If you're running T1 exploration and an Astero points you, you are, in my admittedly slight experience, royally screwed.
I've killed an Astero in a bait fit Heron (admittedly, they were flying a total shitfit), but you're right that the smart money is always on the Astero here. It's important to note that the Astero does have a locking delay upon decloaking though, and it's more than long enough for anyone who is paying attention to simply warp off.
an exploration fitted exploration frig, however, wont kill anything. not even a bomber.
Eh. You can make a combat-capable-enough-for-this frig without really sacrificing much at all though. Alpha clones can't fit a cloak so there's room for two launchers, which combined with the drones should make you out dps a rocket bomber. If you're actually interested in killing shit (as opposed to just making it leave) then a single mid slot needs to be devoted to a scram, and that's it really. Also jamming drones are a thing, and will often save your arse if deployed quickly enough.
As a sidenote: rockets should basically never be fit to a bomber. It's one of the very few cases where the sensible choice is to ignore the ship bonuses and just stick blasters on.
[Manticore, Blasterhawks]
Magnetic Field Stabilizer II
Magnetic Field Stabilizer II
Warp Scrambler II
Stasis Webifier II
1MN Afterburner II
Stasis Webifier II
Light Neutron Blaster II, Void S
Light Neutron Blaster II, Void S
Rocket Launcher II, Caldari Navy Inferno Rocket
Covert Ops Cloaking Device II
Core Probe Launcher II, Sisters Core Scanner Probe
Small Hybrid Burst Aerator I
Small Hybrid Collision Accelerator I
Far higher dps than rockets would offer you, and the nature of explorer hunting + dual web means you'll easily maintain the optimal range for them. Can be made even more effective with a little bling, consider this the 'I'm a poor' version. I have literally never come across someone else doing this unless I've previously told them to though.