Exploring nine simultaneously occurring transients on April 12th 1950

Beatriz Villarroel,Stefan Geier,Geoffrey W Marcy,Enrique Solano,Alina Streblyanska,Lars Mattsson,Alok C Gupta,Vitaly N Andruk,Matthew E Shultz

doi:10.1038/s41598-021-92162-7

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-m Gran Telescopio Canarias, 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, Gamma Ray Bursts 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.

Highlights

Nine point sources appeared within half an hour on a region within ∼ 10 arcmin of a red-sensitive photographic plate taken in April 1950 as part of the historic Palomar Sky Survey
Tens of thousands of variable or flaring stars, supernovae, asteroids and variable Active Galactic Nuclei (AGN) have been found, and an increasing number of new sub-classes of transients are continuously expanding the variety of phenomena in the transient sky
Time scales of the transients may vary from events shorter than a few minutes, e.g. the optical counterpart of a Gamma Ray Burst (GRB), to those lasting for years, for example the long-term variability of an AGN like e.g. Mrk 590, 3C 454.3 and Mrk 421

Summary

Introduction

Nine point sources appeared within half an hour on a region within ∼ 10 arcmin of a red-sensitive photographic plate taken in April 1950 as part of the historic Palomar Sky Survey. We have further examined the VASCO candidates and find that several images show at least two or three transients In this Scientific Report, we report a special case where we find nine objects present at the POSS-I red plate from April 12th 1950 at the Palomar Observatory, which reaches a depth of r ∼ 20 mag. On one of the POSS red plates (XE 325), eight star-like objects and one with possible elongation, appear within a10 ∗ 10 arcmin[2] field-of-view centered at (RA,DEC) = (212.9291,+26.8311) (eq J2000.0). We investigate possible causes for the nine transients and present new, deep observations of the same field-of-view

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Conclusion