BL Lac object S5 0716+71 in outburst

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BL Lac object S5 0716+71 in outburst

Postby Robin Leadbeater » Mon Jan 19, 2015 12:04 am

I had a quick look at this object tonight using the Star Analyser SA200. 2 spectra, each ~50x20 sec response corrected using MILES reference star HD43378 , though it might not be too accurate due to background subtraction limitations.
The spectrum is rather flat with no strong features which I understand is characteristic of such objects. It would be interesting if anyone can see any more detail with with a LISA or ALPY

Robin
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s5_0716+71_20150118.png
s5_0716+71_20150118.png (9.11 KiB) Viewed 5528 times
s5_0716+71_46x20sec.jpg
s5_0716+71_46x20sec.jpg (21.62 KiB) Viewed 5528 times
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Re: BL Lac object S5 0716+71 in outburst

Postby David Boyd » Tue Jan 20, 2015 3:45 pm

Here's a spectrum of S5 0716+714 taken with a LISA and 18x5min exposures. I used the same MILES reference star as Robin. I've flux-calibrated the spectrum using B and V mag measurements of the object taken at the same time which gave V=12.54 and (B-V)=0.47.

As seems to be normal for this kind of object where we are looking at a relativistic jet pointing towards us, the spectrum has no emission lines. I've looked in the literature but have not so far found a published optical spectrum of this object, although there are analyses of the spectral energy distribution based on multi-waveband photometry. If anyone knows of a published optical spectrum, I'd be interested in the reference.

David
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_s50716_20150119_791_D.Boyd_flux.png
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Re: BL Lac object S5 0716+71 in outburst

Postby Francois Teyssier » Thu Jan 22, 2015 4:23 pm

Nice spectra ! Congratulations.
Unfortunatly, the spectrum is very flat

I found this spectrum in a publication (but forgot to note the reference, I'll have to serach again ...)
0716+714.PNG
0716+714.PNG (16.05 KiB) Viewed 5256 times


David, I think you have to check your flux calibration.

All the best,

François
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Re: BL Lac object S5 0716+71 in outburst

Postby David Boyd » Mon Jan 26, 2015 7:39 pm

Francois,

I've just used Robin's Spitzer website to check the flux calibration. Given a Johnson V magnitude of 12.54 which I measured at the same time, the website gives a corresponding flux density of 3.6e-14 erg/cm2/s/A which agrees with my calibration in the V-band.

There are no units mentioned on the spectrum you found. Assuming it is also erg/cm2/s/A, this would correspond to a V mag of ~11.2 which is brighter than it has been seen in the last 10 years. So I don't know what to make of that plot. It would be interesting to read the paper.

David
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Re: BL Lac object S5 0716+71 in outburst

Postby Francois Teyssier » Tue Jan 27, 2015 4:40 pm

I think you're right David
The problem is in the flux calibration of the published spectrum
I have to find again the Publication

François
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Re: BL Lac object S5 0716+71 in outburst

Postby Joan Guarro Flo » Wed Jan 28, 2015 3:28 pm

Hello all:

Leave a graph of the last night of the S5 0716 + 71, the signal is full of noise.

We'll try again .......

J.Guarro.
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_s50716+71_20150127_921_J. Guarro.png
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Re: BL Lac object S5 0716+71 in outburst

Postby Robin Leadbeater » Wed Jan 28, 2015 6:50 pm

I have now calibrated my spectrum in absolute flux using Christian's 2 spectrum method here (part 1 method 2)

http://www.astrosurf.com/buil/calibrati ... ion_en.htm

The Star Analyser has an advantage over a slit spectrograph in this instance as there is no risk of lost of light at the slit.

I believe this may be the first time this has been attempted using the Star Analyser. The result looks encouraging with a V magnitude of 12.3, (estimated from the flux in the spectrum at 5500A) which is consistent with measurements in the AAVSO database around this date. The flux levels in David's flux calibrated spectrum are approximately 20% lower but there was 1 day between the observations and the brightness was varying rapidly.

Note that conditions were not photometric at the time so there is potential for error in the relative flux between target and reference spectra measured some tens of minutes apart and no correction has been made for the difference in air mass between target and reference.

Robin
Attachments
s5_0716_71_20150118_810-824.png
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Re: BL Lac object S5 0716+71 in outburst

Postby Peter Somogyi » Mon Feb 02, 2015 10:35 pm

I also tried it but clouds came (2 x 30 min succeeded only), dependent on cosmic rays removal:

_S50716+71_20150131_956_psomogyi.png
_S50716+71_20150131_956_psomogyi.png (6.89 KiB) Viewed 4993 times


At least the SNR can be read visually.
AAVSO tells it was around 13 mag.
Ref.star: HD 53609
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