A 3-day Continuous Monitoring Campaign of 0716+714

 

from February 23.5 to 26.5, 2009 (UT)

 

 

Background

 

0716+714 is a BL Lac which shows violent activity in optical range. It is well known for showing microvariability (<0.1 Mag) with time scales as low as ~ 18 minutes and we have measured a duty cycle as high as 90%. The main objective of this campaign will be to obtain an extended (> 24 hours) micro-variability curve and analyze the time series using our time series analysis programs. Individual micro-variability curves are apparently too short to contain important timescale information, and previous coordinated observations have always had significant gaps so no reliable time series analysis could be done. The light curve observed by the WEBT consortium in March of 2000 (Villata et al. 2000) and also the light curve by WEBT (Ostorero et al. 2006) of this object were the closest anyone has come to observing an extended micro-variability light curve, but the significant gaps prevent the types of period finding analysis we would like to do.

We propose to try and observe 0716+71 utilizing the network of observatories around the globe and positioned as many longitudes as possible. If properly organized, and weather cooperates, we would like to obtain an extended micro-variability curve over more than 24 hours in duration. This technique has been explored by Pollock, Webb et al (AJ, 133, 487, 2007) where we used the Dark sky observatory in North Carolina and the SARA observatory at Kitt Peak to get an extend light curve of 0716+71 over that which was obtainable by any one instrument.

Time Series Analysis, using unequal interval FT and Wavelets, of the microvariability light curves will provide us with information relevant to the structure of the optical jet which is unresolved. Models for the micro-variations seen in these objects range from plasma instability processes and shock front dimensions to blob collisions. Benford (MNRAS 301, 1998) has also developed a coherent plasma emission model that is applicable to this situation.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


We have been observing micro-variability in this object for several years, collecting 23 high S/N microvariability curves in the process. We note that the major timescales seen in the micro-variations are too long to yield characteristic timescale information during a single nights observing run at a single location. This has compelled us to propose the idea of a multi-observatory, microvariability campaign. A typical microvariability curve obtained from the SARA Observatory 0.9-m telescope for 0716+71 is presented above.

 

Core Campaign Period

 

We propose the observation period of February 23.5 to 26.5 UT as a target to obtain multi-site observations from as many longitudes as possible. This observation date, although not optimal for 0716 transit, has the illumination percentage of the moon around 0% and acceptable HA for most northern sites.

 

Observing plan

 

The plan is to track the object continuously during observation period covering all the possible longitudes around the globe. Although we would like most of the observations in R filter, observations in the V and I filter are also useful. Especially if two sites at the same longitude could observe in different frequency bands in order to get color information as well. We request the observers perform bias/dark correction and flat-fielding on their frames and aperture photometry if possible, sending us the reduced magnitudes. EXCEL spread sheets are a convenient way to transmit the large amounts of data if available, otherwise text files with the appropriate data columns are fine. We can also accept images and perform photometry reductions if needed. Photometry should be done using the comparison stars 3, 4 and 5, and star 6 as a check star in addition to the object. The sequence is shown below. Also helpful would be the sky background data for the images for our microvariability analysis.

 

 

 

 

 

Comparison stars

star

B

V

R

I

3

13.04(0.01)

12.43(0.02)

12.06(0.01)

11.79 (0.05)

4

13.66(0.01)

13.19(0.02)

12.89(0.01)

 

5

14.15(0.01)

13.55(0.02)

13.18(0.01)

12.85 (0.05)

6 (Check)

14.24(0.01)

13.63(0.02)

13.26(0.01)

12.97 (0.04)

 

Comparison stars from Villata et al., 1998, A&AS 130, 305
I-data from Ghisellini G. et al., 1997, A&A 327, 61
Field of view is 10'x10'

(This is the same Finder and comp stars as in GASP except for star 2 which we have found could vary at a very low level and in some cases overexposes easily and star 4)

 

 

 

 

 

Observing Details

 

       Filters Johnson-Cousins R (V and I also acceptable)

 

       Exposure time depending on telescope/detector to yield about a precision of 0.002 magnitude (S/N ~ 500) if possible. For the SARA 30-inch with CCD we usually take 30 sec. exposures, however, 60-second or 120 second can be used. The micro-variation amplitudes are on the order of 0.02 magnitudes or more.

 

       Observations should be taken from twilight target acquisition until the target is too low for observing or morning twilight. (recommended airmasses of 2 or less, extreme limit of airmass ~3).

 

       Observations should be taken at as regular an interval as possible, and exposure times as accurate as practical with system. Small gaps due to re-focusing might be necessary and is acceptable.

 

       All observations from multiple sites will be analyzed and joined into one long time series, hopefully covering at least 24 consecutive hours.

 

       Observations from similar longitudes will be compared and combined to obtain as accurate a light curve as possible.

 

       Color changes will be tracked if multicolor observations are done in the same longitude (or overlapping) with different filters.

 

        Aperture photometry The aperture size should be held constant for a particular microvariability data set (one nights data set). To determine the optimum aperture size for the data set, start with the average FWHM of several comparison stars throughout the data set. Choose the initial aperture size as this average FWHM. If the comparison stars show significant scatter when plotted, try aperture sizes greater than and less than the initial value, and then choose the light curve in which the scatter in the comparison stars in minimum.

 

       Credit for observations and all other standards of the WEBT will apply.

 

Contact

All observers interested in participating in the campaign are invited to contact Professor James Webb and Massimo Villata providing information on their instrumentation (telescope, detector and filters) and possible observing periods dates and times.