Gamma-Ray Bursts and Gravitational Waves

Gamma-Ray Bursts and Gravitational Waves Shiho Kobayashi (Penn State)

Gamma-Ray Bursts (GRBs) sudden, intense flashes of 0.1- 1MeV rays arriving from random directions in the sky. luminosity Time[sec]

Short Bursts Long Bursts events Hardness Duration [sec] >2sec

Discovery of counterparts of (long) GRBs in longer wave lengths “afterglow” Confirm (1) Cosmological model Emission and absorption lines in optical afterglow Isotropic gamma-ray energy (2) Relativistic Fireball model

Internal Shocks External Shocks Faster and slower shells Outflow and ambient matter GRB afterglow ? Relativistic Outflow Lorentz factor > 100

We know HOW GRBs are produced. ---- relativistic shocks and synchrotron process What produces the relativistic flow? Catastrophic events involving Neutron Star or a Stellar-mass Black Hole? Bulk of energy radiated into ray band Energy budget comparable to kinetic energy in Supernovae Variability in GRBs: msec time scale

NS-NS NS-BH White dwarf - BH Helium star - BH Short Bursts? The engine must active much longer than its variablity timescale! BH - massive Accretion Disk System Massive stellar collapse Compact mergers Collapsar, Hypernova, failed SN: iron core collapses to BH

afterglow X O R GW GRB Bloom

In-spiral merger Ring-down Merger begins when orbital evolution is so rapid that adiabatic evolution is not a good approximation. Masses violently merger to form a BH. BH is initially deformed. Energy associated with deformation is radiated as GWs As binary losses energy by GW the masses gradually spiral in toward each other. S.K & Meszaros, astro-ph/0210211

Massive stellar collapseleading to a GRB requires a high core rotation rate, which may be easier to achieve if the star is in a binary system, although this is not necessary. Anyway, In-spiral signal terminates at a frequency well below seismic cutoff. Fryer, Woosley & Hartmann 99

Numerical calculations of GW radiation from collapsars have been done in the Newtonian approximation in 2D ( e.g. Fryer et al 1999; MacFadyen & Woosley 1999 ), relativistic in 2D (Dimmelmeier et al. 2002). They suggest that GW emission from collapsars may be much less important than from compact binaries, even though these numerical estimates are not conclusive as a number of effects ( GR, secular evolution, non-axisymmetry) are neglected. High rotation rate is required to form centrifugally supported disk around BH to power GRB jet. The same high rotation rate could lead to a bar or fragmentation type instability in the collapsing core or/and in the massive disk. (Nakamura & Fukugita 1989; Fryer et al 2002; van Putten 2002; Davies et al 2002) Infalling matter perturbs BH’s geometry.

GRBs and GWBs GRBs and Afterglows can give the occurrence times and the directions. Binaries, bars, fragmentations and QNMs ( ) emit GWs more strongly along the polar axis, along which GRB jets are also launched. Then, GRB souces are stonger than the average. (Kochanek & Piran 1993; S.K & Meszaros in prep)

t Internal shocks Gamma-rays R ringdown Relativistic Jet merger Lorentz factor> 100 inspiral GW World line of observer

msec-sec EM waves ???Waveform??? GWs BH formation The correlated output of two GW detectors evaluated in the moment just prior to GRB (on) will differ from that evaluated at other time (off). (Finn et al. 1999)

Output of two detectors(identical locations and arm orientations) Cross-correlation Averaged over source population Filter function if we knew

if By collecting many sample, we can get some information on association between GRBs and GWs. (99% signicance)

We should select nearby GRBs. Typical GRB at 3000Mpc GRO : almost full sky coverage but large error box HETE, Swift: smaller coverage accurate positioning allow the follow up by optical-telescope

When we analyze the nearest events in a year Typical distance (uniform distribution) The number of events needed to detect the association The number of years it takes to collect sample

Contamination to estimate on by undetected GRBs Possibly we do not see a large fraction of GRBs Sky coverage by gamma-ray detectors Beaming of GRB jets If the reduction factor is

Bloom

Light curves of afterglow Distribution of Opening Angles We can observe Sample : 10+5 GRBs (Frail et al. 2001)

Fast X-ray Transients (FXTs) BATSE(>20keV) SAX-WFC(2-26keV) GRB FXT??? Kippen et al. 2001

Binary , QNM(l=m=2), bar... The amplitude and polarization of GWs depend on the viewing angle from the polar axis! GRB Luminosity also depends on the polar angle!!!

Correlation GW Linear Polarization degree GRB luminosity LIGO observatories are co-aligned, no information about P (S.K. & Meszaros in prep)

Distance to GRB sources might be determined by GW observation! “Dark GRBs” 26 well localized GRBs Kulkarni et al. 2000

Detection of counterparts of GRBs in GWs will revolutionize GRB field. GRBs and Afterglows provide occurrence time and sky position. Cross-correlation technique can be used to get some information of association between GRBs and GWBs.

Gamma-Ray Bursts and Gravitational Waves