searching for continuous gravitational-waves from galactic ...mmgw2019/slide/1st/piccinni.pdfcw...

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


Overview

Intro on Continuous waves signals

Focus on directed searches

The Galactic Center O2 case

New sources from Fermi and Integral catalogs for O3



Gravitational waves sources

Modeled waveform Unknown waveform

Long-lived

Transients


T ∼ monthsor years

T ∼ up to100 s




Long-lived

Transients



T ∼ up to100 s

Compact binary coalescenceh0 ∼ 10−21




Long-lived

Transients



T ∼ up to100 s


Bursth0 ∼ 10−21




Long-lived

Transients



T ∼ up to100 s

Stochastic backgroundh0 ∼ 10−28


Bursth0 ∼ 10−21




Long-lived

Transients



T ∼ up to100 s

Continuous wavesh0 ∼ 10−25

Stochastic backgroundh0 ∼ 10−28


Bursth0 ∼ 10−21




Long-lived

Transients



T ∼ up to100 s


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)]



Isolated neutron stars

Credit: S. Mastrogiovanni

h0 =4π2Gc4

Izzf2

d �Izz: moment of inertia�: ellipticity


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))


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



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



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)


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


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



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.


Frequency: [10, 710] Hz

Spin-down: [−1.8 × 10−9, 3.7 × 10−11] Hz/s


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


� ≤ 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


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


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







the IBIS-INTEGRAL soft gamma-ray source catalog (Bird+ 2016):10 SNR, 19 pulsar-like sources and 216 unidentified ones (23%)



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+







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



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



Theoretical indirect upper limits: O3

Potentially detectable sources by our directed search pipeline, with hagebigger than our search sensitivity.


hage 6 1d

√5GIzz8c3τ

h0min ≈√Sn(f)

α


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


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


CW signals Directed searches O2 GC O3 new sources Conclusion


Thank you!

CW signalsDirected searchesO2 GCO3 new sourcesâ•¢Conclusion

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