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CW signals Directed searches O2 GC O3 new sources
Searching for continuous gravitational-wavesfrom Galactic
neutron stars
Ornella Juliana Piccinni for the Rome CW groupAstone P.,
D’Antonio S., Frasca S., Intini G., Leaci P.,
Mastrogiovanni S., Miller A., Palomba C., La Rosa I.
University of Rome ’Sapienza’ & INFN Roma1
September 26, 2019
YITP workshop 2019 September 26, 2019 0 / 16
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CW signals Directed searches O2 GC O3 new sources
Overview
Intro on Continuous waves signals
Focus on directed searches
The Galactic Center O2 case
New sources from Fermi and Integral catalogs for O3
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CW signals Directed searches O2 GC O3 new sources
Gravitational waves sources
Modeled waveform Unknown waveform
Long-lived
Transients
YITP workshop 2019 September 26, 2019 2 / 16
T ∼ monthsor years
T ∼ up to100 s
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CW signals Directed searches O2 GC O3 new sources
Gravitational waves sources
Modeled waveform Unknown waveform
Long-lived
Transients
YITP workshop 2019 September 26, 2019 2 / 16
T ∼ monthsor years
T ∼ up to100 s
Compact binary coalescenceh0 ∼ 10−21
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CW signals Directed searches O2 GC O3 new sources
Gravitational waves sources
Modeled waveform Unknown waveform
Long-lived
Transients
YITP workshop 2019 September 26, 2019 2 / 16
T ∼ monthsor years
T ∼ up to100 s
Compact binary coalescenceh0 ∼ 10−21
Bursth0 ∼ 10−21
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CW signals Directed searches O2 GC O3 new sources
Gravitational waves sources
Modeled waveform Unknown waveform
Long-lived
Transients
YITP workshop 2019 September 26, 2019 2 / 16
T ∼ monthsor years
T ∼ up to100 s
Stochastic backgroundh0 ∼ 10−28
Compact binary coalescenceh0 ∼ 10−21
Bursth0 ∼ 10−21
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CW signals Directed searches O2 GC O3 new sources
Gravitational waves sources
Modeled waveform Unknown waveform
Long-lived
Transients
YITP workshop 2019 September 26, 2019 2 / 16
T ∼ monthsor years
T ∼ up to100 s
Continuous wavesh0 ∼ 10−25
Stochastic backgroundh0 ∼ 10−28
Compact binary coalescenceh0 ∼ 10−21
Bursth0 ∼ 10−21
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CW signals Directed searches O2 GC O3 new sources
Gravitational waves sources
Modeled waveform Unknown waveform
Long-lived
Transients
YITP workshop 2019 September 26, 2019 2 / 16
T ∼ monthsor years
T ∼ up to100 s
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CW signals Directed searches O2 GC O3 new sources
What is a Continuous Wave (CW)?
Credit: C. Reed, Penn State/Mc Gill University
Persistent signal (long-lived)
Produced by a nearly periodic mass quadrupole moment
variation
Expected sources
Isolated neutron stars (NS) or NSs in binary systems
(Non-axisymmetric)
Expected strain
h0 ∼= 10−27(
Izz1038kg·m2
)(10kpcd
)(f
100Hz
)2 (�
10−6
)� h0CBC
[For a CW review: Lasky PASA 32, pp. 34 (2015), Riles Mod Phys
Lett A 32, No. 39, 1730035 (2017)]
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CW signals Directed searches O2 GC O3 new sources
Isolated neutron stars
Credit: S. Mastrogiovanni
h0 =4π2Gc4
Izzf2
d �Izz: moment of inertia�: ellipticity
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The signal is modulated: Doppler effect, spin-down, sidereal day
variation,antenna response, etc.
The ellipticity can be triggered by different factors: elastic
stress, stronginternal magnetic fields, thermal gradients, etc.
Lasky PASA 32, pp. 34 (2015)
The maximum ellipticity that a neutron star can sustain is
related to theequation of state and to the neutron stare interior
model (Johnson-McDaniel+ PRD 88,044004 (2013))
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CW signals Directed searches O2 GC O3 new sources
Estimates on �
Theoretical models (K. Glampedakis & L. Gualtieri 2018
[Astro. and Space Science Lib., vol457. Springer])
Solid strange stars: � 6 6× 10−4
Hybrid and meson condensates stars: � 6 3− 9× 10−6
Canonical magnetic deformations: � 6 2− 6× 10−7
Buried magnetic field in MSPs: �fid ∼ 10−9 and a buriedmagnetic
field of 1011 G G. Woan+[ApJL,863:L40, 2018]
These are even more stringent than (Johnson-McDaniel+ PRD 88,
044004 (2013))
� ≤ 10−5 normal NS
� ≤ 10−3 hybrid stars
� ≤ 10−1 extreme quark stars
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CW signals Directed searches O2 GC O3 new sources
Directed searches so far
In directed searches interesting sky regions or astrophysical
objectsare investigated:
O1: 15 SNR + Fomalhaut b (LVC, ApJ 875 122, 2019)
O1: LMXB Scorpius X-1 (LVC, ApJ 847 47, 2017)
O1: Terzan 5 and the galactic center (Dergachev et
al.arXiv:1903.02389)
O1: Vela Jr., Cassiopeia A and G347.3 (Ming et
al.arXiv:1903.09119)
Other (LIGO S6): the Orion Spur, NGC 6544, LMXB XTEJ1751-305
Coherent or incoherent methods can be used
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CW signals Directed searches O2 GC O3 new sources
BSD directed search pipeline
BSD time series(Piccinni+ CQG 36, 015008, 2019)
2.30465 2.3047 2.30475 2.3048 2.30485 2.3049 2.30495
time (s) 10 6
-6
-4
-2
0
2
4
6
10-3 TIme series
Partial Dopplercorrection
Time-frequency peaks(Astone+ CQG 22, S1197, 2005)
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Frequency Hough map(Astone+ PRD 90, 042002, 2014)
The most significant candidates are selected onthe final HM. The
total computational power
needed for this search is ∼ 100 CPU hours pertarget for a ”wide”
frequency/spin-down range
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CW signals Directed searches O2 GC O3 new sources
Motivation for a Galactic center search
Several independent lines of evidence predict a sizable
population ofneutron stars in the region (O(108 − 109) expected in
the fullGalaxy, only a fraction observed)
Given the large number of massive stars, the central parsec
likelyhosts a large neutron star population (mostly MSP (Macquart,
J.P. et al.2015))
A GC pulsar population could explain the Galactic Center GeV
excessmeasured by Fermi (Bartels et al. 2016, Lee et al. 2016,
Fermi-LAT coll. 2017)
The size of the potentially EM observable population (i.e.
thosebeaming towards us) could include up to 50 canonical pulsars
and10000 millisecond pulsars (Rajwade et al. 2016)
The Galactic center is a good place to look for CWssince it is
likely to host several candidates
YITP workshop 2019 September 26, 2019 8 / 16
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CW signals Directed searches O2 GC O3 new sources
Motivation for a Galactic center search
Several independent lines of evidence predict a sizable
population ofneutron stars in the region (O(108 − 109) expected in
the fullGalaxy, only a fraction observed)
Given the large number of massive stars, the central parsec
likelyhosts a large neutron star population (mostly MSP (Macquart,
J.P. et al.2015))
A GC pulsar population could explain the Galactic Center GeV
excessmeasured by Fermi (Bartels et al. 2016, Lee et al. 2016,
Fermi-LAT coll. 2017)
The size of the potentially EM observable population (i.e.
thosebeaming towards us) could include up to 50 canonical pulsars
and10000 millisecond pulsars (Rajwade et al. 2016)
The Galactic center is a good place to look for CWssince it is
likely to host several candidates
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CW signals Directed searches O2 GC O3 new sources
The Galactic center case: O2
Best results h01.4× 10−25 for L @ 163 Hz, 1.6× 10−25 for H @ 195
Hz at 95% C.L.
10 1 10 2
Frequency [Hz]
10 -25
10 -24
10 -23
10 -22
10 -21
h95
%0
H 95% C.L.L 95% C.L.
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Frequency: [10, 710] Hz
Spin-down: [−1.8 × 10−9, 3.7 × 10−11] Hz/s
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CW signals Directed searches O2 GC O3 new sources
The Galactic center case: O2
Since h0 ∝ Izzd �f2 → � = c
4
4π2G
(dIzz
)h0f2
d=8 kpc and a moment of inertia Izz = Ifid = 1038 kg m2 for
standard
NSs or 5 times larger for more exotic objects
0 100 200 300 400 500 600 700Frequency [Hz]
10 -6
10 -4
10 -2
10 0
10 2
95 %
H, Ifid
L, Ifid
H, 5Ifid
L, 5Ifid
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� ≤ 10−5 normal NS� ≤ 10−3 hybrid stars� ≤ 10−1 extreme quark
stars(Johnson-McDaniel+ PRD 88, 044004 (2013))
We can exclude the presence ofstars with ellipticity bigger
than10−6 in the GC region at thehighest frequency
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CW signals Directed searches O2 GC O3 new sources
Other potential sources
Sources which are likely hosting a NS are interesting candidates
forour searches.
Several potential sources are present in the astronomical
catalogslike:
the pre-release of the 8-years Fermi-LAT point sources
catalog1:identified or associated Supernova remnants or Pulsar Wind
Nebulaor unassociated sources (∼ 39%)
1https://fermi.gsfc.nasa.gov/ssc/data/access/lat/fl8y/YITP
workshop 2019 September 26, 2019 10 / 16
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CW signals Directed searches O2 GC O3 new sources
Fermi-LAT unassociated
Unassociated: 2132 in Fermi-LAT (∼ 39%) we have only
gamma-raysobservation, no counterparts at other wavelengths
0 50 100 150 200 250 300 350 400
(o)
-100
-50
0
50
100
(o)
unassociatedGC
YITP workshop 2019 September 26, 2019 11 / 16
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CW signals Directed searches O2 GC O3 new sources
Other potential sources
Sources which are likely hosting a NS are interesting candidates
forour searches.
Several potential sources are present in the astronomical
catalogslike:
the pre-release of the 8-years Fermi-LAT point sources
catalog2:identified or associated Supernova remnants or Pulsar Wind
Nebulaor unassociated sources (∼ 39%)
the IBIS-INTEGRAL soft gamma-ray source catalog (Bird+ 2016):10
SNR, 19 pulsar-like sources and 216 unidentified ones (23%)
2https://fermi.gsfc.nasa.gov/ssc/data/access/lat/fl8y/YITP
workshop 2019 September 26, 2019 11 / 16
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CW signals Directed searches O2 GC O3 new sources
IBIS-INTEGRAL
INTEGRAL catalog presents the following interesting sources: 10
SNR,19 pulsar-like sources and 216 unidentified ones (23%) which
skydistribution is shown below:
0 50 100 150 200 250 300 350 400
( o )
-100
-80
-60
-40
-20
0
20
40
60
80
100
(o)
unidentifiedbinariesGCPSR+SNR+
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CW signals Directed searches O2 GC O3 new sources
Other potential sources
Sources which are likely hosting a NS are interesting candidates
forour searches.
Several potential sources are present in the astronomical
catalogslike:
the pre-release of the 8-years Fermi-LAT point sources
catalog3:identified or associated Supernova remnants or Pulsar Wind
Nebulaor unassociated sources (∼ 39%)
the IBIS-INTEGRAL soft gamma-ray source catalog (Bird+ 2016):10
SNR, 19 pulsar-like sources and 216 unidentified ones (23%)
Most of the sources lie on the Galactic plane
3https://fermi.gsfc.nasa.gov/ssc/data/access/lat/fl8y/YITP
workshop 2019 September 26, 2019 12 / 16
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CW signals Directed searches O2 GC O3 new sources
How good is a target
For a given pipeline we can have an estimate of the search
sensitivity
(Astone+ 2014) as h0min ≈√Sn(f)
α (minimum detectable GWstrain amplitude)
For directed searches we use the age based upper limit hage
forthose sources whose age and distance is known (Wette 2008)
A good target will have hage > h0min
All these quantities can be translated in terms of the star
ellipticity�age and �min
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CW signals Directed searches O2 GC O3 new sources
Theoretical indirect upper limits: O3
Potentially detectable sources by our directed search pipeline,
with hagebigger than our search sensitivity.
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hage 6 1d
√5GIzz8c3τ
h0min ≈√Sn(f)
α
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CW signals Directed searches O2 GC O3 new sources
Theoretical indirect upper limits on the ellipticity
Since h0 ∝ Izzd �f2 → �min = c
4
4π2G
(dIzz
)h0minf2
�min at 95 % C.L. for Avanced LIGOand Advanced Virgo at
designsensitivity for sources at d = 1 kpc and20 kpc The �age
theoretical indirectupper limit is
�age ≤√
5c5
128π4GIzzτf4
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CW signals Directed searches O2 GC O3 new sources Conclusion
Conclusion
CW could be the next surprise in GW astronomy given the
enhancedsensitivity of the detectors along with the development of
newpipelines
Astronomical catalogs (Fermi, INTEGRAL,...) provide good
targetsfor our searches, EM observation are crucial
We plan to analyze O3 data looking for sources from the
Galacticcenter plus other targets
A CW detection will provide information on the
quadrupolardeformation (ellipticity)
With a joint CW and EM observation we can measure NS
radius,mass, magnetic field and ellipticity ⇒ EOS
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CW signals Directed searches O2 GC O3 new sources Conclusion
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Thank you!
CW signalsDirected searchesO2 GCO3 new sourcesâ•¢Conclusion