I'm trying to identify a specific component on a circuit board here (circled in red on the photo, and highlighted in red as "Q1" in the circuit). Note that the four diodes, one capacitor, and the voltage regulator are all lumped together as "DC 5v" in the circuit diagram, while the three 470 ohm resistors on the right are lumped together as R3:
For context, I should probably describe the function of the circuit. When voltage is first applied to the circuit, LED D1 is lit. However, when S1 is closed momentarily, D1 is turned off and stays off until S1 is pressed again (at which point it turns on, rinse and repeat).
Obviously, without any identifying markings, it's impossible to identify the component Q1 is exactly, but I just need some initial direction so that I can choose a component of similar function and value.