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Observations of Blazar S5 1803+78 critically needed

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daveh
daveh's picture
Observations of Blazar S5 1803+78 critically needed

Blazar S5 1803+78 is rapidly brightnening. Observers in Spain and Germany have contributed recent observations, but the weather in Europe has been overcast and probably will be until at least this weekend. Observations outside of these areas are encouraged until the weather clears. The next several days may be critical as the blazar seems to be reaching a peak magnitude. Please make observations if possible and upload to light curve for S5 1803+78.

Thanks.

Dave (HDHA)

Bikeman
Bikeman's picture
I'm on it now

Against expectations, the sky cleared up and I'm currently taking frames .. I'm right at the edge of a cloud system ... not sure how long this will last, but the target is still bright so I a meaningful measurement is almost certainly possible already.

Cheers

HB

 

Bikeman
Bikeman's picture
ATEL on Fermi-LAT data

More news on recent gamma ray emission from this source:

http://www.astronomerstelegram.org/?read=13633

CS

HB

CTX
CTX's picture
S5 1803+78

S5 1803+78 Has an Updated & Expanded Sequence, just finished.

Ad Astra & Good Observing,

Tim Crawford, Sequence Team

daveh
daveh's picture
Thanks Tim,

Thanks Tim,

This is good...things are moving very quickly.

Dave

Ccolvin968
Ccolvin968's picture
I'll try to get some tonight.

I'll try to get some tonight.

Will only be Tricolor bands, but it's what I can do. 

Bikeman
Bikeman's picture
It could already be fading

It could already be fading again, last nights measurements were a bit fainter than previously.

Cheers

HB

Bikeman
Bikeman's picture
I'm quite confident I can

I'm quite confident I can take a measurement tonite

Good observing

HB

dam
Confirmation of the discovery

To be honest, Gianpiero Locatelli from Italy was the first to confirm the Blazar explosion.
The next day Jordi Berenguer was from Spain, he confirmed it even more.

I also appreciate the observations of Heinz-Bernd Eggenstein from Germany who also provided this confirmation of the Blazar S5 1803+78 explosion.

I sincerely thank all three for their confirmation and possible monitoring. It is really interesting to watch.

I thank Dave Hinzel for putting this thread in and getting us together so we can get ahead of NASA 4 days before his confirmation on his Atel.

All of this was triggered by a simple observation from David Lane a few days earlier. It had to be confirmed.

Thank you
Adolfo Darriba

Bikeman
Bikeman's picture
Observing now

okish conditions.

Still at around 14.5 mag (V)

CS

HB

Bikeman
Bikeman's picture
Next two nights

It looks like the next two nights will be cloudy for me here, I hope all the others here have better forecasts. We had a wonderful coverage so far

 

HB

Bikeman
Bikeman's picture
Again cloudy

It's again cloudy in Germany. S5 1803+78 seems to be close to it's upper end of quiesence variability now, so a few more days and we'll have concluded the coverage of the flare I guess,

Is anyone else able to observe?

Cheers

HB

daveh
daveh's picture
Again cloudy

I wanted to do some observing but the iTelescope site in Nerpio, Spain has been shut down due to a combination of bad weather and problems of getting people to the site because of the pandemic. So, we might have to sit this one out unless there are observers in other locations that can do observations.

Dave

Bikeman
Bikeman's picture
I took a measurement from

I took a measurement from iTelescope's T11 instrument in New Mexico

Cheers

HB

Bikeman
Bikeman's picture
I made another reservation

I made another reservation for Saturday night/Sunday morning on T21, forecast looks good so far. So if someone else wants to throw in an iTelescope measurement, perhaps take another day to get the best coverage  for the buck.

Cheers

HB

 

Bikeman
Bikeman's picture
ATEL

Here is another ATEL on "our" blazar:

http://www.astronomerstelegram.org/?read=13711

The reoported data points are , IMHO, not as impressive as the light curve that was collected here, so I wonder if this group here should do its own ATELs in the future for similar events. I notified one of the ATEL's authors about the obsevartions collected here, but got no response so far.  

CS

HB

 

Bikeman
Bikeman's picture
I now got a response, the

I now got a response, the team that published the ATEL are now aware of our observations and will contact us if our data poinrts are used in their research. I forwarded a link to this forum discussion to them.

CS

HB

daveh
daveh's picture
Are ATEL and AAVSO normally

Are ATEL and AAVSO normally in communications or is this a one time event? If there is good communications we should use them as much as possible, but if not then an AAVSO "internal ATEL" is a good idea since we published before they did. What do you think?

Bikeman
Bikeman's picture
I think it's not uncommon

I think it's not uncommon that AAVSO amateur observers publish ATELs , e.g. Josch Hambsch  and Tonny Vanmunster  for CVs. I guess the threshold is "would other astronomers find it useful", as when responding to urgent observation requests in other ATELs or when observing something rare or unexpected. Here, the current flare seems to be pretty record-setting, even more than reported in ATEL 13711 because they observed one week after we observed the peak, so if their observations were "good" for an ATEL, I guess our's are even more so :-)

Just my 2 cents.

 

Bikeman
Bikeman's picture
14.44 (V)

Hi!

I've just finished measuring some image form iTel11 in New Mexico *last night* and it was back at 14.44 mag (V) . This night I'm trying to continue observing it from Germany but conditions are not optimal.

For comparison, the brightest V value in the light curve for the recent flare was close to 14.1 , the object made a "V shape recovery" :-) 

CS

HB

 

Bikeman
Bikeman's picture
This source is amazing!

This source is amazing!

It flared up fast to 14.1 ish, dropped quite fast, then continued to rise up again to 14.4 ish and now lingers at 14.5 +/- 0.2 for more than a week !

Is this something that Blazars of this type usually do?

Cheers

HB

 

CrossoverManiac
CrossoverManiac's picture
S5 1803+78 is overlapping a

S5 1803+78 is overlapping a 17.5 magnitude comp star, at least in my image anyway.

The aperture annulus is at 3 pixels with angular resolution of 2.54" per pixel.  I can't separate the two without going to a higher focal length or smaller pixels.  My question is should I just scrap my data? 

Bikeman
Bikeman's picture
FITS image?

Hi

I have a really hard time recognizing the field from your image, The image seems to be blurred or have JPEG artifacts in it, perhaps?

Are you really sure this is infact S5 1803+78? I take images which are a bit oversampled at 0.5" / pixel, so I resampled one of my images to 20% the resolution to simulate a 2.5"/pix resolution, and I get something like the attached image. It should still be possible to avoid overlap with the nearest star that is bright enough to affect the photometry, especially the 17.5 star on AAVSO finder charts (the one I placed in the inner annulus in my simulated image). 

If you like you could upload the FITS image and have us look at it. I really think there is something going wrong here.

CS

HB

CrossoverManiac
CrossoverManiac's picture
I sent the stacked FIT files.

I sent the stacked FIT files.  If you need the unstacked version, let me know.

Bikeman
Bikeman's picture
THX

Ahhh ok, I see. The screenshot was from VPHOT with a single frame, and I got distracted by some bad pixels and mistook them for stars, Sorry for my ignorance,

 

Anyway, this is interesting!

The position that VPHOT tells you is comp star 175 is actually significantly wrong! I guess VPHOT just calculates where the star should be according to the plate solving, and then looks for the nearest centroid, allowing some very generous deviation from the calculated position, and ends up snapping the centroid to our target star (see the end of the post for a fix).

What is worse is that the "Measurement details " that VPHOT optionally displays for each comp star is misleading and wrong:

You get this (I did that for the stacked V image you sent me )

==================

General information:

175

Instr.Mag,:
-2.792

SNR:
51

Error (SNR):
0.021

Airmass:
1.268

FWHM:
2.03

Centroid X:
358.37

Centroid Y:
292.61

RA Catalogue:
270.18780

Decl. Catalogue:
78.46889

RA Estimate:
18:00:45.07117

RA Estimate:
270.18780

Decl. Estimate:
78:28:07.98895

Decl. Estimate:
78.46889

===================

Huh??? Catalog location and estimated position are a perfect match in RA and Decl?? That's suspicious and actually wrong, because if you look it up in the finder chart table, the actual coordinates for 175 are :

000-BNL-903
18:00:41.65 [270.17355347°]
78:28:17.2 [78.47144318°]
175

So...that 175 star really isn't nearly as close to the target star as VPHOT makes you believe, and is indeed easily avoided by chosing the aperture wisely (e.g. radii 4-8-4 in the aperture settings) . That 175 comp star is just too faint to be detectable even in the  stacked V frame (it's kind of visible in the stacked I frame, tho), so VPHOT just tries a bit too hard to identify it in your images and misidentifies it in the process.

How to fix this? Fortunately VPHOT allows you to configure the way it tries to identify stars on the frame ==> Tools ==> Settings > Centroid Determination,

When I went there, "it displayed Search-radius in Pixels" : 5  and "Initial FWHM (pixels)" : 5

Because your plate scale of 2.54" / pixel is a bit on the coarse end, 5 pixels is a bit too generous. If you try setting both to 3, then when you load the comp stars from the AAVSO, VPHOT will no longer even give you the 175 star because it fails to identify it on your frame with sufficient SNR, and this is the right thing to do. Because the limits for trying to identify the star near it's computed position are now less generous, VPHOT will no longer mistake the target star for star 175.

So mystery and (perceived) problem solved I guess, You can do photometry and submit it all right, just don't include the 175 star or configure VPHOT in the described way so VPHOT won't misidentify it.

The whole thing is captured in the attached screenshot. It shows the stacked I-filter frame you sent me.

I put a crosshair to the right of the 175 star to highlight it, I made the aperture avoid that star, and in the right top corner you see the config dialog that lets you pick the parameters for identifying stars in VPHOT.

Hope this helps,

HBE

 

File upload: 
daveh
daveh's picture
I believe the AAVSO criteria

I believe the AAVSO criteria for good data is as follows:

Star SNR >= 10 (which your measurement is).

Magnitude estimate error <0.05 good; <= 0.015 excellent; 0.05 to 0.100 still worth reporting to AAVSO; >0.100 probably shouldn't report.

Hope this helps.

Dave

Bikeman
Bikeman's picture
More than two month after

More than two month after what must have been one of the brightest recorded flares of S5 1803+78, it still refuses to go back to its optical pre-flare state (at around 16.5 mag (V) ).

The weather is horrible in Germany now (I should not complain tho, the rain is much needed after a record braking dry spring). Even some iTelescope New Mexico observation was cancelled because of high winds :-( . I hope others have more luck, I'm sure the data will be useful .

CS

HB

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