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J/ApJ/411/614    Monitoring of PKS 2155-304 I. The IUE Campaign  (Urry+, 1993)
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Multiwavelength Monitoring of the BL Lac Object PKS 2155-304 I. The IUE Campaign
      Urry C.M., Maraschi L., Edelson R., Koratkar A., Krolik J.,
      Madejski G., Pian E., Pike G., Reichert G., Treves A., 
      Wamsteker W., Bohlin R., Bregman J., Brinkmann W., Chiappetti L., 
      Courvoisier T., Filippenko A.V., Fink H., George I.M., Kondo Y., 
      Martin P.G., Miller H.R., O'Brien P., Shull J.M., Sitko M., 
      Szymkowiak A.E., Tagliaferri G., Wagner S., Warwick R.
      <Astrophys. J. 411, 614, (1993)>
      =1993ApJ...411..614U
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ADC_Keywords: BL Lac objects; Spectra, ultraviolet

Abstract:
   Daily monitoring of PKS 2155-304 with the IUE satellite throughout 
   November 1991 revealed dramatic large-amplitude rapid variations in 
   the UV flux of this BL Lac object. Many smaller, rapid flares are 
   superposed on a general doubling of the intensity. During the five-day 
   period when sampling was roughly continuous, the rapid flaring had an 
   apparent quasi-periodic nature, with peaks repeating every 0.7 day. The 
   short- and long-wavelength UV light curves are well correlated with each 
   other, and with the optical light curve deduced from the Fine Error Sensor
   on IUE. The formal lag is zero, but the cross-correlation is asymmetric in 
   the sense that the shorter wavelengthemission leads the longer. The UV 
   spectral shape varies a small but significant amount. The correlation 
   between spectral shape and intensity is complex. The sign of the 
   correlation is consistent with the nonthermal acceleration processes 
   expected in relativistic plasmas, so that the present results are 
   consistent with relativistic jet models, which can also account for 
   quasi-periodic flaring. 

File Summary:
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 FileName        Lrecl  Records     Explanations
------------------------------------------------------------------------------
ReadMe              80        .     This file
table1.dat          26      201     Log of IUE observations
table2.dat          50      201     Power-law fits to IUE spectra
table3.dat          55      105     Power-law fits to merged IUE spectra
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Byte-by-byte Description of the file: table1.dat
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Bytes   Format   Units   Label    Explanations
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 1-8    A8       ---     num      IUE image number
10-15   F6.3     d       time     Start time (day of November 91) in UT
17-18   I2       min     exp      Exposure time
20-24   F5.2     mag     Vmag     ?V Magnitude (from FES counts)
26-26   A1       ---     obsrvtry IUE Observatory (G=Goddard or V=Vilspa)
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Byte-by-byte Description of the file: table2.dat
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Bytes  Format    Units       Label   Explanation
--------------------------------------------------------------------------------
 1-8   A8        ---         num    *IUE image number
10-17  F8.5      d           time    Observation midpoint (day of November 91) U
19-25  F7.4   10+15mW/m2/nm  flux   *Flux at 1400/2800 angstrom
27-32  F6.4   10+15mW/m2/nm  e_flux  Error on flux
34-38  F5.3      ---         alpha   Spectral index
40-44  F5.3      ---         e_alpha Error on spectral index
46-50  F5.3      ---         chisq   Chi squared of spectral fit
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Note on num:
       SWP images first, then LWP
Note on flux:
       flux at 1400 A for SWP and at 2800 A for LWP

Byte-by-byte Description of the file:  table3.dat
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Bytes Format   Units         Label      Explanation
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 1-5   I5        ---         SWP_num    Image numbers SWP
 7-11  I5        ---         LWP_num    Image numbers LWP
13-20  F8.5      d           time       Observation midpoint (day of November)
22-28  F7.4   10+15mW/m2/nm  flux       Flux at 2000 angstrom
30-35  F6.4   10+15mW/m2/nm  e_flux     Error on flux at 2000 angstrom
37-42  F6.4      ---         alpha      Spectral index
44-49  F6.4      ---         e_alpha    Error on spectral index
51-55  F5.3      ---         chisq      Chi squared of spectral fit
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Acknowledgment:
   This work was supported in part by NASA grant NAG 5-1034. If there
   are comments/corrections/questions, please contact:
                C. Megan Urry           cmu@stsci.edu
                STScI                   Tel.:  410-338-4593
                3700 San Martin Drive   FAX:   410-338-4767
                Baltimore, MD  21218
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(End)       J. Pesce         [STScI]                21-Mar-1995