ASASSN-23bd: A Dim Tidal Disruption Event

We present a significant discovery of a tidal disruption event (TDE) named ASASSN-23bd in the galaxy NGC 3799. This TDE is noteworthy because it has the lowest redshift and is the least bright TDE ever found. TDEs occur when a star gets too close to a supermassive black hole and gets pulled apart by its strong gravity, leading to a bright explosion of light.

In this article, we share details about ASASSN-23bd, its discovery, follow-up observations, and how it compares to other known TDEs.

#Discovery of ASASSN-23bd

ASASSN-23bd was discovered through the All-Sky Automated Survey for SuperNovae (ASAS-SN). The event was first spotted in NGC 3799, a galaxy that has not shown strong signs of active galactic nuclei (AGN) activity in the past ten years. The discovery occurred on a specific date when the light from ASASSN-23bd was first detected, indicating that the event happened days earlier.

The Brightness of ASASSN-23bd was measured in the ultraviolet (UV) and optical bands, showing it was a dim event. Researchers examined the spectrum of the light produced by ASASSN-23bd and noted the presence of specific elements, including hydrogen and nitrogen, while typical signs of active Black Holes, like strong emissions from carbon and magnesium, were missing.

#Features of ASASSN-23bd

ASASSN-23bd is a faint X-ray source, meaning it does not emit much X-ray light, which is often associated with more energetic events. The initial observations suggested it started to brighten before the discovery, reaching its peak brightness shortly after. The light curve, a graph showing how the brightness changes over time, showed a rapid rise and a slow decline.

The characteristics of ASASSN-23bd suggest it belongs to a new class of TDEs that are dim and rise quickly. These events are different from more typical, brighter TDEs.

#Understanding Tidal Disruption Events

TDEs happen when a star passes close to a supermassive black hole. The black hole's gravity pulls the star apart, resulting in a burst of light as material from the star falls into the black hole. TDEs are useful for studying black holes and the environments around them.

Observations of TDEs cover a wide range of light wavelengths. This includes X-rays, UV, and optical light, making them important for understanding the different processes happening when stars meet black holes. They also allow scientists to study black holes that are usually inactive.

#The Complexity of TDE Physics

The physics behind TDEs can be quite complex. Various factors influence how these events unfold, such as the star's age, mass, and composition, as well as the black hole's characteristics. Despite this complexity, the light from TDEs can often be modeled as blackbody radiation, which is a theoretical model that describes how idealized objects emit light.

Researchers can estimate the mass and spin of black holes using light curves from TDEs, and these estimates generally align well with other methods. TDEs also show a relationship between their brightness and how quickly their light fades.

#Spectroscopy and TDEs

Spectroscopy, the study of how light interacts with matter, plays a significant role in understanding TDEs. By analyzing light from TDEs, researchers can observe emission lines from elements like hydrogen and helium. Variations in these lines can provide insights into the nature of the star being disrupted and the environment near the black hole.

As more TDEs are observed, scientists hope to learn more about their differences and similarities, which could lead to a better understanding of the black holes responsible for these events.

#Surveying the Sky for TDEs

With many transient surveys currently in operation, more TDEs are being discovered every year. These surveys help identify events before they reach peak brightness, allowing researchers to study the early stages of TDEs. This early detection is crucial for understanding fast, low-luminosity TDEs.

TDEs that are low in brightness and evolve quickly may not be detected as easily compared to brighter counterparts. However, the ongoing surveys increase the chances of finding these fainter events.

#Data and Methodology

The discovery of ASASSN-23bd involved multiple observations from different telescopes and surveys. Data were collected across various wavelengths, including optical and UV bands. The data were carefully stacked and analyzed to produce light curves and spectra, which were then used to derive physical parameters of the event.

The follow-up observations included imaging from ground-based and space-based telescopes, which provided insights into the light emitted during the event and allowed for the study of its characteristics over time.

#Analysis of NGC 3799

NGC 3799, the host galaxy of ASASSN-23bd, is a peculiar galaxy with evidence of interactions with its neighbor, NGC 3800. This interaction may increase the likelihood of TDEs occurring. As a Low Ionization Nuclear Emission Line Region (LINER) galaxy, NGC 3799 shows active regions but has not displayed strong AGN behavior.

An in-depth analysis of the galaxy's previous data revealed that there was no significant AGN activity before the discovery of ASASSN-23bd. This finding suggests that ASASSN-23bd is more likely to be a TDE rather than an AGN flare.

#Photometric Observations and Light Curves

Photometric data from various surveys revealed the brightness changes of ASASSN-23bd over time. Light curves showed how ASASSN-23bd rose in brightness rapidly and then faded. This behavior is consistent with TDEs observed in the past, which typically have similar light curves.

Different models were used to analyze the rising light curve of ASASSN-23bd, helping to estimate the time of peak brightness. The results indicated that ASASSN-23bd had unique characteristics compared to other known TDEs.

#Spectroscopy of ASASSN-23bd

The optical spectra of ASASSN-23bd were examined to identify key features. The spectra revealed the presence of hydrogen and nitrogen emissions, which are characteristic of TDEs. The behavior of these spectral lines over time also informed researchers about the dynamics of the event.

The spectrum was calibrated with photometry data to ensure accuracy, and comparisons were made with other TDEs to assess the differences in their light and spectral properties.

#Comparison with Other TDEs

When compared to other TDEs, ASASSN-23bd stands out for its low luminosity and redshift. Its characteristics align with a subclass of TDEs that are dim and evolve rapidly. By analyzing a sample of well-known TDEs, researchers found that ASASSN-23bd had unique features that added to the understanding of tidal disruption events.

Other TDEs exhibited different properties in terms of brightness and light-curve shapes, highlighting the diverse behaviors of such events.

#Significance of ASASSN-23bd

The discovery of ASASSN-23bd adds valuable information to the catalog of TDEs. Its low luminosity and redshift suggest there may be more undetected events out there, especially those that are fainter. This finding emphasizes the need for continuous monitoring of the skies to catch these elusive events.

ASASSN-23bd is a significant addition to the growing collection of TDEs and highlights the diversity of such phenomena in different types of galaxies.

#Future Directions

As more TDEs are discovered, researchers hope to refine their models and understand the underlying mechanisms driving these events. Future studies may involve deeper sky surveys capable of detecting more low-luminosity events, further enriching the knowledge of nuclear transients.

This research will enhance the understanding of black holes and their interactions with stars, contributing to a broader understanding of the universe's workings.

#Conclusion

In conclusion, the discovery of ASASSN-23bd marks an important step in the study of tidal disruption events. It showcases the variety of behaviors in TDEs and emphasizes the need for ongoing observation and analysis. ASASSN-23bd, with its unique characteristics, not only adds to the existing knowledge of TDEs but also opens up avenues for future research in this intriguing area of astrophysics.