These documents are for schema v4.01.
ZTF uses nested schemas to organize the data in the alert packet.
ztf.alert (defined in alert.avsc) is the top-level namespace. ztf.alert in turn relies on candidate.avsc, prv_candidate.avsc, fp_hist.avsc and cutout.avsc.
The top-level alert contains the following fields:
| Field | Type | Contents |
|---|---|---|
schemavsn |
string | schema version used |
publisher |
string | origin of alert packet |
objectId |
long | unique identifier for this object |
candid |
long | unique identifier for the subtraction candidate |
candidate |
ztf.alert.candidate |
candidate record |
prv_candidates |
array of ztf.alert.prv_candidate or null |
candidate records for 30 days’ past history |
fp_hists |
array of ztf.alert.fp_hist or null |
forced photometry measurements at the candidate position on past difference images |
cutoutScience |
ztf.alert.cutout or null |
cutout of the science image |
cutoutTemplate |
ztf.alert.cutout or null |
cutout of the coadded reference image |
cutoutDifference |
ztf.alert.cutout or null |
cutout of the resulting difference image |
| Field | Type | Contents |
|---|---|---|
jd |
double | Observation Julian date at start of exposure [days] |
fid |
int | Filter ID (1=g; 2=r; 3=i) |
pid |
long | Processing ID for image |
diffmaglim |
[float, null], default: null | 5-sigma mag limit in difference image based on PSF-fit photometry [mag] |
pdiffimfilename |
[string, null], default: null | filename of positive (sci minus ref) difference image |
programpi |
[string, null], default: null | Principal investigator attached to program ID |
programid |
int | Program ID: encodes either public, collab, or caltech mode |
candid |
long | Candidate ID from operations DB |
isdiffpos |
string | t or 1 => candidate is from positive (sci minus ref) subtraction; f or 0 => candidate is from negative (ref minus sci) subtraction |
tblid |
[long, null], default: null | Internal pipeline table extraction ID |
nid |
[int, null], default: null | Night ID |
rcid |
[int, null], default: null | Readout channel ID [00 .. 63] |
field |
[int, null], default: null | ZTF field ID |
xpos |
[float, null], default: null | x-image position of candidate [pixels] |
ypos |
[float, null], default: null | y-image position of candidate [pixels] |
ra |
double | Right Ascension of candidate; J2000 [deg] |
dec |
double | Declination of candidate; J2000 [deg] |
magpsf |
float | magnitude from PSF-fit photometry [mag] |
sigmapsf |
float | 1-sigma uncertainty in magpsf [mag] |
chipsf |
[float, null], default: null | Reduced chi-square for PSF-fit |
magap |
[float, null], default: null | Aperture mag using 8 pixel diameter aperture [mag] |
sigmagap |
[float, null], default: null | 1-sigma uncertainty in magap [mag] |
distnr |
[float, null], default: null | distance to nearest source in reference image PSF-catalog within 30 arcsec [pixels] |
magnr |
[float, null], default: null | magnitude of nearest source in reference image PSF-catalog within 30 arcsec [mag] |
sigmagnr |
[float, null], default: null | 1-sigma uncertainty in magnr within 30 arcsec [mag] |
chinr |
[float, null], default: null | DAOPhot chi parameter of nearest source in reference image PSF-catalog within 30 arcsec |
sharpnr |
[float, null], default: null | DAOPhot sharp parameter of nearest source in reference image PSF-catalog within 30 arcsec |
sky |
[float, null], default: null | Local sky background estimate [DN] |
magdiff |
[float, null], default: null | Difference: magap - magpsf [mag] |
fwhm |
[float, null], default: null | Full Width Half Max assuming a Gaussian core, from SExtractor [pixels] |
classtar |
[float, null], default: null | Star/Galaxy classification score from SExtractor |
mindtoedge |
[float, null], default: null | Distance to nearest edge in image [pixels] |
magfromlim |
[float, null], default: null | Difference: diffmaglim - magap [mag] |
seeratio |
[float, null], default: null | Ratio: difffwhm / fwhm |
aimage |
[float, null], default: null | Windowed profile RMS afloat major axis from SExtractor [pixels] |
bimage |
[float, null], default: null | Windowed profile RMS afloat minor axis from SExtractor [pixels] |
aimagerat |
[float, null], default: null | Ratio: aimage / fwhm |
bimagerat |
[float, null], default: null | Ratio: bimage / fwhm |
elong |
[float, null], default: null | Ratio: aimage / bimage |
nneg |
[int, null], default: null | number of negative pixels in a 5 x 5 pixel stamp |
nbad |
[int, null], default: null | number of prior-tagged bad pixels in a 5 x 5 pixel stamp |
rb |
[float, null], default: null | RealBogus quality score; range is 0 to 1 where closer to 1 is more reliable |
rbversion |
string | version of RealBogus model/classifier used to assign rb quality score |
drb |
[float, null], default: null | RealBogus quality score from Deep-Learning-based classifier; range is 0 to 1 where closer to 1 is more reliable |
drbversion |
string | version of Deep-Learning-based classifier model used to assign RealBogus (drb) quality score |
ssdistnr |
[float, null], default: null | distance to nearest known solar system object; set to -999.0 if none [arcsec] |
ssmagnr |
[float, null], default: null | magnitude of nearest known solar system object (usually V-band from MPC archive); set to -999.0 if none [mag] |
ssnamenr |
[string, null], default: null | name of nearest known solar system object (from MPC archive); ‘null’ if none |
sumrat |
[float, null], default: null | Ratio: sum(pixels) / sum(abs(pixels)) in a 5 x 5 pixel stamp where stamp is first median-filtered to mitigate outliers |
magapbig |
[float, null], default: null | Aperture mag using 18 pixel diameter aperture [mag] |
sigmagapbig |
[float, null], default: null | 1-sigma uncertainty in magapbig [mag] |
ranr |
double | Right Ascension of nearest source in reference image PSF-catalog; J2000 [deg] |
decnr |
double | Declination of nearest source in reference image PSF-catalog; J2000 [deg] |
ndethist |
int | Number of spatially-coincident detections falling within 1.5 arcsec going back to beginning of survey; only detections that fell on the same field and readout-channel ID where the input candidate was observed are counted. All raw detections down to a photometric S/N of ~ 3 are included. |
ncovhist |
int | Number of times input candidate position fell on any field and readout-channel going back to beginning of survey |
jdstarthist |
[double, null], default: null | Earliest Julian date of epoch corresponding to ndethist [days] |
jdendhist |
[double, null], default: null | Latest Julian date of epoch corresponding to ndethist [days] |
scorr |
[double, null], default: null | Peak-pixel signal-to-noise ratio in point source matched-filtered detection image |
tooflag |
[int, null], default: null | 1 => candidate is from a Target-of-Opportunity (ToO) exposure; 0 => candidate is from a non-ToO exposure |
objectidps1 |
[long, null], default: null | Object ID of closest source from PS1 catalog; if exists within 30 arcsec |
sgmag1 |
[float, null], default: null | g-band PSF magnitude of closest source from PS1 catalog; if exists within 30 arcsec [mag] |
srmag1 |
[float, null], default: null | r-band PSF magnitude of closest source from PS1 catalog; if exists within 30 arcsec [mag] |
simag1 |
[float, null], default: null | i-band PSF magnitude of closest source from PS1 catalog; if exists within 30 arcsec [mag] |
szmag1 |
[float, null], default: null | z-band PSF magnitude of closest source from PS1 catalog; if exists within 30 arcsec [mag] |
sgscore1 |
[float, null], default: null | Star/Galaxy score of closest source from PS1 catalog 0 <= sgscore <= 1 where closer to 1 implies higher likelihood of being a star |
distpsnr1 |
[float, null], default: null | Distance of closest source from PS1 catalog; if exists within 30 arcsec [arcsec] |
objectidps2 |
[long, null], default: null | Object ID of second closest source from PS1 catalog; if exists within 30 arcsec |
sgmag2 |
[float, null], default: null | g-band PSF magnitude of second closest source from PS1 catalog; if exists within 30 arcsec [mag] |
srmag2 |
[float, null], default: null | r-band PSF magnitude of second closest source from PS1 catalog; if exists within 30 arcsec [mag] |
simag2 |
[float, null], default: null | i-band PSF magnitude of second closest source from PS1 catalog; if exists within 30 arcsec [mag] |
szmag2 |
[float, null], default: null | z-band PSF magnitude of second closest source from PS1 catalog; if exists within 30 arcsec [mag] |
sgscore2 |
[float, null], default: null | Star/Galaxy score of second closest source from PS1 catalog; if exists within 30 arcsec: 0 <= sgscore <= 1 where closer to 1 implies higher likelihood of being a star |
distpsnr2 |
[float, null], default: null | Distance to second closest source from PS1 catalog; if exists within 30 arcsec [arcsec] |
objectidps3 |
[long, null], default: null | Object ID of third closest source from PS1 catalog; if exists within 30 arcsec |
sgmag3 |
[float, null], default: null | g-band PSF magnitude of third closest source from PS1 catalog; if exists within 30 arcsec [mag] |
srmag3 |
[float, null], default: null | r-band PSF magnitude of third closest source from PS1 catalog; if exists within 30 arcsec [mag] |
simag3 |
[float, null], default: null | i-band PSF magnitude of third closest source from PS1 catalog; if exists within 30 arcsec [mag] |
szmag3 |
[float, null], default: null | z-band PSF magnitude of third closest source from PS1 catalog; if exists within 30 arcsec [mag] |
sgscore3 |
[float, null], default: null | Star/Galaxy score of third closest source from PS1 catalog; if exists within 30 arcsec: 0 <= sgscore <= 1 where closer to 1 implies higher likelihood of being a star |
distpsnr3 |
[float, null], default: null | Distance to third closest source from PS1 catalog; if exists within 30 arcsec [arcsec] |
nmtchps |
int | Number of source matches from PS1 catalog falling within 30 arcsec |
rfid |
long | Processing ID for reference image to facilitate archive retrieval |
jdstartref |
double | Observation Julian date of earliest exposure used to generate reference image [days] |
jdendref |
double | Observation Julian date of latest exposure used to generate reference image [days] |
nframesref |
int | Number of frames (epochal images) used to generate reference image |
dsnrms |
[float, null], default: null | Ratio: D/stddev(D) on event position where D = difference image |
ssnrms |
[float, null], default: null | Ratio: S/stddev(S) on event position where S = image of convolution: D (x) PSF(D) |
dsdiff |
[float, null], default: null | Difference of statistics: dsnrms - ssnrms |
magzpsci |
[float, null], default: null | Magnitude zero point for photometry estimates [mag] |
magzpsciunc |
[float, null], default: null | Magnitude zero point uncertainty (in magzpsci) [mag] |
magzpscirms |
[float, null], default: null | RMS (deviation from average) in all differences between instrumental photometry and matched photometric calibrators from science image processing [mag] |
nmatches |
int | Number of PS1 photometric calibrators used to calibrate science image from science image processing |
clrcoeff |
[float, null], default: null | Color coefficient from linear fit from photometric calibration of science image |
clrcounc |
[float, null], default: null | Color coefficient uncertainty from linear fit (corresponding to clrcoeff) |
zpclrcov |
[float, null], default: null | Covariance in magzpsci and clrcoeff from science image processing [mag^2] |
zpmed |
[float, null], default: null | Magnitude zero point from median of all differences between instrumental photometry and matched photometric calibrators from science image processing [mag] |
clrmed |
[float, null], default: null | Median color of all PS1 photometric calibrators used from science image processing [mag]: for filter (fid) = 1, 2, 3, PS1 color used = g-r, g-r, r-i respectively |
clrrms |
[float, null], default: null | RMS color (deviation from average) of all PS1 photometric calibrators used from science image processing [mag] |
neargaia |
[float, null], default: null | Distance to closest source from Gaia DR1 catalog irrespective of magnitude; if exists within 90 arcsec [arcsec] |
neargaiabright |
[float, null], default: null | Distance to closest source from Gaia DR1 catalog brighter than magnitude 14; if exists within 90 arcsec [arcsec] |
maggaia |
[float, null], default: null | Gaia (G-band) magnitude of closest source from Gaia DR1 catalog irrespective of magnitude; if exists within 90 arcsec [mag] |
maggaiabright |
[float, null], default: null | Gaia (G-band) magnitude of closest source from Gaia DR1 catalog brighter than magnitude 14; if exists within 90 arcsec [mag] |
exptime |
[float, null], default: null | Integration time of camera exposure [sec] |
The prv_candidates field contains an array of one or more previous subtraction candidates at the position of the alert. These are obtained by a simple cone search at the position of the alert candidate on the last 30 days of history. If there are no previous candidates or upper limits, this field is null.
The fields for an individual prv_candidate are identical to candidate except for the omission of the PS1 and Gaia matches, previous detection history, tooflag, and reference image information.
Additionally, if the previous image has a nondetection at position of the new candidate, candid, isdiffpos, ra, dec, magpsf, sigmapsf, ranr, and decr will be null. In this case diffmaglim provides an estimate of the limiting magnitude over the entire image.
Introduced in the v4 schemas in 2023, these records provide forced photometry measurements at the candidate position on earlier differnece images.
| Field | Type | Contents |
|---|---|---|
field |
[null, int], default: null | ZTF field ID |
rcid |
[null, int], default: null | Readout channel ID [00 .. 63] |
fid |
int | Filter ID (1=g; 2=R; 3=i) |
pid |
long | Processing ID for image |
rfid |
long | Processing ID for reference image to facilitate archive retrieval |
sciinpseeing |
[null, float], default: null | Effective FWHM of sci image [pixels] |
scibckgnd |
[null, float], default: null | Background level in sci image [DN] |
scisigpix |
[null, float], default: null | Robust sigma per pixel in sci image [DN] |
magzpsci |
[null, float], default: null | Magnitude zero point for photometry estimates [mag] |
magzpsciunc |
[null, float], default: null | Magnitude zero point uncertainty (in magzpsci) [mag] |
magzpscirms |
[null, float], default: null | RMS (deviation from average) in all differences between instrumental photometry and matched photometric calibrators from science image processing [mag] |
clrcoeff |
[null, float], default: null | Color coefficient from linear fit from photometric calibration of science image |
clrcounc |
[null, float], default: null | Color coefficient uncertainty from linear fit (corresponding to clrcoeff) |
exptime |
[null, float], default: null | Integration time of camera exposure [sec] |
adpctdif1 |
[null, float], default: null | Full sci image astrometric RMS along R.A. with respect to Gaia1 [arcsec] |
adpctdif2 |
[null, float], default: null | Full sci image astrometric RMS along Dec. with respect to Gaia1 [arcsec] |
diffmaglim |
[null, float], default: null | Expected 5-sigma mag limit in difference image based on global noise estimate [mag] |
programid |
int | Program ID: encodes either public, collab, or caltech mode |
jd |
double | Observation Julian date at start of exposure [days] |
forcediffimflux |
[null, float], default: null | Forced difference image PSF-fit flux [DN] |
forcediffimfluxunc |
[null, float], default: null | 1-sigma uncertainty in forcediffimflux [DN] |
procstatus |
[null, string], default: null | Forced photometry processing status codes (0 => no warnings); see documentation |
distnr |
[null, float], default: null | distance to nearest source in reference image PSF-catalog [arcsec] |
ranr |
double | Right Ascension of nearest source in reference image PSF-catalog; J2000 [deg] |
decnr |
double | Declination of nearest source in reference image PSF-catalog; J2000 [deg] |
magnr |
[null, float], default: null | magnitude of nearest source in reference image PSF-catalog [mag] |
sigmagnr |
[null, float], default: null | 1-sigma uncertainty in magnr [mag] |
chinr |
[null, float], default: null | DAOPhot chi parameter of nearest source in reference image PSF-catalog |
sharpnr |
[null, float], default: null | DAOPhot sharp parameter of nearest source in reference image PSF-catalog |
Each cutout contains two fields:
| Field | Type | Contents |
|---|---|---|
fileName |
string | Original cutout location |
stampData |
bytes | gzip-compressed FITS cutout image |