Visualizing Multiwavelength Properties of Classified X-ray Sources from Chandra Source Catalog

We present a simple but informative online tool to visualize the multiwavelength properties of about 2,700 X-ray sources from Chandra Source Catalog version 2.0 with literature verified classifications. Here we describe the catalogs that we used to collect the classifications and extract the MW properties of these sources, and the properties themselves. We also describe the design and functionality of the tool.

as globular clusters and the Galactic center as well as sources strongly affected by complex extended emission around them (e.g., bright pulsar wind nebulae). Sources from populous classes (AGN, HM-STAR, LM-STAR and YSO) were omitted if their X-ray PUs were > 1 . There are several cases of X-ray detected sources from underpopulated classes that are offset by more than 1 from their catalog positions, likely due to poor absolute astrometry. For these sources, we confirmed the classifications/matches by reviewing the literature and inspecting the X-ray and MW images. Finally, we removed unreliable X-ray sources if they had NaNs and/or zero fluxes in multiple X-ray bands or if they had true sat src flag and/or streak src flag in CSC 2.0.
The X-ray sources were then cross-matched, using X-ray error circles, to the optical Gaia eDR3 catalog (Gaia Collaboration et al. 2020), the near-infrared Two Micron All Sky Survey (2MASS; Skrutskie et al. 2006), the CatWISE2020 catalog (Marocco et al. 2021), the unWISE catalog (Schlafly et al. 2019), and the AllWISE catalog (Cutri et al. 2021) in the infrared. For X-ray sources having more than one MW counterpart located within the cross-matching radius, we took the nearest counterpart to the X-ray source as its MW counterpart. We removed unreliable sources such as YSOs or STARs with no matched MW counterparts. We also removed MW counterparts matched with isolated NSs by chance coincidence because virtually all of them are too faint to be detected in those surveys. As a result, we are left with 2,687 X-ray sources. The number of sources for each source class is given at the top of Figure 1.
The visualization tool allows for plotting of various permutations of two of the following features: • master-level X-ray properties 5 from CSC 2.0 including the energy fluxes in the broad (F b ; 0.5-7 keV), hard (F h ; 2-7 keV), medium (F m ; 1.2-2 keV), and soft (F s ; 0.5-1.2 keV) bands, intra-observation Kuiper's test variability probability (P intra) 6 , inter-observation variability probability (P inter), and X-ray flux significance (Signif.); • three X-ray hardness ratios derived from the energy fluxes using HR ms = • G, G BP (BP) and G RP (RP) magnitudes from the Gaia eDR3; • J, H, and K magnitudes from the 2MASS; • W 1 and W 2 magnitudes from the CatWISE2020 and the unWISE and W 3 magnitude from the AllWISE; • a selection of colors (e.g., G − J) using various MW magnitudes; • X-ray to optical flux ratio, F X /F o , with F X = F b and F o based on Gaia's G band magnitude.

THE VISUALIZATION TOOL GUI
The tool, publicly available on a dedicated webpage, https://home.gwu.edu/ ∼ kargaltsev/XCLASS/, allows for easy interactive plotting of MW properties of the sources for a user-selected subset of source classes. The Graphical User Interface (GUI) is written in Java while plotting is done on-the-fly using the Bokeh Python library 7 . As shown in Figure 1, the user can choose from multiple MW features by clicking the corresponding buttons to the left of the Y-axis and below the X-axis. At the top there are buttons corresponding to the distinct astrophysical classes with the numbers of sources within each class. Users can choose to display different combinations of the classes by toggling/untoggling the class names. Whenever appropriate, a logarithmic scale is used in the plot (which is reflected in the axis labels). The user can select a source by clicking on it and some information about the source will be shown. A lasso tool can be used to select a group of sources which then remain selected for any combination of features plotted. The plot can be easily saved as a PNG file by clicking the corresponding button to the right of the plot.
An example, with HR ms hardness ratio plotted versus X-ray to optical flux ratio, is shown in the upper panel of Figure 1. One can see a clear separation between AGN and HM-STAR/LM-STAR/YSO while other types of sources are overlapping, requiring an investigation of different sets of features to distinguish between them. Another example, in the lower panel if Figure 1, shows the BP -H color against G-W 2 color for AGN in red and HM-STAR in green. A subset of HM-STAR with bluer colors compared to other HM-STAR and AGN is selected by the lasso tool marked by highlighted cyan circles and shaded region will remain highlighted after changing to other combination of features plotted.

SUMMARY
We provide an online tool, based on previously published X-ray source classifications and data from CSC 2.0 and multiple all-sky surveys, to visualize MW properties of X-ray sources with known classes. We ask anyone who will be using this tool in their work to cite this publication. Support for this work was provided by NASA through CXO Awards AR8-19009B, AR9-20005A, AR0-21007X, and NASA ADAP award 80NSSC19K0576. JH acknowledges support from an appointment to the NASA Postdoctoral Program at the Goddard Space Flight Center, administered by the USRA through a contract with NASA.