Explanatory Notes for the Full-Resolution Flux and Polarization Spectra

Gzipped Tar files containing the full-resolution flux and polarization spectra for objects observed during the monitoring program can be downloaded from http://james.as.arizona.edu/~psmith/Fermi/DATA/specdata.html for data obtained after the beginning of Fermi Cycle 2 (2009 August). Spectra obtained in Cycle 1 (2008 Oct--2009 May) can be found using the links to individual objects at http://james.as.arizona.edu/~psmith/Fermi/DATA/individual.html. All files are FITS. All spectra are in the observed frame of reference.

Flux Spectra:

The spectra are identified using the following conventions:
- <object>.spec_<UT date>.fits
- <object>.fc.spec_<UT date>.fits
The UT year-month-day of the observation date is given in the format of yymmdd.
Objects that have had multiple spectra obtained during a single night are denoted by the convention: <object>_1..., <object>_2..., etc., corresponding to the order of the observations.
The spectra span the range of 4000-7550 Å with a dispersion 4 Å/pixel. Depending on the width of the slit used for the observation, the resolution is typically between 16-24 Å.
Slit width, exposure duration, airmass and epoch of the observation can be found in the FITS header. The 'APERTURE' values correspond to the following slit widths: 1 = 2", 2 = 3", 3 = 4.1", 4 = 5.1", 5 = 7.6", 6 = 12.7".
Flux density, F_λ, is given in erg cm^-2 s^-1 Å^-1. Wavelength, λ, is given in Å.
The atmospheric O₂ B-band absorption feature at about 6980 Å has not been removed from the spectra. On particularly humid nights, the H₂O atmospheric absortion feature at about 7200-7300 Å can also be seen.
At wavelengths longer than about 7000 Å, fringing by the thinned CCD of SPOL is apparent in most spectra. As with the atmospheric absorption features, the fringing does not corrupt the polarimetry and so the spectra provided are extended out in the red to where blue light from the 2nd-order spectrum begins to contaminate the first order spectrum. Because properly correcting the fringing of the detector would consume a substantial amount of time at the telescope, we have opted not to make this correction for the flux spectra.
Files containing ".fc." in the filename denote spectra that have been scaled to match the V-band magnitude determined from the differential spectrophotometry on that night. Specifically, the flux density averaged between 5400-5600 Å in the spectrum has been scaled to agree with the flux density determined from the synthetic V-band photometry. The adopted conversion from flux density (in mJy = 10^-26 erg cm^-2 s^-1 Hz^-1) to V apparent magnitude is given by V = 15 - 2.5 log (F_ν/3.64).
Flux density levels for the spectra without ".fc." in the filename should NOT be used as true measurements of an objects's brightness, though the spectral shape is as valid, having been corrected for airmass (using the standard KPNO extinction curve within IRAF) and the instrumental sensitivity.
No corrections to the spectra have been made for Galactic interstellar extinction and reddening.

Polarization Spectra:

The full-resolution Stokes spectra are identified using the following conventions:

<object>.q_<UT date>.fits
<object>.u_<UT date>.fits

The UT year-month-day of the observation date is given in the format of yymmdd.

Objects that have had multiple measurements obtained during a single night are denoted by the convention: <object>_1..., <object>_2..., etc., corresponding to the order of the observations.

These "q" and "u" spectra are the normalized linear polarization Stokes parameters as a function wavelength (in Å).

The Stokes parameters are rotated from the instrumental frame to the usual astronomical reference frame such that the polarization position angle (θ) is given by 0.5 tan^-1 (u/q), where θ = 0º when u = 0 and q > 0 (N); θ = 90º when u = 0 and q < 0 (E); θ = 45º when q = 0 and u > 0; θ = 135º when q = 0 and u < 0.

The percentage linear polarization is given by P = SQRT(q² + u²), modulo a correction needed to account for the non-normal error distribution of P (see e.g., Wardle & Kronberg 1974).

The spectra span the range of 4000-7550 Å with a dispersion 4 Å/pixel. Depending on the width of the slit used for the observation, the resolution is typically between 16-24 Å.

Slit width, exposure duration, airmass and epoch of the observation can be found in the FITS header. The 'APERTURE' values correspond to the following slit widths: 1 = 2", 2 = 3", 3 = 4.1", 4 = 5.1", 5 = 7.6", 6 = 12.7".

No corrections to the spectra have been made for Galactic interstellar polarization.

Please contact Paul Smith (pssmith@arizona.edu) if you have questions concerning these web pages.