Discovery of a Pulse-phase-transient Cyclotron Line in the X-Ray pulsar GRO J2058+42

Molkov, S.; Lutovinov, A.; Tsygankov, Sergey S.; Mereminskiy, I. A.; Mushtukov, Alexander A.

doi:10.3847/2041-8213/ab3e4d

Cited by 48 publications

(36 citation statements)

References 43 publications

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“…Despite a non-detection of any cyclotron line in the spectra, we are not entirely rejecting the idea of presence of it and provided an upper limit of the optical depth for each energy (Figure 4). In this context, we would like to mention Molkov et al (2019). They reported a cyclotron line at 10 keV along with itâȂŹs two harmonics at a particular pulse phase.…”

Section: Discussionmentioning

confidence: 96%

Broad-band X-ray characteristics of the transient pulsar GRO J2058+42

Kabiraj

Paul

2020

Monthly Notices of the Royal Astronomical Society

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The Be X-ray binary GRO J2058+42 recently went through a Type-II outburst during March-April 2019 lasting for about 50 days. This outburst was detected with the operating all sky X-ray monitors like the Fermi-GBM, Swift-BAT and MAXI-GSC. Two NuSTAR observations were also made, one during the rise and other during the decay of the outburst. It gave us the unique opportunity to analyze the broadband characteristics of the pulsar for the first time and accretion torque characteristics of the pulsar over a range of X-ray luminosity. The pulse profiles are strongly energy dependent, with at least four different pulse components at low energy (< 20 keV) which evolves to a single-peaked profile at high energy (> 30 keV). In each of the narrow energy bands, the pulse profiles are nearly identical in the two NuSTAR observations. The spectra from both the observations are fitted well to a power-law with a Fermi-Dirac type high energy cutoff. We ruled out presence of a cyclotron line in the pulse phase averaged X-ray spectrum in the NuSTAR band with an optical depth greater than 0.15. An iron emission line is detected in both the NuSTAR spectra with an equivalent width of about 125 eV. We looked at the dependence of the spin-up rate on the luminosity and estimated the magnetic field strength from that, which came out to be much higher compared to other known BeXRB pulsars. Lastly, we discussed the inadequacy of the torque-luminosity relation for determination of magnetic field strength of neutron stars.

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Section: Discussionmentioning

confidence: 96%

Broad-band X-ray characteristics of the transient pulsar GRO J2058+42

Kabiraj

Paul

2020

Monthly Notices of the Royal Astronomical Society

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“…The absence of the cyclotron line in some observed energy spectra of the XRBs' can possibly due to a large gradient of B-field strength over the visible column height or the latitude on the surface of a neutron star. The appearance of cyclotron line in certain pulse phases can be due to the partial eclipsing of the accretion column during which an observer is able to see some parts of the column (Molkov et al 2019). In such a case, the magnetic field in the visible part of the accretion column is not so varied and we can observe cyclotron line in these phases like in the case of GRO J2058+42 (Molkov et al 2019).…”

Section: Discussionmentioning

confidence: 99%

“…The appearance of cyclotron line in certain pulse phases can be due to the partial eclipsing of the accretion column during which an observer is able to see some parts of the column (Molkov et al 2019). In such a case, the magnetic field in the visible part of the accretion column is not so varied and we can observe cyclotron line in these phases like in the case of GRO J2058+42 (Molkov et al 2019). This can also be due to the gravitational bending of light as it affects the visibility of both the accretion columns and neutron star (see eg.…”

Section: Discussionmentioning

confidence: 99%

Timing and spectral properties of Be/Xray pulsar 4U 1901+03 during 2019 outburst

Rai,

Paul

2021

Preprint

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We have studied the timing and spectral properties of the BeXB 4U 1901+03 during the 2019 outburst using NuSTAR, Swift, and NICER observations. Flares are in all observations and were of tens to hundreds of seconds duration. Pulse profiles were changing significantly with time and the luminosity of the source. An increase in the height of the peak of the pulse profiles was observed with energy. The pulse fraction increases with energy and at the end of the outburst. The variation of the pulse profile with time indicates the transition of the pulsar in different accretion regimes. The absorption like feature at 10 keV shows a positive correlation with the luminosity and along with other spectral parameters this feature was also pulse phase dependent. As the distance to the source is not precisely known hence we cannot confirm this feature to be CSRF and also cannot ignore other possible explanations of the feature. Another absorption like feature about 30 keV was observed in the spectra of the last two NuSTAR observations and has line energy of about 30.37±0.55 and 30.23±0.62 keV respectively. We have also studied the variation of the line energy, width, and optical depth of this feature with pulse phase. The softening of the spectrum along with the increase in pulse fraction at the end of the outburst and absence of pulsation after 58665.09 MJD suggest that pulsar has entered propeller phase, also abrupt decrease in Swift -XRT flux supports the fact.

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“…monics are appeared only at certain phases of rotation of the neutron star (see, e.g. Molkov et al 2019Molkov et al , 2021. Particularly, we produced energy spectra of the source in 10 evenly distributed phase bins.…”

Section: Broad-band X-ray Spectrummentioning

confidence: 99%

SRG/ART-XC discovery of SRGA J204318.2+443815: Towards the complete population of faint X-ray pulsars

Lutovinov

Tsygankov

Mereminskiy

et al. 2022

A&A

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We report a discovery of a new long-period X-ray pulsar SRGA J204318.2+443815/SRGe J204319.0+443820 in the Be binary system. The source was found in the second all-sky survey by the Mikhail Pavlinsky ART-XC telescope on board the SRG mission. The follow-up observations with XMM-Newton, NICER and NuSTAR observatories allowed us to discover a strong coherent signal in the source light curve with the period of ∼ 742 s. The pulsed fraction was found to depend on the energy increasing from ∼ 20% in soft X-rays to > 50% at high energies, as it is typical for X-ray pulsars. The source demonstrate a quite hard spectrum with an exponential cutoff at high energies and bolometric luminosity of L X 4 × 10 35 erg s −1 . Dedicated optical and infrared observations with the RTT-150, NOT, Keck and Palomar telescopes revealed a number of emission lines (H α , He i, Pashen and Braket series) with the strongly absorbed continuum. All of above suggests that SRGA J204318.2+443815/SRGe J204319.0+443820 is a new persistent low luminosity X-ray pulsar in a distant binary system with a Be-star of the B0-B2e class. Thus the SRG observatory allow us to unveil the hidden population of faint persistent objects including the population of slowly rotating X-ray pulsars in Be systems.

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Discovery of a Pulse-phase-transient Cyclotron Line in the X-Ray pulsar GRO J2058+42

Cited by 48 publications

References 43 publications

Broad-band X-ray characteristics of the transient pulsar GRO J2058+42

Broad-band X-ray characteristics of the transient pulsar GRO J2058+42

Timing and spectral properties of Be/Xray pulsar 4U 1901+03 during 2019 outburst

SRG/ART-XC discovery of SRGA J204318.2+443815: Towards the complete population of faint X-ray pulsars

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