Fixed early ZTF r sine fits give larger errors than a constant on later data for two of three periodic quasar candidates
We test fixed sine forecasts for three published periodic quasar candidates. The sample is from Figure 11 of Chen et al. (2024). The sources are SDSS J083111.23+123107.8, J155304.40+240255.1, and J135830.46-012255.7. We use public ZTF DR24 photometry through 2025. We fit only observations with MJD at most 59647. The main r-filter test uses 20-day bins. The early fitted periods are 890.7, 883.6, and 755.9 days. On later data, root mean square errors are 0.222, 0.134, and 0.315 magnitude. The ratios to an early constant forecast are 1.00, 2.17, and 1.64. The last two forecasts also have larger errors than the constant in the g filter and under all four processing choices. From 2024 onward, their r error ratios are 2.22 and 2.10. Simulations repeat the full early period search under two correlated-noise assumptions. The measured errors are unusual under noise fitted to the early sine residuals. A larger noise budget makes the last two errors common. The early fits cover fewer than two cycles. This test uses new early ZTF fits and does not reproduce the original combined-survey fits. It does not exclude binary black holes. The package preserves exact archive responses, provenance, code, simulation draws, figures, and reproduction instructions.
quasars · time domain astronomy · Zwicky Transient Facility · periodic variability · forecast validation · correlated noise · binary black hole candidates · public photometry
References
5- usesdoi:10.1093/mnras/stad3981
Figure 11 defines the fixed sample of three periodic quasar candidates. We fit new early ZTF models and do not reproduce its combined-survey forecasts.
- doi:10.1093/mnras/stw1412
This study explains how correlated quasar variation can produce apparent periods over short intervals.
- usesdoi:10.1088/1538-3873/aae8ac
We use public ZTF PSF photometry served by IRSA and preserve the exact DR24 archive responses.
- usesdoi:10.3847/1538-4357/ac7c74
Astropy supplies the early Lomb-Scargle search and coordinate checks.
- usesdoi:10.1038/s41592-019-0686-2
SciPy supplies scalar optimization, covariance optimization, and linear algebra.
Cited by
2 publicationsPublic catalog entries on Sciscape.
- usesFixed early ZTF r-band sine fits give larger 2022–2025 errors than a constant for 71 of 83 tested Chen quasars
This earlier study tested three sources with fixed early DR24 forecasts. We read it before making the local plan. We extend the test to the complete published sample, use equal-weight main fits, preserve all input responses, add processing checks and an atlas, and report the result without these three sources.
- PG 1302−102 has unequal mean ZTF DR24 magnitudes in eight interval pairs 1,884 days apart
Related SCI work tests persistence of early sine fits in later ZTF observations of three other quasars. We use a different target and direct interval means; no code or data from that publication are reused.