IN NS LMXB Equat ator orial ial geomet ometry Outf tflow w - PowerPoint PPT Presentation

P HO HOTOI OIONIZ ONIZATION TION INSTABILIT ABILITY OF OF WI WINDS IN IN X- RA RAY BI BINAR ARIES IES S TEFANO ANO B IANCHI CHI June 8 th 2017 – The X-ray Universe 2017 – Rome, Italy

4U1630-472 Suzaku IN GBH S DS IN W INDS GROJ1655-40 40 XMM Kubota+ + 07 Diaz az-Trig rigo+ 07

Equ quat ator orial ial geomet ometry IN GBH S Ubi biquito quitous us in soft ft state ate (jet et off) f) Absen ent in hard d state ate (jet et on) DS IN W INDS Outf tflow velocit locities ies ~𝟐𝟏 𝟑 − 𝟐𝟏 𝟒 km s -1 Ponti ti+ + 12 Ponti ti+ + 12

Díaz az Trigo & Boirin rin 16 16 XB S IN NS LMXB Equat ator orial ial geomet ometry Outf tflow w velocit locitie ies: : ~𝟐𝟏 𝟑 − 𝟐𝟏 𝟒 km s -1 1 (wind inds) DS IN ~𝟏 km s -1 1 ( disc sc atmosphe tmospheres es ) W INDS Stat ate e (jet) et) conn nnect ectio ion? n? NSs LMXBs Bs fit it in the e cano nonica nical state ate schem eme e of BH system tems: s: variab riabilit lity y is the e key for clas assifi sificat ation ion Only y two o sour urces ces have e exten tensiv sive e moni onitoring ring campaig ampaigns ns Mu Muñoz z Darí rías as+ + 14

In the he two o best st moni onitored ed NS system tems, s, the he wind nd is pres esent ent only y in the e soft ft stat ates, s, and always ys disapp ppear ears in the he hard d states ates EXO 0748-676 Pon onti+ ti+ 14 14 The connection nection betw tween een Fe K ab absorptio ption n an and stat ates es is a a ge genera eral l charact aracteristic eristic of of accr cret eting ing sources ces AX J1745.6 .6-2901 Ponti ti+ + 15

AX J1745.6 .6-2901 XMM + NuSTAR AR The SEDs are modelled by a multi-colour disc emission (dominant in the soft state) and a powerlaw arising from Comptonization of its seed photons (dominant in the hard state) The optical and infrared band of the SEDs are due to emission from the irradiated disc The contribution at radio-to-infrared frequencies from a compact jet is only added in the hard state Ponti ti+ + 15 If the wind retains its physical properties ( 𝑜𝑠 2 = 𝑑𝑝𝑜𝑡𝑢 ) in the hard states, it would remain detectable with the available observations Fe K K absor sorpt ption ion does not ot disappear ppear because cause of over-ion oniz ization tion in the he hard state ate

A photoionised gas will reach an equilibrium at a ionisation parameter 𝜊 = 𝑀/𝑜𝑠 2 and temperature 𝑈 , as a consequence of competing heating and cooling processes depending on its physical and chemical properties, and the illuminating radiation field These equilibrium states can be drawn in a stabi ability ity cur urve, where 𝜊 𝑜𝑈𝑠 2 ∼ 1 𝑀 𝑈 ∼ 𝑞 An equilibrium state where the slope of the curve is positive is thermally stable If the slope of the stability curve is negative, the state is thermally unstable and is likely to collapse into a different stable equilibrium state

Bian anch chi+ + in prep ep. The wind observed in the soft ft state ate lies in a thermally stable able branch of the stability curve If the physical properties of the wind do not ate ( 𝑜𝑠 2 = 𝑑𝑝𝑡𝑢 ), the change in the hard d state different illuminating SED dramatically changes the curve, and the gas would now be in a thermally unstab stable branch (see also Chakravorty+ 2013, 2016; Higginbottom+ 2015, 2016 ; Dyda+ 2016) Bian anch chi+ + in prep ep. All the ionisation parameters dominated by Fe XXV and Fe XXVI are in a stable branch of the stability curve in the soft state, while they are all in unstable branches for the hard state: the e absor sorpt ptio ion featur atures s are e expe pected cted to disappear ppear, as observed

T OY OY M ODEL EL Stat atic ic clou oud d ( 𝒘 = 𝟏 ) at distanc tance e 𝒔 , n not ot replenished plenished After the transition from the soft to the hard state, the gas instantaneously moves to the new equilibrium state (recombination, ionization and thermal time-scales are less than tens of seconds): 𝑜 and 𝑠 can be assumed constant Bian anch chi+ + in prep ep. The new equilibrium state is unstable, and any perturbation will make the gas migrate to a stable solution in few hours (dynamical time-scale) Assuming that 𝑠 will not change in this time-scale, the new stable equilibrium will be characterized by different values of 𝑈 , 𝜊 , and 𝑜

T OY OY M ODEL EL Stat atic ic clou oud d ( 𝒘 = 𝟏 ) at distanc tance e 𝒔 , n not ot replenished plenished In the hard state, several phases of the gas can coexist in pressure equilibrium For an isobaric displacement from the initial unstable solution, we have two stable able soluti ution ons: 𝐼1 (cold, high density) and 𝐼2 (hot, low density) Bian anch chi+ + in prep ep. There is no easy way to predict which log𝜊 𝐼2 = 4. 76 𝑈 𝐼2 = 1.3 × 10 8 K stable solution the plasma will choose: 𝑜 𝐼2 = 2.7 × 10 10 𝑑𝑛 −3 hot and cold clumps can coexist adopting an unknown geometry, or a hot, dilute medium may confine cold, denser clumps, and a part of the cold phase may continuously evaporate to the hot phase and vice-versa in a log𝜊 𝐼1 = 1.10 dynamical time-scale 𝑈 𝐼1 = 2.8 × 10 4 K 𝑜 𝐼1 = 1.2 × 10 14 𝑑𝑛 −3

T OY OY M ODEL EL Stat atic ic clou oud d ( 𝒘 = 𝟏 ) at distanc tance e 𝒔 , n not ot replenished plenished The hot phase has a very high ionization parameter, corresponding to negligible fractions of Fe XXV and Fe XXVI : this is componen mponent of the e wind d will ll becom come e unobs obser ervab vable le The cold ld phas hase e is substan bstantial ially y neutr utral al Hyodo do+ 09 09 If 𝑚𝑝𝑕𝑂 𝐼 = 23.5 (as for the wind in the soft log𝜊 𝐼2 = 4. 76 𝑈 𝐼2 = 1.3 × 10 8 K state), this would absorb the X-ray emission 𝑜 𝐼2 = 2.7 × 10 10 𝑑𝑛 −3 up to ~3 keV Incidentally, this value is the same as the neutral column density observed in AXJ both in the hard and in the soft state, so it would be only observed as a change of the persistent neutral absorption log𝜊 𝐼1 = 1.10 𝑈 𝐼1 = 2.8 × 10 4 K 𝑜 𝐼1 = 1.2 × 10 14 𝑑𝑛 −3 Any y conne nect ction on with th the dips? s?

F ROM A T OY OY M ODEL TO THE ‘R EAL EAL ’ W ORLD TO THE A simple toy model explains the disappearance of Fe absorption in the hard state because of instability, but: -A cold phase in the hard state is expected: is it observed? Dips are also observed in the soft state -A static disk atmosphere is still in agreement with data in AXJ, but in other sources outflowing winds need a continuous replenishment log𝜊 𝐼2 = 4. 76 𝑈 𝐼2 = 1.3 × 10 8 K 𝑜 𝐼2 = 2.7 × 10 10 𝑑𝑛 −3 -With the same assumptions, we should come back to the initial wind passing from hard to soft (as observed). The hot phase will remain transparent, while the cold phase would not be ionized enough to produce Fe absorption A ‘fountain’ is needed to re -launch launch the he wind! nd! The launching mechanism must change from the soft to the hard state (see e.g. Chakravorty+ 2016) log𝜊 𝐼1 = 1.10 𝑈 𝐼1 = 2.8 × 10 4 K 𝑜 𝐼1 = 1.2 × 10 14 𝑑𝑛 −3

P HOTOION IN X- RAY BINAR IES ( IN IN A S LIDE ) IONIZA IZATI TION INSTAB ABIL ILIT ITY OF OF WINDS DS IN ARIES  Equatorial winds are ubiquitous in LMXBs  The connection between Fe K absorption and states is a general characteristic of accreting sources  Fe K absorption does not disappear because of over-ionization in the hard state  A si simp mple e toy y model del expl plai ains ns the he disappeara ppearanc nce e of Fe ab absor sorpti ption on in the he hard d state ate because cause of phot otoi oion oniza ization ion inst stab ability ility  A cold phase in the hard state is expected: is it connected to dips?  Outflowing winds need a continuous replenishment  The toy y model del cannot nnot repr produ oduce ce the e wind nd back ck to the he soft t state ate  A ‘fountain’ is needed to re -launch launch the he wind! nd!  The launching mechanism must change from the soft to the hard state

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