Abstract Located in the Perseus galaxy cluster, NGC 1275 ( z = 0.0179 ), is the brightest radio galaxy detected in both high energy (HE ; E > 100 MeV) and very high energy (VHE ; E > 100 GeV) regimes. Here we present the results from the observations of NGC 1275 with TACTIC for 37.1 h between December, 2016 and February, 2017. In the absence of a statistically significant VHE γ-ray detection from the TACTIC observations, we estimate the 3σ upper limit on the integral flux above 0.85 TeV to be ∼ 2.85 × 10 − 11 erg cm − 2 s − 1 . We also report the results of near simultaneous multiwavelength observations of the source from the Fermi-LAT, Swift-XRT/UVOT and OVRO. We find the source to be in flaring state on the night of 31 December, 2016 – 1 January, 2017 when the HE γ-ray flux above 0.1 GeV went up to ∼ 2.0 × 10 − 6 ph cm − 2 s − 1 which is approximately 4 times the flux level during its low state. We present the broad-band spectral energy distributions (SED) of the source during its flaring and low states. It is evident from the SED that the VHE upper limit obtained from the TACTIC observations is consistent with the low emission state of the source.

中文翻译：

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2016 年 12 月至 2017 年 2 月期间使用 TACTIC、Fermi 和 Swift 对射电星系 NGC 1275 进行多波长研究

摘要 位于英仙座星系团的 NGC 1275 ( z = 0.0179 ) 是在高能量 (HE ; E > 100 MeV) 和极高能量 (VHE ; E > 100 GeV) 状态下探测到的最亮的射电星系。在这里，我们展示了 2016 年 12 月至 2017 年 2 月期间 NGC 1275 使用 TACTIC 观测 37.1 小时的结果。由于 TACTIC 观测没有统计显着的 VHE γ 射线探测，我们估计了 3σ 上限0.85 TeV 以上的积分通量为 ∼ 2.85 × 10 − 11 erg cm − 2 s − 1 。我们还报告了来自 Fermi-LAT、Swift-XRT/UVOT 和 OVRO 源的近同步多波长观测结果。我们发现源在 2016 年 12 月 31 日至 2017 年 1 月 1 日晚上处于燃烧状态，此时 0.1 GeV 以上的 HE γ 射线通量上升到 ~ 2。0 × 10 − 6 ph cm − 2 s − 1 大约是低态通量水平的 4 倍。我们展示了光源在燃烧和低状态期间的宽带光谱能量分布 (SED)。从 SED 可以明显看出，从 TACTIC 观测获得的 VHE 上限与源的低发射状态一致。