Extragalactic Observations with HESS: Past and Future

TL;DR

The paper reviews H.E.S.S. II's advancements in lowering energy thresholds for extragalactic observations, highlighting recent AGN detections, improved GRB observations, and prospects for discovering new transient phenomena.

Contribution

It presents the first results from H.E.S.S. II, demonstrating enhanced sensitivity to lower-energy gamma rays and discussing implications for extragalactic source studies.

Findings

Increased detections of bright FSRQ AGNs with H.E.S.S. II.

Improved rapid response to GRB alerts.

Insights into intrinsic spectra of HBL class AGNs.

Abstract

The present H.E.S.S. II era of the H.E.S.S. collaboration follows from the successful upgrade of the H.E.S.S. array, and the first published results obtained with this new instrument. Thanks to these achievements, a lower energy threshold with H.E.S.S. II than that obtained previously with H.E.S.S. I has been clearly demonstrated. The success of these developments has now opened up a whole new lower-energy window to the Universe. I here explore, from the extragalactic point of view, both what has been learnt so far from the H.E.S.S. observations through this new window, and postulate also on what else might still be seen beyond this. I will firstly reflect upon the AGN result highlights, obtained using the new H.E.S.S. II instrument. Specifically, the rise in detections of bright FSRQ AGN with H.E.S.S. II will be addressed [eg. PKS 0736 (z=0.19), PKS 1510 (z=0.36), and 3C 279 (z=0.54)]. Hand in hand with this recent progress, the benefits brought to our efforts to observe GRBs through both access to this new lower energy window, and the quick instrument response to ToO alerts, will be covered. Furthermore, the potential for the discovery of new transient phenomena in the H.E.S.S. II era will also be emphasised. Lastly, the question as to lessons learnt from previous H.E.S.S. I AGN results about the intrinsic source spectra, primarily focusing on the HBL class, will be considered.