three candidate magnetar- powered fast x-ray transients...
TRANSCRIPT
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Three candidate magnetar-powered fast X-ray transients from Chandra archival data
20 Years of Chandra Symposium, Dec 6th 2019
Dacheng LinUniversity of New Hampshire
Credit: NASA
Collaborators: Jimmy Irwin, Edo Berger
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Outline
Highly magnetized supramassive millisecond pulsars (magnetars) formed in binary neutron-star (BNS) mergers
CDF-S XT2: a fast X-ray transient (FXT) powered by a protomagnetar?
Three new FXTs from Chandra archival data.
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Multi-messenger era
GW 170817
Credit: NASA/CXC/Trinity/Pooley
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Association of short GRBs with BNS mergers
Credit: NASA/GSFC
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EM signal highly depends on the viewing angle
Metzger & Berger 2012
BH
θobs
θjTidal Tail & Disk Wind
Ejecta−ISM Shock
Merger Ejecta
v ~ 0.1−0.3 c
Optical (hours−days)
KilonovaOptical (t ~ 1 day)
Jet−ISM Shock (Afterglow)
GRB(t ~ 0.1−1 s)
Radio (weeks−years)
Radio (years)
Narrowly collimated jets
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Big question: Most GW events have large positional error and should be GRB-less, how to search for their EM counterparts
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Search for strong EM signal of GRB-less GW events
Credit: NASA/Swift/Dana Berry Credit: NASA
Highly magnetized supramassive millisecond pulsars (magnetars) formed in BNS mergers
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A proto-magnetar from a BNS merger?
Credit: NASA/Swift/Dana Berry
Magnetar-powered ejecta(Gao et al. 2013)
Free magnetar wind (Zhang 2013)
⇒bright X-ray transients lasting for order of thousand seconds
Important: (1) EM counterparts to GW events; (2) EoS of dense matter
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CDF-S XT2
Circularization
Special light curve: a plateau of 2 ks followed by a steep decay of index! ∼ − 2.0 Xue et al. 2019, Nature
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CDF-S XT2
Circularization
Host-galaxy related properties similar to most short GRBs Redshift at 0.738
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Explanations: proto-magnetar from BNS merger
Xiao et al. 2019
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Explanations: white dwarf TDE by IMBH
Xiao et al. 2019
White dwarf tidal disruption event by intermediate-mass black hole
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Mining Chandra archival data
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Mining Chandra Archival Data
Circularization
A decade-long super-Eddington accreting tidal disruption event
circle: Chandra X-ray 95% positional error, radius 0.18″ or 0.5 kpc)
Lin, et al. 2017, Nature Astronomy, 1, 33
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Mining Chandra Archival Data
Circularization
An off-center intermediate-mass black hole tidal disruption event
Lin, et al. 2018, Nature Astronomy, 1, 656
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Three new FXTs from Chandra archival data(Lin et al. 2019, in preparation)
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Three new FXTs from Chandra archival searchLight curves
�peak
quiescence> 400 � > 300 � > 100
Large amplitude flare (factor >100) Fast rise (<few ten seconds) No quiescence emission
Faint (peak X-ray flux ! )
Non-recurrent No GRB association
∼ 10−12 erg s−1 cm−2
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Three new FXTs from Chandra archival searchLight curve fitted with broken power law
Initial index: � Break (ks): �Second index: �
0.1+0.3−0.1
1.5+0.3−0.6
−1.6+0.5−0.4
���
0.1 ± 0.11.7 ± 0.1−2.3 ± 0.2
���
0.0 ± 0.21.9 ± 0.3−2.0 ± 0.3
Initial plateau (index ! ), break at ! ks, and steep decay (index ! )
∼ 0 ∼ 1.7∼ − 2.0
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Three new FXTs from Chandra archival searchFits to X-ray spectra in peak and decay
�Plateau � Decay �
NH,i = 4.4 ± 2.0 × 1022 cm−2
Γ = 2.0 ± 0.2Γ = 2.3 ± 0.3
�Plateau � Decay �
NH,i = 0.4+0.7−0.4 × 1022 cm−2
Γ = 1.6 ± 0.2Γ = 2.1 ± 0.3
�Plateau � Decay �
NH,i = 0.0+0.4 × 1022 cm−2
Γ = 1.5 ± 0.3Γ = 3.1 ± 0.4
Hard spectra in plateau and softening in decay
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Three new FXTs from Chandra archival search
Green circle: Chandra 95% positional uncertainty
XRT 170901 HST F606W image
A blue irregular host galaxy F606W: 24.92 AB mag, F160W: 24.69 AB mag
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Three new FXTs from Chandra archival search
No counterpart (r limit: 24.0 AB mag, J limit 20.4 mag)
Green circle: Chandra 95% positional uncertainty
XRT 030511 DES r image
10 -7.3 -4.4 -1.4 1.5 4.4 7.3 10 13 16 1
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Three new FXTs from Chandra archival search
No counterpart (r limit: 24.0 AB mag, J limit 20.6 mag)
Green circle: Chandra 95% positional uncertainty
XRT 110919 DES r image
10 -7.4 -4.4 -1.3 1.7 4.8 7.8 11 14 17 2
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Explanations:
Magnetar-powered FXTs as aftermath of BNS mergers
White Dwarf TDEs by IMBHs
Very distant on-axis GRBs afterglow (very unlikely: no prompt emission)
Galactic Stellar flares (very unlikely: no counterpart, not recurrent)
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