Broad-band spectral analysis of the accreting millisecond X-ray pulsar SAX J1748.9−2021

Pintore, Fabio; Sanna, A.; Salvo, T. Di; Santo, M. Del; Riggio, A.; D’Aí, A.; Burderi, L.; Scarano, F.; Iaria, R.

doi:10.1093/mnras/stw176

Cited by 41 publications

(48 citation statements)

References 82 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Therefore, we have not determined a best-fit NH for SAX J1808.4−3658. Our values for the other sources are consistent with those reported in the literature Papitto et al 2013;Linares et al 2014;Del Santo et al 2014;Bozzo et al 2015;Ludlam et al 2016;Pintore et al 2016;Tetarenko et al 2016;Degenaar et al 2016).…”

Section: Resultssupporting

confidence: 92%

Very hard states in neutron star low-mass X-ray binaries

Parikh

Wijnands

Degenaar

et al. 2017

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

We report on unusually very hard spectral states in three confirmed neutron-star low-mass X-ray binaries (1RXS J180408.9−342058, EXO 1745−248, and IGR J18245−2452) at a luminosity between ∼ 10 36−37 erg s −1. When fitting the Swift X-ray spectra (0.5 -10 keV) in those states with an absorbed power-law model, we found photon indices of Γ ∼ 1, significantly lower than the Γ = 1.5 -2.0 typically seen when such systems are in their so called hard state. For individual sources very hard spectra were already previously identified but here we show for the first time that likely our sources were in a distinct spectral state (i.e., different from the hard state) when they exhibited such very hard spectra. It is unclear how such very hard spectra can be formed; if the emission mechanism is similar to that operating in their hard states (i.e., up-scattering of soft photons due to hot electrons) then the electrons should have higher temperatures or a higher optical depth in the very hard state compared to those observed in the hard state. By using our obtained Γ as a tracer for the spectral evolution with luminosity, we have compared our results with those obtained by Wijnands et al. (2015). We confirm their general results in that also our sample of sources follow the same track as the other neutron star systems, although we do not find that the accreting millisecond pulsars are systematically harder than the non-pulsating systems.

show abstract

Section: Resultssupporting

confidence: 92%

Very hard states in neutron star low-mass X-ray binaries

Parikh

Wijnands

Degenaar

et al. 2017

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

show abstract

“…Light curves are binned with a binsize of 1 sec. SAX J1748.9-2021 has exhibited a wide variety of burst profiles (Galloway et al 2008;Beri et al 2016;Pintore et al 2016Pintore et al , 2018Li et al 2018). To quantify the behavior of observed bursts, decay times were measured by modeling the bursts profiles using linear rise followed by an exponential decay.…”

Section: Burst Profilesmentioning

confidence: 99%

“…SAX J1748.9-2021 shows the hard and soft spectral states (in 't Zand et al 1999;Patruno et al 2009;Pintore et al 2016Pintore et al , 2018Li et al 2018;Wu et al 2018;Sharma et al 2019) as of the atoll sources (Hasinger & van der Klis 1989). The spectrum of SAX J1748.9-2021 has been described with a combination of following components: thermal emission from an accretion disc and/or NS surface, thermal comptonization and the reflected emission from the accretion disc (in 't Zand et al 1999;Pintore et al 2016Pintore et al , 2018Li et al 2018;Wu et al 2018;Sharma et al 2019). An additional hard power-law tail was observed during the soft state of the 2015 outburst (Pintore et al 2016).…”

Section: Introductionmentioning

confidence: 99%

“…The spectrum of SAX J1748.9-2021 has been described with a combination of following components: thermal emission from an accretion disc and/or NS surface, thermal comptonization and the reflected emission from the accretion disc (in 't Zand et al 1999;Pintore et al 2016Pintore et al , 2018Li et al 2018;Wu et al 2018;Sharma et al 2019). An additional hard power-law tail was observed during the soft state of the 2015 outburst (Pintore et al 2016).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

A broad-band look of the accreting millisecond X-ray pulsar SAX J1748.9−2021 using AstroSat and XMM–Newton

Sharma

Beri

Sanna

et al. 2020

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

SAX J1748.9-2021 is a transient accretion powered millisecond X-ray pulsar located in the Globular cluster NGC 6440. We report on the spectral and timing analysis of SAX J1748.9-2021 performed on AstroSat data taken during its faint and short outburst of 2017. We derived the best-fitting orbital solution for the 2017 outburst and obtained an average local spin frequency of 442.361098(3) Hz. The pulse profile obtained from 3-7 keV and 7-20 keV energy bands suggest constant fractional amplitude ∼ 0.5% for fundamental component, contrary to previously observed energy pulse profile dependence. Our AstroSat observations revealed the source to be in a hard spectral state. The 1-50 keV spectrum from SXT and LAXPC on-board AstroSat can be well described with a single temperature blackbody and thermal Comptonization. Moreover, we found that the combined spectra from XMM-Newton (EPIC-PN) and AstroSat (SXT+LAXPC) indicated the presence of reflection features in the form of iron (Fe Kα) line that we modeled with the reflection model xillvercp. One of the two X-ray burst observed during the AstroSat/LAXPC observation showed hard Xray emission (>30 keV) due to Compton up-scattering of thermal photons by the hot corona. Time resolved analysis performed on the bursts revealed complex evolution in emission radius of blackbody for second burst suggestive of mild photospheric radius expansion.

show abstract

“…The shape of such lines depends on the chemical abundances and ionization state of the accretion disk, but also on its inner radial extent since both relativistic and dynamical effects act to broaden reflected emission lines. Disk reflection studies suggest that in some neutron star LMXBs the stellar magnetic field is strong c 0000 RAS enough to truncate the inner accretion disk (Degenaar et al 2014a;Pintore et al 2016;King et al 2016), whereas in others it can extend all the way down to the innermost stable circular orbit (ISCO) or the neutron star surface (e.g., Bhattacharyya & Strohmayer 2007;D'Aì et al 2009;Papitto et al 2009;Cackett et al 2010;Miller et al 2013;Degenaar et al 2015a;Di Salvo et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Disc reflection and a possible disc wind during a soft X-ray state in the neutron star low-mass X-ray binary 1RXS J180408.9–342058

Degenaar

Altamirano

Parker

et al. 2016

Mon. Not. R. Astron. Soc.

View full text Add to dashboard Cite

ABSTRACT1RXS J180408.9-342058 is a transient neutron star low-mass X-ray binary that exhibited a bright accretion outburst in 2015. We present NuSTAR, Swift, and Chandra observations obtained around the peak brightness of this outburst. The source was in a soft X-ray spectral state and displayed an X-ray luminosity of L X ≃(2 − 3) × 10 37 (D/5.8 kpc) 2 erg s −1 (0.5-10 keV). The NuSTAR data reveal a broad Fe-K emission line that we model as relativistically broadened reflection to constrain the accretion geometry. We found that the accretion disk is viewed at an inclination of i≃27 • -35 • and extended close to the neutron star, down to R in ≃5-7.5 gravitational radii (≃11-17 km). This inner disk radius suggests that the neutron star magnetic field strength is B 2×10 8 G. We find a narrow absorption line in the Chandra/HEG data at an energy of ≃7.64 keV with a significance of ≃4.8σ. This feature could correspond to blue-shifted Fe XXVI and arise from an accretion disk wind, which would imply an outflow velocity of v out ≃0.086c (≃25 800 km s −1 ). However, this would be extreme for an X-ray binary and it is unclear if a disk wind should be visible at the low inclination angle that we infer from our reflection analysis. Finally, we discuss how the X-ray and optical properties of 1RXS J180408.9-342058 are consistent with a relatively small (P orb 3 hr) binary orbit.

show abstract

Broad-band spectral analysis of the accreting millisecond X-ray pulsar SAX J1748.9−2021

Cited by 41 publications

References 82 publications

Very hard states in neutron star low-mass X-ray binaries

Very hard states in neutron star low-mass X-ray binaries

A broad-band look of the accreting millisecond X-ray pulsar SAX J1748.9−2021 using AstroSat and XMM–Newton

Disc reflection and a possible disc wind during a soft X-ray state in the neutron star low-mass X-ray binary 1RXS J180408.9–342058

Contact Info

Product

Resources

About