Neutrino emission from a flaring blazar Neutrinos interact only very weakly with matter, but giant detectors have succeeded in detecting small numbers of astrophysical neutrinos. Aside from a diffuse background, only two individual sources have been identified: the Sun and a nearby supernova in 1987. A multiteam collaboration detected a high-energy neutrino event whose arrival direction was consistent with a known blazar—a type of quasar with a relativistic jet oriented directly along our line of sight. The blazar, TXS 0506+056, was found to be undergoing a gamma-ray flare, prompting an extensive multiwavelength campaign. Motivated by this discovery, the IceCube collaboration examined lower-energy neutrinos detected over the previous several years, finding an excess emission at the location of the blazar. Thus, blazars are a source of astrophysical neutrinos. Science, this issue p. 147, p. eaat1378 A high-energy neutrino was emitted by a blazar during a flare, prompting observations across the electromagnetic spectrum. INTRODUCTION Neutrinos are tracers of cosmic-ray acceleration: electrically neutral and traveling at nearly the speed of light, they can escape the densest environments and may be traced back to their source of origin. High-energy neutrinos are expected to be produced in blazars: intense extragalactic radio, optical, x-ray, and, in some cases, γ-ray sources characterized by relativistic jets of plasma pointing close to our line of sight. Blazars are among the most powerful objects in the Universe and are widely speculated to be sources of high-energy cosmic rays. These cosmic rays generate high-energy neutrinos and γ-rays, which are produced when the cosmic rays accelerated in the jet interact with nearby gas or photons. On 22 September 2017, the cubic-kilometer IceCube Neutrino Observatory detected a ~290-TeV neutrino from a direction consistent with the flaring γ-ray blazar TXS 0506+056. We report the details of this observation and the results of a multiwavelength follow-up campaign. RATIONALE Multimessenger astronomy aims for globally coordinated observations of cosmic rays, neutrinos, gravitational waves, and electromagnetic radiation across a broad range of wavelengths. The combination is expected to yield crucial information on the mechanisms energizing the most powerful astrophysical sources. That the production of neutrinos is accompanied by electromagnetic radiation from the source favors the chances of a multiwavelength identification. In particular, a measured association of high-energy neutrinos with a flaring source of γ-rays would elucidate the mechanisms and conditions for acceleration of the highest-energy cosmic rays. The discovery of an extraterrestrial diffuse flux of high-energy neutrinos, announced by IceCube in 2013, has characteristic properties that hint at contributions from extragalactic sources, although the individual sources remain as yet unidentified. Continuously monitoring the entire sky for astrophysical neutrinos, IceCube provides real-time triggers for observatories around the world measuring γ-rays, x-rays, optical, radio, and gravitational waves, allowing for the potential identification of even rapidly fading sources. RESULTS A high-energy neutrino-induced muon track was detected on 22 September 2017, automatically generating an alert that was distributed worldwide within 1 min of detection and prompted follow-up searches by telescopes over a broad range of wavelengths. On 28 September 2017, the Fermi Large Area Telescope Collaboration reported that the direction of the neutrino was coincident with a cataloged γ-ray source, 0.1° from the neutrino direction. The source, a blazar known as TXS 0506+056 at a measured redshift of 0.34, was in a flaring state at the time with enhanced γ-ray activity in the GeV range. Follow-up observations by imaging atmospheric Cherenkov telescopes, notably the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescopes, revealed periods where the detected γ-ray flux from the blazar reached energies up to 400 GeV. Measurements of the source have also been completed at x-ray, optical, and radio wavelengths. We have investigated models associating neutrino and γ-ray production and find that correlation of the neutrino with the flare of TXS 0506+056 is statistically significant at the level of 3 standard deviations (sigma). On the basis of the redshift of TXS 0506+056, we derive constraints for the muon-neutrino luminosity for this source and find them to be similar to the luminosity observed in γ-rays. CONCLUSION The energies of the γ-rays and the neutrino indicate that blazar jets may accelerate cosmic rays to at least several PeV. The observed association of a high-energy neutrino with a blazar during a period of enhanced γ-ray emission suggests that blazars may indeed be one of the long-sought sources of very-high-energy cosmic rays, and hence responsible for a sizable fraction of the cosmic neutrino flux observed by IceCube. Multimessenger observations of blazar TXS 0506+056. The 50% and 90% containment regions for the neutrino IceCube-170922A (dashed red and solid gray contours, respectively), overlain on a V-band optical image of the sky. Gamma-ray sources in this region previously detected with the Fermi spacecraft are shown as blue circles, with sizes representing their 95% positional uncertainty and labeled with the source names. The IceCube neutrino is coincident with the blazar TXS 0506+056, whose optical position is shown by the pink square. The yellow circle shows the 95% positional uncertainty of very-high-energy γ-rays detected by the MAGIC telescopes during the follow-up campaign. The inset shows a magnified view of the region around TXS 0506+056 on an R-band optical image of the sky. IMAGES: PHOASAS-SN FOR THE V-BAND OPTICAL; KANATA FOR THE R-BAND IN MAGNIFIED VIEW Previous detections of individual astrophysical sources of neutrinos are limited to the Sun and the supernova 1987A, whereas the origins of the diffuse flux of high-energy cosmic neutrinos remain unidentified. On 22 September 2017, we detected a high-energy neutrino, IceCube-170922A, with an energy of ~290 tera–electron volts. Its arrival direction was consistent with the location of a known γ-ray blazar, TXS 0506+056, observed to be in a flaring state. An extensive multiwavelength campaign followed, ranging from radio frequencies to γ-rays. These observations characterize the variability and energetics of the blazar and include the detection of TXS 0506+056 in very-high-energy γ-rays. This observation of a neutrino in spatial coincidence with a γ-ray–emitting blazar during an active phase suggests that blazars may be a source of high-energy neutrinos.

中文翻译：

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对与高能中微子 IceCube-170922A 重合的燃烧耀变体的多信使观测

来自燃烧的耀变体中微子发射的中微子与物质的相互作用非常微弱，但巨型探测器已成功探测到少量的天体物理中微子。除了漫反射背景外，仅确定了两个单独的来源：太阳和附近的 1987 年超新星。多团队合作检测到了一个高能中微子事件，其到达方向与已知的耀变体（一种具有相对论的类星体）一致射流直接沿着我们的视线定向。耀变体 TXS 0506+056 被发现正在经历伽马射线耀斑，引发了广泛的多波长运动。受这一发现的启发，IceCube 合作研究了过去几年检测到的低能中微子，在耀变体的位置发现了过量排放。因此，耀变体是天体物理学中微子的来源。科学，这个问题 p。147 页。eaat1378 耀变体在耀斑期间发出高能中微子，促使人们对整个电磁频谱进行观测。介绍 中微子是宇宙射线加速的示踪剂：电中性并以接近光速的速度行进，它们可以逃离最密集的环境，并且可以追溯到它们的起源。高能中微子预计会在耀变体中产生：强烈的河外射电、光学、X 射线，以及在某些情况下，以接近我们视线的等离子体相对论射流为特征的 γ 射线源。耀变体是宇宙中最强大的物体之一，被广泛推测是高能宇宙射线的来源。这些宇宙射线产生高能中微子和γ射线，当在射流中加速的宇宙射线与附近的气体或光子相互作用时产生。2017 年 9 月 22 日，立方公里的冰立方中微子天文台从与燃烧的 γ 射线耀变体 TXS 0506+056 一致的方向探测到了一个 ~290-TeV 的中微子。我们报告了这一观察的细节以及多波长后续活动的结果。基本原理 Multimessenger 天文学旨在对宇宙射线、中微子、引力波和各种波长的电磁辐射进行全球协调观测。预计这种结合将产生关于为最强大的天体物理源提供能量的机制的关键信息。中微子的产生伴随着来自源的电磁辐射，这有利于多波长识别。特别是，高能中微子与 γ 射线耀斑源的测量关联将阐明最高能量宇宙射线加速的机制和条件。IceCube 于 2013 年宣布了高能中微子的外星扩散通量的发现，具有暗示来自河外来源的贡献的特征，尽管个别来源尚未确定。IceCube 持续监测整个天空的天体物理中微子，为世界各地的天文台提供实时触发，测量 γ 射线、X 射线、光学、无线电和引力波，甚至可以识别快速衰落的源。结果 2017 年 9 月 22 日探测到一条高能中微子诱导的介子轨迹，自动生成警报，在检测后 1 分钟内分发到全球，并促使望远镜在广泛的波长范围内进行后续搜索。2017 年 9 月 28 日，费米大面积望远镜合作组织报告称，中微子的方向与编目 γ 射线源重合，与中微子方向成 0.1°。该源是一种被称为 TXS 0506+056 的耀变体，其测量红移为 0.34，当时处于燃烧状态，在 GeV 范围内具有增强的 γ 射线活动。通过大气切伦科夫成像望远镜进行的后续观测，特别是主要大气伽马成像切伦科夫（MAGIC）望远镜，揭示了从耀变体中检测到的 γ 射线通量达到能量高达 400 GeV 的时期。源的测量也已在 X 射线、光学和无线电波长下完成。我们研究了将中微子和 γ 射线产生相关联的模型，发现中微子与 TXS 0506+056 耀斑的相关性在 3 个标准差 (sigma) 水平上具有统计显着性。根据 TXS 0506+056 的红移，我们推导出该源的 μ 中微子光度约束，并发现它们与在 γ 射线中观察到的光度相似。结论 γ 射线和中微子的能量表明耀变体喷流可能将宇宙射线加速到至少几个 PeV。在增强的 γ 射线发射期间观察到的高能中微子与耀变体的关联表明耀变体确实可能是长期寻找的超高能宇宙射线的来源之一，因此占相当大的比例IceCube 观测到的宇宙中微子通量。Blazar TXS 0506+056 的多信使观测。中微子 IceCube-170922A 的 50% 和 90% 包容区域（分别为红色虚线和灰色实线轮廓），覆盖在天空的 V 波段光学图像上。先前由费米航天器检测到的该区域中的伽马射线源显示为蓝色圆圈，大小代表其 95% 的位置不确定性，并标有源名称。IceCube 中微子与耀变体 TXS 0506+056 重合，其光学位置由粉红色方块表示。黄色圆圈显示了 MAGIC 望远镜在后续活动中探测到的超高能 γ 射线的 95% 位置不确定性。插图显示了天空的 R 波段光学图像上 TXS 0506+056 周围区域的放大视图。图像：用于 V 波段光学器件的 PHOASAS-SN；放大视图中 R 带的 KANATA 先前对中微子的单个天体物理来源的探测仅限于太阳和超新星 1987A，而高能宇宙中微子的漫射通量的起源仍未确定。2017 年 9 月 22 日，我们探测到了一个高能中微子 IceCube-170922A，其能量约为 290 太电子伏特。它的到达方向与已知处于燃烧状态的 γ 射线耀变体 TXS 0506+056 的位置一致。随后进行了广泛的多波长活动，范围从无线电频率到 γ 射线。这些观察结果表征了耀变体的可变性和能量学，包括在超高能 γ 射线中检测到 TXS 0506+056。