LIGO/Virgo GW170817
GCN Circular 23139
Subject
LIGO/Virgo GW170817: A steep decline in the radio light curve and prediction for the X-rays
Date
2018-08-13T18:38:03Z (7 years ago)
From
Tara Murphy at U of Sydney <tara.murphy@sydney.edu.au>
D. Dobie (University of Sydney), K. Mooley (Caltech),
T. Murphy (University of Sydney), D. Kaplan (UWM), E. Lenc (CSIRO),
A. Corsi (TTU), D. Frail (NRAO), report on behalf of a larger collaboration
Our continued observations of GW170817 with the ATCA and the VLA up to 300
days post-merger (Mooley et al. in prep) confirm the t^(-2) decline in the
radio light curve initially reported in Mooley et al. 2018 (arXiv:1806.09693).
Such a slope rules out a cocoon-dominated outflow at late times, and is
instead the classic signature of a relativistic jet, consistent with the
VLBI result from Mooley et al. 2018. The t^(-2) decline is also expected in
the X-ray light curve, and may be confirmed by the Chandra observation carried
out on 2018 Aug 10.
GCN Circular 22371
Subject
LIGO/Virgo GW170817: Chandra X-ray Emission Continues to Rise ~156 Days Post-Merger
Date
2018-01-29T19:21:22Z (8 years ago)
From
Daryl Haggard at McGill U <daryl.haggard@mcgill.ca>
Daryl Haggard, Melania Nynka, John J. Ruan (McGill/MSI), Phil Evans
(Leicester), and Vicky Kalogera (Northwestern/CIERA) report:
We have obtained new X-ray observations of GW170817 via Chandra
Director's Discretionary Time (PI: Wilkes, Program Number 19408607). The
X-ray counterpart to GW170817/GRB170817A/SSS17a continues to be detected
and the X-ray emission continues to brighten approximately 156 days
after the neutron star merger. This contradicts previous claims of the
X-ray fading of GW170817 in XMM-Newton observations at 135 days
(D'Avanzo et al. 2018, arXiv: 1801.06164).
This new Chandra program acquired several exposures of GRB170817A:
ObsID, ExpTime, StartDate, Days Post-Burst
----- ------- --------- ---------------
20936 31.75 ks 2018-01-17 21:55:17 153.5 days
20938 15.86 ks 2018-01-21 13:45:18 157.1 days
20939 22.25 ks 2018-01-24 08:18:48 159.9 days
Since these new Chandra exposures are close in time and the X-ray
emission of GRB170817A is not expected to vary significantly over <10
day timescales, we co-add these three data sets into one 69.86 ks
exposure at 156.4 days post-burst.
We perform spectral extractions assuming an absorbed power-law spectral
model with fixed NH = 7.5e20 cm^���2 and find that the X-ray flux of
GRB170817A has an absorbed flux of f(0.3���8 keV) = 1.93(+0.39/-0.32)e���14
erg s^���1 cm^���2 (with Gamma ~ 1.67) at 156.4 days post-burst, which
corresponds to an unabsorbed luminosity of L(0.3���10 keV) =
5.23(+1.30/-0.95)e39 erg s^���1 (assuming a luminosity distance of 42.5 Mpc).
This represents continued X-ray brightening compared to Chandra
observations at 15.6 and 109.2 days post-burst, for which we find an
absorbed flux of f(0.3���8 keV) = 0.36(+0.1/-0.07)e���14 erg s^���1 cm^���2
(with Gamma = 2.4 +/- 0.8, unabsorbed L(0.3���10 keV) = 10.4(+2.0/-1.6)e38
erg s^���1; Haggard et al. 2017) and f(0.3���8 keV) = 1.58(+0.14/-0.13)e���14
erg s^���1 cm^���2 (with Gamma = 1.6 +/- 0.3, unabsorbed L(0.3���10 keV) =
42.5(+3.7/-3.5)e38 erg s^���1; Ruan et al. 2018), respectively.
Our findings here contradict recent reports of dimming in the X-ray flux
from XMM Newton at 135 days (D'Avanzo et al. 2018), which was reported
to be 2.1(+0.7/-0.5)e-15 erg s^���1 cm^���2 (0.3-10 keV unabsorbed).
However, this reported flux value is a typo, and should be
2.1(+0.7/-0.5)e-14 erg s^���1 cm^���2 (D���Avanzo 2018, private
communication). Taking this corrected flux and rescaling to a 0.3-8 keV
absorbed flux for comparison to the previous Chandra measurements above
gives 1.67(+0.87/-0.64)e-14 erg s^���1 cm^���2. Thus, the recent X-ray data
at 15.6 days (Chandra), 109.2 days (Chandra), 135 days (XMM), and 156.4
days (Chandra) are all consistent with continued X-ray brightening. We
provide a light curve table summarizing these measurements:
Days, Telescope, Flux* (0.3-8 abs), Ref
---- --------- ---------------- ---
15.6 Chandra 0.36(+0.10/-0.07)e���14 Haggard et al. (2017)
109.2 Chandra 1.58(+0.14/-0.13)e���14 Ruan et al. (2018)
135 XMM 1.67(+0.87/-0.64)e-14 D'Avanzo et al. (2018)
156.4 Chandra 1.93(+0.39/-0.32)e-14 This work
*Flux units: erg s^���1 cm^���2; all uncertainties are 90% confidence interval
Current post-merger models suggest that the origin of the X-rays could
be afterglow emission from either a mildly-relativistic cocoon or a
structured jet. For a cocoon, the continued rise of X-ray emission
suggest that the cocoon has not yet reached a deceleration phase. For a
structured jet, the rising X-ray emission suggest emission from the jet
core has not yet entered the observed line of sight. Continued
monitoring of GW170817 will be critical for discriminating between these
and other models.
Note that another ~30 ks of Chandra observations during this same time
interval are forthcoming.
We thank Belinda Wilkes and the Chandra scheduling, data processing, and
archive teams for making these observations possible.
GCN Circular 22211
Subject
LIGO/Virgo GW170817: X-ray observations confirm prediction made from radio data
Date
2017-12-08T21:30:16Z (8 years ago)
From
Kunal Mooley at Oxford U <kunal.mooley@physics.ox.ac.uk>
K. P. Mooley (Oxford, NRAO/Caltech) et al. report
The X-ray flux of GW170817 on December 03-06 (reported by Troja et al.
2017, GCN 22201; Margutti et al. 2017, GCN 22203, Haggard et al. 2017,
GCN 22206 based on the Chandra observations) is exactly as predicted
last week by Mooley et al. 2017 (http://arxiv.org/abs/1711.11573) based
on radio spectral indices.
This suggests that the radio and X-ray emission both arise from a mildly
relativistic wide-angle outflow, consistent with the cocoon model (see
also Gottlieb et al. 2017, Hallinan et al. 2017, Kasliwal et al. 2017).
A relativistic jet core, if it exists, is either too weak (having a
sub-dominant contribution to the radio light curve early on) or too
strong (such that its electromagnetic signatures will be observed in the
future). See Mooley et al. 2017 for details.
GCN Circular 22207
Subject
LIGO/Virgo GW170817: Further Hubble Space Telescope observations
Date
2017-12-07T22:47:21Z (8 years ago)
From
Andrew Levan at U.of Leicester <A.J.Levan@warwick.ac.uk>
A.J. Levan, J.D. Lyman (U. Warwick), N.R. Tanvir (U. Leicester), I. Mandel (U. Birmingham), J. Hjorth (DARK/NBI), A.S. Fruchter, T. Kangas (STScI), B. Gompertz, K. Wiersema, D. Steeghs (U. Warwick), S. Rosswog (Stockholm) report on behalf of a larger collaboration:
"We obtained further observations of the counterpart of GW170817 with the Hubble Space Telescope. Observations took place on 6 Dec 2017 and utilised both optical (F606W, F814W) and infrared (F140W,F160W) filters.
At the location of the transient we recover the source in both optical filters, but do not detect it in the infrared, where the background from the galaxy is higher. The measured magnitudes of the source in the optical bands are broadly consistent with the extrapolation from the 93 day radio epoch (Mooley et al. 2017 arXiv 1711.11573) to the near contemporaneous observations with Chandra (Troja et al. 2017 GCN 22201, Margutti et al. 2017 GCN 22202).
We thank the staff of STScI for their excellent support with these observations."
GCN Circular 22203
Subject
LIGO/Virgo GW170817: Chandra X-ray brightening of the counterpart 108 days since merger
Date
2017-12-07T18:04:04Z (8 years ago)
From
Raffaella Margutti at Northwestern U <rafmargutti@gmail.com>
R. Margutti, W. Fong (Northwestern), T. Eftekhari, K. Alexander, E. Berger
(Harvard), R. Chornock (Ohio University) report:
���The Chandra X-ray Observatory (CXO) started observing GW170817 on 2017
December 3 at 01:38:45UT for a total of 74.09 ksec (obs ID 20860, PI
Wilkes). At the position of the electromagnetic counterpart, an X-ray
source is clearly detected with a significance of ~33-sigma (RA =
13:09:48.090, Dec = -23:22:52.87, J2000), with a net count-rate of 1.47e-3
cps (0.5-8 keV).
The CXO observed the field for an additional 24.74 ksec starting on 2017
December 6 at 10:43:31UT (obs ID 20861, PI Wilkes). The X-ray source is
still detected with a significance of ~15-sigma with a net count-rate of
1.41e-3 cps (0.5-8 keV).
The joint spectrum can be fit with an absorbed power-law spectral model
with photon index Gamma= 1.50 +\-0.16 (1 sigma c.l.). We find no evidence
for intrinsic neutral hydrogen absorption in addition to the Galactic value
(NH_MW=0.0784e22 cm-2, Kalberla et al., 2005) and place a 3 sigma upper
limit of NHint<0.7e22 cm-2. These properties are consistent with the X-ray
spectral properties of GW170817 at t<15 days inferred by Margutti et al.,
2017 and Troja et al., 2017.
Based on our best fitting spectral parameters, the 0.3-10 keV unabsorbed
flux is
2.3e-14 erg/s/cm^2, indicating a substantial brightening of the X-ray
source during the last ~90 days, in agreement with the results from Troja
et al., GCN 22201. A comparison with radio observations acquired 93 days
since merger (Mooley et al., 2017) indicates a spectral slope beta~-0.6 of
the Fnu ~nu^-beta spectrum, similar to the radio-to-Xray spectrum of
GW170817 before Sun block (Alexander et al., 2017; Margutti et al., 2017;
Troja et al., 2017; Haggard et al., 2017; Hallinan et al., 2017; Mooley et
al., 2017). This result suggests negligible spectral evolution of GW170817
in the last 90 days, and that the radio and X-ray emission continue to
represent the same emission component.
Based on this spectrum, we expect GW170817 to be detectable at optical-NIR
wavelengths at approximately 26.5 AB magnitude.
We thank Belinda Wilkes and the entire CXO team for approving these DDT
requests and making these observations possible.���