Solar Orbiter truthfulness of STIX data

[tniickck]

yall know that recently a X6.3 flare occured on the Earth facing side of the Sun. the problem is that the Solar Orbiter saw it too and measured as X15.4 (screenshot below). my question: should the SolO be trusted for measuring farside solar flares? if we take the recent flare it multiplied 6.3 by nearly 2.5 to get X15. so maybe all these three X9 and a few more flares which were only seen by SolO on the farside were not this powerful? like multiplied by 2-2.5 too, so X9 becomes an X4 etc. this might be a big step to solve "the farside powerful flares mystery" 😁

[MinYoongi]

What a great finding, @tniickck!! great thread.

[Philalethes]

1 hour ago, tniickck said:

yall know that recently a X6.3 flare occured on the Earth facing side of the Sun. the problem is that the Solar Orbiter saw it too and measured as X15.4 (screenshot below). my question: should the SolO be trusted for measuring farside solar flares? if we take the recent flare it multiplied 6.3 by nearly 2.5 to get X15. so maybe all these three X9 and a few more flares which were only seen by SolO on the farside were not this powerful? like multiplied by 2-2.5 too, so X9 becomes an X4 etc. this might be a big step to solve "the farside powerful flares mystery" 😁

I don't think the number of counts measured there corresponds exactly to X-ray flux, i.e. 15e+7 counts of 4-10 keV X-ray photons doesn't mean X15, although I have noticed that there seems to be a certain amount of correspondence before myself, but I suspect that's coincidental.

When looking at the GOES approximations it gives a range of [X5, X21]; I suppose that's also quite exaggerated, but X6.3 does at least fall within it. It estimates it as X10, which isn't that far from the truth, but clearly not as exact.

But you're certainly right that it's something to take into consideration. If its estimate is X10 and the value was X6.3, the adjustment factor there would be ~1.6. However, we don't know whether that applies to other flares as well. If we also look at the preceding X1.9 and X1.7 flares, it estimates both as X2 (funnily enough as X1 and M10 respectively on each side of the attenuator being inserted there, and we all know there's a big difference between M10 and X1).

So I'm guessing it's first at even higher intensities that it becomes less accurate. Maybe it has something to do with improper calibration of the attenuated data? Until we have more data points it would probably be a good idea to adjust down similarly strong flares by roughly the same factor (e.g. X9 / 1.6 = X5.6), or maybe even try to scale the factor since it seems to be more precise around X1 (scaled geometrically it would yield ~X5.9 for an X9 instead).

It's a great observation in any case, we should definitely be on the lookout for more such strong flares whenever we can and see how they match up.

[helios]

Where should I see the X15 in this?

the ABCMX scale is the flux per square meter in the 0.5-4 Angstrom band, that's 3.1 to 25 keV, that's wider than any of the channels.

Solar orbiter is also closer to the sun, which results in a higher flux. At 0.71 AU distance it is almost twice the flux compared to 1 AU.
An X6.3 flare at 1 AU corresponds to a X12.5 flare at 0.71 AU.

The count does not seem to be linear with the energy, as far as I understand, so it can't be used for comparison.
https://www.research-collection.ethz.ch/bitstream/handle/20.500.11850/560745/s11207-022-02029-x.pdf

Edited February 26 by helios

[tniickck]

49 minutes ago, Philalethes said:

I don't think the number of counts measured there corresponds exactly to X-ray flux, i.e. 15e+7 counts of 4-10 keV X-ray photons doesn't mean X15, although I have noticed that there seems to be a certain amount of correspondence before myself, but I suspect that's coincidental.

When looking at the GOES approximations it gives a range of [X5, X21]; I suppose that's also quite exaggerated, but X6.3 does at least fall within it. It estimates it as X10, which isn't that far from the truth, but clearly not as exact.

But you're certainly right that it's something to take into consideration. If its estimate is X10 and the value was X6.3, the adjustment factor there would be ~1.6. However, we don't know whether that applies to other flares as well. If we also look at the preceding X1.9 and X1.7 flares, it estimates both as X2 (funnily enough as X1 and M10 respectively on each side of the attenuator being inserted there, and we all know there's a big difference between M10 and X1).

So I'm guessing it's first at even higher intensities that it becomes less accurate. Maybe it has something to do with improper calibration of the attenuated data? Until we have more data points it would probably be a good idea to adjust down similarly strong flares by roughly the same factor (e.g. X9 / 1.6 = X5.6), or maybe even try to scale the factor since it seems to be more precise around X1 (scaled geometrically it would yield ~X5.9 for an X9 instead).

It's a great observation in any case, we should definitely be on the lookout for more such strong flares whenever we can and see how they match up.

excellent answer. thank you! 

[Philalethes]

10 minutes ago, helios said:

Solar orbiter is also closer to the sun, which results in a higher flux. At 0.71 AU distance it is almost twice the flux compared to 1 AU.
An X6.3 flare at 1 AU corresponds to a X12.5 flare at 0.71 AU.

This is true, but I'm fairly sure this part is accounted for when calculating the GOES approximation, which is more accurate at lower intensities.

You're right about the graph though, that's the same thing I mentioned above; I think the "counts" axis indicates the number of X-ray photons of those energies measured within a given time interval, or something of the sort. Maybe someone else knows.