ZTF19abvizsw
GCN Circular 25643
Subject
Liverpool Telescope observations of ZTF19abvizsw, a candidate untriggered GRB afterglow
Date
2019-09-04T04:50:36Z (6 years ago)
From
Daniel Perley at Liverpool JMU <d.a.perley@ljmu.ac.uk>
D. A. Perley (LJMU), A. Y. Q. Ho (Caltech), and C. M. Copperwheat (LJMU)
report on behalf of the GROWTH collaboration:
We obtained Liverpool Telescope IO:O imaging observations of
ZTF19abvizsw/AT2019pim (Kool et al., GCN 25616), initially reported as a
candidate counterpart to S190901ap but recently shown (Burdge et al.,
GCN 25639) to be an unrelated luminous transient at high redshift. Three
r-band images of 150 seconds each were acquired between UT 20:28 and
20:35, followed by a griz sequence (3x150s per filter) between 22:33 and
23:08.
The transient is well-detected in all four bands, but has faded
substantially since the ZTF discovery epoch (see also Wei et al., GCN
15640). We report the following photometry (times given as UT midpoints):
Time (UT) filter mag(AB) unc
------------------- ------ ------ ----
2019-09-03 22:37:50 r 21.62 0.09
2019-09-03 22:46:33 g 22.02 0.10
2019-09-03 22:55:16 i 21.16 0.07
2019-09-03 23:03:57 z 20.87 0.12
After correcting for Galactic extinction (Schlafly et al. 2011, ApJ 737
103) the SED is well-fit by to a power-law in frequency with spectral
index (F_nu ~ nu^beta) of beta ~ -1.4.
As noted in GCN 25616, this field was imaged by ZTF every night during
the 30 days prior to the ZTF discovery. No source was detected in any
of these observations, with the most recent nondetection corresponding
to 2019-09-01 UT 07:35, 0.86 days prior to the ZTF discovery observation.
The fast rise, red power-law spectrum, and fast decline are consistent
with observations of known GRB optical afterglows. However, we searched
the Fermi GBM subthreshold GRB catalog over the window between the last
ZTF detection and the discovery observation and found no GRB consistent
with the location of the transient over time window.
Further observations, including multiwavelength observations, have been
requested.
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GCN Circular 25655
Subject
ZTF19abvizsw: COATLI Optical Observations
Date
2019-09-04T14:39:06Z (6 years ago)
From
Rosa Leticia Becerra Godinez at Inst. de Astronoma,UNAM <rbecerra@astro.unam.mx>
Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Nat Butler (ASU),
Diego Gonz��lez (UNAM), Alexander Kutyrev (GSFC), William H. Lee (UNAM),
Margarita Pereyra (UNAM), and Eleonora Troja (GSFC) report:
We observed the field of ZTF19abvizsw/AT2019pim (Kool et al., GCN Circ.
25616;
Perley et al., GCN Circ. 25643) with the COATLI 50-cm telescope and
interim imager
at the Observatorio Astron��mico Nacional on the Sierra de San Pedro M��rtir
(http://coatli.astroscu.unam.mx) from 2019-09-04 07:32 to 12:10, obtaining
a total
of 3.04 hours of exposure in the w filter.
We detect the source at w = 21.60 +/- 0.10.
Our w magnitudes are calibrated against the Pan-STARRS1 catalog, are on
an approximate AB system, and are not corrected for Galactic extinction
in the direction of the GRB.
Applying the color transformation of Becerra et al. (2019, ApJ, 872, 118)
to the g-r color of Perley et al., we predict r = 21.50 +/- 0.10. Thus, we
do
not see fading compared to the measurement of r = 21.62 +/- 0.09 reported by
Perley et al. but do confirm their measurement of fading compared to the
discovery magnitude of r = 19.45 +/- 0.11 reported by Kool et al.
Further observations are planned.
We thank the COATLI technical team and the staff of the Observatorio
Astron��mico Nacional.
GCN Circular 25658
Subject
Swift XRT Detection of X-ray Emission from ZTF19abvizsw
Date
2019-09-04T16:40:24Z (6 years ago)
From
Anna Ho at Caltech <annayqho@gmail.com>
Swift XRT Detection of X-ray Emission from ZTF19abvizsw
A. Y.Q. Ho (Caltech), S. B. Cenko (UMd/Goddard), D. A. Perley (LJMU), on behalf of the GROWTH collaboration
We observed the position of ZTF19abvizsw/AT2019pim (Kool et al., GCN 25616) with Swift/XRT on 2019 Sep 04 03:14:54.853 UT. In a 3ks exposure, we detect X-ray emission with a 0.3-10 keV count rate of 0.021 +/- 0.003 ct/s. This corresponds to an unabsorbed flux density of 8.4E-13 erg/cm^2/s. At z=1.26, this is a luminosity of 8.2E45 erg/s, typical of an X-ray afterglow of a long-duration GRB at this epoch.
There is no source within 20 arcseconds of this position in the Swift X-ray point source catalog.
Further observations are planned.
We thank the Swift staff for rapidly approving and executing our observations.
GCN Circular 25683
Subject
ZTF19abvizsw: AbAO and CrAO photometry
Date
2019-09-07T14:05:41Z (6 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
S. Belkin (IKI), A. Pozanenko (IKI), R. Ya. Inasaridze (AbAO), V.
Rumyantsev (CrAO), A. Volnova (IKI), E. Mazaeva (IKI), I. Molotov
(KIAM) report on behalf of IKI GRB FuN collaboration:
We observed the ZTF19abvizsw/AT2019pim (Kool et al., GCN 25616; Burdge
et al., GCN 25639; Wei et al., GCN 15640; Perley et al., GCN 25643;
Levan et al., GCN 25653; Becerra et al., GCN 25655;) with AS-32 (0.7m)
telescope of Abastumani Observatory and ZTSh telescope of CrAO.
Preliminary photometry of the the optical transients is following.
date UT start MJD Filter Exp. OT OT_err Obs./Tel.
(mid, d) (s)
2019-09-04 16:54:07 58730.723 R 54*60 21.27 0.16 AbAO/AS-32
2019-09-05 21:49:03 58731.923 R 20*120 21.33 0.14 CrAO/ZTSh
The photometry of the latest epoch of 2019-09-05 might be slightly
contaminated by red southward star (see also Burdge et al., GCN 25639).
We note the flattening of the initial decay previously reported by
Becerra (GCN 25655).
The photometry is based on nearby USNO-B1.0 stars
USNO-B1.0_id R2
1514-0239703 18.81
1514-0239806 19.68
GCN Circular 25684
Subject
ZTF19abvizsw: 15GHz observations with AMI
Date
2019-09-07T14:29:10Z (6 years ago)
From
Lauren Rhodes at Oxford <lauren.rhodes@physics.ox.ac.uk>
L. Rhodes, R. Fender, D. Williams, J. Bright (Oxford), K. Mooley (NRAO, Caltech; Jansky Fellow), A. Horesh (The Hebrew University of Jerusalem), D. Green, D. Titterington (MRAO) and the JAGWAR collaboration.
We observed the position of ZTF19abvizsw/AT2019pim (Kool et al., GCN 25616) with the AMI Large Array at 15GHz. Initially reported as a potential counterpart to S190901ap, ZTF19abvizsw/AT2019pim has been shown to be an unrelated transient. We started observing on 5th September 2019 at 15:40:41UT. A 4hr observation showed a point source at the phase centre with a flux of 404 +/- 10 uJy/beam. The rms noise in the field is 30uJy. There are two 2MASS sources within the AMI clean beam (~40"x20").
We thank the MRAO staff for scheduling these observations.
GCN Circular 25686
Subject
ZTF19abvizsw/AT2019pim, search for GRB in SPI-ACS/INTEGRAL data
Date
2019-09-08T15:12:03Z (6 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
I. Chelovekov, A. Pozanenko, P. Minaev, S. Grebenev on behalf of the IKI
GRB FuN collaboration report:
Using SPI-ACS/INTEGRAL data we performed a search for a possible GRB
which can be a source of the orphan transient ZTF19abvizsw discovered
and observed in optic (Kool et al., GCN 25616; Burdge et al., GCN 25639;
Wei et al., GCN 15640; Perley et al., GCN 25643; Belkin GCN 25683).
The search was performed in a time window between the last ZTF
non-detection (2019-09-01 UT 07:35) and the discovery of
ZTF19abvizsw/AT2019pim (2019-09-02 03:08). The SPI-ACS was switch off at
low orbit radiation belts pass between 2019-09-01 09:09:36 - 2019-09-01
19:28:44, and operating normally in other time intervals. A blind search
for impulsed events was performed on two time scales, 1s and 5 s. We
found following candidates for long duration GRBs. Below we present UTC
time of the trigger, light curve figure and comment. Some event data is
also presented in the figures.
1.
UTC: 2019-09-01T07:24:05
ref:
http://193.232.11.154/ZTF19abvizsw_binned/png/213100540010.000_acs_lc_T1__00452_00515.png
2019-09-01T07:24:05
comment: not visible in GBM
2.
UTC: 2019-09-01T21:24:43
ref:
http://193.232.11.154/ZTF19abvizsw_binned/png/213200030010.000_acs_lc_T1__00043_00071.png
comment: might be coinciding with the tail of GBM trigger bn190901890 at
2019-09-01 21:19:37.514
3.
UTC: 2019-09-02T01:36:16
ref:
http://193.232.11.154/ZTF19abvizsw_binned/png/213200070010.000_acs_lc_T1__01320_01395.png
comment: no GBM data yet
comment: the event is also triggered IBAS
One more triggered event at 2019-09-01T19:32:19 is most probably
geophysical origin because of coincidence with IREM channel of e- with
energies more than 500 keV. We also note the absence of any trigger in
GBM data at that time. We do not consider it as a candidate, we plot it
only for the reference.
ref:
http://193.232.11.154/ZTF19abvizsw_binned/png/213200010010.000_acs_lc_T1__00205_00256.png
GCN Circular 25697
Subject
ZTF19abvizsw: No counterpart candidates from Swift/BAT targeted search
Date
2019-09-10T03:31:59Z (6 years ago)
From
Aaron Tohuvavohu at PSU/Swift <auc444@psu.edu>
Aaron Tohuvavohu (U Toronto) reports:
We have performed a search for an un-triggered GRB counterpart to the
claimed afterglow candidate ZTF19abvizsw (GCN 25616, 25643, 25658) in
the Swift/BAT raw light curves. The temporal window for the search was
chosen to be 2019-09-01 07:35 --- 2019-09-02 03:08 corresponding to
the times of the last ZTF non-detection and of the discovery
observation respectively.
During this time period, the location of ZTF19abvizsw was above the
Earth-limb with respect to the spacecraft (and thus a priori capable
of depositing flux onto the detector) 64.2% of the time. The location
was inside the BAT coded field-of-view 19% of the time.
No compelling candidates were found in the BAT raw light curves with
time bins of 64ms, 1 s and 1.6 s. Due to the long temporal window for
the search, the average background, and thus upper-limit sensitivity,
varies widely over the search window. After excising times when the
spacecraft was near the South Atlantic Anomaly, the average 5-sigma
flux upper limit achieved for a long GRB in the 1-s binned data with a
typical spectrum corresponds to ~3 x 10^-7 erg/s/cm^2 in the BAT coded
field-of-view, and approximately an order of magnitude higher for
locations outside of the field-of-view.
We also performed spot checks for the three candidates reported from
INTEGRAL (GCN 25686). None of these candidates are seen in the
Swift/BAT data.
GCN Circular 25982
Subject
TESS Detection of the Optical Emission from the Possible Untriggered GRB Associated with ZTF19abvizsw
Date
2019-10-08T14:16:56Z (6 years ago)
From
Roland Vanderspek at MIT <roland@space.mit.edu>
M. M. Fausnaugh, R. Vanderspek, on behalf of the TESS team
TESS observed the location of the optical transient ZTF19abvizsw (Kool et al. 2019, GCN 25616) and associated new X-ray source (Ho et al. 2019, GCN 25658) nearly continuously during Sector 15 from 2019-08-15 to 2019-09-10 in Camera 2, CCD 2. The location was imaged in nearly 2400 30-minute full-frame images (FFIs) over that period.
A light curve for ZTF19abvizsw was constructed from the FFIs using difference imaging. First, we constructed a reference image by median stacking 20 FFIs with low background levels. We then subtracted the reference image from each epoch using the ISIS software (Alard & Lupton 1998; Alard 2000), which solves for a spatially variable kernel that matches the PSF of the reference image to individual FFIs. This procedure removes systematic errors due to pointing shifts/jitter and thermal variations. We extracted a light curve by fitting a model of the PSF to the difference images at the predicted location of the transient in the FFIs based on the coordinates of ZTF19abvizsw reported to the Transient Name Server, and subtracted a local background based on the median of pixel values in an annulus of inner/outer radius 8/12 pixels. Uncertainties were estimated from the photon noise of the source and the observed scatter of the light curve at early times.
We flux-calibrated the differential light curve by shifting the baseline before the transient to zero. We estimated the 3-sigma TESS limiting magnitude at each epoch by taking a factor of 3 times the flux uncertainty at each epoch and converting to TESS magnitudes (the TESS passband spans 600-1000 nm). The average 3-sigma limiting magnitude during the time of the transient is 19.11 and is dominated by the background flux in each FFI.
ZTF19abvizsw was seen to brighten above the limiting magnitude in the FFI centered at UT 2019-09-02 03:15 - - one hour before the ZTF measurement at 2019-09-02 04:19:12 (https://wis-tns.weizmann.ac.il/object/2019pim <https://wis-tns.weizmann.ac.il/object/2019pim>) - - and peak at a TESS magnitude of 18.37 +/- 0.18 at in the FFI centered at UT 2019-09-02 04:15. The discrepancy between this measurement and the ZTF r-band magnitude of 19.45 may be due to the redness of the source (Kool et al. 2019, GCN 25616) or brightness variations within the 30-minute FFI integration.
The light curve has a sharp rise and a slower decline. The duration (T90) of the transient over the background limit is 1.44 days, and the integrated S/N of the transient was 10.4. We also fit a fast rise/exponential decay model to the light curve, from which we estimate the rise time to be 1.21 +/- 0.30 hours. The fit yields a peak magnitude of 18.40 +/- 0.07 at 2019-09-02 04:19:29. This is in family with the measured early brightness of optical counterparts of GRBs with redshifts near the measured redshift of ZTF19abvizsw of 1.26 (Levan et al. 2019, GCN 25653).
The differenced image is seen at approximately RA=18:37:53.57, Dec=+61:29:55.58, with an estimated error of 3 arcseconds, based on the flux-weighted centroid. This position is in excellent agreement with the discovery coordinates of ZTF19abvizsw.
GCN Circular 26197
Subject
ZTF19abvizsw: Upper limits from Konus-Wind observations
Date
2019-11-07T08:18:07Z (6 years ago)
From
Anna Kozlova at Ioffe Institute <ann_kozlova@mail.ioffe.ru>
A. Ridnaia, S. Golenetskii, R. Aptekar, D. Frederiks,
M. Ulanov, D. Svinkin, A. Tsvetkova, A. Lysenko, and T. Cline
on behalf of the Konus-Wind team, report:
Konus-Wind (KW) was observing the whole sky during a day before
discovery of ZTF19abvizsw (2019-09-02 04:19:12 UTC;
Kool et al., GCN Circ. 25616) including the time of TESS detection
(2019-09-02 03:15 UTC, hereafter T0; Fausnaugh et al., GCN Circ. 25982)
One triggered and one waiting-mode KW events were detected during
~1-day interval before T0. The burst localizations are inconsistent
with the ZTF19abvizsw.
For the interval excluding the KW events, we estimate
an upper limit (90% conf.) on the 20 - 1500 keV fluence to
6.3x10^-7 erg/cm^2 for a burst lasting less than 2.944 s and having a
typical KW short GRB spectrum (an exponentially cut off power law with
alpha =-0.5 and Ep=500 keV). For a typical long GRB spectrum (the Band
function with alpha=-1, beta=-2.5, and Ep=300 keV), the corresponding
limiting peak flux is 1.3x10^-7 erg/cm^2/s (20 - 1500 keV, 2.944 s
scale).
Assuming the redshift z=1.26 (Burdge et al. GCN circ. 25639)
and a standard cosmology model with H_0 = 67.3 km/s/Mpc,
Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014),
we estimate an upper limit on a long GRB peak luminosity L_iso ~
1.3x10^51 erg/s.
All the quoted values are preliminary.