Mon, 09/05/2022 - 19:42
Hi, folks,
GX 339-4 is in outburst. We will be observing it with JWST on September 10 from 00:42:23 to 3:03:17 UT. It's currently about 16.5 mag in V, and it's likely to be getting brighter.
The goal of the JWST program is to look at the rapid variability, so sub-second timescale time series photometry would be especially valuable for anyone who has that capability, but any time series photometry with accurate timestamping would be useful.
GX339-4 is also known as V821 Ara (an HMXB), at coordinates
17 02 49.4 -48 47 23.09
so only visible to southern hemisphere observers. For those that are interested, these early X-ray/Radio sources are identified by their galactic coordinates, in this case longitude 339 and latitude -4. This means that it is not far from the galactic center, which is why the field is pretty crowded. Take care when you are doing your photometry. Subsecond on 16th magnitude objects also may require a larger telescope to get decent signal/noise. The rule of thumb at V is a 15th magnitude star takes 1 minute to obtain S/N=100 with a 40cm telescope, so at 16th you will get about S/N=10 in a couple of seconds. If the target gets brighter, you win.
Arne
Yes, thanks for the added context (it's actually a low mass X-ray binary, with a subgiant star and a black hole in the binary, despite what SIMBAD says). This should be observable from South America, but it will have set in South Africa by the time that it comes up.
Also, I totally agree with Arne that a larger telescope may be needed, but this does remind me to give a bit more detail on what we have in mind for what we will do with the data. We plan to do (1) cross-correlation with the JWST data (although unfortunately, the clock accuracy on JWST might be a problem) and (2) Fourier analysis with the data (in which case, as long as the total signal to noise of the data set is good, we can deal very well with large numbers of low signal to noise data points). For the purposes we have in mind, a lot of S/N of 2 data points would be terrific, as long as you are still dominated by sky background and photon noise from the source itself. For CMOS systems, this is likely to be the case, and going faster might make the individual data points look worse, but we'd still rather have the high time resolution. There might be a bit more scintillation noise, as well, in a large number of short exposures, but we'd still prefer to deal with that than not to have the time resolution we want.
HI,
I am trying to get time series of 10 sec with Clear filter on a 50 cm scope f/5 tonight from Chile.
I did this on AR Sco with a similar exposure on a mag 16 star in 2016, although the quality of the CCD (FLI 16803 CCD) has deteriorated.
On the long term I will change it to a CMOS (QHY600 type camera), but not the next days, though.
Regards,
Josch
OK, great, thanks! We can do something with that, but we especially want data strictly simultaneous with the JWST data on the 10th.
Ok, I will try to get simultaneous observations on Sept. 19.
I will try tonight again with 20 sec as the 10 sec was on the limit.
Regards,
Josch
I'll also aim to monitor with 20s V subs ... I have a very similar setup to Josch - The weather in the next few days isn't looking great hopefully we are clear by the 10th.
HI,
I actually realized that it was not Sept. 19 but Sept. 10 where there were JWST observations.
I got data for Sept. 10 with 45 sec exposure (total time close to 50 sec).
I can make them available to you if you are interested.
Regards,
Josch
PS: Actually the data are with the AAVSO database (look for HMB as observer)
Thanks, Josch. Whether one wants to view this as fortunate or unfortunate, JWST actually seems not to have acquired the right star for us. HST had this problem occasionally, especially in globular clusters, and it seems to have followed over to JWST. Basically, after a long slew, in a crowded region of the sky, they sometimes incorrectly guess where they are pointed and set up for the wrong star.
The silver lining for us is that the weather for a lot of our concurrent observations was poor, and hence we didn't get most of them done, either, and maybe we can get JWST to re-do our observation. The source goes out of visibility for JWST on the 18th, so it will have to be soon or not at all, and I'll make another posting if we get another observation.