Transient X-ray binaries in Magellanic Clouds & Milky Way

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1 IAU Symp 339: Southern Horizons in Time Domain Astronomy Transient X-ray binaries in Magellanic Clouds & Milky Way Phil Charles University of Southampton/IAC/UCT (and Dave Buckley, Piet Meintjes, Andry Rajoelimanana, Daniel Mata, Lee Townsend...) Image: Rob Hynes

2 SALT Transients ToO (Buckley PI) - tale of 3 very different XRTs - all with rich time-domain properties 1) SMC X-3 (triggered by Swift) - HMXB 2) MAXI J LMXB 3) ASASSN 16oh SSS (in SMC) Hope to find new BH XRTs - but these actually consist of 2 NS and a WD!

3 CTIO

4 SMC

5 Properties of Luminous HMXBs in the Magellanic Clouds LMC X-1 LMC X-3 LMC X-4 A (XRT) SMC X-1 7x LX erg s-1 >1038 5x1038 Porb d Pspin s Sp.type O8III B3III/V O8III/V B1III/IVe B0I M < MX e Psup d - N.B. A peak LX ~ 10 LE! ~420 L E M erg/s M Sun

6 SMC BeX Pulsars

7 X-ray outbursts Pulse period of the NS Orbital period ( d) And super-orbital periods (2-10 yrs) such as seen in A Types of periodicities seen in BeX systems

8 XRB populations Milky Way SG BeX ~140 HMXBs (BeX+SG) ~190 LMXBs (inc. BHC) SMC ~90 HMXBs (SMC) ~40 (LMC) 1 LMXB (LMC X-2) ~dozen SSS BeX where are SGs? - or the LMXBs/BHCs? - or Be+WD systems? (1?) - or Be+BH systems?

9 1. SMC X-3 Swift SMC Survey (S3) - shallow, wide, high cadence - Kennea, Evans & Coe S3 covers SMC in 142 overlapping 60s Swift pointings (~12ks/week). Detects everything >1036 erg s-1 (~1% Eddington) S3 covers diferent parameter space from Chandra/XMM deep surveys: long-term temporal variability, not deep source detection Operational from June 2016 June 2018

10 ~300 S3 results so far 7 X-ray Pulsars in outburst: SXP 15.3 (Kennea+ ATel #10600) SXP 59.0 (Kennea+ ATel #10250) SMC X-3 (Kennea+ ATel #9362) SXP 202A (Coe+ ATel #9307) SXP 6.85 (Kennea+ ATel #9299) IGR J AKA SXP 2.16 (Kennea+ ATel #9299) 3XMM J (Evans+ ATel #9197). Chandra follow-up found 15.6s periodicity (Vasilopoulos+ ATel #9229)

11 Super-Eddington outburst of SMC X-3 Townsend+2017 Tsygankov+2017 Weng years 400 days Combined S3 and ToO Peak flu erg s 1 (0.510 kev) 45 day Porb visible post outburst Spin-up during outburst > total spindown from previous 20 years! Binary + Spin-up model ft to derive orbital parameters for frst time

12 Super-Eddington outburst of SMC X-3 OGLE 16 years SALT spectrum (upper) confrms large disk with Balmer inflling + transient accretion disk For details, see Townsend+2017

13 ~18 yr light-curves (Rajoelimanana+11) SXP = SMC X-ray Pulsar i > 90o - α (where α = disk opening angle) i < 90o - α

14 BeX Superorbital vs. Orbital periods Rajoelimanana et al, 2011

15 2. MAXI J high latitude (-13o) Mata, Charles, Buckley et al 2017 MN

16 Optical ID

17

18 Swift J Durant+09

19 So, what is MAXI J1957? Properties: 4 v short (<5d) outbursts within 16 months, with v fast turn-off No type I XR bursts No known source at that location High latitude low extinction (good for UV) Optical ID Δm>5 Hard X-ray spectrum (not BB) What it is not! BeX or CI Cam-like (HMXB) XRT (has to be an LMXB) Superburster (too long, not BB) Clone of the Rapid Burster (MXB ), as no type II XR bursts BH XRT cf Swift J1753.5/J1118 (much longer XR outbursts) GX339-4 or Aql X-1 like XRT

20 XTE ASM 15-yr LCs Yan+15

21

22 Wang et al 01

23 Wang et al 01

24 Heinke et al 10 NGC6440 X-2

25 cf J and N6440X2 MAXI J1957 at d~5-6kpc and van Paradijs & McClintock 94 LX Porb MV relation ~7kpc (depends on Porb) So we await the next observing season to search for MSPs!

26 3. ASASSN 16oh Work in progress, with Piet Meintjes, Andry Rajoelimanana, Alida Odendaal (all at UFS) and Dave Buckley + input from OGLE Haleakala, Maui LCO site: CTIO, LCO site: Each unit is an array of 4 telescopes called Brutus & Cassius

27 ASASSN 16oh In SMC 15 Dec (!) (Jha+16, ATel 9859) OGLE light curve (Mroz+16, ATel 9867)

28 Transient ToO invoked by DB Collaboration with India, UFS Andry Rajoelimanana Piet Meintjes RSS spectra over next 2 wks + Swift monitoring HeII 1037 erg s-1 kt~80ev Hα

29 + ASTROSAT (first SSS!) KP Singh BB kt~80ev HeII velocities do change over ~100km/s range No periodicity in quiescent OGLE data DB organised LCOGT monitoring to search for shorter periods Andry s preliminary analysis P<12hrs (from photometry) SALT RVs consistent with this (although phase sampling is poor) N.B. low amplitude low I

30 Hachisu, Kato models for SSS

31 Accreting White Dwarf Model (van den Heuvel et al 92) v high Lbol (sources in LMC) + v low kt (for BB) R ~ RWD WD compact object + sub-giant donor (i.e. ~ CV) for near LEdd luminosities require steady nuclear burning at WD surface (exceeds Lacc by ~x10) requires v high accretion rate (~ x higher than in CVs) > 10-7 MO yr-1 needs q~1 thermally unstable mass transfer ( short-lived phase) Southwell et al 96 need masses, but MX ~ 1MO (WD), M2 slightly larger ( faint wrt SSS) circumstantial evidence: e.g. bipolar outflow (emission lines) from RXJ vesc ~ WD

32 Strange behaviour of ASASSN 16oh: Light-curve completely unlike any other SSS Very long, slow climb to outburst, and no nova outburst! It s in the SMC, so we know it s close to Eddington-limited Substantial variability in pre-outburst interval Prospect (because it is so faint in quiescence) of detecting the donor for the first time in a luminous SSS have been trying this now! Apparent short P hard to reconcile with canonical SSS model Alternative (Maccarone+16 Atel9866) requires longer P and A-star donor hard to reconcile with quiescent properties

33 Conclusions Transients program on XR binaries is ideal for SALT key strength of fully Q-scheduled operations but note access/sampling constraints of SALT (and we re linking these observations with related programs at GTC, VLT...) In X-ray Astronomy now have MAXI and ASTROSAT operating with ASMs, but also receiving targets from OGLE, PTF, MASTER, ASASSN, Gaia... Valuable experience in preparing for ZTF/LSST/SKA-ThunderKAT where rapid spec. follow-up is critical Still in early days of this large SALT program, but it brings together many of the SALT partners and uses their own complementary facilities (e.g. OGLE, ASTROSAT, GTC ), and the number of ToO papers is increasing rapidly!