An adaptive-binning method for generating constant-uncertainty/constant-significance light curves with Fermi-LAT data

B. Lott^1,2, L. Escande^1,2, S. Larsson^3,4,5 and J. Ballet⁶

¹ Univ. Bordeaux, CENBG, UMR 5797, 33170 Gradignan, France
e-mail: lott@cenbg.in2p3.fr
² CNRS, IN2P3, CENBG, UMR 5797, 33170 Gradignan, France
³ Department of Physics, Stockholm University, AlbaNova, 106 91 Stockholm, Sweden
⁴ The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova, 106 91 Stockholm, Sweden
⁵ Department of Astronomy, Stockholm University, 106 91 Stockholm, Sweden
⁶ Laboratoire AIM, CEA-IRFU/CNRS/Université Paris Diderot, Service d’Astrophysique, CEA Saclay, 91191 Gif-sur-Yvette, France

Received: 23 January 2012
Accepted: 18 June 2012

Abstract

Aims. We present a method enabling the creation of constant-uncertainty/constant-significance light curves with the data of the Fermi-Large Area Telescope (LAT). The adaptive-binning method enables more information to be encapsulated within the light curve than with the fixed-binning method. Although primarily developed for blazar studies, it can be applied to any sources.

Methods. This method allows the starting and ending times of each interval to be calculated in a simple and quick way during a first step. The reported mean flux and spectral index (assuming the spectrum is a power-law distribution) in the interval are calculated via the standard LAT analysis during a second step.

Results. The absence of major caveats associated with this method has been established by means of Monte-Carlo simulations. We present the performance of this method in determining duty cycles as well as power-density spectra relative to the traditional fixed-binning method.