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We expect T Coronae Borealis to go nova in the next months. When it does, will space telescopes already be watching it, or will they turn to observe it, or will big ones like Hubble and JWST miss it entirely?

And if they can adjust to observe it, how quickly can they "spin their head" to target it?

For context, I'm wondering about this, curious about how suddenly this nova event unfolds (whether the first few milliseconds are important to observe, or the months that follow, doesn't matter), and will we be able to catch those critical moments (whatever length of time they are), or will we miss them because we can't retarget quickly enough, or can't dedicate our gaze to them for the entire window that the event is likely to occur. And I'm wondering how quickly space telescopes can adjust to catch sudden events. (Or perhaps there's a different strategy for catching sudden events that I am not aware of.)

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Novae get brighter very quickly compared to most other astronomical bodies, but they are not "blink and you miss it" events. A nova will initially brighten over a period of hours to days, and reach peak brightness a few days after the eruption begins.

Whether this event is judged to be important enough to cancel whatever the various space telescopes were doing, I don't know. Novae are fairly common, and the benefits of a space telescope (improved resolution, observation of IR band) are not particularly needed. Light curves and spectra can be obtained by ground-based observers.

If necessary, there are protocols for urgent observations with both Hubble and JWST. They can be turned in a matter of minutes if the need arises.

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    $\begingroup$ While Target of Opportunity (ToO) observations with Hubble can be made quickly (within 2 days), the number of these extremely disruptive ToOs per cycle is extremely limited, see ToO rules. 2 weeks is the "normal" time from trigger to observation for most programs that have had ToO permission granted. $\endgroup$
    – astrosnapper
    Commented Aug 5 at 19:15
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    $\begingroup$ @astrosnapper Is that before or after the gyro failure and going to single gyro mode? My understanding is the single-gyro operation makes rapid retargeting much more difficult and ToOs are the biggest impact. $\endgroup$
    – Darth Pseudonym
    Commented Aug 6 at 21:25
  • $\begingroup$ I'm fairly certain that these restrictions predate the Reduced Gyro Mode. RGM makes the amount of available sky to execute a ToO in smaller due to the smaller field of regard, larger solar exclusion angle & reduction in allowed slew rates (taken from this presentation). Only been semi-involved in HST ToOs but that was to provide astrometry to predict positions less than the WFC3 FOV 17 days out when the ToO was scheduled $\endgroup$
    – astrosnapper
    Commented Aug 6 at 23:06
  • $\begingroup$ "The benefits of a space telescope are not particularly needed" doesn't mean they won't be employed. Fermi will observe T CrB when the nova eruption is detected, along with other space-based missions including James Webb Space Telescope, Neil Gehrels Swift Observatory, IXPE (Imaging X-ray Polarimetry Explorer), NuSTAR (Nuclear Spectroscopic Telescope Array), NICER (Neutron star Interior Composition Explorer), and the European Space Agency’s INTEGRAL (Extreme Universe Surveyor) source $\endgroup$
    – Wyck
    Commented Aug 7 at 16:10
  • $\begingroup$ I feel like your answer should explicitly include the term "Targets of Opportunity (ToOs)" when you say "protocols for urgent observations" as mentioned in astrosnapper's comment because that seems to be what all the missions are calling them. $\endgroup$
    – Wyck
    Commented Aug 7 at 17:30
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It is possible to request target of opportunity observations with HST. The observer "triggers" the ToO in response to some astrophysical event. The fastest that HST will respond to the trigger is between 36 and 48 hours.

JWST has a very similar policy and capacity.

Some other space telescopes, for example Swift in the X-ray, UV and optical bands can slew and point within hours for some targets if necessary.

I am no expert on the Astrophysics of novae. There are numerous studies of novae in the literature, using HST, Swift and other space telescopes (e.g., Page et al. 2022). The usual focus is on UV and X-ray wavelengths that cannot be studied from the ground. The rise times for novae is measured in days, the decay time in weeks (e.g., Strope et al. 2010). That means HST would generally miss the rise phase but be able to well-sample the decay phase as required.

On occasion, Swift has managed to obtain UV and X-ray observations within a day of an outburst being reported (e.g., Osborne et al. 2015).

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