English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We present a likelihood profile stacking technique based on the {\itFermi}-Large Area Telescope (LAT) data to explore the $\gamma$-raycharacteristics of {\it Fermi}-LAT undetected astrophysical populations. Thepipeline is applied to a sample of $\gamma$-ray unresolved extreme blazars,i.e., sources with the highest synchrotron peak frequencies ($\nu_{\rmSyn}^{\rm peak}\geqslant 10^{17}$ Hz), and we report a cumulative $\gamma$-raydetection with more than 32$\sigma$ confidence for 2 degrees of freedom.Comparing the generated stacked $\gamma$-ray spectrum with the sensitivitylimits of the upcoming Cherenkov Telescope Array (CTA), we find that the {\itFermi}-LAT undetected population of such extreme blazars, on average, mayremain well below the CTA detection threshold due to their faintness andextragalactic background light (EBL) absorption. However, $\gamma$-ray detectedblazars belonging to the same class are promising candidates for CTAobservations. The EBL corrected stacked spectra of these sources do not showany softening up to 1 TeV. This finding suggests the inverse Compton peak ofextreme blazars to lie above 1 TeV, thus indicating a hard intrinsic TeVspectrum. Our analysis also predicts that at 100 GeV, at least $\sim$10\% ofthe diffuse extragalactic $\gamma$-ray background originates from the$\gamma$-ray undetected extreme blazars. These results highlight theeffectiveness of the developed stacking technique to explore the unchartedterritory of $\gamma$-ray undetected astrophysical objects.

{\it Fermi}-LAT Stacking Analysis Technique: An Application to Extreme Blazars and Prospects for their CTA Detection