20.7.1 epoch_photometry

The epoch photometry table contains the light curve for a given object in bands G, BP and RP as stored in the Datalink Massive data base. This table makes extensive use of array types. The column set defined here is obtained by selecting the RAW data structure option. A flat table (sparse cube), with one photometric point per source per row, is obtained by selecting either INDIVIDUAL or COMBINED.
In the flat tables, the 25 boolean flags are combined into a bit mask, other_flags, as detailed in https://www.cosmos.esa.int/web/gaia-users/archive/datalink-products.
Note this table is not available through the main archive TAP interface. Data are delivered via the Massive Data service indexed by the VO Datalink protocol and described in Chapter 18. For example this can be actioned in the archive user interface by querying the main source catalogue gaia_source and selecting has_epoch_photometry = 't'.

Columns description:

solution_id : Solution Identifier (long)

All Gaia data processed by the Data Processing and Analysis Consortium comes tagged with a solution identifier. This is a numeric field attached to each table row that can be used to unequivocally identify the version of all the subsystems that were used in the generation of the data as well as the input data used. It is mainly for internal DPAC use but is included in the published data releases to enable end users to examine the provenance of processed data products. To decode a given solution ID visit https://gaia.esac.esa.int/decoder/solnDecoder.jsp

source_id : Unique source identifier (unique within a particular Data Release) (long)

A unique single numerical identifier of the source obtained from gaia_source (for a detailed description see gaia_source.source_id)

n_transits : Number of Gaia transits (short)

Number of Gaia transits.

transit_id : Transit unique identifier (long[n_transits] array)

The transit_id is a unique identifier assigned to each detected (and confirmed) source as it transits the Gaia focal plane. Each time a given source is detected as Gaia scans and re-scans the sky a new transit_id will be created to badge that apparition. Hence the along–scan time and the across–scan position along with the telescope in which the source was detected are used to form a unique integer with which to label the transit.

The several features of a detection that are encoded in transit_id can be easily retrieved using bit masks (&) and shifts ($\gg$) as follows:

• •

  On-Board Mission Time line [ns]
  = 204800 * ((transit_id $\gg$ 17) & (0x000003FFFFFFFFFF))

• •

  Field-of-view = 1 + (transit_id $\gg$ 15) & 0x03 [1 for ‘preceding’ and 2 for ‘following’ fields-of-view respectively]

• •

  CCD row = (transit_id $\gg$ 12) & 0x07 [dimensionless, in the range 1 to 7]

• •

  Across-scan ‘reference acquisition pixel’ in strip AF1 = (transit_id) & 0x0FFF [pixels] (this is the across-scan centre of the AF1 window and is odd if immediately below the mid-point of the window and even if immediately above)

where the bit mask prefix ‘0x’ denotes hexadecimal.

For further details see Portell et al. (2020). For convenience a decoder for transit_id is available on-line at

https://gaia.esac.esa.int/decoder/transitidDecoder.jsp

g_transit_time : Transit averaged G band observing time (double[n_transits] array, Time[Barycentric JD in TCB $-$ 2 455 197.5 (day)])

Field-of-view transit averaged observation time in units of Barycentric JD (in TCB), in days minus 2 455 197.5, computed as follows. First the observation time is converted from On-board Mission Time (OBMT) into Julian date in TCB (Temps Coordonnée Barycentrique). Next a correction is applied for the light-travel time to the Solar system barycentre, resulting in Barycentric Julian Date (BJD). Finally an offset of 2 455 197.5 days is applied (corresponding to a reference time $T_0$ at 2010-01-01T00:00:00) to have a conveniently small numerical value. Although the centroiding time accuracy of the individual CCD observations is (much) below 1 ms, this per-FoV observation time is averaged over typically 9 CCD observations taken in a time range of about 44 sec.

g_transit_flux : Transit averaged G band flux (double[n_transits] array, Flux[e${}^{-}$ s${}^{-1}$] )

The average G flux value, a combination of individual SM-AF CCD fluxes

g_transit_flux_error : Transit averaged G band flux error (double[n_transits] array, Flux[e${}^{-}$ s${}^{-1}$] )

The uncertainty flux_error on flux is the uncertainty on the weighted mean G flux of the set of SM/AF individual CCD observations for the transit. This accounts for intrinsic scatter in the data. The exact formula and further details are given in Carrasco et al. (2017).

g_transit_flux_over_error : Transit averaged G band flux divided by its error (float[n_transits] array)

Mean flux in the band divided by its error.

g_transit_mag : Transit averaged G band Vega magnitude (double[n_transits] array, Magnitude[mag])

G band Vega magnitude. It is computed from the flux applying the E/DR3 zero-point defined in https://www.cosmos.esa.int/web/gaia/edr3-passbands.

g_transit_n_obs : Number of CCD observations contributing to transit averaged G band flux (byte[n_transits] array)

Number of CCD transits contributing to the transit averaged G flux (g_flux and g_flux_error).

bp_obs_time : BP CCD transit observing time (double[n_transits] array, Time[Barycentric JD in TCB $-$ 2 455 197.5 (day)])

Observation time of the BP CCD transit in units of Barycentric JD (in TCB), in days minus 2 455 197.5, computed as follows. First the observation time is converted from On-board Mission Time (OBMT) into Julian date in TCB (Temps Coordonnée Barycentrique). Next a correction is applied for the light-travel time to the Solar system barycentre, resulting in Barycentric Julian Date (BJD). Finally an offset of 2 455 197.5 days is applied (corresponding to a reference time $T_0$ at 2010-01-01T00:00:00) to have a conveniently small numerical value.

bp_flux : BP band flux (double[n_transits] array, Flux[e${}^{-}$ s${}^{-1}$] )

The integrated BP flux value of the transit. If the BP flux has been rejected or is unavailable, the flux will be set to NaN.

bp_flux_error : BP band flux error (double[n_transits] array, Flux[e${}^{-}$ s${}^{-1}$] )

The uncertainty flux_error on flux is the uncertainty on the BP flux. This is the uncertainty associated with the single BP CCD transit available for a FoV transit. It includes photon noise and all applicable calibration errors. If the BP flux has been rejected or is unavailable, the value will be set to NaN (in VOTable and FITS formats) and an empty string (in plain text CSV format).

bp_flux_over_error : BP band flux divided by its error (float[n_transits] array)

Mean flux in the band divided by its error. If the BP flux has been rejected or is unavailable, this value will be set to NaN.

bp_mag : BP band Vega magnitude (double[n_transits] array, Magnitude[mag])

BP band Vega magnitude. It is computed from the flux applying the E/DR3 zero-point defined in https://www.cosmos.esa.int/web/gaia/edr3-passbands.

rp_obs_time : RP CCD transit observing time (double[n_transits] array, Time[Barycentric JD in TCB $-$ 2 455 197.5 (day)])

Observation time of the RP CCD transit in units of Barycentric JD (in TCB), in days minus 2 455 197.5, computed as follows. First the observation time is converted from On-board Mission Time (OBMT) into Julian date in TCB (Temps Coordonnée Barycentrique). Next a correction is applied for the light-travel time to the Solar system barycentre, resulting in Barycentric Julian Date (BJD). Finally an offset of 2 455 197.5 days is applied (corresponding to a reference time $T_0$ at 2010-01-01T00:00:00) to have a conveniently small numerical value.

rp_flux : RP band flux (double[n_transits] array, Flux[e${}^{-}$ s${}^{-1}$] )

The integrated RP flux value of the transit. If the RP flux has been rejected or is unavailable, the flux will be set to NaN.

rp_flux_error : RP band flux error (double[n_transits] array, Flux[e${}^{-}$ s${}^{-1}$] )

The uncertainty flux_error on flux is the uncertainty on the RP flux. This is the uncertainty associated with the single RP CCD transit available for a FoV transit. It includes photon noise and all applicable calibration errors. If the RP flux has been rejected or is unavailable, the value will be set to NaN (in VOTable and FITS formats) and an empty string (in plain text CSV format).

rp_flux_over_error : RP band flux divided by its error (float[n_transits] array)

Mean flux in the band divided by its error. If the RP flux has been rejected or is unavailable, this value will be set to NaN.

rp_mag : RP band Vega magnitude (double[n_transits] array, Magnitude[mag])

RP band Vega magnitude. It is computed from the flux applying the E/DR3 zero-point defined in https://www.cosmos.esa.int/web/gaia/edr3-passbands.

photometry_flag_noisy_data : G band flux scatter larger than expected by photometry processing (all CCDs considered) (boolean[n_transits] array)

G band flux scatter larger than expected by photometry processing (all CCDs considered)

photometry_flag_sm_unavailable : SM transit unavailable by photometry processing (boolean[n_transits] array)

Flag indicating whether the SM transit was unavailable for photometry processing.

photometry_flag_af1_unavailable : AF1 transit unavailable by photometry processing (boolean[n_transits] array)

Flag indicating whether the AF1 transit was unavailable for photometry processing.

photometry_flag_af2_unavailable : AF2 transit unavailable by photometry processing (boolean[n_transits] array)

Flag indicating whether the AF2 transit was unavailable for photometry processing.

photometry_flag_af3_unavailable : AF3 transit unavailable by photometry processing (boolean[n_transits] array)

Flag indicating whether the AF3 transit was unavailable for photometry processing.

photometry_flag_af4_unavailable : AF4 transit unavailable by photometry processing (boolean[n_transits] array)

Flag indicating whether the AF4 transit was unavailable for photometry processing.

photometry_flag_af5_unavailable : AF5 transit unavailable by photometry processing (boolean[n_transits] array)

Flag indicating whether the AF5 transit was unavailable for photometry processing.

photometry_flag_af6_unavailable : AF6 transit unavailable by photometry processing (boolean[n_transits] array)

Flag indicating whether the AF6 transit was unavailable for photometry processing.

photometry_flag_af7_unavailable : AF7 transit unavailable by photometry processing (boolean[n_transits] array)

Flag indicating whether the AF7 transit was unavailable for photometry processing.

photometry_flag_af8_unavailable : AF8 transit unavailable by photometry processing (boolean[n_transits] array)

Flag indicating whether the AF8 transit was unavailable for photometry processing.

photometry_flag_af9_unavailable : AF9 transit unavailable by photometry processing (boolean[n_transits] array)

Flag indicating whether the AF9 transit was unavailable for photometry processing. For CCD row 4, which has no AF9, this flag is ‘true’.

photometry_flag_bp_unavailable : BP transit unavailable by photometry processing (boolean[n_transits] array)

Flag indicating whether the BP transit was unavailable for photometry processing.

photometry_flag_rp_unavailable : RP transit unavailable by photometry processing (boolean[n_transits] array)

Flag indicating whether the RP transit was unavailable for photometry processing.

photometry_flag_sm_reject : SM transit rejected by photometry processing (boolean[n_transits] array)

Flag indicating whether the SM transit was rejected by photometry processing.

photometry_flag_af1_reject : AF1 transit rejected by photometry processing (boolean[n_transits] array)

Flag indicating whether the AF1 transit was rejected by photometry processing.

photometry_flag_af2_reject : AF2 transit rejected by photometry processing (boolean[n_transits] array)

Flag indicating whether the AF2 transit was rejected by photometry processing.

photometry_flag_af3_reject : AF3 transit rejected by photometry processing (boolean[n_transits] array)

Flag indicating whether the AF3 transit was rejected by photometry processing.

photometry_flag_af4_reject : AF4 transit rejected by photometry processing (boolean[n_transits] array)

Flag indicating whether the AF4 transit was rejected by photometry processing.

photometry_flag_af5_reject : AF5 transit rejected by photometry processing (boolean[n_transits] array)

Flag indicating whether the AF5 transit was rejected by photometry processing.

photometry_flag_af6_reject : AF6 transit rejected by photometry processing (boolean[n_transits] array)

Flag indicating whether the AF6 transit was rejected by photometry processing.

photometry_flag_af7_reject : AF7 transit rejected by photometry processing (boolean[n_transits] array)

Flag indicating whether the AF7 transit was rejected by photometry processing.

photometry_flag_af8_reject : AF8 transit rejected by photometry processing (boolean[n_transits] array)

Flag indicating whether the AF8 transit was rejected by photometry processing.

photometry_flag_af9_reject : AF9 transit rejected by photometry processing (boolean[n_transits] array)

Flag indicating whether the AF9 transit was rejected by photometry processing. For CCD row 4, which has no AF9, this flag is ‘false’.

photometry_flag_bp_reject : BP transit rejected by photometry processing (boolean[n_transits] array)

Flag indicating whether the BP transit was rejected by photometry processing.

photometry_flag_rp_reject : RP transit rejected by photometry processing (boolean[n_transits] array)

Flag indicating whether the RP transit was rejected by photometry processing.

variability_flag_g_reject : Average G transit photometry rejected by variability processing (boolean[n_transits] array)

Rejected by DPAC variability processing (or variability analysis), or negative (unphysical) flux.

variability_flag_bp_reject : BP transit photometry rejected by variability processing (boolean[n_transits] array)

Rejected by DPAC variability processing (or variability analysis), or negative (unphysical) flux.

variability_flag_rp_reject : RP transit photometry rejected by variability processing (boolean[n_transits] array)

Rejected by DPAC variability processing (or variability analysis), or negative (unphysical) flux.