Download The X-ray/hard X-ray/gamma-ray connection of gamma

The X-ray/hard X-ray/gamma-ray connection of
gamma-ray binaries and possible propeller states
Diego F. Torres Special thanks to
Daniela Hadasch, Jian Li, Alessandro Papitto, & Nanda Rea Research done with the support of
www.ice.csic.es/research/map
LS I +61 303
Is it a neutron star binary?
•  There are no detected pulsations •  But there were two flares, ~0.1 s, with ‘high’ Lx (orders of magnitude beyond bolometric lum.) •  The bursts were in all aspects similar to SGR ones.
•  LS I +61 303 relate gamma-ray binaries with magnetar systems
•  Take into account that magnetar phenomenology is related to the inner magnetic field of neutron stars, not the dipolar: two (relatively) low-B magnetars are know. We are not necessarily speaking of >1014 G NS.
Super-orbital variability
•  Known in radio and Hα (e.g. Gregory 2002)
•  Discovered in X-rays after DFT, et al. 2012
5+ years of monitoring with RXTE (Li et el. 2012,
Chernyakova et al. 2012)
•  Today, hints of superorbital variability in hard X-rays (INTEGRAL/IBIS)
Due to the large (4 years) super-orbital period:
•  Yet unclear with MAGIC/VERITAS @ TeV
Li, et al. 2012
•  …and with LAT @ GeV
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Hints of inter-relation
Peak flux per orbit in TeV shown in red (all of them happening in the 0.6–1.0 orbital phase range) as a
function of super-orbital phase, together with radio, Hα (black, Zamanov et al. 2000) and X-ray data
Li, DFT, et al. 2012
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Changes of state in a pulsar binary
EjectorPropellerAccretor (and sometimes backwards)
Ideas go back up to Gnusareva & Lipunov 1985, application to LSI +61 303 in Zamanov et al. 1995; DFT et al. 2012; Papitto, DFT, Rea 2012 4
Idea: changes of state in a pulsar binary
EjectorPropellerAccretor (and sometimes backwards)
see e.g., Bednarek 2009 for ability of propellers to accelerate particles up to HE
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Idea: changes of state in a pulsar binary
EjectorPropellerAccretor (and sometimes backwards)
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Mass accreted change a lot along eccentric orbits apastron
e.g., for Be stars, with winds of 2
components, poloidal and equatorial,
changes can reach up to 3-4 orders of
magnitude
See Papitto, DFT, Rea 2012, ApJ
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Flip-flop between states is possible depending on the pulsar period
Papitto, DFT, Rea 2012
Example for a fixed magnetic field of B=1013 G
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Flip-flop between states is possible depending on the pulsar period
Papitto, DFT, Rea 2012
Example for a fixed magnetic field of B=1013 G
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Flip-flop life is larger than the ejector’s
The time it takes for a NS to reach a period P under the action of a spindown torque N (P) is obtained from the integration of the equation
See Papitto, DFT, Rea 2012, ApJ
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Flip-flop life is larger than the ejector’s
The time it takes for a NS to reach a period P under the action of a spindown torque N (P) is obtained from the integration of the equation
(conservative scenario) See Papitto, DFT, Rea 2012, ApJ
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Parameter space limited by bolometric luminosity
If the apastron luminosity
is all ejector-generated
the system must be to the
left of the red curves
It could always be an ejector
or stay flip-flopping along
the orbit depending on (P,B) Papitto, DFT, Rea 2012, ApJ
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Parameter space limited by bolometric luminosity
i.e.,: in periastron is a
propeller, in apastron
is an ejector
If the apastron luminosity
is all ejector-generated
the system must be to the
left of the red curves
It could always be an ejector
or stay flip-flopping along
the orbit depending on (P,B) Papitto, DFT, Rea 2012, ApJ
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Parameter space limited by imposing superorbital variability
If the disc dominates the apastron (suppose: having grown larger at the maximum of the
superorbital variability); the transition to the propeller moves to the left, and depending on
(P,B) the system could be a permanent propeller (to the right of the green line) or a flipflopper (to the left)
Papitto, DFT, Rea 2012, ApJ
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Parameter space limited by imposing superorbital variability
At such enlarged mass accretion rates, the disc may not reach the apastron but may reach
intermediate phases of the orbit. The mass accretion rate at these intermediate orbital phases
is larger than at apastron, and the system is more likely to be flip-flopping for a given (P,B).
Papitto, DFT, Rea 2012, ApJ
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LS I +61 303: significant increase in the hard X-ray dataset
Data published by Zhang, DFT, 2010
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LS I +61 303: significant increase in the hard X-ray dataset
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counts/s (18-60 keV)
Binned
lightcurve
departs from a constant
behavior
1
0
-1
53000
54000
MJD
55000
56000
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LS I +61 303: significant increase in the hard X-ray dataset
Folded in the
superorbital
phase
The hard X-ray
profile
coincides with
the soft X-ray
one.
Both have
maxima at the Superorbital
phase where
Halpha is
maximal too.
counts/s (18-60 keV)
1
0.5
0
0
0.2
0.4
0.6
0.8
1
1.2 1.4
Super-orbital Phase
1.6
1.8
2
Li, DFT et al. 2011
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LS I +61 303: significant increase in the hard X-ray dataset
0.5
0
0
0.2
0.4
0.6
0.8
1
1.2
Super-orbital Phase
1.4
1.6
1.8
2
0.2
0.4
0.6
0.8
1
1.2
Super-orbital Phase
1.4
1.6
1.8
2
300
exposure (ks)
Folded in the
superorbital
phase
The hard X-ray
profile
coincides with
the soft X-ray
one.
Both have
maxima at the Superorbital
phase where
Halpha is
maximal too.
counts/s (18-60 keV)
1
200
100
0
0
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XSS J12270-4859: a LMXB emitting at GeV? A faint low mass X-ray binary with a γ-ray counterpart [De Martino+ 2010,2012; Hill+ 2011; Saitou+
2009,2011]; 140 off the Galactic plane.
Steady gamma-ray emission, no orbital or spin period.
L(0.2-100keV) = L(> 100MeV) = 2 x 1034 d2kpc2 erg/s
→ comparable X-ray and γ-ray output
Flares and dips in soft X-rays also suggesting variations
by an optically thick absorber
Steady in hard X-rays and GeV
No pulsations detected in radio and X-rays either (but loose upper limit in X-rays)
Optical continuum: K2-K5 star + disc
Broad Hα, Hβ and He II detected indicate accretion
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XSS J12270-4859
Possible interpretations:
•  Is a jet involved?
-Lradio/Lgamma implies B~10-8 G, much lower
than typical µG fields in extended radio structures
-Steady γ-ray emission never observed from
accreting BH
•  An isolated pulsar?
-No pulsation found, and steep spectrum / high
cutoff would be uncommon. -Rotation powered pulsar are not bright X-ray
emitters (LX/Lγ~10-3; instead of 1 like for XSS)
•  A pulsar in a binary?
-Galactic latitude would suggest a MSP acting as
an ejector (recycling scenario). -Signature of accretion down to the NS are not
observed.
-But optical emission suggests accretion. No steady
hard X-ray emission expected if it is non-accreting.
-Propeller?
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XSS J12270-4859: INTEGRAL analysis
IBIS/ISGRI data (18-60 keV): Left, the whole dataset (553 ks) since 2003 (~14σ)
Right: only at the Fermi-LAT period detection (2008-2010), 73ks in IBIS (~5σ) The source is steady along the whole dataset (2003-2012), and thus it is not seen to
vary between accretor and ejector phases along the last 10 years (as in the case of
J1023+0038).
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XSS J12270-4859: the source is stable in hard X-rays (2003-2012)
The 553.7 ks IBIS/ISGRI exposure is cut into 7 time spans of 79 ks each. XSS J12270-4859 is detected
with similar significance around 4σ in all but one, there is no long-term variability of XSS J12270-4859 in
18–60 kev band. The 3rd time span has the lowest significance. Though with similar exposure time, only a
short time period (15 days) is covered compared to the others (each with ~600 days). XSS J12270-4859
may have experienced a short time low state there. Dips observed in soft X-rays too.
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XSS J12270-4859: energetics
Luminosity of 1035 erg s-1
For P=2.5 ms, fastness = 2
(ms)
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Concluding remarks • 
On long timescales (due to pulsar spin down) a NS in a binary must pass through
ejector, propeller, and accretor phases. • 
On short timescales, this is governed by the accretion rate; this is large if the orbit is
eccentric. Alternating systems are a natural consequence.
• 
For LS I +61 303, at relatively high spin-down (few 1035- few 1036 erg s-1), the time
spent in flip-flop mode exceeds by a factor of 3 the time spent as ejector.
• 
Changes in the mass accretion rate can also come from the superorbital behavior, and
these could be enough to induce MW long term behavior. • 
The X-rays / hard X-rays holds interesting keys to understand the emission properties
and the long-term behavior of gamma-ray binaries. • 
LS I 61 303 and XSS J12270-4859 are insteresting cases of possible propeller states in
neutron star binaries.
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