Galactic eROSITA Sources

The targets were taken from the optical and/or infrared counterparts identified by the eROSITA Stars group from the catalog known internally as EROSITASupersetStars. This catalog was created using the techniques described in Freund et al (2022).

The eROSITA compact objects group produced the catalog known internally as EROSITASupersetCompactobjects. Briefly, the catalog was constructed by taking all sources from eROSITA that meet the criteria below, where the following lists relevant definitions:

• p: Gaia DR2 parallax (mas)
• p_err: Gaia DR2 parallax error (mas)
• G: Gaia DR2 mean photometric G magnitude
• varproxy = log₁₀(sqrt(phot_g_n_obs/phot_g_mean_flux_over_error))  where phot_g_n_obs and phot_g_mean_flux_over_error are taken from Gaia DR2
• L=-ln(P), where P is the probability that the source is caused by a random background fluctuation
• f_x= total X-ray flux from eROSITA
• f_opt: flux in the optical, determined by G/2.5 + 4.86
• radec_err: position uncertain in eROSITA position
• pm: the total proper motion (mas/yr)
• pm_err: the total error in proper motion (mas/yr)
• logpmdpm = log₁₀(pm/pm_err)

The selection criteria for counterpart identification are as follows. Bolded conditions below are common to both this carton and to mwm_erosita_compact_var.

• Point source
• G > 16
• L > 8 in at least one of the three eROSITA energy bands.
• Detections in three energy bands
• log(f_x/f_opt) < 2.7
• Matches a Gaia DR2 source within 30 arcsec AND the source has radec_err > 0 AND angdist/radec_err < 2.1
• Neither of the two following conditions are met:
  • (logpmdpm < 0.301) AND (p/p_err > -1.4996 * logpmdpm – 4.05) AND (p/p_err < 1.4995 * logpmdpm + 4.05)
  • (logpmdpm – 0.301)²/0.39794² + (p/p_err)²/4.5² ≤ 1
• Closest object with the above criteria

Because there is often more than one possible compact object counterpart in Gaia, two distinct cartons were generated. This carton uses the bolded conditions in mwm_erosita_compact_gen but additionally calculates a variability index (varproxy, defined below) and selects the counterpart with the largest variability.

• varproxy = log10(sqrt(phot_g_n_obs/phot_g_mean_flux_over_error)) 

This is the v1 update to mwm_erosita_stars. Select from erosita_superset_v1_stars database table keeping targets if they have xmatch_metric > 0.0 and G > 13.0.

This is a v1 carton that selects aCWDB candidates (accreting Compact White-Dwarf Binaries) from a parent table generated by the crossmatch of the eROSITA/eRASS:3 X-ray point-source hemisphere catalogue with the Gaia DR3 catalogue. In V0.5 two cartons were defined mwm_erosita_compact_gen & mwm_erosita_compact_var

The same carton at mwm_erosita_compact_boss, but the deepest cadence is now dark_flexible_3x1.

This is a v1 carton that selects aCWDB candidates (accreting Compact White-Dwarf Binaries) from a parent table generated by the crossmatch of the eROSITA/eRASS:3 X-ray point-source hemisphere catalogue with the Gaia DR3 catalogue. In V0.5 two cartons were defined mwm_erosita_compact_gen & mwm_erosita_compact_var. Similar to mwm_erosita_compact_boss, but with a different cadence. Note that priority value increased by one in targeting generations v1.0.5,v1.0.5-boss-only.