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Spectral and Temporal Properties of the Ultra-Luminous X-Ray Pulsar in M82 from 15 Years of Chandra Observations and Analysis of the Pulsed Emission Using NuSTARThe recent discovery by Bachetti et al. of a pulsar in M82 that can reach luminosities of up to 10(exp 40) erg s(exp -1), a factor of approximately 100 times the Eddington luminosity for a 1.4 solar mass compact object, poses a challenge for accretion physics. In order to better understand the nature of this source and its duty cycle, and in light of several physical models that have been subsequently published, we conduct a spectral and temporal analysis of the 0.58 keV X-ray emission from this source from 15 years of Chandra observations. We analyze 19 ACIS observations where the point-spread function (PSF) of the pulsar is not contaminated by nearby sources. We fit the Chandra spectra of the pulsar with a power-law model and a disk blackbody model, subjected to interstellar absorption in M82. We carefully assess for the effect of pile-up in our observations, where four observations have a pile-up fraction of 10, which we account for during spectral modeling with a convolution model. When fitted with a power-law model, the average photon index when the source is at high luminosity (LX greater than 10(exp 39) erg s(exp -1) is equal to gamma 1.33 +/-.0.15. For the disk blackbody model, the average temperature is T(sub in) 3.24 +/- 0.65 keV, the spectral shape being consistent with other luminous X-ray pulsars. We also investigated the inclusion of a soft excess component and spectral break, finding that the spectra are also consistent with these features common to luminous X-ray pulsars. In addition, we present spectral analysis from NuSTAR over the 3-50 keV range where we have isolated the pulsed component. We find that the pulsed emission in this band is best fit by a power-law with a high-energy cutoff, where gamma is equal to 0.6 +/- 0.3 and E(sub C) is equal to 14(exp +5) (sub -3)) keV. While the pulsar has previously been identified as a transient, we find from our longer-baseline study that it has been remarkably active over the 15-year period, where for 9/19 (47%) observations that we analyzed, the pulsar appears to be emitting at a luminosity in excess of 10( exp (39) erg s (exp −1), greater than 10 times its Eddington limit.
Document ID
20170002312
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Brightman, Murray
(California Inst. of Tech. Pasadena, CA, United States)
Harrison, Fiona
(California Inst. of Tech. Pasadena, CA, United States)
Walton, Dominic J.
(California Inst. of Tech. Pasadena, CA, United States)
Fuerst, Felis
(California Inst. of Tech. Pasadena, CA, United States)
Zezas, Andreas
(Crete Univ. Heraklion, Greece)
Bachetti, Matteo
(Osservatorio Astronomico di Cagliari Italy)
Grefenstette, Brian
(California Inst. of Tech. Pasadena, CA, United States)
Ptak, Andrew
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Tendulkar, Shriharsh
(California Inst. of Tech. Pasadena, CA, United States)
Yukita, Mihoko
(Johns Hopkins Univ. Baltimore, MD, United States)
Date Acquired
March 17, 2017
Publication Date
January 5, 2016
Publication Information
Publication: The Astrophysical Journal
Publisher: The American Astronomical Society
Volume: 816
Issue: 2
ISSN: 0004-637X
e-ISSN: 1538-4357
Subject Category
Astrophysics
Report/Patent Number
GSFC-E-DAA-TN40083
Funding Number(s)
CONTRACT_GRANT: NNX14AB76A
Distribution Limits
Public
Copyright
Other
Keywords
individual (M82) - stars: neutron X rays; binaries

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