J/ApJ/738/128 RXTE observations of 4U 1728-34 (Seifina+, 2011) ================================================================================ On the constancy of the photon index of X-ray spectra of 4U 1728-34 through all spectral states. Seifina E., Titarchuk L. =2011ApJ...738..128S ================================================================================ ADC_Keywords: Binaries, X-ray ; Equivalent widths Keywords: accretion, accretion disks - black hole physics - stars: neutron - radiation mechanisms: non-thermal - stars: individual (4U 1728-34) Abstract: We present an analysis of the spectral properties observed in X-rays from neutron star X-ray binary 4U 1728-34 during transitions between the low- and high-luminosity states when the electron temperature kT_e_ of the Compton cloud monotonically decreases from 15 to 2.5keV. We analyze the transition episodes from this source observed with BeppoSAX and RXTE satellites. We find that the X-ray broadband energy spectra of 4U 1728-34 during all spectral states can be modeled by a combination of a thermal (blackbody-like) component, a Comptonized component (which we herein denote as COMPTB), and a Gaussian component. Spectral analysis using this model provides evidence that the photon power-law index {Gamma} is almost constant ({Gamma}=1.99+/-0.02) when kT_e_ changes from 15 to 2.5keV during these spectral transitions. Description: We analyzed the available data obtained with RXTE (Rossi X-ray timing explorer; Bradt et al. 1993A&AS...97..355B), which were found in the time period from 1996 February to 2000 July (see also the review by Galloway et al. 2008, Cat. J/ApJS/179/360). In our investigation we selected 127 observations made at different count rates (luminosity states) with a good coverage of rise-decay flare track. We performed an analysis of RXTE observations of 4U 1728-34 during four years for eight intervals. Objects: ---------------------------------------------------------- RA (2000) DE Designation(s) ---------------------------------------------------------- 17 31 57.73 -33 50 02.5 4U 1728-34 = NAME SLOW BURSTER ---------------------------------------------------------- File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table4.dat 139 127 *Best-fit parameters of the spectral analysis of PCA & HEXTE/RXTE observations of 4U 1728-34 in the 3-60keV energy range -------------------------------------------------------------------------------- Note on table4.dat: The spectral model is wabs*(blackbody+COMPTB+Gaussian), where N_H_ is fixed at a value 2.73x10^22^/cm^2^ (Piraino et al. 2000A&A...360L..35P); color temperatures T_s_ and T_BB_ are fixed at 1.3 and 0.7keV, respectively (see comments in the text). -------------------------------------------------------------------------------- See also: B/cb : Cataclysmic Binaries, LMXBs, and related objects (Ritter+, 2013) J/A+A/545/A27 : INTEGRAL/IBIS Galactic Hard X-Ray Survey (Krivonos+, 2012) J/ApJ/714/1424 : Isolated neutron stars from Rosat and Swift (Turner+, 2010) J/A+A/523/A61 : INTEGRAL survey of hard X-ray sources (Krivonos+, 2010) J/A+A/522/A68 : Variable sources detected by INTEGRAL (Telezhinsky+, 2010) J/ApJS/179/360 : Thermonuclear X-ray bursts observed by RXTE (Galloway+, 2008) J/A+A/467/585 : Sources detected by ISGRI (Bodaghee+, 2007) J/A+A/469/807 : Catalogue of Galactic low-mass X-ray binaries (Liu+, 2007) J/A+A/458/21 : INTEGRAL burst observations of 4U 1728-34 (Falanga+, 2006) Byte-by-byte Description of file: table4.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 15 A15 --- ObsID Observational identification 17- 25 F9.3 d MJD [50128/51734] Start time (Modified Julian Date) 27- 31 I5 s Exp Exposure time 33- 38 F6.1 ct/s Rate Count rate, background corrected (1) 40- 44 F5.3 --- alpha Energy index of the Comptonization spectrum {alpha}={Gamma}-1 46- 50 F5.3 --- e_alpha alpha uncertainty 52- 56 F5.2 keV Te Electron temperature 58- 61 F4.2 keV e_Te Te uncertainty 63- 66 F4.2 [-] logA COMPTB parameter log(A) 67 A1 --- f_logA [b] logA fixed (2) 69- 72 F4.2 [-] e_logA ? logA uncertainty 74- 77 F4.2 --- Ncomp Normalization of the seed photon spectrum N_COMPTB_ (3) 79- 82 F4.2 --- e_Ncomp Ncompt uncertainty 84- 87 F4.2 --- Nbb Normalization of the blackbody component N_BB_ (3) 89- 92 F4.2 --- e_Nbb Nbb uncertainty 94- 97 F4.2 keV Eline Centroid line energy 99-102 F4.2 keV e_Eline Eline uncertainty 104-107 F4.2 --- Nline Normalization N_line_ to fit the data in the 6-8keV range (3) 109-112 F4.2 --- e_Nline Nline uncertainty 114-116 I3 eV EW Equivalent width of iron line EW_line_ 118-119 I2 eV e_EW EW uncertainty 121-124 F4.2 --- chi2 {chi}^2^ fit 126-129 F4.2 --- e_chi2 chi2 uncertainty 131-134 F4.2 pW/m2 F1 Spectral flux for 3-10keV energy range (4) 136-139 F4.2 pW/m2 F2 Spectral flux for 10-60keV energy range (4) -------------------------------------------------------------------------------- Note (1): The count rate corresponds to 5PCA units and corrected for background. Note (2): b = When parameter log(A)>>1, it is fixed at 1.0, because in any case of log(A)>>1 a Comptonization fraction f=A/(1+A) is approximately 1 and variations of A>>1 do not further improve the fit quality. See section 3. Note (3): Normalization parameters of blackbody and COMPTB components are in units of L_37_/d^2^_10_erg^-1^/s/kpc^2^, where L_37_ is the source luminosity in units of 10^37^erg/s (10^30^W), d_10_ is the distance to the source in units of 10kpc, and the Gaussian component is in units of 10^-2^xtotal photons/cm^2^/s in line. Note (4): Spectral fluxes (F1/F2) in units of x10^-9^ergs/s/cm^2^ for (3-10) and (10-60) keV energy ranges, respectively. -------------------------------------------------------------------------------- History: From electronic version of the journal ================================================================================ (End) Emmanuelle Perret [CDS] 24-May-2013