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

Kabiraj, Sanhita; Paul, Biswajit

doi:10.1093/mnras/staa2079

Cited by 12 publications

(4 citation statements)

References 23 publications

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“…Another giant X-ray outburst occurred in March 2019 with a peak luminosity in the energy range 3−78 keV of L X = 5.6 × 10 37 erg s −1 (Kabiraj & Paul 2020), similar to the discovery luminosity back in 1995. NuSTAR and AstroSat observations performed during this outburst revealed the possible presence of a cyclotron line at 10 keV together with some harmonics (Molkov et al 2019;Mukerjee et al 2020).…”

Section: Introductionsupporting

confidence: 57%

“…During AstroSat observations, a quasi-periodic oscillation at 0.090 Hz was detected during the decay of the outburst (Mukerjee et al 2020). The NuSTAR observations only detected the cyclotron line in a very narrow range of the spin phases of GRO J2058+42 and covering only ∼10% of the entire spin period (Molkov et al 2019), but it did not seem to be present in the pulse-average spectrum (Kabiraj & Paul 2020).…”

Section: Introductionmentioning

confidence: 99%

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Long-term optical variability of the Be/X-ray binary GRO J2058+42

Reig

Tzouvanou

Blinov

et al. 2023

A&A

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Context. GRO J2058+42 is a transient hard X-ray pulsar that occasionally goes into outburst. The optical counterpart is a poorly studied OB-type companion. Aims. We investigate the long-term optical variability of the Be/X-ray binary GRO J2058+42 and the possible connection with periods of enhanced X-ray activity. Methods. We performed an optical spectroscopic and photometric analysis on data collected during about 18 yr. We also present the first optical polarimetric observations of this source. Results. The long-term optical light curves in the BVRI bands and the evolution of the Hα equivalent width display a sinusoidal pattern with maxima and minima that repeat every ∼9.5 yr. The amplitude of this variability increases as the wavelength increases from 0.3 mag in the B band to 0.7 in the I band. The Hα equivalent width varied from about −0.3 to −15 Å. We found a significant decrease in the polarization degree during the low optical state. The intrinsic polarization degree changed by ∼1% from maximum to minimum. The optical maxima occur near periods of enhanced X-ray activity and are followed by a drop in the optical emission. Unlike many other Be/X-ray binaries, GRO J2058+42 does not display V/R variability. Conclusions. The long-term optical variability agrees with the standard model of a Be/X-ray binary, where the circumstellar disk of the Be star grows and dissipates on timescales of 9−10 yr. We find that the dissipation of the disk started after a major X-ray outburst. However, the stability of the Hα line shape as a double-peak profile and the lack of asymmetries suggest the absence of a warped disk and argue against the presence of a highly distorted disk during major X-ray outbursts.

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Section: Introductionsupporting

confidence: 57%

Section: Introductionmentioning

confidence: 99%

Long-term optical variability of the Be/X-ray binary GRO J2058+42

Reig

Tzouvanou

Blinov

et al. 2023

A&A

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“…Send offprint requests to: pau@physics.uoc.gr Another giant X-ray outburst occurred in March 2019 with a peak luminosity in the energy range 3-78 keV of L x = 5.6 × 10 37 erg s −1 (Kabiraj & Paul 2020), similar to the discovery luminosity back in 1995. NuSTAR and AstroSat observations performed during this outburst revealed the possible presence of a cyclotron line at 10 keV together with some harmonics (Molkov et al 2019;Mukerjee et al 2020).…”

Section: Introductionmentioning

confidence: 72%

Long-term optical variability of the Be/X-ray binary GRO J2058+42

Reig¹,

Tzouvano²,

Blinov³

et al. 2023

Preprint

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Context. GRO J2058+42 is a transient hard X-ray pulsar that occasionally goes into outburst. The optical counterpart is a poorly studied OB-type companion. Aims. We investigate the long-term optical variability of the Be/X-ray binary GRO J2058+42 and the possible connection with periods of enhanced X-ray activity. Methods. We performed an optical spectroscopic and photometric analysis on data collected during about 18 years. We also present the first optical polarimetric observations of this source.Results. The long-term optical light curves in the BVRI bands and the evolution of the Hα equivalent width display a sinusoidal pattern with maxima and minima that repeat every ∼9.5 years. The amplitude of this variability increases as the wavelength increases from 0.3 mag in the B band to 0.8 in the I band. The Hα equivalent width varied from about −0.3 to −15 Å. We found a significant decrease in the polarization degree during the low optical state. The intrinsic polarization degree changed by ∼ 1% from maximum to minimum. The optical maxima occur near periods of enhanced X-ray activity and are followed by a drop in the optical emission. Unlike many other Be/X-ray binaries, GRO J2058+42 does not display V/R variability. Conclusions. The long-term optical variability agrees with the standard model of a Be/X-ray binary, where the circumstellar disk of the Be star grows and dissipates on timescales of 9-10 years. We find that the dissipation of the disk started after a major X-ray outburst. However, the stability of the Hα line shape as a double-peak profile and the lack of asymmetries suggest the absence of a warped disk and argue against the presence of a highly distorted disk during major X-ray outbursts.

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“…Using this method Lutovinov et al (2019) estimate the field strength of GRO 1750-27 to be in the range of 3.5 -4.5 ×10 12 G. The value that we estimate is consistent with this. However, as noted by Kabiraj & Paul (2020), the estimates of the magnetic field using both these methods are not always consistent. The likely contributions could be due to the difference between the canonical NS parameters that we choose and the actual scenario.…”

Section: Discussionmentioning

confidence: 92%

NuSTAR discovery of a cyclotron line in GRO J1750-27

Devaraj,

Paul

2022

Preprint

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GRO J1750-27, discovered during an outburst in 1995 with CGRO-BATSE, is one of the farthest known Be-X-ray binary systems. This relatively poorly studied system recently went into an outburst. From the measurements of the spin-up rate of this pulsar, the X-ray fluxes during the two previous outbursts in 2008 and 2014-2015, and using the standard theory of accretion torque on magnetized neutron stars, the magnetic field strength was estimated to be 2 × 10 12 G and 3.5 − 4.5 × 10 12 G respectively. The uncertainty in the distance causes large uncertainty in the estimated magnetic field. The source was observed during the latest outburst using the NuSTAR telescope during the rising phase of the outburst. We estimate the spin period of the source to be 4.45s using which we produced energy resolved pulse profiles between 3 and 79 keV. We find that the profiles appear to be double peaked at low energies (<20 keV) while evolving into a single peak at higher energies (>20 keV). The broadband spectrum of this source was described by a power-law modified by an exponential cut off and we report the discovery of a cyclotron resonant scattering feature (CRSF) in this hard X-ray spectrum of this source at 43 keV indicating a magnetic field strength of 3.7 ×10 12 G. Our estimate of the magnetic field strength using the cyclotron line is consistent with the estimate made using the accretion torque model.

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

Cited by 12 publications

References 23 publications

Long-term optical variability of the Be/X-ray binary GRO J2058+42

Long-term optical variability of the Be/X-ray binary GRO J2058+42

Long-term optical variability of the Be/X-ray binary GRO J2058+42

NuSTAR discovery of a cyclotron line in GRO J1750-27

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