An XMM-Newton view of the dipping low-mass X-ray binary XTE J1710-281

摘要

Context. Studying the spectral changes during the dips exhibited by almost edge-on, low-mass X-ray binaries (LMXBs) is a powerfulmeans of probing the structure of accretion disks. The XMM-Newton, Chandra, or Suzaku discovery of absorption lines from Fe xxvand other highly-ionized species in many dippers has revealed a highly-ionized atmosphere above the disk. A highly (but less strongly)ionized plasma is also present in the vertical structure causing the dips, together with neutral material.Aims. We aim to investigate the spectral changes during the dips of XTE J1710-281, a still poorly studied LMXB known to exhibitbursts, dips, and eclipses.Methods. We analyze the archived XMM-Newton observation of XTE J 1710-281 performed in 2004 that covered one orbital periodof the system (3.8 h). We modeled the spectral changes between persistent and dips in the framework of the partial covering modeland the ionized absorber approach.Results. The persistent spectrum can be fit by a power law with a photon index of 1.94 ± 0.02 affected by absorption from coolmaterial with a hydrogen column density of (0.401 ± 0.007) x 10~22cm~(-2).The spectral changes from persistent to deep-dippingintervals are consistent with the partial covering of the power-law emission. Twenty-six percent of the continuum is covered duringshallow dipping, and 78 during deep dipping. The column density decreases from 77~(+67)_(38)××× 10~22cm~(-2)during shallow dipping to(14 ± 2) x 10~22 cm~(-2)during the deep-dipping interval. We do not detect any absorption line from highly ionized species such asFe xxv. However, the upper-limits we derive on their equivalent width (EW) are not constraining. Despite not detecting any narrowspectral signatures of a warm absorber, we show that the spectral changes are consistent with an increase in column density anda decrease in ionization state of a highly-ionized absorber, associated with an increase in column density of a neutral absorber, inagreement with the recent results found in other dippers. In XTE J1710-281, the column density of the ionized absorber increasesfrom 4.3~(+0.5)_(-0.4)×10~22cm~(-2)during shallow dipping to 11.6~(+0.6)_(-deep dipping, while the ionization parameter decreasesfrom 10~2.52to10~2.29erg s~(-1)cm. The parameters of the ionized absorber are not constrained during persistent emission. The neutralabsorber only slightly increases from (0.410 ± 0.007) x 10~22cm~(-2)during persistent emission to (0.420 ± 0.009) x 10~duringshallow dipping and to (0.45 ± 0.03) x 10~22 cm~(-2)during deep dipping. The warm absorber model better accounts for the ~I keVdepression visible in the pn dipping spectra, and naturally explains it as a blend of lines and edges unresolved by pn. A deeperobservation of XTE J1710-281 would enable this interpretation to be confirmed.