VERITAS OBSERVATIONS OF THE BL LAC OBJECT PG 1553+113

E Aliu; A Archer; M Beilicke; J. H Buckley; V Bugaev; T Aune; A Barnacka; B Behera; X Chen; W Benbow; M Cerruti; K Berger; R Bird; K Byrum; J. V Cardenzana; H. J Dickinson; L Ciupik; M. P Connolly; W Cui; VERITAS Collaboration; J Dumm

doi:10.1088/0004-637X/799/1/7

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VERITAS OBSERVATIONS OF THE BL LAC OBJECT PG 1553+113

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VERITAS OBSERVATIONS OF THE BL LAC OBJECT PG 1553+113

E Aliu, A Archer, M Beilicke, J. H Buckley, V Bugaev, T Aune, A Barnacka, B Behera, X Chen, W Benbow, …

The Astrophysical journal, Vol.799(1), 7

01/20/2015

DOI: 10.1088/0004-637X/799/1/7

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Abstract

We present results from VERITAS observations of the BL Lac object PG 1553+113 spanning the years 2010, 2011, and 2012. The time-averaged spectrum, measured between 160 and 560 GeV, is well described by a power law with a spectral index of 4.33 ± 0.09. The time-averaged integral flux above 200 GeV measured for this period was (1.69 ± 0.06) × 10{sup –11} photons cm{sup –2} s{sup –1}, corresponding to 6.9% of the Crab Nebula flux. We also present the combined γ-ray spectrum from the Fermi Large Area Telescope and VERITAS covering an energy range from 100 MeV to 560 GeV. The data are well fit by a power law with an exponential cutoff at 101.9 ± 3.2 GeV. The origin of the cutoff could be intrinsic to PG 1553+113 or be due to the γ-ray opacity of our universe through pair production off the extragalactic background light (EBL). Given lower limits to the redshift of z > 0.395 based on optical/UV observations of PG 1553+113, the cutoff would be dominated by EBL absorption. Conversely, the small statistical uncertainties of the VERITAS energy spectrum have allowed us to provide a robust upper limit on the redshift of PG 1553+113 of z ≤ 0.62. A strongly elevated mean flux of (2.50 ± 0.14) × 10{sup –11} photons cm{sup –2} s{sup –1} (10.3% of the Crab Nebula flux) was observed during 2012, with the daily flux reaching as high as (4.44±0.71)×10{sup −11} photons cm{sup −2} s{sup −1} (18.3% of the Crab Nebula flux) on MJD 56048. The light curve measured during the 2012 observing season is marginally inconsistent with a steady flux, giving a χ{sup 2} probability for a steady flux of 0.03%.

Probability

Telescopes

ASTROPHYSICS, COSMOLOGY AND ASTRONOMY

BL LACERTAE OBJECTS

COSMIC PHOTONS

CRAB NEBULA

ENERGY SPECTRA

GEV RANGE

INDEXES

MEV RANGE

OPACITY

ORIGIN

PAIR PRODUCTION

RED SHIFT

UNIVERSE

VISIBLE RADIATION

Details

Title: Subtitle: VERITAS OBSERVATIONS OF THE BL LAC OBJECT PG 1553+113
Creators: E Aliu - Columbia University
A Archer - Washington University in St. Louis
M Beilicke - Washington University in St. Louis
J. H Buckley - Washington University in St. Louis
V Bugaev - Washington University in St. Louis
T Aune - University of California, Los Angeles
A Barnacka - Harvard University
B Behera - Deutsches Elektronen-Synchrotron DESY
X Chen - University of Potsdam
W Benbow - Harvard University
M Cerruti - Harvard University
K Berger - University of Delaware
R Bird - University College Dublin
K Byrum - Argonne National Laboratory
J. V Cardenzana - Iowa State University
H. J Dickinson - Iowa State University
L Ciupik - Adler Planetarium
M. P Connolly - Ollscoil na Gaillimhe – University of Galway
W Cui - Purdue University West Lafayette
VERITAS Collaboration
J Dumm - University of Minnesota
Contributors: P Kaaret (Contributor) - University of Iowa, Physics and Astronomy
Resource Type: Journal article
Publication Details: The Astrophysical journal, Vol.799(1), 7
DOI: 10.1088/0004-637X/799/1/7
ISSN: 0004-637X
eISSN: 1538-4357
Publisher: Institute of Physics (IOP)
Language: English
Date published: 01/20/2015
Academic Unit: Physics and Astronomy
Record Identifier: 9984199823202771

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