I'm tracking the currently flaring blazar S5 1803+78 in photometry (v~14.6 and falling 0.1 per day now).
I got over-ambitious (only 8" aperture!) and tried to do a low res spectrum...what I get is something that looks as if there was a red component (host???) and a very steep blue component (the flare?????) , all complicated by a redshift of ~0.68. I'm still a beginner in all this and am wondering if all this can at least be qualitatively correct). There's a lot of contamination from other stars
Maybe people with bigger scopes would like to give it a try.The flaring won't last for much longer and you could do a before-after comparison in a few days/weeks.
EDIT: coadded image here: http://bikeman.selfhost.eu/astro/S5_1803%2B78/calib_stacked_728_S5%2018…
CS
HB
Have I got the right target ? If so the spectrum looks pretty featureless to me though there is some overlap from other spectra at both ends, particulalry at the red end.
I took a spectrum with the ALPY 200 last night. I will reduce it and post later
Cheers
Robin
Yup, that's the one. No idea what it's supposed to look like except that it's not a Planck spectrum.
Looking forward seeing your spectrum, thanks for picking up the suggestion.
HB
Here is the spectrum. R~130. Mag 14.6 is relatively bright for the ALPY 200 so the SNR is a little disappointing. (Rather windy so the guiding was not great.) I have also overlaid a spectrum from 1996 from NED.
https://ned.ipac.caltech.edu/results?source=NEDspectra_output_32_page1_details.html#8C_1803+784_4
(There is a more complete one there but it is in rest wavelength and the flux is in Jankys so would need converting to compare)
Nothing really stands out above the noise. Just a flat continuum sloping up from red to blue
Cheers
Robin
Thanks for sharing, So I guess you might have a chance to also get a spectrum in quiescence, and maybe one sees a difference, I guess I'll try to avaoid the overlap of spectra next time with my SA 100.
CS
HB
Good tips are to rotate the Star Analyser so the spectrum is horizontal in the camera field as rotation to process it introduces artifacts and study the field beforehand in DSS for example looking for stars which might lie along the line of the spectrum. You can then if necessary rotate the camera plus grating slightly to avoid them. (I have in the past used a calibrated rotating coupling to help with this)
http://www.threehillsobservatory.co.uk/astro/spectra_42.htm
Cheers
Robin
Thanks for the tips. I guess I'll be looking for a solution that lets me rotate the camera in a reproducible way and that is flat enough to work with the limited backfocus of my telescope. Maybe something as simple as a way to rotate the clamped filter-wheel-side adapter back into a fixed position where the photometry flat fields were taken in, so I don't "break" each time after experimenting with the Star Analyzer (which sits in the filter wheel).
Hmm..
Thanks again
HB
A spectrum the following night at Vmag 15.0. The same resolution ( R~130) but with better S/N. Still not very exciting though
Both spectra in the BAA spectroscopy database
Cheers
Robin
Interesting.
Do you think the "flattening of the curve" :-) towards the UV end is real?
At one point I made a U filter attempt on photemetry but couln't find any comparision stars.
Cheers
HB
I wondered about this too. I can't see any obvious problems with the reduction. For example the instrument/atmospheric correction based on the reference star data is consistent between the two dates but down at this brightness the continuum shape tends to be rather "approximate" as the accurate subtraction of sky background in this region of the spectrum is getting increasingly difficult for me due to increasing light pollution from blue LED lighting so it is probably prudent not to claim too much about the continuum shape in this case beyond than it slopes up towards the blue.
Cheers
Robin
OK so when I reduce my only two U filter runs against B zeropoints , I will not get correct magnitudes but the drop in U band between the two dates should be correct, and when I compare that to the drop in V magnitude, I see with a lot of hand waving that indeed the U band seems to drop faster than the V band (0.75 vs 0.55 ) between JD 2458959.5 and 2458965.5 . So based on this I have no reason to doubt that the continuum difference you saw could be real.
And even if the spectrum itself is featureless, I think it's a cool thing to do spectroscopy on a source that is several Gpc away
Cheers
HB
Yes it is fun to see how deep you can go. My deepest spectrum is the relatively bright gravitationally lensed APM 8279+5255 at Z=3.9. Straightforward here with the ALPY 200
and also reachable with the Star Analyser
http://www.threehillsobservatory.co.uk/astro/spectra_22.htm
but I think the deepest amateur spectra I have seen have been by Etienne Bertrand. PSS J1458+6813 at z=4.3 for example
http://www.spectro-aras.com/forum/viewtopic.php?f=6&t=1752
Cheers
Robin
So S5 1803+78 dimmed after the flare in Mid April, but never quite reached its usual minimum, instead it made a "V shape recovery" and rebrightened steadily .... last night it was just a few 0.1 mag below its maximum during the latest flare event. No gamma ray flare has been reported on ATEL yet, I'm not sure whether that's because there was none, or the source hasn't just yet been revisted or maybe it's not important enough to report? Anyway, another chance to try low-res spectroscopy perhaps.
CS
HB
This source just doesn't want to go back to pre-April 2020 state :-).
Right now, it's close to 14.1...14.2 mag again, that is where it peaked in April.
CS
HBE