Transcript Gal-Yam et al. 2006, ApJ, Submitted, astro-ph/0509891

The Progenitors of Short-Hard GRBs
from an Extended Sample of Events
Avishay Gal-Yam
Hubble Fellow
CALTECH
Outline
- Observational breakthrough 2005
- An extended sample from the IPN
- Population analysis – hosts
- Final remarks
Short GRBs (SHBs) - Papers:
Nakar, Gal-Yam, Piran & Fox 2005, ApJ
Fox et al. 2005, ApJL, 050509b
Fox et al. 2005, Nature, Oct. 6, 050709
Berger et al. 2005, Nature, Nov. issue, 050724
Gal-Yam et al. 2006, ApJ, Submitted, astro-ph/0509891
Nakar et al. 2006, ApJ, in press, astro-ph/0511254
Also:
Bloom et al. 2005
Prochaska et al. 2005
Tanvir et al. 2005
…
People:
E. Nakar (Caltech)
T. Piran (HUJI), D. Fox (Penn State),
E. Ofek (Caltech)
(Extended) Caltech GRB group (Kulkarni, Frail,
Berger, Cenko…)
The new SHB (Swift-HETE-Bursts) era
•
•
Arcmin -> arcsec localizations -> hosts
4 relevant bursts, as of August 2005
Gehrels et al. 2005
GRB 050509B: Swift Detection
T90=40 ms
Very faint GRB
X-ray: T+62 s detects 11
photons(!)
No optical, no radio. Very
faint limits.
Giant elliptical galaxy in a
cluster. z=0.22 . Host?
No SN
HST Imaging: No Supernova
48 sources in XRT error circle
Error radius = 9.3 arcsec
4 HST Epochs
May 14 to June 10
Giant elliptical (Bloom et al 2005)
L=1.5L*
SFR<0.1 M yr-1
Fox et al. 2006
SHB 050709: HETE Detection
Villasenor et al. 2005
A Hard spike, 84 keV
A Soft bump
Roughly equal energy in
each component
T90=70 ms
SHB 050709 - localization
•
•
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•
X-ray afterglow
Optical afterglow
Secure association with a
galaxy: late-type, z=0.16,
moderate SFR (MW), lots
of old stars (>1 GY) Covino et al. 2005
No SN
GRB 050724: Swift Detection
15-150 keV
250 ms
T90=3 s
T90=40 ms
15-25 keV
Gal-Yam et al. 2005
100 s
Hard spike/soft bump
X-ray, optical, IR and
radio afterglow detected
Secure association with
elliptical galaxy, z=0.26
No SN (Berger et al.
2006)
SHB 050813: Swift Detection
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Another Swift SHB
Deep imaging identifies a high-z cluster (Gladders et
al. 2006)
Initial spectroscopy shows z=0.722 (Berger 2005,
Prochaska et al. 2005) (but perhaps revised higher,
z=1.8)
Recent Swift/HETE sample:
• Low redshift
• Most in early types
• No SNe
So:
• Different from long GRBs
• Similar to SNe Ia
• Long lived progenitors
• “A merger origin”?
Extended Sample from IPN
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•
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Goal: Search for luminosity over-density inside
or around old, small, IPN error boxes (either
single luminous galaxies or galaxy overdensities
- clusters)
Sample: 4 small error boxes
Method: multicolor imaging (P60, LCO100),
spectoscopy (P200)
Comparison with SDSS luminosity functions
and galaxy densities.
SHB 790613
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Smallest IPN box (<1
arcmin2)
4 reddish galaxies with
similar colors – very high
density (~1% prob.)
6.5’ away from Abell 1892
(z=0.09), <1% chance
association in our entire
sample
Therefore assume: z=0.09
(nearest SHB), host likely
early type, in cluster
26 years … !
SHB 000607
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Small IPN box (5.6
arcmin2)
A single luminous galaxy
(R=17.57)
Sb galaxy at z=0.14, ~1.4
L* in SDSS r,i
Chance association 2% for
this error box, 7% for
entire sample
Therefore assume: z=0.14,
intermediate spiral host
SHBs 001204, 021201
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SHB 001204: Small IPN
box (6 arcmin2)
Several galaxies
Inconsistent redshifts
(0.31, 0.39), insignificant
overdensity
z>0.25 (1)
Z=0.31
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•
SHB 021201: insignificant
overdensity
z>0.25 (1)
Extended SHB sample
SHB
050509b
050709
050724
050813
790613
000607
001204
021201
Host
E
Sbc/Sc
E
E/S0
E/S0
Sb
Redshift
0.22
0.16
0.26
>=0.72
0.09
0.14
>0.25
>0.25
Comparison with SNe Ia
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Mannucci et al. 2005
SNe Ia occur in galaxies of
all types
But most of them occur in
late-type galaxies !
The normalized SN rate in
Irr galaxies is 20 times
that in E galaxies
Comparison of the
observed relative rates
disfavors an identical
distribution (P=7%)
It appears like SHBs come
from older progenitors
(several Gy) (also: Zheng &
Ramirez-Ruiz 2006)
Gal-Yam et al. 2006
Do we rule out NS-NS mergers?
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No.
Main limit is small numbers (both
SHBs and observed NS-NS pairs)
E to fit the
But, you really need to stretch
data
Observations disfavor DNS models
Belczynski et al. 2006
This is not changed by 050813 z>0.72
and 051221 (Soderberg et al. 2006)
Soderberg et al. 2006
Concluding remarks
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Similar results from redshift distribution
(Nakar, Gal-Yam & Fox 2006)
Recent SHBs useless for similar analysis due
to sample incompleteness (~1/10 with data)
and obvious strong selection effects (in
favor of gas-rich systems)
Additional observational effort imperative
for further progress
Possible high local rates of SHBs (See
Nakar, Gal-Yam & Fox) mean the LIGO (I or
II) may provide conclusive evidence for
compact binary models
Thanks
The rate and progenitor lifetime of SHBs
(Nakar, Gal-yam & Fox 2005)
Goals:
•Using the extended sample to constrain the
local rate and the progenitors lifetime of short
GRBs.
•Evaluate the compatibility of these results with
the compact binary progenitor model.
•Explore the implications for gravitational wave
detection of these events with LIGO.
Method:
Comparing the observed redshift and luminosity
distributions to predictions of various models of
intrinsic redshift and luminosity distributions.
(this method is an extension of a method used by Piran
1992; Ando 2004; Guetta & Piran 2005,2006)
Consistency test
Several bursts with known z
Redshift distribution
Intrinsic
Cosmology
+
Detector
Observed
~400 BATSE bursts with unknown z
Luminosity function
If f(L) is a single power-law:
Cosmology
Observed
Intrinsic
Detector
In the case of BATSE SHBS a single power-law fits the
data very well: f(L)  L-2±0.1
Star formation rate
+
Porciani & Madau 2001
Progenitor lifetime
distribution
Intrinsic redshift
distribution
=
Results
Progenitor lifetime
ttypical > 4[1]Gyr
(95% [99.9%] c.l.)
or if f(t)  th then h > -0.5[-1] (95% [99.5%] c.l.)
*Similar results are obtained when we take z050813>0.72
**Similar results are obtained by Guetta & Piran 2006
Main uncertainties and limitations
•Luminosity function – any “knee” shaped broken power-law
results in similar constraints. A short lifetime may be consistent
with an “ankle” shaped broken power-law (expected in case of two
populations of SHBs).
•Star-Formation History – the results are valid for any of the
three Porciani & Madau (2001) SFH functions (all peak at z≈1.5).
•Detector Thresholds – important only if the luminosity
function is not a single power-law (only Swift SHbs can be used).
The results are valid for a range of reasonable threshold functions
of Swift.
•Small sample – the results are only at a level of ~3 and might
be affected by unaccounted selection effects or wrong
measurements.
Observed Local Rate
(and robust lower limit)
-BATSE observed rate was  170 yr-1
-At least ¼ of these bursts are at D < 1Gpc
3
SHB,obs  10 Gpc yr
-1
Similar result is obtained by Guetta & Piran 2006
Total Local rate
1
 SHB


Lmin
3
-1
 Gpc yr
 40 f b  49
 10 erg/sec 
We consdider here f(L)  L-2 with a lower cutoff Lmin
fb – beaming correction (30-50 Fox et al. 2005 ???)
Lmin – The current observation are insensitive to Lmin < 1049
erg/sec. Evidence for population of SHBs within ~100Mpc
(Tanvir et al. 2005) suggests Lmin < 1047 erg/sec
Local rate – upper limit
SHB progenitors are (almost certainly) the end
products of core-collapse supernovae (SNe).
The rate of core-collapse SNe at z~0.7 is
5×105 Gpc-3 yr-1 (Dahlen et al. 2004), therefore:
3
 SHB  5 10 Gpc yr
5
-1
Observed NS-NS systems in our galaxy
Based on three systems, Kalogera et al. (2004) find:
5
4
1.7 10   NS  NS  2.9 10 yr (95%)
-1
in our galaxy
And when extrapolating to the local universe:
200   NS NS  3000 Gpc -3 yr -1
This rate is dominated by the NS-NS system with
the shortest lifetime – t~100 Myr (the double pulsar
PSR J0737-3039). Excluding this system the rate is
lower by a factor 6-7 (Kalogera et al. 2004).
SHBs and NS-NS mergers
NS-NS (Kalogera et al. 2004):
200<RNS-NS< 3000 Gpc-3 yr-1
Dominated by binaries that
merge within ~100 Myr
SHBs (Nakar et al. 2005):
10<RSHB< 5·105 Gpc-3 yr-1
Dominated by old
progenitors >4 Gyr
For the two to be compatible there should be a hidden
population of old long-lived NS-NS systems.
Can it be a result of selection effects?
Maybe, but we cannot think of an obvious one.
Caveat: small number statistics
Detection of SHB increases LIGO range by
a factor of 1.5-2.5 (Kochanek & Piran 1993):
•Timing information (~1.5)
•Beaming perpendicular to the orbital plane (~1.5)
•Localization information
LIGO-I: Probability for simultaneous detection
Swift detects and localizes ~10 SHBs yr-1. If
Lmin~1047 erg/s and f(L)L-2 then ~3% of these
SHBs are at D<100 Mpc and ~1% at D<50 Mpc
R(merger+SHB) ~ 0.1
-1
yr
Notes:
•This result depends weakly on beaming
•In this scenario RSHB ~ 1000 fb Gpc-3yr-1
•Comparison with Swift and IPN non-localized bursts may
significantly increase this rate
Thanks!
Single power-law fit to f(L)
Maximum likelihood: f(L)  L-2±0.1
c2/d.o.f  1  a good fit
The extended sample (8 SHB) can be used
SHBs
Galaxies at D<100Mpc
SHBs (E-Sbc galaxies)
SHBs
Long GRBs
At least 5% of BATSE
SHBs are at D<100Mpc
Tanvir et al. 2005
Our model predicts that 3% of the SHBs are at
D<100Mpc if Lmin 1047 erg/s
Broken power-law fit to f(L)
 L1 L  L*
f ( L)    2
L  L*
L
1   2
For each f(t), 1 and 2 we fit L* to BATSE dN/dP
Only Swift bursts can be used (unknown detector
response for the rest). However we can carry a
comparison with the two-dimensional L-z distribution
ttypical > 3Gyr
or
h>-0.5
Probability for blind search detection
LIGO-I: Taking a speculative but reasonable SHB rate
of 104 Gpc-3 yr-1 predicts a detection rate of:
R(NS-NS) ~ 0.3 yr-1
R(BH*-NS) ~ 3 yr-1
LIGO-II: The SHB rate lower limit of 10 Gpc-3 yr-1 implies:
R(NS-NS) ≥ 1 yr-1
R(BH*-NS) ≥ 10 yr-1
*MBH ~ 10M
GRB missions
Mission
Swift
SHB rate (yr-1)
localized non-localized
2005-2007+
~10
?
Operational
HETE-2
2001-2005+
~1
-
IPN
yes
~1
~10*
GLAST
2007-
~30*
-
*my rough estimate
LIGO-II: Probability for simultaneous detection
•This year 3 bursts detected at D < 1Gpc
•GLAST is expected to detect several SHBs at
D<500Mpc every year
•LIGO-II range for simultaneous detection is
~700 Mpc (NS-NS) and ~1.3 Gpc (BH-NS)
Simultaneous operation of LIGO-II and an
efficient SHB detector could yield at least
several simultaneous detections each year.
Non-detection will exclude the compact merger
progenitor model
Offset
39 ± 13 kpc
3.5 ± 1.3 kpc
2.4 ± 0.9 kpc
Prochaska et al., 2005