J/ApJ/848/L16 Counterpart of GW170817. I. DECam obs. (Soares-Santos+, 2017)
The electromagnetic counterpart of the binary neutron star merger LIGO/VIRGO
GW170817.
I. Discovery of the optical counterpart using the Dark Energy Camera.
Soares-Santos M., Holz D.E., Annis J., Chornock R., Herner K., Berger E.,
Brout D., Chen H.-Y., Kessler R., Sako M., Allam S., Tucker D.L.,
Butler R.E., Palmese A., Doctor Z., Diehl H.T., Frieman J., Yanny B.,
Lin H., Scolnic D., Cowperthwaite P., Neilsen E., Marriner J.,
Kuropatkin N., Hartley W.G., Paz-Chinchon F., Alexander K.D., Balbinot E.,
Blanchard P., Brown D.A., Carlin J.L., Conselice C., Cook E.R.,
Drlica-Wagner A., Drout M.R., Durret F., Eftekhari T., Farr B., Finley D.A.,
Foley R.J., Fong W., Fryer C.L., Garcia-Bellido J., Gill M.S..S.,
Gruendl R.A., Hanna C., Kasen D., Li T.S., Lopes P.A.A., Lourenco A.C.C.,
Margutti R., Marshall J.L., Matheson T., Medina G.E., Metzger B.D.,
Munoz R.R., Muir J., Nicholl M., Quataert E., Rest A., Sauseda M.,
Schlegel D.J., Secco L.F., Sobreira F., Stebbins A., Villar V.A., Vivas K.,
Walker A.R., Wester W., Williams P.K.G., Zenteno A., Zhang Y.,
Abbott T.M.C., Abdalla F.B., Banerji M., Bechtol K., Benoit-Levy A.,
Bertin E., Brooks D., Buckley-Geer E., Burke D.L., Carnero Rosell A.,
Carrasco Kind M., Carretero J., Castander F.J., Crocce M., Cunha C.E.,
D'Andrea C.B., da Costa L.N., Davis C., Desai S., Dietrich J.P., Doel P.,
Eifler T.F., Fernandez E., Flaugher B., Fosalba P., Gaztanaga E.,
Gerdes D.W., Giannantonio T., Goldstein D.A., Gruen D., Gschwend J.,
Gutierrez G., Honscheid K., Jain B., James D.J., Jeltema T., Johnson M.W.G.,
Johnson M.D., Kent S., Krause E., Kron R., Kuehn K., Kuhlmann S., Lahav O.,
Lima M., Maia M.A.G., March M., McMahon R.G., Menanteau F., Miquel R.,
Mohr J.J., Nichol R.C., Nord B., Ogando R.L.C., Petravick D., Plazas A.A.,
Romer A.K., Roodman A., Rykoff E.S., Sanchez E., Scarpine V., Schubnell M.,
Sevilla-Noarbe I., Smith M., Smith R.C., Suchyta E., Swanson M.E.C.,
Tarle G., Thomas D., Thomas R.C., Troxel M.A., Vikram V., Wechsler R.H.,
Weller J.
<Astrophys. J., 848, L16 (2017)>
=2017ApJ...848L..16S 2017ApJ...848L..16S
ADC_Keywords: Gravitational wave; Stars, neutron; Photometry, ugriz
Keywords: binaries: close; catalogs; gravitational waves; stars: neutron;
surveys
Abstract:
We present the Dark Energy Camera (DECam) discovery of the optical
counterpart of the first binary neutron star merger detected through
gravitational-wave emission, GW170817. Our observations commenced
10.5hr post-merger, as soon as the localization region became
accessible from Chile. We imaged 70deg2 in the i and z bands,
covering 93% of the initial integrated localization probability, to a
depth necessary to identify likely optical counterparts (e.g., a
kilonova). At 11.4hr post-merger we detected a bright optical
transient located 10.6" from the nucleus of NGC 4993 at redshift
z=0.0098, consistent (for H0=70km/s/Mpc) with the distance of
40±8Mpc reported by the LIGO Scientific Collaboration and the Virgo
Collaboration (LVC). At detection the transient had magnitudes of
i=17.3 and z=17.4, and thus an absolute magnitude of Mi=-15.7, in the
luminosity range expected for a kilonova. We identified 1500 potential
transient candidates. Applying simple selection criteria aimed at
rejecting background events such as supernovae, we find the transient
associated with NGC 4993 as the only remaining plausible counterpart,
and reject chance coincidence at the 99.5% confidence level. We
therefore conclude that the optical counterpart we have identified
near NGC 4993 is associated with GW170817. This discovery ushers in
the era of multi-messenger astronomy with gravitational waves and
demonstrates the power of DECam to identify the optical counterparts
of gravitational-wave sources.
Description:
Our Dark Energy Camera (DECam) observations on the Blanco 4m telescope
at the Cerro Tololo Inter-American Observatory (CTIO) commenced on
2017 August 17 at at 23:13 UT (10.53hr post-merger) with 30s exposures
in the i and z bands. The resulting 5σ limiting magnitudes are
i∼22.0 and z∼21.3 for point sources. The areal coverage was
70.4deg2, corresponding to an integrated probability of 93.4% of the
initial GW skymap.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
13 09 48.09 -23 22 53.3 GrW 170817 = NAME AT 2017gfo
----------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 27 48 Light curve constructed from u, g, r, i, z, Y
observations
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See also:
J/ApJ/848/L29 : Opt. follow-up of GW170817 counterpart (Diaz+, 2017)
J/ApJ/848/L33 : Opt. follow-up of GW events with LCO (Arcavi+, 2017)
J/ApJ/851/L21 : UV-NIR obs. compilation of GW170817 counterpart (Villar+, 2017)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 12 F12.6 d MJD [57983/57996] Time of observation in
Modified Julian Days
14 A1 --- Band [ugrizY] Band used for observation
16- 21 F6.3 mag mag [17.2/25.3] Reddening corrected AB PSF magnitude
in Band (1)
23- 27 F5.3 mag e_mag [0.004/2.7]? Error in mag (2)
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Note (1): Magnitudes are galactic extinction corrected AB PSF magnitudes.
E(B-V)SFD98=0.123, and RV=3.963, 3.186, 2.140, 1.569, 1.196,
1.048 for u, g, r, i, z, Y bands, respectively.
Note (2): When value of the magnitude error is lower than 1e-2, it is not
considered.
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History:
From electronic version of the journal
References:
Cowperthwaite et al. Paper II. 2017ApJ...848L..17C 2017ApJ...848L..17C
Nicholl et al. Paper III. 2017ApJ...848L..18N 2017ApJ...848L..18N
Chornock et al. Paper IV. 2017ApJ...848L..19C 2017ApJ...848L..19C
Margutti et al. Paper V. 2017ApJ...848L..20M 2017ApJ...848L..20M
Alexander et al. Paper VI. 2017ApJ...848L..21A 2017ApJ...848L..21A
Blanchard et al. Paper VII. 2017ApJ...848L..22B 2017ApJ...848L..22B
Fong et al. Paper VIII. 2017ApJ...848L..23F 2017ApJ...848L..23F
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 12-Jun-2018