{"title":"Broad-band non-thermal emission of odd radio circles induced by explosive galactic outflow remnants and their evolution","authors":"Yutaka Fujita, Norita Kawanaka, Susumu Inoue","doi":"10.1093/pasj/psae046","DOIUrl":null,"url":null,"abstract":"Odd radio circles (ORCs) are mysterious rings of faint, diffuse emission recently discovered in radio surveys, some of which may be associated with galaxies in relatively dense environments. We propose that such ORCs are synchrotron emission from remnants of explosive galactic outflows, calling them OGREs, and discuss their broad-band non-thermal emission and evolution. We posit that a large amount of energy was ejected from the central galaxy in the past, creating an outgoing shock that accelerates cosmic rays. Assuming plausible values for the density, temperature and magnetic field of the ambient medium, consistency with the observed spectral index, size, and power of the ORCs requires the energy to be as high as ∼1060 erg, suggesting that their sources could be active galactic nuclei. We calculate the spectral energy distributions (SEDs) of the OGREs and their evolution, including synchrotron, inverse Compton (IC), and bremsstrahlung emission from electrons, and pion-decay emission from protons. We find that the SEDs of the younger OGREs are not greatly different from those of older ones currently observable as ORCs if radiative cooling of electrons is effective. As such younger OGREs are expected to be rarer and smaller, they may not be readily observable. However, if radiative cooling of electrons is ineffective, younger OGREs may be detectable in X-rays.","PeriodicalId":20733,"journal":{"name":"Publications of the Astronomical Society of Japan","volume":null,"pages":null},"PeriodicalIF":2.2000,"publicationDate":"2024-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Publications of the Astronomical Society of Japan","FirstCategoryId":"101","ListUrlMain":"https://doi.org/10.1093/pasj/psae046","RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"ASTRONOMY & ASTROPHYSICS","Score":null,"Total":0}
引用次数: 0
Abstract
Odd radio circles (ORCs) are mysterious rings of faint, diffuse emission recently discovered in radio surveys, some of which may be associated with galaxies in relatively dense environments. We propose that such ORCs are synchrotron emission from remnants of explosive galactic outflows, calling them OGREs, and discuss their broad-band non-thermal emission and evolution. We posit that a large amount of energy was ejected from the central galaxy in the past, creating an outgoing shock that accelerates cosmic rays. Assuming plausible values for the density, temperature and magnetic field of the ambient medium, consistency with the observed spectral index, size, and power of the ORCs requires the energy to be as high as ∼1060 erg, suggesting that their sources could be active galactic nuclei. We calculate the spectral energy distributions (SEDs) of the OGREs and their evolution, including synchrotron, inverse Compton (IC), and bremsstrahlung emission from electrons, and pion-decay emission from protons. We find that the SEDs of the younger OGREs are not greatly different from those of older ones currently observable as ORCs if radiative cooling of electrons is effective. As such younger OGREs are expected to be rarer and smaller, they may not be readily observable. However, if radiative cooling of electrons is ineffective, younger OGREs may be detectable in X-rays.
古怪射电圈(ORCs)是最近在射电巡天中发现的神秘的微弱弥散发射环,其中一些可能与处于相对致密环境中的星系有关。我们认为这些射电怪圈是星系爆炸性流出的残余物发出的同步辐射,称之为射电怪圈(OGREs),并讨论了它们的宽波段非热辐射和演化。我们假设过去有大量的能量从中央星系喷射出来,形成了外流冲击,加速了宇宙射线。假定环境介质的密度、温度和磁场值是可信的,要与观测到的ORC的光谱指数、大小和功率相一致,其能量必须高达∼1060 erg,这表明它们的来源可能是活动星系核。我们计算了OGREs的光谱能量分布(SEDs)及其演化过程,包括电子的同步辐射、反康普顿辐射(IC)和轫致辐射,以及质子的先驱衰变辐射。我们发现,如果电子的辐射冷却是有效的,那么较年轻的 OGREs 的 SED 与目前作为 ORC 观测到的较老的 OGREs 的 SED 并无太大区别。由于较年轻的 OGREs 比较罕见,体积也较小,因此可能不容易观测到。不过,如果电子的辐射冷却无效,较年轻的 OGRE 可能会在 X 射线中被探测到。
期刊介绍:
Publications of the Astronomical Society of Japan (PASJ) publishes the results of original research in all aspects of astronomy, astrophysics, and fields closely related to them.