A Kilonova Associated with theShort GRB 130603B
Andy Fruchter(STScI)N. Tanvir, A. Levan, R. Hounsell et al.

LGRBs are Decisive• Long bursts (LGRBs) are largely found on rapidly

star-forming irregular galaxies (Fruchter+1999, Bloom+1999...)• LGRB hosts are generally dominated by extremely
young stellar populations (<10 Myr) (Levesque+ 2010)
and are largely metal poor (≲ 1/3 solar) (Modjaz+2008)• LGRBs are preferentially found on brightest
regions of their hosts (Fruchter et al. 2006)• Most, if not all LGRBs, are associated with Type Ic
SNe (Hjorth + 2003, Stanek + 2003 ...)

SGRBs Are Tentative• SGRBs are found in all types of galaxies,
from star-forming dwarfs to ellipticals (Fox +2005, Bloom + 2005)• Stellar populations of hosts have typical agesof few hundred Myrs (Liebler & Berger 2010)• No SGRBs are associated with SNe (to verystrong limits in many cases)• SGRBs are widely distributed on hosts (Berger& Fong 2010); ∼ 10% may be hostlessYou say Macronova,
I say Kilonova• Merging neutron stars should throwout few percent of their mass as tidal
tails -- this material would be hot, andneutron rich. (Eichler + 1989, Li & Paczynski 1998,)• No search had yet found such a “nova”• Barnes and Kasen (2013) proposed
the nova would be very red due toextraordinary optical depth of rprocess ejecta.

First SGRB Host Absorption
Spectrum of GRB 130603B

Figure 1: (a) Spectrum of the afterglow of GRB 130603B obtained using the OSIRIS instrument on the 10.4 mGTC telescope 7.4 hr after the burst onset. The contribution of the host galaxy was subtracted using a secondspectrum, that was obtained 5 days later when the afterglow had faded away. Panel (b) shows this second spectrumof the host galaxy. Dotted vertical lines indicate the location of some of the absorption and emission features. Grey
vertical bands mark the position of strong telluric features.

de Ugarte Postigoet al. 2013

Environment of GRB
GRB 130603B

SGRB 130603B in Blackand White





GRB 130603B LightCurveTanvir et al.
2013

Do We Say Kilonova?
• Absolute magnitude of J=-15.35 at 7days is in good agreement with KNmodels -- and makes it in luminosity
at least a “kilonova”• Timescale of “bump” consistent withKN predictions• But our data are not as constraining
as one might like

GRB 080503
Figure 5. Ground-based and space-based images showing the evolution of the faint OT associated with GRB 080503. The transient peaked at about t = 1 d, shownin an image from Gemini-North at left. Thereafter it faded rapidly and is barely detected in the first HST epoch in F606W only. Later observations failed to reveal agalaxy coincident with the transient position. Two very faint nearby (but noncoincident) galaxies are designated “S1” and “S4.”(A color version of this figure is available in the online journal.)
R. Hascoët et al.: The origin of the late rebrightening in GRB 080503

Fν (µJy)magnitude

UVOT
Gemini
KeckHSTin Figure 5). Although faint, this galaxy is clearly extended,with its stellar field continuing to ∼0."" 3 from the GRB position.
BAT105(It is plausible that deeper observations or images in redder
Bwavebands may extend its disk further, but we have no evidence
104F450Wg15that this is the case.) Additionally, there is a brighter galaxy
3White10(“S1,” F606W ≈ 26.3 mag) ∼2"" to the north of the afterglow
F606W
position, also visible in the Gemini images. Given the faintness
r2
10
Rof these galaxies and the moderate offset from the afterglow
20i
position, the probability of chance alignment is nontrivial (aF814W
101zfew percent, following Bloom et al. 2002), and we cannot makeK
firm statements about their association with GRB 080503.
10025The extremely deep limit on a host galaxy puts GRB 080503
10in very rare company. Among short bursts, no comparably deeplimit exists for any previous event except GRB 061201, although
10a study with deep HST imaging of short-burst hosts has yet to be
30
published. However, ground-based searches for hosts of other101010100101
SGRBs with subarcsecond positions have identified coincident
trigger (day)host galaxies in nine of 11 cases. The two exceptions are GRB
Figure 6. X-ray and optical light curves of GRB 080503. The optical bands
061201 (Stratta et al. 2007) and GRB 070809 (Perley et al.
have been shifted to the r band assuming an optical spectral index of β = 1.2;
Fig. 2. Refreshed shocks: long-lived reverse shock model. Left panel: initial distribution of the Lorentz factor (lower part) and kinetic power (upper
the X-ray light curve has been shifted by a factor of 125 to match the optical2008); bothof theseat relativelypart) in the flow as a function of injection time tinj . Right panel: syntheticlight-curves
at 2appeareV (black,dotted line) smalland 10 physicalkeV (grey,offsetdotted line)(corresponding to βOX = 0.75). The BAT light curve is extrapolated into thefrom
nearbyspirals
which
have
as
hostcandidates.
spikebeen claimed
spikeeetogetherwith the data.
The kinetic
energiesin thespike
and extended emission components are Ekin = 7 × 1050 erg and Ekin= 30 Ekin . The
X-ray band using
the high-energy
spectrum.
3σ upperlimits areshownwithShort
GRB 070707
has asa coincident
hostwithmicrophysics
R = 27.3 mag
density of the external medium, redshift and slope p of the electron
distribution
are the samein Fig. 1. The
adoptedparameters
arrows.
1/2(Piranomonteetal.
2008),
about
thesameas
themagnitude
ofare !e = !B = 0.16 in the shocked ejecta.
the nearest galaxy to the GRB 080503 OT position. In fact, evenAt the location of the afterglow in our first-epoch F606W imcompared with long bursts, the lack of host galaxy is unusual;age we found a faint point source, with a magnitude of F606W =only five events have host-galaxy measurements or limits fainter27.01 ± 0.20 after charge-transfer efficiency correction followthan 28.5 mag.
10Perley et al. 2009

Hascoët et al. 2012

Et tu, 060313B?
Short GRB 130603B

5310NIR H−band

2hostH−band Flux Density (µJy)

6.7 GHz Flux Density (µJy)

10tjet

AV210110010Radiotjet−110110 −11001−221010Time after Burst (d)=1 mag−110103010110Time after Burst (d)

10210

10

X−ray

Optical r−band
Ahost=1 mag
V1998bw
2006aj110010101 keV Flux Density (µJy)

r−band Flux Density (µJy)

2101010−110−210Swift/XRT−3XMM−Newton

10ttjet−110−210−1jet

01010Time after Burst (d)110−310−210−110Time after burst (d)010110Figure 2. Radio through X-ray afterglow light curves of GRB 130603B. Error bars correspond to 1σ confidence, and triangles denote 3σ upper limits. Theafterglow model is shown as a black line, while the jet break time of t j ≈ 0.47 d is marked by a vertical grey dashed line. Also shown is a model with energy
injection (dark grey dashed line) that fits the X-ray excess but violates the detections and limits in the optical, NIR, and radio bands. Top left: 6.7 GHz observations
with the VLA (red). Top right: H-band observations (green; Berger et al. 2013; de Ugarte Postigo et al. 2013; Tanvir et al. 2013), where JK-band observations
are extrapolated to H-band using βopt = −2. The observed values (open green squares) are corrected for AVhost = 1 mag (filled green symbols). The circled
asterisk at δt ≈ 9 d is the “kilonova” associated with GRB 130603B (Berger et al. 2013; Tanvir et al. 2013). Bottom left: Optical r-band observations (orange;
this work, Cucchiara et al. 2013; de Ugarte Postigo et al. 2013; Tanvir et al. 2013), where giz-band observations are extrapolated to r-band using βopt = −2. Theobserved values (open orange squares) are corrected for AVhost = 1 mag (filled orange symbols). The displayed upper limits (orange triangles) are also corrected
for extinction. Also shown are the optical light curves of GRB-SN 1998bw (Galama et al. 1998; Clocchiatti et al. 2011) and GRB-SN 2006aj (dot-dashed lines;Mirabal et al. 2006) corrected for extinction and redshifted to z = 0.3565. Bottom right: Observations from Swift/XRT (blue circles) and XMM-Newton (bluesquares) at 1 keV.

Fong et al. 2013

The Nearest(?) SGRB

GRB 080905a z=0.12? (480 Mpc)

Kilonovae as Markers• Advanced LIGO should find NSmergers out to ∼200 Mpc• Will have error circles of 10s of squaredegrees• But at 200 Mpc, 130603B would have

had J≈21, I∼22-25. Can be found fromground but will likely require image
subtraction (so not trivial) and large
aperture (Subaru, LSST?)

Conclusions• The simplest explanation for ourobservations is a kilonova.

• Our results do not eliminate thepossibility of a rare afterglow
phenomenon, but we appear to beconfirming a PREdiction.

• There is a good chance we will have an
opportunity to repeat the experiment
within another eighteen months.