Simultaneous NICER and NuSTAR Observations of the Ultracompact X-Ray Binary 4U 1543–624

Ludlam, R. M.; Jaodand, Amruta; García, Javier A.; Degenaar, N.; Tomsick, John A.; Cackett, E.; Fabian, A. C.; Gandhi, P.; Buisson, D. J. K.; Shaw, A. W.; Chakrabarty, Deepto

doi:10.3847/1538-4357/abedb0

Cited by 12 publications

(10 citation statements)

References 58 publications

(95 reference statements)

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“…Joint NuSTAR and NICER observations of the ultracompact x-ray binary (UCXB) 4U 1543-624 (Obsid 30601006002) were obtained in April 2020, and the data published by Ludlam et al 28 The comparison was made for the NuSTAR data only, and just for the continuum modeling using Fig. 17 The statistical errors are the same for the model flux before and after and not shown as they are not relevant to the flux increase estimation.…”

Section: Ultra-compact X-ray Binary 4u 1543-624mentioning

confidence: 99%

Effective area calibration of the Nuclear Spectroscopic Telescope Array

Madsen

Grefenstette

Harrison

et al. 2022

J. Astron. Telesc. Instrum. Syst.

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We present here the updated calibration of the Nuclear Spectroscopic Telescope Array, which was performed using data on the Crab accumulated over the last nine years in orbit. The basis for this new calibration contains over 250 ks of focused Crab observations (imaged through the optics) and over 500 ks of stray-light (SL) Crab observations (not imaged through optics). We measured an epoch averaged spectrum of the SL Crab data and define a canonical Crab spectrum of Γ ¼ 2.103 AE 0.001 and N ¼ 9.69 AE 0.02 keV −1 cm −2 s −1 at 1 keV, which we use as our calibration standard. This calibration released in the Calibration Data Base update 20211020 provides significant updates to: (1) the detector absorption component, (2) the detector response function, and (3) the effective area vignetting function. The calibration improves agreement between FPMA and FPMB across detectors with a standard deviation of 1.7% for repeat observations between off-axis angles of 1′ to 4′. As a consequence of the measured SL observations, the absolute flux of the instrument has increased by 5% to 15%, with 5% below 1′ off-axis angle, 10% between 1 and 2′, and 15% above 4′.

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Section: Ultra-compact X-ray Binary 4u 1543-624mentioning

confidence: 99%

Effective area calibration of the Nuclear Spectroscopic Telescope Array

Madsen

Grefenstette

Harrison

et al. 2022

J. Astron. Telesc. Instrum. Syst.

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“…In most of the cases, the reflection spectrum can show the so-called Compton hump above 10 keV (see e.g. Egron et al 2013;Miller et al 2013;Ludlam et al 2017;Coughenour et al 2018;Ludlam et al 2020Ludlam et al , 2021. The reflection component also shows some discrete features due to the fluorescence emission and photoelectric absorption by heavy ions in the accretion disc.…”

Section: Introductionmentioning

confidence: 99%

Fe Kαand Fe Kβline detection in theNuSTARspectrum of the ultra-bright Z source Scorpius X–1

Mazzola

Iaria

Salvo

et al. 2021

A&A

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Context. Low-mass X-ray binaries hosting a low-magnetised neutron star, which accretes matter via Roche-lobe overflow, are generally grouped into two classes called Atoll and Z sources after the path described in their X-ray colour-colour diagrams. Scorpius X–1 is the brightest persistent low-mass X-ray binary known so far, and it is the prototype of the Z sources. Aims. We analysed the first NuSTAR observation of this source to study its spectral emission, exploiting the high-statistics data collected by this satellite. The colour-colour diagram shows that the source was probably observed during the lower normal and flaring branches of its Z track. We separated the data from the two branches in order to investigate the evolution of the source along the track. Methods. We fitted the 3−60 keV NuSTAR spectra using the same models for the two branches. We adopted two descriptions for the continuum: in the first case, we used a blackbody and a thermal Comptonisation with seed photons originating in the accretion disc, and in the second case, we adopted a disc-blackbody and a Comptonisation with a blackbody-shaped spectrum of the incoming seed photons. A power-law fitting of the high-energy emission above 20 keV was also required in both cases. Results. The two models provide the same physical scenario for the source in the two branches: a blackbody temperature between 0.8 and 1.5 keV, a disc-blackbody with a temperature between 0.4 and 0.6 keV, and an optically thick Comptonising corona with an optical depth between 6 and 10 and a temperature about 3 keV. Furthermore, two lines related to the Kα and Kβ transitions of the He-like Fe XXV ions were detected at 6.6 keV and 7.8 keV, respectively. A hard tail modelled by a power law with a photon index between 2 and 3 was also required for the two models.

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“…We stress, however, that important exceptions exist to the arguments outlined above, since evidence for iron emission lines has been actually found in a few UCXBs with possibly carbon-oxygen white dwarf donors (e.g. van den Eijnden et al 2018;Ludlam et al 2019Ludlam et al , 2021. Alternatively, the lack of the iron emission line in J0840 may be related to an increase in the ionization of the inner accretion flow towards lower mass accretion rates, similarly to what has been proposed by van den Eijnden et al (2020a) for the case of 4U 1608−52.…”

Section: X-ray Emission Mechanismsmentioning

confidence: 81%

Multi-band observations of Swift J0840.7−3516: A new transient ultra-compact X-ray binary candidate

Zelati

Postigo

Russell

et al. 2021

A&A

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We report on multi-band observations of the transient source Swift J0840.7−3516, which was detected in outburst in 2020 February by the Neil Gehrels Swift Observatory. The outburst episode lasted just ∼5 days, during which the X-ray luminosity quickly decreased from LX ≈ 3 × 1037 d102 erg s−1 at peak down to LX ≈ 5 × 1033 d102 erg s−1 in quiescence (0.3−10 keV; d10 is the distance to the source in units of 10 kpc). Such a marked and rapid decrease in the flux was also registered at UV and optical wavelengths. In outburst, the source showed considerable aperiodic variability in the X-rays on timescales as short as a few seconds. The spectrum of the source in the energy range 0.3−20 keV was well described by a thermal, blackbody-like, component plus a non-thermal, power law-like, component and it softened considerably as the source returned to quiescence. The spectrum of the optical counterpart in quiescence showed broad emission features mainly associated with ionised carbon and oxygen, superposed on a blue continuum. No evidence for bright continuum radio emission was found in quiescence. We discuss possible scenarios for the nature of this source and show that the observed phenomenology points to a transient ultra-compact X-ray binary system.

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Simultaneous NICER and NuSTAR Observations of the Ultracompact X-Ray Binary 4U 1543–624

Cited by 12 publications

References 58 publications

Effective area calibration of the Nuclear Spectroscopic Telescope Array

Effective area calibration of the Nuclear Spectroscopic Telescope Array

Fe Kαand Fe Kβline detection in theNuSTARspectrum of the ultra-bright Z source Scorpius X–1

Multi-band observations of Swift J0840.7−3516: A new transient ultra-compact X-ray binary candidate

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