Swift-XRT Monitoring of Fermi-LAT Sources of Interest


The monitoring data shown on this site provides near real-time results from Swift observations of Fermi-LAT "sources of interest" and flaring sources. While this list is dominated by blazars, some X-ray binaries and Galactic transients are also included. The preliminary results on this page are intended to provide rapid feedback to the scientific community to aid in target of opportunity planning, multiwavelength campaigns, and planning of interesting scientific publications.

Data on this site is available to the public (thanks to support from the Fermi GI program and the Swift Team). If you make use of any of these data, we ask that you reference M.C. Stroh & A.D. Falcone 2013, ApJS, 207, 28; arXiv: 1305.4949 and that you notify Abe Falcone and Michael Stroh at monitoring@swift.psu.edu.


The results presented on this page are from a preliminary analysis of the Swift-XRT data. The analysis procedure is described in this README file. Since the analysis is performed using automated scripts and the results are not always reviewed by human eyes, we recommend that these data be reviewed by hand before use in publications.

For questions or requests for more detailed analysis, please contact Abe Falcone and Michael Stroh at monitoring@swift.psu.edu. This web site is under construction so please report any web site related problems to the email address listed above.

ChangeLog - Last Updated: 2017-04-01

Upcoming Observations


Data Analysis

The Swift-XRT data were processed using the most recent versions of the standard Swift tools: Swift Software version 3.9, FTOOLS version 6.12 and XSPEC version 12.7.1. Light curves are generated using xrtgrblc version 1.6.

Circular and annular regions are used to describe the source and background areas respectively and the radii of both depend on the current count rate. In order to handle both piled-up observations and cases where the sources land on bad columns, psf correction is handled using xrtlccorr. The hardness ratio is defined as R_2/R_1, where R_2 is the rate in the 2-10 keV band and R_1 is the rate in the 0.3-2 keV band.

The overall light curves use a bin size of one observation per bin and contain all Swift-XRT observations in Photon Counting (PC) and Windowed Timing (WT) modes from November 20th, 2004 to present. Single observation light curves use a step binning procedure so that if the count rate is less than 0.4, 1, 10, 100 and 10000 cts/s, then 20 cts/bin, 50 cts/bin, 200 cts/bin, 1000 cts/bin and 2000 cts/bin are used respectively. In cases where the single observation light curves result in an upper limit but the overall light curve method results in a non-upper limit for the same observation, the single observation light curve will use the overall light curve bin. Finely binned overall light curves contain all of the bins from the single observation light curves. Mode switching in the light curves is filtered out by rejecting Windowed Timing bins with less than 15 raw counts in the source region. WT hardness ratio bins are rejected if they do not temporally overlap at least one WT bin in the light curve.

3-sigma upper limits are used for light curves and hardness ratios, and all error bars are reported at the 1-sigma level.

Full details of our procedure can be found in M.C. Stroh & A.D. Falcone, ApJS, 207, 28; arXiv: 1305.4949.

Photon Counting Images

Images are created by summing up all of the available PC data that successfully made it through xrtpipeline. The red and green circles represent the largest source and backround region sizes respectively that were used in creating light curves using the PC data. Sometimes an annulus is used instead of a circle to describe the source region; however, we do not plot the inner radius since it would most likely be difficult to see.

External Links

We have included links to additional programs that monitor some of these sources. When available, we link to:


If you would like your project or page available to be linked to from our source pages, please email us!


Penn State University Goddard Space Flight Center Swift