Exploring nine simultaneously occurring transients on April 12th 1950 (2106.11780v1)

Abstract: Nine point sources appeared within half an hour on a region within $\sim$ 10 arcmin of a red-sensitive photographic plate taken in April 1950 as part of the historic Palomar Sky Survey. All nine sources are absent on both previous and later photographic images, and absent in modern surveys with CCD detectors which go several magnitudes deeper. We present deep CCD images with the 10.4-meter Gran Telescopio Canarias (GTC), reaching brightness $r \sim 26$ mag, that reveal possible optical counterparts, although these counterparts could equally well be just chance projections. The incidence of transients in the investigated photographic plate is far higher than expected from known detection rates of optical counterparts to e.g.\ flaring dwarf stars, Fast Radio Bursts (FRBs), Gamma Ray Bursts (GRBs) or microlensing events. One possible explanation is that the plates have been subjected to an unknown type of contamination producing mainly point sources with of varying intensities along with some mechanism of concentration within a radius of $\sim$ 10 arcmin on the plate. If contamination as an explanation can be fully excluded, another possibility is fast (t $<0.5$ s) solar reflections from objects near geosynchronous orbits. An alternative route to confirm the latter scenario is by looking for images from the First Palomar Sky Survey where multiple transients follow a line.

• The paper examines nine simultaneous transients from a 1950 POSS-I plate to evaluate whether they stem from astrophysical events or instrumental anomalies.
• It employs a cross-analysis of historical photographic data and deep CCD imaging from the Gran Telescopio Canarias to validate the findings.
• The findings highlight the need for advanced verification methods to improve the accuracy of archival astrophysical data and artifact discrimination.

Analysis of Simultaneous Transient Events from 1950: An Investigative Approach

The paper authored by Beatriz Villarroel and colleagues examines an unusual astronomical occurrence: on April 12, 1950, nine simultaneous transients were recorded on a red-sensitive photographic plate from the Palomar Sky Survey. This paper provides a comprehensive investigation into the origins of these transients, examining whether they could be attributed to astrophysical phenomena or resulted from instrumental or environmental contamination.

Methodological Framework

The paper relies on both historical photographic plates and modern observational techniques. Initially, the authors reference data from the first Palomar Sky Survey (POSS-I) and modern comparative datasets, including deep CCD images from the 10.4-meter Gran Telescopio Canarias (GTC). This approach allows them to cross-examine the transients' presence and seek potential counterparts. The analysis also incorporates photometric procedures from prior literature, optimized specifically for POSS-I data. The field investigated is substantial yet requires meticulous astrometric correction for conclusive cross-matching across data sets.

Key Findings

Significant findings include the absence of these transients in preceding and successive photographic data, as well as modern observational archives such as Pan-STARRS and SDSS, which delve several magnitudes deeper. This absence suggests either a transient natural occurrence or some anomaly in the older plate's production. Deep images from the GTC suggest possible counterparts; however, statistical estimation portrays these could be chance alignments due to the density of sources in the field.

The authors explore potential natural and artificial sources for these transients:

• Contamination by Radioactive Particles: The paper considers instrumental contamination such as radioactive particles — potentially from mid-20th-century nuclear testing — as a fragment of the transients' origins.
• Astrophysical Phenomena: The possibility of fast-moving astronomical objects, such as flaring stars or meteoroids, fails to account for the number and rapid coincidence across a concentrated sky region.
• Artificial Causes: Suggestions include glints from objects orbiting in geosynchronous locations, though such satellites were not known during the time.

Implications and Future Considerations

The paper’s implications extend to calibrating the accuracy of historical astrophysical data and suggest methodologies for distinguishing genuine celestial phenomena from artifactual occurrences. Although no definitive conclusion is drawn about the transients' nature, identifying the probable solutions carries practical significance in fields utilizing archival astronomical data. Further, observational methodology improvements over time safeguard contemporary and future studies from similar anomalies. The cross-verification approach using modern technology emphasizes learning from historical observations, advocating for revisiting these data during ongoing analyses of astronomical transients.

Conclusion

While the work conducted by Villarroel et al. paves the groundwork for analyzing historical astronomical data, future developments in AI and data processing might optimize recognition technologies to better segregate coincidental and real events. These technologies could enhance current surveys' capabilities in distinguishing rare phenomena from artifacts, enabling a higher fidelity in time-domain astronomy. Continued examination of archival materials, such as POSS-I plates, with innovative methodologies and current devices will likely yield further insights in the field of astrophysical transient phenomena.