J/ApJ/939/106 GRB 180618A light curves (Jordana-Mitjans+, 2022)
A short gamma-ray burst from a proto-magnetar remnant.
Jordana-Mitjans N., Mundell C.G., Guidorzi C., Smith R.J., Ramirez-Ruiz E.,
Metzger B.D., Kobayashi S., Gomboc A., Steele I.A., Shrestha M.,
Marongiu M., Rossi A., Rothberg B.
<Astrophys. J. 939, 106 (2022)>
=2022ApJ...939..106J 2022ApJ...939..106J (SIMBAD/NED BibCode)
ADC_Keywords: Gamma rays ; GRB ; Photometry ; Optical ; Ultraviolet
Keywords: high energy astrophysics - time domain astronomy - gamma-ray bursts -
magnetars - polarimetry
Abstract:
The contemporaneous detection of gravitational waves and gamma rays
from GW170817/GRB 170817A, followed by kilonova emission a day after,
confirmed compact binary neutron star mergers as progenitors of
short-duration gamma-ray bursts (GRBs) and cosmic sources of heavy
r-process nuclei. However, the nature (and life span) of the merger
remnant and the energy reservoir powering these bright gamma-ray
flashes remains debated, while the first minutes after the merger are
unexplored at optical wavelengths. Here, we report the earliest
discovery of bright thermal optical emission associated with short GRB
180618A with extended gamma-ray emission-with ultraviolet and optical
multicolor observations starting as soon as 1.4 minutes post-burst.
The spectrum is consistent with a fast-fading afterglow and emerging
thermal optical emission 15 minutes post-burst, which fades abruptly
and chromatically (flux density Fv∼t-alpha , alpha=4.6±0.3) just
35 minutes after the GRB. Our observations from gamma rays to optical
wavelengths are consistent with a hot nebula expanding at relativistic
speeds, powered by the plasma winds from a newborn, rapidly spinning
and highly magnetized neutron star (i.e., a millisecond magnetar),
whose rotational energy is released at a rate
Lth∝t-(2.22±0.14) to reheat the unbound merger-remnant
material. These results suggest that such neutron stars can survive
the collapse to a black hole on timescales much larger than a few
hundred milliseconds after the merger and power the GRB itself through
accretion. Bright thermal optical counterparts to binary merger
gravitational wave sources may be common in future wide-field
fast-cadence sky surveys.
Description:
Here, we present the GRB 180618A ultraviolet and optical photometry
corresponding to the Swift UltraViolet and Optical Telescope (UVOT)
white,v,b,u,uvw1,uvm2, uvw2 bands, Liverpool Telescope (LT) RINGO3
BV,R,I bands and LT IO:O g,r,i bands.
At 86s after the detection of the GRB 180618A by the Swift Burst Alert
Telescope (BAT), the UVOT from the Neil Gehrels Swift Observatory
started optical observations in an unfiltered band (white).
Subsequently, the UVOT continued observations with the uvw1,uvm2,uvw2
ultraviolet and the v,b,u optical filters. At 202.5 s after the BAT
alert, the 2-m fully robotic LT - with site at Roque de Los Muchachos
Observatory (ORM, Spain) - automatically started follow-up
observations with the RINGO3 three-band polarimeter and imager. The LT
observations consisted of three consecutive observing sequences of 10
minutes each with the RINGO3 in three simultaneous bands (BV,R,I),
followed by six single 10 s exposures with the r filter of the IO:O
optical widefield camera, and two extra observing sets of 10 minutes
with the RINGO3. Three 300-s exposures with the IO:O g,r,i filters
were also scheduled via the LT phase2UI, and autonomously executed by
the LT at 7.4x104s post-burst.
The tabulated data includes the bandpass name, the mean observing time
corrected by T0 (Swift trigger time), the length of the observing
window and the GRB magnitudes and flux density with their
uncertainties or limits. The magnitudes and the flux density are not
corrected by Galactic extinction (reddening of E(B-V)=0.065±0.003;
Schlegel et al. 1998, 1998ApJ...500..525S 1998ApJ...500..525S) or host galactic extinction
(E(B-V)<0.02).
Objects:
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RA (2000) DE Designation(s)
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11 19 45.84 +73 50 13.5 GRB 180618A = Fermi bn180618030
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 54 154 GRB 180618A ultraviolet and optical photometry
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Band Bandpass name (1)
11- 16 I6 s tmid Mean observing time (2)
18- 22 I5 s texp/2 Half of the length of the observation window
24 A1 --- l_mag Limit flag on observed magnitude
26- 30 F5.2 mag mag Observed magnitude in Band (3)
32- 35 F4.2 mag e_mag ? Photometric uncertainty for observed magnitude
37 A1 --- l_Flux Limit flag on flux density
39- 46 E8.3 Jy Flux Flux density in Band (3)
48- 54 E7.2 Jy e_Flux ? Photometric uncertainty for flux density
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Note (1): Bands as follows:
white = Swift UVOT white
uvw2 = Swift UVOT uvw2
uvm2 = Swift UVOT uvm2
uvw1 = Swift UVOT uvw1
u = Swift UVOT u
b = Swift UVOT b
v = Swift UVOT v
g = Liverpool Telescope IO:O g
RINGO3 BV = Liverpool Telescope RINGO3 BV
r = Liverpool Telescope IO:O r
RINGO3 R = Liverpool Telescope RINGO3 R
i = Liverpool Telescope IO:O i
RINGO3 I = Liverpool Telescope RINGO3 I
Note (2): tmid corresponds to the mean observing time less T0,
where T0 is BAT trigger time, 18 June 2018 at 00:43:13 Universal Time.
Note (3): The photometry is not corrected for neither Galactic nor
host galaxy extinction.
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Acknowledgements:
Nuria Jordana-Mitjans, N.Jordana(at)bath.ac.uk
(End) Patricia Vannier [CDS] 16-Nov-2022