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Radio continuum, microwave and gamma-ray images of the Milky Way reveal a conspicuous, loop-like structure that fills almost half of the northern Galactic hemisphere, called Loop I. The interior of Loop I is shining in soft X-rays, and its…

Astrophysics of Galaxies · Physics 2023-04-27 Rosine Lallement

The Fermi bubbles were possibly created by large injections of energy into the Galactic Center (GC), either by an active galactic nucleus (AGN) or by nuclear starburst more than ~10 Myr ago. However, the origin of the diffuse gamma-ray…

High Energy Astrophysical Phenomena · Physics 2018-03-12 Jun Kataoka , Yoshiaki Sofue , Yoshiyuki Inoue , Masahiro Akita , Shinya Nakashima , Tomonori Totani

There are two spectacular structures in our Milky Way: the {\it Fermi} bubbles in gamma-ray observations and the North Polar Spur (NPS) structure in X-ray observations. Because of their morphological similarities, they may share the same…

Astrophysics of Galaxies · Physics 2018-12-26 Guobin Mou , Dongze Sun , Fuguo Xie

Loop I/North Polar Spur (NPS) is the giant arc structure above the Galactic plane observed at radio wavelengths ($\lesssim 10$ GHz). There has been long-standing debate about its origin. While many people believe that it black consists of…

Astrophysics of Galaxies · Physics 2025-04-08 Yanping Cong , Bin Yue , Yidong Xu , Furen Deng , Jiajun Zhang , Xuelei Chen

We argue that the North Polar Spur (NPS) and many less prominent structures are formed by gaseous metal-rich plumes associated with star-forming regions (SFRs). The SFRs located at the tangent to the 3-5~kpc rings might be particularly…

High Energy Astrophysical Phenomena · Physics 2024-11-27 E. Churazov , I. Khabibullin , A. M. Bykov , N. N. Chugai , R. A. Sunyaev , V. P. Utrobin , I. I. Zinchenko

The North Polar Spur (NPS) is a prominent diffuse X-ray feature whose origin has remained uncertain for decades. Using a uniform analysis of archival \textit{Suzaku} and \textit{XMM--Newton} data with new \textit{Chandra} observations, we…

High Energy Astrophysical Phenomena · Physics 2026-05-21 Anjali Gupta , Smita Mathur , Joshua Kingsbury , Anthony Taylor , Sanskriti Das , Joy Bhattacharya , Manami Roy , Yair Krongold

Loop I is a nearby giant radio loop spanning over 100 degrees and centered on the Sco-Cen OB association. It may correspond to a superbubble formed by the joint action of stellar winds and supernova remnants. ROSAT observations revealed…

High Energy Astrophysical Phenomena · Physics 2019-08-13 Jean-Marc Casandjian , Isabelle Grenier

The North Polar Spur (NPS) is one of the largest structures observed in the Milky Way in both the radio and soft x-rays. While several predictions have been made regarding the origin of the NPS, modelling the structure is difficult without…

Astrophysics of Galaxies · Physics 2020-10-28 Kaustav K. Das , Catherine Zucker , Joshua S. Speagle , Alyssa Goodman , Gregory M. Green , João Alves

The North Polar Spur (NPS) is the brightest filament of Loop I, a large circular feature in the radio continuum sky. In this paper, a model consisting of two synchrotron emitting shells is presented that reproduces large-scale structures…

Astrophysics · Physics 2009-06-23 M. Wolleben

We report a correspondence between giant, polarized microwave structures emerging north from the Galactic plane near the Galactic center and a number of GeV gamma-ray features, including the eastern edge of the recently-discovered northern…

High Energy Astrophysical Phenomena · Physics 2012-02-17 David I. Jones , Roland M. Crocker , Wolfgang Reich , Jürgen Ott , Felix A. Aharonian

Most models identify the X-ray bright North Polar Spur (NPS) with a hot interstellar (IS) bubble in the Sco-Cen star-forming region at $\simeq$130 pc. An opposite view considers the NPS as a distant structure associated with Galactic…

Astrophysics of Galaxies · Physics 2016-11-23 R. Lallement , S. Snowden , K. D. Kuntz , T. M. Dame , D. Koutroumpa , I. Grenier , J. M. Casandjian

We constrain the origin of Fermi Bubbles using 2D hydrodynamical simulations of both star formation driven and black hole accretion driven wind models. We compare our results with recent observations of OVIII to OVII line ratio within and…

Astrophysics of Galaxies · Physics 2017-03-22 Kartick C. Sarkar , Biman B. Nath , Prateek Sharma

The Fermi bubbles are large gamma-ray-emitting structures. They are symmetric about the Galactic Centre (GC), and their creation is therefore attributed to intensive energy injection at the GC. In this study, we focus on the non-equilibrium…

High Energy Astrophysical Phenomena · Physics 2022-12-16 Yutaka Fujita

Using hydrodynamical simulations, we show for the first time that an episode of star formation in the center of the Milky Way, with a star-formation-rate (SFR) $\sim 0.5$ M$_\odot$ yr$^{-1}$ for $\sim 30$ Myr, can produce bubbles that…

Astrophysics of Galaxies · Physics 2015-09-30 Kartick Chandra Sarkar , Biman B. Nath , Prateek Sharma

Data from the Fermi-LAT reveal two large gamma-ray bubbles, extending 50 degrees above and below the Galactic center, with a width of about 40 degrees in longitude. The gamma-ray emission associated with these bubbles has a significantly…

High Energy Astrophysical Phenomena · Physics 2011-01-03 Meng Su , Tracy R. Slatyer , Douglas P. Finkbeiner

We present Suzaku X-ray observations along two edge regions of the Fermi Bubbles, with eight ~20 ksec pointings across the northern part of the North Polar Spur (NPS) surrounding the north bubble and six across the southernmost edge of the…

High Energy Astrophysical Phenomena · Physics 2015-06-17 J. Kataoka , M. Tahara , T. Totani , Y. Sofue , L. Stawarz , Y. Takahashi , Y. Takeuchi , H. Tsunemi , M. Kimura , Y. Takei , C. C. Cheung , Y. Inoue , T. Nakamori

We present radio continuum and polarization images of the North Polar Spur (NPS) from the Global Magneto-Ionic Medium Survey (GMIMS) conducted with the Dominion Radio Astrophysical Observatory 26-m Telescope. We fit polarization angle…

The Fermi Bubbles are gamma-ray structures extending from the center of the Milky Way to +/-50 degree Galactic latitude that were discovered in data obtained by the Fermi/LAT instrument. Their origin and power source remain uncertain. To…

High Energy Astrophysical Phenomena · Physics 2025-11-11 Ami Tank , Roland Crocker , Mark R. Krumholz

The nature of the bipolar, $\gamma$-ray Fermi bubbles (FB) is still unclear, in part because their faint, high-latitude X-ray counterpart has until now eluded a clear detection. We stack ROSAT data at varying distances from the FB edges,…

High Energy Astrophysical Phenomena · Physics 2020-01-24 Uri Keshet , Ilya Gurwich

The Fermi Bubbles are giant Galactic structures observed in both gamma-rays and microwaves. Recent studies have found support for the hypothesis that the gamma-ray and microwave emission can both be understood as arising from a hard…

High Energy Astrophysical Phenomena · Physics 2017-05-03 Sruthi A. Narayanan , Tracy R. Slatyer
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