# Detection of the high energy cut-off from the Seyfert 1.5 galaxy NGC 5273

## TL;DR

This study detects a high energy cut-off at around 143 keV in the Seyfert galaxy NGC 5273 using joint NuSTAR and Swift/XRT observations, providing insights into its coronal properties and variability over 12 years.

## Contribution

First detection of the high energy cut-off in NGC 5273 using combined spectral fitting, revealing coronal characteristics similar to certain radio galaxies and challenging simple correlations with luminosity.

## Key findings

- High energy cut-off at 143 keV with 2-sigma significance.
- Moderate X-ray variability observed over 12 years.
- Coronal properties suggest electron-dominated plasma similar to some radio galaxies.

## Abstract

We perform the NuSTAR and Swift/XRT joint energy spectral fitting of simultaneous observations from the broad-line Seyfert 1.5 galaxy NGC 5273. When fitted with the combination of an exponential cut-off power-law and a reflection model, a high energy cut-off is detected at 143$^{+96}_{-40}$ keV with 2-sigma significance. Existence of such cut-off is also consistent with the observed Comptonizing electron temperature when fitted with a Comptonization model independently. We observe a moderate hard X-ray variability of the source over the time-scale of ~12 years using INTEGRAL/ISGRI observations in the energy range of 20-100 keV. When the hard band count rate (6-20 keV) is plotted against the soft band count rate (3-6 keV), a hard offset is observed. Our results indicate that the cut-off energy may not correlate with the coronal X-ray luminosity in a simple manner. Similarities in parameters that describe coronal properties indicate that the coronal structure of NGC 5273 may be similar to that of the broad-line radio galaxy 3C 390.3 and another galaxy MCG-5-23-16 where the coronal plasma is dominated by electrons, rather than electron-positron pairs. Therefore, the coronal cooling is equally efficient to the heating mechanism keeping the cut-off energy at low even at the low accretion rate.