Context. GX9 +9 (4U 1728 16) is a low mass X-ray binary source harboring a neutron star. Although it belongs to the subclass of the bright Atoll sources together with GX9 +1, GX3 +1, and GX13 +1, its broadband spectrum is poorly studied and apparently does not show reflection features in the spectrum.Aims. To constrain the continuum well and verify whether a relativistic smeared reflection component is present, we analyze the broadband spectrum of GX9 +9 using BeppoSAX and XMM-Newton spectra covering the 0.3 40 keV energy band.Methods. We fit the spectrum adopting a model composed of a disk-blackbody plus a Comptonized component whose seed photons have a blackbody spectrum (Eastern Model). A statistically equivalent model is composed of a Comptonized component whose seed photons have a disk-blackbody distribution plus a blackbody that mimics a saturated Comptonization likely associated with a boundary layer (Western model). Other trials did not return a good fit.Results. The spectrum of GX9 +9 was observed in a soft state and its luminosity is 2.3 x 10(37) erg s(-1) assuming a distance to the source of 5 kpc. In the Eastern Model scenario, we find the seed-photon temperature and electron temperature of the Comptonized component to be 1.14(-00.07)(+0.1) keV and 2.80(-0.04)(+0.09) keV, respectively, while the optical depth of the Comptonizing corona is 8.9 +/- 0.4. The color temperature of the inner accretion disk is 0.86(-0.02)(+0.08) keV and 0.82 +/- 0.02 keV for the BeppoSAX and XMM-Newton spectrum, respectively. In theWestern Model scenario, instead, we find that the seed-photon temperature is 0.87 +/- 0.07 keV and 1.01 +/- 0.08 keV for the BeppoSAX and XMM-Newton spectrum, respectively. The electron temperature of the Comptonized component is 2.9 +/- 0.2 keV, while the optical depth is 9.4(-1.1)(+1.5). The blackbody temperature is 1.79(-0.18)(+0.09) keV and 1.85(-0.15)(+0.07) keV for the BeppoSAX and XMM-Newton spectrum, respectively. The addition of a relativistic smeared reflection component improved the fit in both the scenarios, giving compatible values of the parameters, even though a significant broad emission line in the Fe-K region is not observed.Conclusions. From the reflection component we estimated an inclination angle of about 43(-4)(+6) deg and 51(-2)(+9) deg for the Eastern and Western Model, respectively. The value of the reflection fraction Omega/2 pi is 0.18 +/- 0.04 and 0.21 +/- 0.03 for the Eastern and Western Model, respectively, suggesting that the Comptonized corona should be compact and close to the innermost region of the system.

Iaria R., Mazzola S.M., Di Salvo T., Marino A., Gambino A.F., Sanna A., et al. (2020). Reflection component in the Bright Atoll Source GX 9+9. ASTRONOMY & ASTROPHYSICS, 635, A209 [10.1051/0004-6361/202037491].

Reflection component in the Bright Atoll Source GX 9+9

Iaria R.
Membro del Collaboration Group
;
Mazzola S. M.;Di Salvo T.;Marino A.;Gambino A. F.;
2020-01-01

Abstract

Context. GX9 +9 (4U 1728 16) is a low mass X-ray binary source harboring a neutron star. Although it belongs to the subclass of the bright Atoll sources together with GX9 +1, GX3 +1, and GX13 +1, its broadband spectrum is poorly studied and apparently does not show reflection features in the spectrum.Aims. To constrain the continuum well and verify whether a relativistic smeared reflection component is present, we analyze the broadband spectrum of GX9 +9 using BeppoSAX and XMM-Newton spectra covering the 0.3 40 keV energy band.Methods. We fit the spectrum adopting a model composed of a disk-blackbody plus a Comptonized component whose seed photons have a blackbody spectrum (Eastern Model). A statistically equivalent model is composed of a Comptonized component whose seed photons have a disk-blackbody distribution plus a blackbody that mimics a saturated Comptonization likely associated with a boundary layer (Western model). Other trials did not return a good fit.Results. The spectrum of GX9 +9 was observed in a soft state and its luminosity is 2.3 x 10(37) erg s(-1) assuming a distance to the source of 5 kpc. In the Eastern Model scenario, we find the seed-photon temperature and electron temperature of the Comptonized component to be 1.14(-00.07)(+0.1) keV and 2.80(-0.04)(+0.09) keV, respectively, while the optical depth of the Comptonizing corona is 8.9 +/- 0.4. The color temperature of the inner accretion disk is 0.86(-0.02)(+0.08) keV and 0.82 +/- 0.02 keV for the BeppoSAX and XMM-Newton spectrum, respectively. In theWestern Model scenario, instead, we find that the seed-photon temperature is 0.87 +/- 0.07 keV and 1.01 +/- 0.08 keV for the BeppoSAX and XMM-Newton spectrum, respectively. The electron temperature of the Comptonized component is 2.9 +/- 0.2 keV, while the optical depth is 9.4(-1.1)(+1.5). The blackbody temperature is 1.79(-0.18)(+0.09) keV and 1.85(-0.15)(+0.07) keV for the BeppoSAX and XMM-Newton spectrum, respectively. The addition of a relativistic smeared reflection component improved the fit in both the scenarios, giving compatible values of the parameters, even though a significant broad emission line in the Fe-K region is not observed.Conclusions. From the reflection component we estimated an inclination angle of about 43(-4)(+6) deg and 51(-2)(+9) deg for the Eastern and Western Model, respectively. The value of the reflection fraction Omega/2 pi is 0.18 +/- 0.04 and 0.21 +/- 0.03 for the Eastern and Western Model, respectively, suggesting that the Comptonized corona should be compact and close to the innermost region of the system.
Settore FIS/05 - Astronomia E Astrofisica
Iaria R., Mazzola S.M., Di Salvo T., Marino A., Gambino A.F., Sanna A., et al. (2020). Reflection component in the Bright Atoll Source GX 9+9. ASTRONOMY & ASTROPHYSICS, 635, A209 [10.1051/0004-6361/202037491].
File in questo prodotto:
File Dimensione Formato  
Iaria_2020.pdf

accesso aperto

Descrizione: Articolo principale
Tipologia: Pre-print
Dimensione 1.14 MB
Formato Adobe PDF
1.14 MB Adobe PDF Visualizza/Apri

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10447/409447
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 4
  • ???jsp.display-item.citation.isi??? 4
social impact