Variability of extragalactic x-ray jets on kiloparsec scales

ABSTRACT Unexpectedly strong X-ray emission from extragalactic radio jets on kiloparsec scales has been one of the major discoveries of Chandra, the only X-ray observatory capable of

sub-arcsecond-scale imaging. The origin of this X-ray emission, which appears as a second spectral component from that of the radio emission, has been debated for over two decades. The most

commonly assumed mechanism is inverse-Compton upscattering of the cosmic microwave background by very low-energy electrons in a still highly relativistic jet. Under this mechanism, no

variability in the X-ray emission is expected. Here we report the detection of X-ray variability in the large-scale jet population, using a novel statistical analysis of 53 jets with

multiple Chandra observations. Taken as a population, we find that the distribution of _P_ values from a Poisson model is strongly inconsistent with steady emission, with a global _P_ value

of 1.96 × 10−4 under a Kolmogorov–Smirnov test against the expected uniform (0, 1) distribution. These results strongly imply that the dominant mechanism of X-ray production in

kiloparsec-scale jets is synchrotron emission by a second population of electrons reaching multi-teraelectronvolt energies. X-ray variability on the timescale of months to a few years

implies extremely small emitting volumes much smaller than the cross-section of the jet. Access through your institution Buy or subscribe This is a preview of subscription content, access

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institutional subscriptions * Read our FAQs * Contact customer support SIMILAR CONTENT BEING VIEWED BY OTHERS POWERFUL EXTRAGALACTIC JETS DISSIPATE THEIR KINETIC ENERGY FAR FROM THE CENTRAL

BLACK HOLE Article Open access 30 October 2020 RESOLVING ACCELERATION TO VERY HIGH ENERGIES ALONG THE JET OF CENTAURUS A Article 17 June 2020 GAMMA-RAY FLARES FROM RELATIVISTIC MAGNETIC

RECONNECTION IN THE JET OF THE QUASAR 3C 279 Article Open access 21 August 2020 DATA AVAILABILITY All observations used in this study are publicly available. In particular, the Chandra X-Ray

Observatory archive can be accessed on the web at https://cda.harvard.edu/chaser/. Radio observations with NRAO facilities are available at https://data.nrao.edu, ACTA observations from

https://atoa.atnf.csiro.au/. Extensive tables of reduced data necessary to repeat these analyses are available as supplementary Excel files, further described in Supplementary Section 3.g

CODE AVAILABILITY The analysis software used in this study for reducing astronomical data is described in Methods and publicly available from the respective observatories. The statistical

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Chandra Archival Grant 16700615 (E.T.M.), ADAP grant NNX15AE55G (E.T.M.) and NSF grant 1714380 (E.T.M.), as well as support from the Natural Sciences and Engineering Research Council of

Canada, grant ID RGPIN-2020-05897 (Y.T. and N.R.). This research was made possible through use of data obtained from the Chandra Data Archive and the Chandra Source Catalog, and software

provided by the Chandra X-Ray Center (CXC) in the application packages CIAO and sherpa. The Australia Telescope Compact Array is part of the Australia Telescope National Facility, which is

funded by the Australian Government for operation as a national facility managed by CSIRO. We acknowledge the Gomeroi people as the traditional owners of the observatory site. This paper

makes use of the following ALMA data sets: 2012.1.00688.S, 2016.1.01481.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC

(Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. The NRAO is a

facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * Department of Physics,

University of Maryland, Baltimore County, Baltimore, MD, USA Eileen T. Meyer, Aamil Shaik, Karthik Reddy, Markos Georganopoulos, Nat DeNigris & Max Trevor * Department of Mathematics,

Imperial College London, London, UK Yanbo Tang * Department of Statistical Sciences, University of Toronto, Toronto, Ontario, Canada Nancy Reid * School of Earth and Space Exploration,

Arizona State University, Tempe, AZ, USA Karthik Reddy * The William H. Miller III Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD, USA Peter Breiding & 

Marco Chiaberge * Space Telescope Science Institute for the European Space Agency, Baltimore, MD, USA Marco Chiaberge * Department of Aerospace, Physics and Space Sciences, Florida Institute

of Technology, Melbourne, FL, USA Eric Perlman & Devon Clautice * SETI Institute, Mountain View, CA, USA William Sparks * Space Telescope Science Institute, Baltimore, MD, USA William

Sparks * Department of Astronomy, University of Massachusetts Amherst, Amherst, MA, USA Nat DeNigris * Department of Physics, University of Maryland, College Park, College Park, MD, USA Max

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Scholar CONTRIBUTIONS E.T.M. conceived the project, developed the data analysis methods, contributed to the multiwavelength data analysis and wrote the paper. A.S. carried out the X-ray data

analysis with contributions from E.T.M., K.R., P.B., N.D., D.C. and M.T. Y.T. and N.R. contributed the statistical analysis methods and expertise. K.R. and P.B. contributed to the data

analysis and interpretation. M.G. contributed to the interpretation and theoretical implications. All authors contributed to the editing of the paper and interpretation of results.

CORRESPONDING AUTHOR Correspondence to Eileen T. Meyer. ETHICS DECLARATIONS COMPETING INTERESTS The authors declare no competing interests. PEER REVIEW PEER REVIEW INFORMATION _Nature

Astronomy_ thanks the anonymous reviewers for their contribution to the peer review of this work. ADDITIONAL INFORMATION PUBLISHER’S NOTE Springer Nature remains neutral with regard to

jurisdictional claims in published maps and institutional affiliations. EXTENDED DATA EXTENDED DATA FIG. 1 Histogram of the single-region p-values for the full sample of 155 regions. The

distribution shows an excess at low values relative to the expected uniform (0, 1) distribution, indicating variability in the population. EXTENDED DATA FIG. 2 HISTOGRAM OF THE PERCENT

DIFFERENCE OF EACH EPOCH SOURCE RATE FROM \(\BAR{\MU }\) FOR ALL REGIONS. Including all epochs on all regions, there are 545 distinct observations. The distribution has a mean of 1.02% and a

standard deviation of 28.5%. The mean of the absolute value of the percent difference is 18%. SUPPLEMENTARY INFORMATION SUPPLEMENTARY INFORMATION Supplementary Figs. 1–5, Table 1, Methods,

Discussion and description of Supplementary Tables 2–5. SUPPLEMENTARY DATA 1 Supplementary Tables 2–5. RIGHTS AND PERMISSIONS Springer Nature or its licensor (e.g. a society or other

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article is solely governed by the terms of such publishing agreement and applicable law. Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Meyer, E.T., Shaik, A., Tang, Y. _et

al._ Variability of extragalactic X-ray jets on kiloparsec scales. _Nat Astron_ 7, 967–975 (2023). https://doi.org/10.1038/s41550-023-01983-1 Download citation * Received: 17 May 2022 *

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