The purpose of our broadband monitoring campaign is to measure a detailed radio-through-soft-gamma-ray spectral energy distribution of the quasar 3C279 in its optical high state and to probe its short-term spectral variability with as dense a temporal sampling as possible. In particular, we aim for a probe of simultaneous intraday spectral variability measurements at optical and X-ray frequencies.
We suggest that optical observers perform observations alternately in two bands (Johnson's B and Cousins' R, if possible, other R filters are also accepted) in order to obtain a B, R, B, R ... series of frames during all the available time in each observing night. This allows us to get two simultaneous light curves in the two bands for color variability studies. Exposure times should be chosen in view of a good compromise between high precision (instrumental errors less than 0.03 mag for small telescopes and less than 0.01 for large ones) and high temporal density. When high precision implies gaps of 15-20 minutes in each light curve, we suggest to carry out observations in the R band only. As a matter of fact, the intensive B monitoring should be appropriate only with telescopes larger than, say, 60 cm. At the beginning and end of the B-R (or R-only) sequence, a complete set of filters U-B-V-R-I (Johnson-Cousins when possible) would be very useful to follow the optical spectrum behaviour of the source. We are providing a finding chart of the field of 3C279, including the U, B, V, R, I, J, H, and K magnitudes of several comparison stars. When reporting data, please refer consistently to the numbering scheme on this finding chart. If possible, at least reference stars 2, 4, 9, and 10 should be included in each frame. Star 2 is the brightest one, so that we must be careful that its counts are inside the linear response of the detector, especially under good seeing conditions.
Data will be collected as instrumental mags of the source and reference stars, in order to apply the same analysis and calibration procedures to all datasets. The suggested data format for instrumental magnitudes is:
| JD-2453000 | 3C279 |
2 |
7 |
9 |
10 |
|---|---|---|---|---|---|
| 740.598820 |
18.131 0.004 | 17.492 0.003 | 18.389 0.004 | 16.798 0.002 | 17.742 0.003 |
where JD must be geocentric at mid exposure (if different, specify it and provide exposure times). Times are requested with second precision (e.g. JD - 2453000 = 740.50001 with five decimal digits); mags and errors should have three decimal digits.
Observers are requested to perform bias/dark correction and flat-fielding on their frames, and to obtain the instrumental mags with some procedure. Both aperture photometry (possibly using IRAF or CCDPHOT) or Gaussian fitting are allowed. In the case of aperture photometry, we suggest that all observers use the same parameters, i.e. 12, 15, and 20 arcsec for the radii of the aperture and of the edges of the background annulus. However, the aperture and annulus radii can be seeing-dependent in order to include the "entire" flux from the object and to avoid the inclusion of other objects.
Observers having access to infrared and radio telescope facilities, are invited to contribute infrared and radio observations. J, H, and K magnitudes of comparison stars are included in the table below the provided finding chart.
For more information and suggestions, please contact Markus Böttcher
All observers interested in participating in the campaign are invited to send a message to the Campaign Manager, Markus Böttcher, and the WEBT President, Massimo Villata, providing information on their instrumentation (telescope, detector, filters) and possible observing periods.
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