Gamma-Ray Burst Searches Gamma-Ray Burst Searches with Virgo: current analyses with Virgo: current analyses

& future prospects& future prospectsAlessandra CorsiAlessandra Corsi

1013 cm 1016 cm

If If not not uniform, uniform, faster faster shells shells collide collide with with slower slower ones, ones, and and internal internal shocksshocks formform Part of Part of the the kinetic kinetic energy energy is is converteconverted in d in internal internal prompt prompt emissionemission

Fireball ModelFireball Model The fireball expands The fireball expands and collects ISMand collects ISM

It starts to be It starts to be decelarated and an decelarated and an external shock forms external shock forms

The inital evolution is The inital evolution is inverted: bulk kinetic inverted: bulk kinetic energy is converted energy is converted into internal energy into internal energy across the shock front across the shock front

The accelerated The accelerated electrons radiate via electrons radiate via synchrotron emission synchrotron emission afterglow emissionafterglow emission

Formation of a GRB could begin Formation of a GRB could begin either with the merger of two either with the merger of two compact objects or with the collapse compact objects or with the collapse of a massive starof a massive star

As a result, an energy as high as As a result, an energy as high as EE10105454 ergs can be released in a ergs can be released in a compact volume of spacecompact volume of space ( (101066 cm) cm)

A fireball of e+/e- pairs, photons A fireball of e+/e- pairs, photons and baryons is formed and expands and baryons is formed and expands converting thermal energy in bulk converting thermal energy in bulk kinetic energy carried by the kinetic energy carried by the baryons originally present in the baryons originally present in the explosion site (Mexplosion site (Mbb) )

When the thermal motion becomes When the thermal motion becomes sub-relativistic, the bulk Lorentz sub-relativistic, the bulk Lorentz factor saturates to factor saturates to =E/M =E/Mbbcc22

nn101022 -1

0-1

044 c

m cm

-3-3 and e

viden

ce fo

r a s

tella

r win

d n

and e

viden

ce fo

r a s

tella

r win

d n

r r-2-2

1013 cm 1016 cm

How to derive clues How to derive clues on the nature of the on the nature of the

progenitor?progenitor? n n < 1 cm< 1 cm-3-3 and uniform medium and uniform medium

E.g. afterglow E.g. afterglow phase: phase:

emission emission processes, processes,

circum-burst circum-burst medium medium

(density and (density and structure)structure)

The fireball modelThe fireball model

dI will I will

consider consider the link the link with the with the

GW GW domaindomain

GW emission from GRB progenitorsGW emission from GRB progenitors

Short GRB:Short GRB: we expect the GW signal to be emitted in 3 phases: in-

spiral, merger and ring-down

Long GRB:Long GRB: no in-spiral phase, only merger and ring-down

Collapsar model (e.g. Woosley 1998):Collapsar model (e.g. Woosley 1998):

“ “GRB as the birth cry of a BHGRB as the birth cry of a BH”: when the collapse of the iron core of a ”: when the collapse of the iron core of a rotating massive progenitor proceeds directly to a BH formation, the rotating massive progenitor proceeds directly to a BH formation, the stellar mantle falls into the newly formed BH and angular momentum stellar mantle falls into the newly formed BH and angular momentum slows the collapse along the equator, ultimately forming an accretion disk slows the collapse along the equator, ultimately forming an accretion disk that, within a few seconds, launches particle jets along the rotation axis that, within a few seconds, launches particle jets along the rotation axis powering a GRB”powering a GRB”

“ “The jets pass through the outer shells of the star and, combined with The jets pass through the outer shells of the star and, combined with the vigorous winds of newly forged radioactive metals blowing off the the vigorous winds of newly forged radioactive metals blowing off the disk inside, give rise to the supernova event” disk inside, give rise to the supernova event”

Collisions among shells of the jet moving at different velocities, far Collisions among shells of the jet moving at different velocities, far from the explosion and moving close to light speed, create the GRB, from the explosion and moving close to light speed, create the GRB, which can only be seen if the jet points toward uswhich can only be seen if the jet points toward us

Long GRBs: the progenitorLong GRBs: the progenitor

Short GRBs: the progenitorShort GRBs: the progenitor

General picture:General picture:

Merger events of NS+NS or BH+NS systems widely favored:Merger events of NS+NS or BH+NS systems widely favored:

Seems unlikely that typical energies of short GRBs set free during the Seems unlikely that typical energies of short GRBs set free during the dynamical merging; the following accretion phase in a postmerger system dynamical merging; the following accretion phase in a postmerger system consisting of a consisting of a central BH and a surrounding toruscentral BH and a surrounding torus is much more promising is much more promising

BH-torus system geometryBH-torus system geometry: relatively baryon-poor regions along the : relatively baryon-poor regions along the rotational axis rotational axis thermal energy release preferentially above the BH poles thermal energy release preferentially above the BH poles via e.g. via e.g. anti- anti- annihilation annihilation can lead to collimated, highly relativistic jets can lead to collimated, highly relativistic jets of baryonic matter of baryonic matter if thermal energy deposition rate per unit solid angle if thermal energy deposition rate per unit solid angle sufficiently large. sufficiently large.

-rays produced in internal shocks when blobs of ultra-relativistic matter -rays produced in internal shocks when blobs of ultra-relativistic matter in the jet collide with each other. When the jet hits the ISM, the afterglow is in the jet collide with each other. When the jet hits the ISM, the afterglow is producedproduced

Both progenitor types result in the formation of a Both progenitor types result in the formation of a few solar mass BH, surrounded by a torus whose few solar mass BH, surrounded by a torus whose accretion can provide a sudden release of accretion can provide a sudden release of energy, sufficient to power a burst. But different energy, sufficient to power a burst. But different natural timescales imply different burst natural timescales imply different burst durations:durations:

LONG: death of massive stars LONG: death of massive stars free-fall time free-fall time of the material falling on the disk form outside, of the material falling on the disk form outside,

ttffff ≈ 30s(M/10M ≈ 30s(M/10M⊙⊙) ) −1/2−1/2 (R/10 (R/101010cm)cm)3/23/2

SHORT: coalescing compact objects SHORT: coalescing compact objects duration duration set by the viscous timescale of the gas accreting set by the viscous timescale of the gas accreting onto the newly-formed BH (short due to the small onto the newly-formed BH (short due to the small scale of the system)scale of the system)

GRB: progenitor models and time durationGRB: progenitor models and time duration

GRBs: EM signal and GW

EM signal GW emission

Source position, (distance), trigger time: on-source time window

Total energy output: hints on the disk mass

+From the GW signal: hints on the masses

involved in the processNature of the progenitor

Progenitor models

Detecting GW

Choice for an on-source time window: relevant Choice for an on-source time window: relevant timescalestimescales

The emitted GWs are in the frequency band The emitted GWs are in the frequency band accessible to VIRGO & LIGO only for the accessible to VIRGO & LIGO only for the last few last few minutesminutes of in-spiral (e.g. Cutler & Flanagan of in-spiral (e.g. Cutler & Flanagan 1994);1994);

Simulated launch + evolution of relativistic jets Simulated launch + evolution of relativistic jets driven by thermal energy deposition (e.g. driven by thermal energy deposition (e.g. anti- anti- annihilation) near BH accretion torus systems: annihilation) near BH accretion torus systems: after 100 ms of constant energy supply (i.e. after 100 ms of constant energy supply (i.e. ttaccacc100 ms100 ms)), the fireball is at d , the fireball is at d 3x103x1099 cm. cm.

Standard fireball model: GRB produced at d >10Standard fireball model: GRB produced at d >101313 cm cm another 400 msanother 400 ms after the central engine after the central engine supply shut off are needed to reach typical supply shut off are needed to reach typical internal shock distances (Aloy et al. 2004);internal shock distances (Aloy et al. 2004);

But in long GRBs: delay between GWs and em But in long GRBs: delay between GWs and em signal dominated by the time necessary for the signal dominated by the time necessary for the jet to push through the stellar envelope: can be jet to push through the stellar envelope: can be of the order of of the order of 100s100s (Meszaros) (Meszaros)

Connection between disk mass & energy Connection between disk mass & energy outputoutput

Linking Linking EE,iso,iso of a GRB to the energy output from the central of a GRB to the energy output from the central engine and the mass engine and the mass MMacc acc accreted on the BH (during the accreted on the BH (during the phase when neutrino emission from the accreted torus is phase when neutrino emission from the accreted torus is sufficiently powerful to drive the jets): chain of efficiency sufficiently powerful to drive the jets): chain of efficiency parameters corresponding to the different steps of physical parameters corresponding to the different steps of physical processes between the energy release near the BH and the processes between the energy release near the BH and the -ray emission at distances of -ray emission at distances of 10101313cmcm::

EE,iso,iso == ff11 f f22 f f33 f f-1-1 f f44 M Maccacc cc22

Efficiency at which Efficiency at which accreted rest mass accreted rest mass

energy can be energy can be converted to neutrino converted to neutrino

emissionemissionConversion efficiency of Conversion efficiency of

anti- anti- to e+e to e+e-- pairs pairs

Fraction of eFraction of e+ - + - -photon -photon fireball energy which drives fireball energy which drives the ultra-relativistic outflow the ultra-relativistic outflow

with with >100 >100

ff=2=2jetjet/4/4 =1- =1-coscosjetjet

Fraction of the Fraction of the sky covered by sky covered by the two polar the two polar

jets with semi-jets with semi-opening angles opening angles

jetjet and solid and solid angles angles jetjet::

afterglow light afterglow light curvecurve

Fraction of ultra-Fraction of ultra-relativistic jet relativistic jet

energy emitted energy emitted in in -rays via -rays via dissipative dissipative

shocks when shocks when optically thin optically thin conditions are conditions are

reached:reached: broad-broad-band afterglow band afterglow

modeling + modeling + prompt emissionprompt emission

Disk mass: Disk mass: depends on depends on

thethe mass ratio mass ratio q q enters in enters in the in-spiral the in-spiral GW signal GW signal

(chirp mass)(chirp mass)

Directly Directly measured:measured:

GRB prompt GRB prompt emissionemission

Torus formation in NS mergersTorus formation in NS mergers

q<1: less massive but slightly q<1: less massive but slightly larger star tidally disrupted and larger star tidally disrupted and deformed into an enlongated deformed into an enlongated primary spiral arm which is primary spiral arm which is mostly accreted onto the more mostly accreted onto the more massive companion. Its tail, massive companion. Its tail, however, contributes a major however, contributes a major fraction to the subsequently fraction to the subsequently forming thick disk/torus around forming thick disk/torus around a highly deformed and a highly deformed and oscillating central remnant. oscillating central remnant.

qq1 and 1 and equally sized stars: equally sized stars: both stars tidally stretched but both stars tidally stretched but not disrupted and directly not disrupted and directly plunge together into a deformed plunge together into a deformed merger remnant. merger remnant.

The The disk mass is around 0.05 Mdisk mass is around 0.05 M for q=1 and 0.26 Mfor q=1 and 0.26 M for q=0.55. for q=0.55.

Oechslin & Janka 2006:Oechslin & Janka 2006:

Estimating the strains of GWs from GRB progenitor Estimating the strains of GWs from GRB progenitor candidatescandidates

In-spiral:In-spiral: hhcc(f) (f) 1.4x101.4x10-21-21 (d /10 Mpc)(d /10 Mpc)-1-1 M M 5/65/6 (f /100 Hz) (f /100 Hz)--

1/61/6

f f f fii 1000 [1000 [MM/2.8M/2.8M ] ]-1 -1 HzHz

Merger:Merger: hhcc 2.7x10 2.7x10-22-22 ( (d /10 Mpcd /10 Mpc))-1-1 (4 (4 /M /M)) FF-1/2-1/2(a) ((a) (mm /0.05)/0.05)1/2 1/2

ffii f f f fqq 32 kHz32 kHz F(a) F(a) (M/M(M/M))-1-1

EEmm= = mm (4 (4/M)/M)22 M c M c22

F(a)= 1- 0.63 (1-a)F(a)= 1- 0.63 (1-a)3/103/10

Ring-down:Ring-down: slowly damped mode, l=m=2, peaked at fslowly damped mode, l=m=2, peaked at fqq and and width width f:f:

f f f fqq/Q(a), where Q(a)=2(1-a)/Q(a), where Q(a)=2(1-a)-9/20-9/20

hhcc(f(fqq) ) 2.0x102.0x10-21-21 ( (d /10 Mpcd /10 Mpc) ) -1-1 ( (/M/M ) [Q /14 F] ) [Q /14 F]1/21/2 ( (rr /0.01) /0.01)1/21/2

DetectabilityDetectabilityOptimal filteringOptimal filtering ( (in-spiralin-spiral & ring down): & ring down):

22optopt=4 =4 [h [hcc(f) (f S(f) (f Shh(f))(f))-0.5-0.5] ] 22 d(lnf) d(lnf) (d /10 Mpc)(d /10 Mpc)-1-1 M M 5/65/6 5 5

Typical valuesTypical valuesa a 0.98 0.98 mm 0.05 0.05 rr

0.01 0.01

MM==(m(m1,1, m m2,2,))3/53/5 (m (m1,1, + m + m2,2,))-1/5 -1/5 == (m(m1,1, ) ) qq-2/5-2/5/(q+1)/(q+1)1/51/5 MM=m=m11+m+m2 2 =m=m11/(1+/(1+qq))

Short GRBs, Short GRBs, optimal optimal

filtering can filtering can be appliedbe applied

Short & Long Short & Long GRBs, order of GRBs, order of

magnitude magnitude estimate of hestimate of hcc

Short & Long Short & Long GRBs, but GRBs, but

frequency too frequency too high high

KobayashKobayashi & i &

Meszaros Meszaros 20032003

Kobayashi & Meszaros Kobayashi & Meszaros 20032003

Advanced LIGO Advanced LIGO

Advanced LIGO

Fryer et al. 1999,

Belczynski et al. 2002

Kobayashi & Meszaros 2003

GW signal amplitude and VIRGO sensitivity curve [f GW signal amplitude and VIRGO sensitivity curve [f SShh(f)](f)]1/21/2

ns-ns m1= m2 =1.4 M

- - - - in-spiral - - - - in-spiral - - -merger

bh-ns m1=12 M m2 =1.4 M

- - - in-spiral - -merger ring-down

bh-he m1=3 M m2 =0.4 M

- - - - merger ring-down - - - - merger ring-down

Collapsar m1= m2 =1 M

- - - - merger- - - - merger

53 Mpc

220 Mpc

1100 Mpc

Advanced VirgoVirgo Virgo Advanced Virgo

2300 Mpc

280 Mpc

62 Mpc

Advanced VirgoVirgo

95 Mpc62 Mpc

Advanced VirgoVirgo

110 Mpc

27 Mpc 23 Mpc

490 Mpc

GRB 980425 d=40 MpcGRB 980425 d=40 MpcGRB 980425 d=40 MpcGRB 980425 d=40 Mpc

GRB analysis with VirgoGRB analysis with Virgo

On behalf of Virgo collaborationOn behalf of Virgo collaboration

Virgo-Rome group: Fulvio Ricci Virgo-Rome group: Fulvio Ricci

& EGO: Elena Cuoco& EGO: Elena Cuoco

Vesf-EGO: fellowship support Vesf-EGO: fellowship support

Virgo C7 run & GRB 050915aVirgo C7 run & GRB 050915a

GRB 050915a: good position in one of the data stretch of GRB 050915a: good position in one of the data stretch of the run, z unknown, Tthe run, z unknown, T9090=53 s (15-350 keV), long GRB =53 s (15-350 keV), long GRB we we expect the progenitor to be a collapsar and search for a expect the progenitor to be a collapsar and search for a burst type event in VIRGO data burst type event in VIRGO data

Virgo sensitivity during Virgo sensitivity during C7 run and nominal in C7 run and nominal in black; LIGO Hanford black; LIGO Hanford during S2 (coincidence during S2 (coincidence analysis with GRB analysis with GRB 030329) in red (2 km) 030329) in red (2 km) and blue (4 km).and blue (4 km).

Virgo sensitivity during Virgo sensitivity during C7 run and nominal in C7 run and nominal in black; LIGO Hanford black; LIGO Hanford during S2 (coincidence during S2 (coincidence analysis with GRB analysis with GRB 030329) in red (2 km) 030329) in red (2 km) and blue (4 km).and blue (4 km).

bkg region: a single lock stretch of data, 16500s long around the source region, used to estimate the statistical properties of the bkg and the pipeline efficiency

Source region: a time window 180 s long, 2 min before the EM trigger and 1 min after. Covers most astrophysical predictions, trigger uncertainty and accounts for the favored ordering where GW precede the GRB

Definition of on-source and bkg regionDefinition of on-source and bkg region

On both the on-source and bkg region, we run the “Wavelet Detection Filter” (WDF) by Elena Cuoco (VIR-NOT-EGO-1390-305 & VIR-NOT-EGO-1390-110), selecting all events with SNR > 4.

No events with No events with SNR>10SNR>10

GPS 810818575

http://gcn.gsfc.nasa.go

v/swift2005 grbs.html.

On-source and off-source distrib. are statistically compatible UL analysis

Pipeline efficiency evaluation on bkg region: Pipeline efficiency evaluation on bkg region: e.g. sine-gaussian signalse.g. sine-gaussian signals

Q=2f0 f0=characteristic frequency EGW=(hSGrss)2 c3dL

222f02/[5G(1 + z)]Q=2f0 f0=characteristic frequency EGW=(hSG

rss)2 c3dL222f0

2/[5G(1 + z)]

If the GRB was optimally oriented, the UL would be a factor of If the GRB was optimally oriented, the UL would be a factor of ((F((F++))22+(F+(Fxx))22))-1-1 7 lower. At nominal sensitivity, the noise strain 7 lower. At nominal sensitivity, the noise strain @200 Hz is a factor of 15 lower. Under these optimistic @200 Hz is a factor of 15 lower. Under these optimistic assumptions, our strain UL implies an energy UL of assumptions, our strain UL implies an energy UL of 0.2 M0.2 M at the at the distance of GRB 980425 (40 Mpc). Kobayashi and Meszaros 2003: distance of GRB 980425 (40 Mpc). Kobayashi and Meszaros 2003: in the case of a merger of two blobs of 1 Min the case of a merger of two blobs of 1 M each, assuming that each, assuming that 5% of the mass energy goes in GWs, one expects E5% of the mass energy goes in GWs, one expects EGWGW0.10.1 M M..

ProspectsProspects

WDF and population studies:WDF and population studies: Some changes to the wavelet bases used for the filter in order Some changes to the wavelet bases used for the filter in order to apply the search also to the in-spiral phase of short GRBs to apply the search also to the in-spiral phase of short GRBs (Elena Cuoco)(Elena Cuoco)

Need to set-up a Virgo procedure for population studies: while Need to set-up a Virgo procedure for population studies: while the GW signals from individual GRBs may be too weak to be the GW signals from individual GRBs may be too weak to be detected directly, the small correlations they induce in the data detected directly, the small correlations they induce in the data near the GRB trigger time may still be detectable by statistical near the GRB trigger time may still be detectable by statistical comparison to data from times not associated with a GRBcomparison to data from times not associated with a GRB

Joint LIGO-Virgo searches within the External Trigger group:Joint LIGO-Virgo searches within the External Trigger group: Virgo sensitivity during VSR1 improved nearly of a factor of 10 Virgo sensitivity during VSR1 improved nearly of a factor of 10 @ @ 200 Hz with respect to C7. LIGO-Virgo GRB searches for data 200 Hz with respect to C7. LIGO-Virgo GRB searches for data collected during this period (S5-VSR1) are planned (External collected during this period (S5-VSR1) are planned (External Trigger group activities). Trigger group activities). 50 GRB triggers received during the 50 GRB triggers received during the joint LIGO-Virgo data-taking period (May – Oct. 2007). A joint LIGO-Virgo data-taking period (May – Oct. 2007). A coincident analysis will allow us to quantify how much we gain coincident analysis will allow us to quantify how much we gain by using more than one detectorby using more than one detector

Work in progress: definition of a common set of simulated Work in progress: definition of a common set of simulated signals to estimate pipelines efficiency and compare LIGO-Vigo signals to estimate pipelines efficiency and compare LIGO-Vigo results (LIGO effort)results (LIGO effort)

Currently, starting to test the kind of improvement we may Currently, starting to test the kind of improvement we may have on Virgo ULs by using coincidences with LIGO detectors have on Virgo ULs by using coincidences with LIGO detectors (e.g. GRB 050520B and GRB 070729)(e.g. GRB 050520B and GRB 070729)

E.g.: GRB 070729E.g.: GRB 070729

Starting to analyze 3 hrs of data around the GRB trigger time Starting to analyze 3 hrs of data around the GRB trigger time ((59 windows, 180s long). A preliminary check for the maximum 59 windows, 180s long). A preliminary check for the maximum SNR of the Virgo triggers that survive in a 4 detector coincidence SNR of the Virgo triggers that survive in a 4 detector coincidence search (+/- 20 ms) gives a maximum SNR of search (+/- 20 ms) gives a maximum SNR of 3.5 (to compare 3.5 (to compare with SNR max = 9 during C7 run) in the 3 hrs of data. with SNR max = 9 during C7 run) in the 3 hrs of data.

SNR distribution of triggers found in one

of the 59 windows (180s) considered for bkg studies in coincidence with

GRB 070729

… … waiting for the plus and advanced configurationswaiting for the plus and advanced configurations

10 100 1000 1000010-24

10-23

10-22

10-21

10-20

h(f

) [1

/sq

rt(H

z)]

Frequency [Hz]

AdvVirgo Virgo Virgo semi-advanced Virgo semi-advanced "new mirror model" Advanced LIGO Advanced Virgo without thermo-refractive

Virgo /LIGO (red) Virgo+/eLIGO (green, 2008-09)AdvVirgo/LIGO (blue -2013-14)

• BNS range: 121 MpcBNS range: 121 Mpc• BBH range: 856 MpcBBH range: 856 Mpc• 1 kHz sens.: 6 101 kHz sens.: 6 10-24-24

The EndThe End