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تسجيل مستخدم جديدVERITAS observations of the BL Lac object TXS 0506+056
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On 2017 September 22, the IceCube Neutrino Observatory reported the detection of the high-energy neutrino event icnu, of potential astrophysical origin. It was soon determined that the neutrino direction was consistent with the location of the gamma-ray blazar txs~(3FGL J0509.4+0541), which was in an elevated gamma-ray emission state as measured by the emph{Fermi} satellite. VERITAS observations of the neutrino/blazar region started on 2017 September 23 in response to the neutrino alert and continued through 2018 February 6. While no significant very-high-energy (VHE; E $>$ 100 GeV) emission was observed from the blazar by VERITAS in the two-week period immediately following the IceCube alert, TXS 0506+056 was detected by VERITAS with a significance of 5.8 standard deviations ($sigma$) in the full 35-hour data set. The average photon flux of the source during this period was $(8.9 pm 1.6) times 10^{-12} ; mathrm{cm}^{-2} , mathrm{s}^{-1}$, or 1.6% of the Crab Nebula flux, above an energy threshold of 110 GeV, with a soft spectral index of $4.8 pm 1.3$.
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We present evidence that TXS 0506+056, the first plausible non-stellar neutrino source, despite appearances, is not a blazar of the BL Lac type but is instead a masquerading BL Lac, i.e., intrinsically a flat-spectrum radio quasar with hidden broad l
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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 $4.33 pm 0.
09$. The time-averaged integral flux above $200,$GeV measured for this period was $(1.69 pm 0.06) times 10^{-11} , mathrm{ph} , mathrm{cm}^{-2} , mathrm{s}^{-1}$, corresponding to 6.9% of the Crab Nebula flux. We also present the combined $gamma$-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 $rm {101.9 pm 3.2 , mathrm{GeV}} $. The origin of the cutoff could be intrinsic to PG~1553+113 or be due to the $gamma$-ray opacity of our universe through pair production off the extragalactic background light (EBL). Given lower limits to the redshift of $rm z egthinspace > egthinspace 0.395$ 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 $z egthinspace leq egthinspace 0.62$. A strongly-elevated mean flux of $(2.50 pm 0.14) times 10^{-11} , mathrm{ph} , mathrm{cm}^{-2} , mathrm{s}^{-1}$ (10.3% of the Crab Nebula flux) was observed during 2012, with the daily flux reaching as high as $(4.44 pm 0.71) times 10^{-11} , mathrm{ph} , mathrm{cm}^{-2} , mathrm{s}^{-1}$ (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 $chi^2$ probability for a steady flux of 0.03%.
While blazars have long been one of the candidates in the search for the origin of ultra-high energy cosmic rays and astrophysical neutrinos, the BL Lac object TXS 0506+056 is the first extragalactic source that is correlated with some confidence wit
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For the first time since the discovery of high-energy cosmic neutrinos by IceCube, a multimessenger campaign identified a distant gamma ray blazar, TXS 0506+056, as the source of a high-energy neutrino. The extraordinary brightness of the blazar desp
ite its distance suggests that it may belong to a special class of sources that produce cosmic rays. Moreover, over the last 10 years of data, the high-energy neutrino flux from the source is dominated by a previous neutrino flare in 2014, which implies that flaring sources strongly contribute to the cosmic ray flux. We investigate the contribution of this subclass of flaring blazars to the high-energy neutrino flux and examine its connection to the very high energy cosmic ray observations. We also study the high energy gamma ray emission accompanying the neutrino flare and show that the sources must be more efficient neutrino than gamma ray emitters. This conclusion is supported by the gamma-ray observations during the 2014 neutrino flare.
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