Detection of multi-TeV gamma rays from Markarian 501 during an unforeseen flaring state in 1997 with the Tibet air shower array

Citation
M. Amenomori et al., Detection of multi-TeV gamma rays from Markarian 501 during an unforeseen flaring state in 1997 with the Tibet air shower array, ASTROPHYS J, 532(1), 2000, pp. 302-307
Citations number
16
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Space Sciences
Journal title
ASTROPHYSICAL JOURNAL
ISSN journal
0004-637X → ACNP
Volume
532
Issue
1
Year of publication
2000
Part
1
Pages
302 - 307
Database
ISI
SICI code
0004-637X(20000320)532:1<302:DOMGRF>2.0.ZU;2-B
Abstract
In 1997, the BL Lac object Mrk 501 entered a very active phase and was the brightest source in the sky at TeV energies, showing strong and frequent ba ring. Using the data obtained with a high-density air shower array that has been operating successfully at Yangbajing in Tibet since 1996, we searched for gamma-ray signals from this source during the period in 1997 from Febr uary through August. Our observation detected multi-TeV gamma-ray signals a t the 3.7 sigma level during this period. The most rapid increase in the ex cess counts was observed between April 7 and June 16, and the statistical s ignificance of the excess counts in this period was 4.7 sigma. Among severa l observations of flaring TeV gamma-rays from Mrk 501 in 1997, this is the only observation using a conventional air shower array. We present the ener gy spectrum of gamma-rays, which will be worth comparing with those obtaine d by imaging atmospheric Cerenkov telescopes.