The Search for Failed Supernovae with The Large Binocular Telescope: First Candidates

Abstract: We are monitoring 27 galaxies within 10 Mpc using the Large Binocular Telescope to search for failed supernovae (SNe), massive stars that collapse to form a black hole without a SN explosion. We present the results from the first 4 years of survey data, during which these galaxies were observed to produce 3 successful core-collapse SNe. We search for stars that have "vanished" over the course of our survey, by examining all stars showing a decrease in luminosity of $\Delta \nu L_{\nu} \ge 10<sup>4L_{\odot}$ from the first to the last observation. We also search for the low luminosity, long duration transients predicted by \citet{lovegrove2013} for failed explosions of red supergiants. After analyzing the first 4 years of data in this first direct search for failed SNe, we are left with one candidate requiring further study. This candidate has an estimated mass of 18-25$M_{\odot}$, a mass range likely associated with failed SNe and, if real, implies that failed SN represent a median fraction of $f \simeq 0.30$ of core-collapses, with symmetric 90% confidence limits of $0.07 \le f \le 0.62$. If follow up data eliminate this candidate, we find an upper limit on the fraction of core collapses leading to a failed SN of $f&lt;0.40$ at 90% confidence. As the duration of the survey continues to increase, it will begin to constrain the $f \simeq$ 10-30% failure rates needed to explain the deficit of massive SN progenitors and the observed black hole mass function.

• The paper presents the first candidate for a failed supernova identified by monitoring 27 galaxies with the LBT over four years.
• It employs image subtraction techniques and a luminosity drop threshold (≥ 10⁴ L⊙) to detect stars that vanish without a visible explosion.
• The candidate, with an 18–25 M⊙ progenitor, implies a failed supernova fraction of roughly 30% in core-collapse events.

An Investigation into Failed Supernovae Using the Large Binocular Telescope

This paper presents the initial findings of a research project aimed at identifying and understanding failed supernovae (SNe) using the Large Binocular Telescope (LBT). The study focuses on nearby galaxies located within 10 Mpc, where 27 galaxies have been monitored over four years. The researchers endeavor to detect massive stars that collapse into black holes without a visible supernova explosion. This phenomenon, known as a failed supernova, poses significant challenges to traditional theories of stellar death and black hole formation.

Methodology and Observations

The study's primary approach involves monitoring the luminosity of stars across different epochs to identify those that suddenly disappear, indicative of a failed supernova. This project capitalizes on image subtraction techniques to discern changes in stellar brightness over time. The criteria for identifying potential failed SNe involve detecting stars showing a decrease in luminosity of at least $\Delta \nu L_{\nu} \ge 10^4 L_{\odot}$. Additionally, the researchers sought optical transients consistent with theoretical predictions of failed supernovae in red supergiants.

During the first four years, the surveillance of 27 galaxies has resulted in the recording of three successful core-collapse SNe. However, one compelling candidate for a failed supernova arose from this observational effort. This candidate, if confirmed, allows for quantification of the failed supernova fraction within core collapses.

Key Results and Statistical Analysis

The statistically significant results of this research include a solitary candidate for failed SNe, with an estimated progenitor mass of 18-25 $M_{\odot}$. Should this candidate withstand further scrutiny, it would suggest a non-negligible fraction, $f \approx 0.30$, of core-collapses manifest as failed supernovae, with a 90% confidence interval spanning 0.07 to 0.62. In contrast, if additional data refutes this single candidate, our understanding will cap the failure rate at $f < 0.40$ at 90% confidence.

Despite variations and potential systematic uncertainties in observational data (such as interstellar dust leading to obscuration errors), these results offer meaningful constraints on failed SNe frequencies and consequently on the black hole mass function and massive star formation rates.

Implications and Future Developments

This investigation contributes significantly toward solving the 'red supergiant problem', where observations show a paucity of high-mass supernova progenitors exceeding 18 $M_{\odot}$. It implies that the missing massive stars might indeed collapse into black holes quietly, without a luminous explosion. The results also dovetail with theoretical models of stellar evolution that suggest high rates of failed supernovae may explain observed stellar mass distributions and black hole formations.

As the observational campaign proceeds, the accumulated data will provide increasingly stringent constraints on failed supernovae rates. This study also serves as a groundwork for ongoing and future large-scale optical transient surveys, which will be crucial in confirming the existence of these enigmatic astronomical events. Further improvements, such as enhanced image subtraction techniques and extended temporal baselines, will refine these constraints and potentially capture more failed supernovae, enlightening our understanding of stellar end states in the universe.