Background

Mrk 501 is an optically bright TeV blazar. Currently a project to investigate the optical/gamma-ray variabilty, utilizing Whipple and HEGRA in conjunction with WET, is being planned. The objective of this campaign is to search for possible correlated behavior of the variability at optical and gamma-ray wavelengths and to measure the time lag that is expected between the variability detected at these wavelengths.

Mrk 501 is of considerable interest for low-priority WET observations because it provides an opportunity to test the theory that the TeV gamma-ray emission is due to an inverse Compton process, and thus the variability at high energies should lag(or follow) those observed at low energy(optical).

If a significant flare is detected at either optical or TeV wavelengths, we will request a ToO be declared on RXTE in order to obtain X-ray observations which will complement the observations obtained during this campaign.

Please consult the scientific justification for more information.

Observing Instructions

Continuous monitoring throughout the night is desireable since it is likely that the variability will be erratic with an amplitude of the order of 0.1 mag.

RA             Dec          
16 53 52.2    +39 45 36.6   (2000.0)
        mv=13.5

Run start: Please start your run on an integral multiple of ten seconds (times ending in "0"). Check the computer clock just before the start of a run, synchronizing with your master clock to within 0.1 sec if possible.

Integration times: The optimum integration time should be choosen so that one should achieve 10,000 counts above sky. However, the minimum requirement is that one should choose integration times so that one can achieve at least 2500 counts on object above sky.

Filters: Photoelectric photometer: Use B filters for the continuous monitoring with observations in R at the beginning and end of each night's observations, if an R filter is available. The R observations should last for about five data points. CCD: Same as for photoelectric photometer.

Guide Stars: Please consult the finder chart. Markarian 501 has several stars of comparable brightness in the field. Please keep track of exactly which comparison star was observed.

Sky calibration: Observers with 3-channel photometers should record sky in all three channels near the beginning and the end of each run to permit accurate cross calibration. Observers with 2 channel photometers should take sky by moving the telescope. Try to take sky as often as needed, at least once per hour, for 4 or 5 good sky points.

Calibrations for CCDs: Please make sure to collect a sufficient number of bias and dark frames as well as flat fields for every night (whenever possible).

Apertures: Typical photometer apertures should be 10"-12". Record the size of the aperture (in arcsec) in your observing log.

Control Center: The XCOV 21 control center is at Iowa State University's International Institute of Theoretical and Applied Physics (IITAP).

Contacting the Control Center: Consult the Phone Contact List for information on phone, fax, and email for the control center as well as the other sites for this run.

Time Check: Please do a clock time check each night before taking data and verify your time with HQ at the beginning of the run, and as often during the run as possible. HQ will have an accurate clock available for phone clock checks.

Data Transfer: There are two ways to send your data and logs at the end of each night.

1. By FTP to: wet.physics.iastate.edu
   (Note that this has changed from the previous site of wet.physics.iastate.edu!)
   The username for the FTP site and the password is available through email. This information is only available through email because we have had problems with hackers filling the FTP system in the past. This is not an anonymous FTP transfer, so you will need the username and password to upload your data. If you use the FTP option, load your data into the "wet/incoming/xcov21/" directory.
   
   
2. Via e-mail to: wet.physics.iastate.edu
   

Observing Logs: We ask that you send a copy of your observation log along with the data, at the same time if you can.