# Detection of a gamma-ray flare from the high-redshift blazar DA 193

## TL;DR

This paper reports the first detection of significant gamma-ray emission from the high-redshift blazar DA 193, including a rare intense GeV flare with an unusually hard spectrum, providing insights into high-redshift blazar energetics.

## Contribution

First detection of gamma-ray emission from DA 193, a high-redshift blazar, including a rare intense GeV flare with an unusually hard spectrum, expanding understanding of high-redshift blazar behavior.

## Key findings

- Detected gamma-ray emission from DA 193 at z=2.363.
- Observed an intense GeV flare with a hard gamma-ray spectrum.
- Provided multi-frequency analysis within a single-zone leptonic model.

## Abstract

High-redshift ($z>2$) blazars are the most powerful members of the blazar family. Yet, only a handful of them have both X-ray and $\gamma$-ray detection, thereby making it difficult to characterize the energetics of the most luminous jets. Here, we report, for the first time, the Fermi-Large Area Telescope detection of the significant $\gamma$-ray emission from the high-redshift blazar DA 193 ($z=2.363$). Its time-averaged $\gamma$-ray spectrum is soft ($\gamma$-ray photon index = $2.9\pm0.1$) and together with a relatively flat hard X-ray spectrum (14$-$195 keV photon index = $1.5\pm0.4$), DA 193 presents a case to study a typical high-redshift blazar with inverse Compton peak being located at MeV energies. An intense GeV flare was observed from this object in the first week of 2018 January, a phenomenon rarely observed from high-redshift sources. What makes this event a rare one is the observation of an extremely hard $\gamma$-ray spectrum (photon index = $1.7\pm0.2$), which is somewhat unexpected since high-redshift blazars typically exhibit a steep falling spectrum at GeV energies. The results of our multi-frequency campaign, including both space- (Fermi, NuSTAR, and Swift) and ground-based (Steward and Nordic Optical Telescope) observatories, are presented and this peculiar $\gamma$-ray flare is studied within the framework of a single-zone leptonic emission scenario.