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UVOT Data Analysis
UVOT analysis threads
This page is designed to provide a starting point for the analysis of
UVOT images.
UVOT data are taken in 3 modes: Image mode, Event mode and Image&Event
mode. There are 7 broadband filters and 2 grisms, and various window
sizes. The subsequent pages deal with analysis of Image mode data. Event
mode data are treated in a similar way to X-ray data. For analysis of
Event mode data and grism observations you are referred to the UVOT
Software Guide, the UVOT Digest and Paul Kuin's "brief data reduction guide for UVOT grism data" (though see also limits for the grism).
Online help for any
of the UVOT tasks can be found with fhelp taskname or plist taskname.
Here we assume that at least the first batch of data has come down (after the TDRSS data), and we start from the Level 2 products. Steps to convert Level 1 into Level 2 products are not outlined here; for this you are referred to the Swift UVOT Software Guide. Particular care should be taken with the reduction and analysis if the field is crowded, the background is high or your source is very bright or very faint.
New DRESSCode is a python pipeline to reduce Swift UVOT images of extended sources written by Marjorie Decleir of STSci.
- General introduction
- General processing
- Analysis
Calibration information
- An Updated Ultraviolet Calibration for the Swift/UVOT
Breeveld, A.A. et al., 2011, AIPC, 1358, 373 -
Paper II: Further calibration of the Swift ultraviolet/optical telescope
Breeveld, A.A. et al., 2010, MNRAS, 406, 1687 -
Photometric calibration of the Swift ultraviolet/optical telescope
Poole, T.S. et al., 2008, MNRAS, 383, 627 - The use and calibration of read-out streaks to increase the dynamic range of the Swift Ultraviolet/Optical Telescope
Page, M.J. et al., 2013, MNRAS, 436, 1684 - The Swift-UVOT ultraviolet and visible grism calibration
Kuin, N.P.M. et al., 2015, MNRAS, 449, 2514 - Filter Bandpass Information
- Information about the red leak
- UVOT modes
It is known that there are small areas in the UVOT field of view where the throughout is lower than for the rest of the detector; this can lead to count rates of up to 34% lower than in other areas. As of HEASoft 6.30, this checking is done automatically. More details.
In 2020 September, a new UVOT sensitivity calibration file (swusenscorr20041120v006.fits) was released, to account for the loss of sensitivity with time in the UV and white filters. While it is always important to use the most up-to-date calibration files (in this case, the difference can be up to almost 0.3 mag), it is possible to correct the count rates or magnitudes from the previous v005 senscorr file by determining the required shift using these filter correction files: white, uvw2, uvm2 and uvw1. Note that these corrections for the count rates or fluxes (column 4) are multiplicative, while the magnitudes (column 5) are additive. The dates for the corrections are times in years since 2005 January 01. The date of the observation can be found in the DATE-OBS (calendar date) and TSTART (in terms of MET: seconds since 2001 January 01) keywords.
Where to get help
UK Swift Science Data Centre
Last updated 2024 April 6
Web page maintained by Kim Page
E-mail: swift help
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