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Article

A Long-Term Study of Ultraluminous X-ray Sources in NGC 891

1
Department of Astronomy and Astrophysics, University of Chicago, 5640 S. Ellis Ave, Chicago, IL 60637, USA
2
Department of Physics and Engineering Physics, Fordham University, 441 E. Fordham Rd., Bronx, NY 10458, USA
*
Author to whom correspondence should be addressed.
Academic Editor: Piergiorgio Casella
Universe 2022, 8(1), 18; https://doi.org/10.3390/universe8010018
Received: 25 November 2021 / Revised: 17 December 2021 / Accepted: 21 December 2021 / Published: 29 December 2021
(This article belongs to the Section Compact Objects)
We perform empirical fits to the Chandra and XMM-Newton spectra of three ultraluminous X-ray sources (ULXs) in the edge-on spiral galaxy NGC 891, monitoring the region over a 17-year time window. One of these sources was visible since the early 1990s with ROSAT and was observed multiple times with Chandra and XMM-Newton. Another was visible since 2011. We build upon prior analyses of these sources by analyzing all available data at all epochs. Where possible Chandra data is used, since its superior spatial resolution allows for more effective isolation of the emission from each individual source, thus providing a better determination of their spectral properties. We also identify a new transient ULX, CXOU J022230.1+421937, which faded from view over the course of a two month period from Nov 2016 to Jan 2017. Modeling of each source at every epoch was conducted using six different models ranging from thermal bremsstrahlung to accretion disk models. Unfortunately, but as is common with many ULXs, no single model yielded a much better fit than the others. The two known sources had unabsorbed luminosities that remained fairly consistent over five or more years. Various possibilities for the new transient ULX are explored. View Full-Text
Keywords: X-rays; galaxies; individual (NGC 891); accretion; accretion disks X-rays; galaxies; individual (NGC 891); accretion; accretion disks
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MDPI and ACS Style

Earley , N.M.; Dwarkadas , V.V.; Cirillo , V. A Long-Term Study of Ultraluminous X-ray Sources in NGC 891. Universe 2022, 8, 18. https://doi.org/10.3390/universe8010018

AMA Style

Earley  NM, Dwarkadas  VV, Cirillo  V. A Long-Term Study of Ultraluminous X-ray Sources in NGC 891. Universe. 2022; 8(1):18. https://doi.org/10.3390/universe8010018

Chicago/Turabian Style

Earley , Nicholas M., Vikram V. Dwarkadas , and Victoria Cirillo . 2022. "A Long-Term Study of Ultraluminous X-ray Sources in NGC 891" Universe 8, no. 1: 18. https://doi.org/10.3390/universe8010018

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