GRB 970815 was a well-localized gamma-ray burst ( GRB ) detected by the All-Sky Monitor ( ASM ) on the Rossi X-Ray Timing Explorer ( RXTE ) for which no afterglow was identified despite follow-up ASCA and ROSAT pointings and optical imaging to limiting magnitude R > 23 .
While an X-ray source , AX/RX J1606.8+8130 , was detected just outside the ASM error box , it was never associated with the GRB because it was not clearly fading and because no optical afterglow was ever discovered .
We recently made deep optical observations of the AX/RX J1606.8+8130 position , which is blank to a limit of V > 24.3 and I > 24.0 , implying an X-ray–to–optical flux ratio f _ { X } / f _ { V } > 500 .
In view of this extreme limit , we analyze and reevaluate the ASCA and ROSAT data and conclude that the X-ray source AX/RX J1606.8+8130 was indeed the afterglow of GRB 970815 , which corresponds to an optically “ dark ” GRB .
Alternatively , if AX/RX J1608+8130 is discovered to be a persistent source , then it could be associated with EGRET source 3EG J1621+8203 , whose error box includes this position .