A paper titled Gamma Ray Flares from MRK421in 2008 Observed with the ARGO-YBJ Detector  written by the ARGO-YBJ Collaboration was published on Astrophysical Journal Letter (APLJ) on 25th Feb. 

Observations by ARGO-YBJ & ASM

The paper reported on the observation of huge flares on the blazar Markarian 421 in the first half of June, 2008. With observations of the flares at optical (~10eV), X-rays (a few KeV) gamma rays of up to 100 MeV and even a few TeV (partially observed by Cherenkov telescope experiments which discontinued in the middle of the flares due to the moon ) together, the ARGO-YBJ experiment has completed an excellent experiment. The data obtained clearly correlated with that observed using orbiting X-ray telescope (see Fig. 1).

The publication of this paper, showing the first positive result of ARGO-YBJ experiment in TeV gamma ray astronomy, demonstrates that the ARGO-YBJ detector has a reliable capability of a full-sky survey for gamma ray sources and can be used as a monitor for violate transient phenomena of active galactic nuclei. On Feb 17th, 2010, even larger flares from Mrk421 within a half day were detected.

Through the observations, the ARGO-YBJ Collaboration has established its reputation in the community of gamma ray astronomy. The stable statistical accumulation through observations of the Crab nebula and the standard candle at 14.5 standard deviation above the cosmic ray background proved that more interesting and significant results should come very soon.

The Chinese and Italian teams are now busy working with data analysis, which will further reveal the great advantages of ground-based shower detector array for full-sky survey at high altitude.