard and Components will create the Arc Amplifier
No more bounties were to be unlocked after that. The remaining shards after creating the two items are presumably useless due to only being useful for crafting the two exclusive items. Each shard can be sold for 500 credits, so you could sell your remaining shards for a bit of quick cash, but the future is unknown for the shards, so it would be best to keep them for now.