Exploring Light Echoes

Abstract submitted to PhysCon 2019: Clumps of matter located near luminous astronomical objects can reflect a fraction of the light incident on them. The reflected light travels a longer path compared to a direct light ray, on its way to an observer far away. Therefore there is a delay in the arrival time of the reflected ray. A wide variety of astronomical systems exhibit such delays in their light curves, ranging from broad-line clouds near active galactic nuclei, to X-rays reflected by accretion disks near black holes and neutron stars, to ejected shells by supergiant stars like V838 Monocerotis.

Here we present a python code to study the distribution of light delays created by reflection due a circular disk. We assume a point source of light at the origin and an observer at infinity whose direction cosines are user inputs. The user also provides the disk's radius and the {x,y,z} coordinates of its center. The plane of the disk is parallel to the xy-plane.

We use our code (see link below to download and use) to study time-delay distributions due to different disk geometries as well as different disk/emitter/observer configurations.

Future versions of the code will include added features such as the ability to alter the disk's orientation with respect to the observer, and generating time-delay histograms for an ensemble of disks scattered around the source, e.g to realistically mimic a broad-line region near an active galactic nucleus.

light-echoes.zip (v2019-Nov-14)	A zip file containing the python source code, a ReadMe.txt file describing how to use the codes, a sample input file as well as the output file created by the sample input file.