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Revisiting the spectral and timing properties of 4U 1909+07 with NuSTAR and Astrosat

Revisiting the spectral and timing properties of 4U 1909+07 with NuSTAR and Astrosat
Revisiting the spectral and timing properties of 4U 1909+07 with NuSTAR and Astrosat
We present the results obtained from the analysis of high mass X-ray binary pulsar 4U 1909+07 using NuSTAR and Astrosat observations in 2015 and 2017 July, respectively. X-ray pulsations at ~604 s are clearly detected in our study. Based on the long term spin-frequency evolution, the source is found to spun up in the last 17 years. We observed a strongly energy-dependent pulse profile that evolved from a complex broad structure in soft X-rays into a profile with a narrow emission peak followed by a plateau in energy ranges above 20 keV. This behaviour ensured a positive correlation between the energy and pulse fraction. The pulse profile morphology and its energy-evolution are almost similar during both the observations, suggesting a persistent emission geometry of the pulsar over time. The broadband energy spectrum of the pulsar is approximated by an absorbed high energy exponential cutoff power law model with iron emission lines. In contrast to the previous report, we found no statistical evidence for the presence of cyclotron absorption features in the X-ray spectra. We performed phase-resolved spectroscopy by using data from the NuSTAR observation. Our results showed a clear signature of absorbing material at certain pulse-phases of the pulsar. These findings are discussed in terms of stellar wind distribution and its effect on the beam geometry of this wind-fed accreting neutron star. We also reviewed the subsonic quasi-spherical accretion theory and its implication on the magnetic field of 4U 1909+07 depending on the global spin-up rate.
Pulsars: individual: 4U 1909+07, Stars: neutron, X-rays: stars
0035-8711
4830-4838
Jaisawal, Gaurava K.
4d5dcd39-0881-426d-8ad7-f378238405ae
Naik, Sachindra
af278542-177d-47f9-ae51-00babd03e877
Ho, Wynn C.G.
d78d4c52-8f92-4846-876f-e04a8f803a45
Kumari, Neeraj
dcababb5-60ea-45ed-83aa-e22e67225a64
Epili, Prahlad
d06a01d3-3603-428c-bae2-ae597a70a2de
Vasilopoulos, Grigorios
300d6991-00cb-409a-9412-021eeb96fa49
Jaisawal, Gaurava K.
4d5dcd39-0881-426d-8ad7-f378238405ae
Naik, Sachindra
af278542-177d-47f9-ae51-00babd03e877
Ho, Wynn C.G.
d78d4c52-8f92-4846-876f-e04a8f803a45
Kumari, Neeraj
dcababb5-60ea-45ed-83aa-e22e67225a64
Epili, Prahlad
d06a01d3-3603-428c-bae2-ae597a70a2de
Vasilopoulos, Grigorios
300d6991-00cb-409a-9412-021eeb96fa49

Jaisawal, Gaurava K., Naik, Sachindra, Ho, Wynn C.G., Kumari, Neeraj, Epili, Prahlad and Vasilopoulos, Grigorios (2020) Revisiting the spectral and timing properties of 4U 1909+07 with NuSTAR and Astrosat. Monthly Notices of the Royal Astronomical Society, 498 (4), 4830-4838. (doi:10.1093/mnras/staa2604).

Record type: Article

Abstract

We present the results obtained from the analysis of high mass X-ray binary pulsar 4U 1909+07 using NuSTAR and Astrosat observations in 2015 and 2017 July, respectively. X-ray pulsations at ~604 s are clearly detected in our study. Based on the long term spin-frequency evolution, the source is found to spun up in the last 17 years. We observed a strongly energy-dependent pulse profile that evolved from a complex broad structure in soft X-rays into a profile with a narrow emission peak followed by a plateau in energy ranges above 20 keV. This behaviour ensured a positive correlation between the energy and pulse fraction. The pulse profile morphology and its energy-evolution are almost similar during both the observations, suggesting a persistent emission geometry of the pulsar over time. The broadband energy spectrum of the pulsar is approximated by an absorbed high energy exponential cutoff power law model with iron emission lines. In contrast to the previous report, we found no statistical evidence for the presence of cyclotron absorption features in the X-ray spectra. We performed phase-resolved spectroscopy by using data from the NuSTAR observation. Our results showed a clear signature of absorbing material at certain pulse-phases of the pulsar. These findings are discussed in terms of stellar wind distribution and its effect on the beam geometry of this wind-fed accreting neutron star. We also reviewed the subsonic quasi-spherical accretion theory and its implication on the magnetic field of 4U 1909+07 depending on the global spin-up rate.

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2008.11093 - Accepted Manuscript
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Accepted/In Press date: 24 August 2020
e-pub ahead of print date: 27 August 2020
Published date: November 2020
Keywords: Pulsars: individual: 4U 1909+07, Stars: neutron, X-rays: stars

Identifiers

Local EPrints ID: 443779
URI: http://eprints.soton.ac.uk/id/eprint/443779
ISSN: 0035-8711
PURE UUID: 9cfd3d51-694a-4df5-a7ff-6798ab598f8d
ORCID for Wynn C.G. Ho: ORCID iD orcid.org/0000-0002-6089-6836

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Date deposited: 11 Sep 2020 16:31
Last modified: 26 Nov 2021 02:54

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Contributors

Author: Gaurava K. Jaisawal
Author: Sachindra Naik
Author: Wynn C.G. Ho ORCID iD
Author: Neeraj Kumari
Author: Prahlad Epili
Author: Grigorios Vasilopoulos

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