Chandra went into safe mode on October 10th at around 10:55 AM ET. It started using its backup hardware after the shutdown and shifted its solar panels to get maximum sunlight. Thankfully, the agency concluded after analyzing data from the transition that its scientific instruments are safe and sound. The Chandra observatory uses X-ray technology to keep an eye on black holes and supernova remnants, among other things.
Like the Hubble, Chandra is also getting long in the tooth: it was only supposed to last for five years, but it's been operating for the past 19. Investigation is still underway, but Chandra astronomer Jonathan McDowell said it's just a coincidence that the two high-profile observatories went down almost at the same time. NASA seems confident that the telescope can go back to normal operations, though, and expects it to be able to "continue carrying out forefront science for many years to come."