The duration of this event was not the only weird thing about it. Archival data showed that low-energy X-rays were already present almost a day before the main gamma-ray fireworks—an “X-ray precursor” that is hard to reconcile with standard models of GRBs. Meanwhile, the gamma-ray behavior itself looked like a stuttering engine. Fermi detected a sequence of short flares separated by long gaps, collectively implying multi-hour activity from a central engine rather than the single, clean explosion typical of such events.
So, what could power an event that (1) repeats, (2) lasts for hours to a day, and (3) shows X-rays both before and after the gamma-ray fireworks? Two families of ideas have dominated the discussion. One idea keeps it in the GRB family but pushes the engine to extremes. Typical GRBs arise from the death, or collapse, of massive stars, which can produce a narrow, relativistic jet that emits gamma rays. Perhaps some aspect of the collapse, either the stellar type or the nature of the compact remnant(s) left behind could produce a central power source that simply refuses to shut off on normal timescales. The other main idea is an event completely unlike traditional GRBs and instead invokes a star wandering too close to a black hole, being torn apart, and feeding a jet aimed toward Earth. Such phenomena, known as tidal disruption events, were first predicted in the mid-1970s, but only detected twenty-five years later. Currently, we find a handful of these energetic shredding events each month, but what would make this tidal disruption event so different from the previously observed examples? The catch is that each scenario explains part of the puzzle and strains against the rest, leaving GRB 250702B as a genuine classification stress-test for high-energy astrophysics.
