You are flying your personal rocketcraft at 0.9c from Star A toward Star B. The distance between the stars, in the stars' reference frame, is 1.0 ly. Both stars happen to explode simultaneously in your reference frame at the instant you are exactly halfway between them.
The question asked of the aforementioned scenario is "Do you see the flashes simultaneously?" and what is the time difference between the two?

See explanation.

Explanation:

If both stars explode in simultaneously in the your frame of reference then obviously you will see the two flashes simultaneously, and therefore, the time difference between the events would be zero.

If however, the stars exploded simultaneously in their frame of reference, then you would not observe the flashes simultaneously.  Then the time difference between the events will not be zero, rather, you will observe star B exploding first and star A after.

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explanation:

a longitudinal wave moves energy that is to the direction of the wave’s movement. - true