ZTF21aayokph
GCN Circular 29938
Subject
ZTF and LT observations of ZTF21aayokph (AT2021lfa), a fast-fading red transient
Date
2021-05-05T02:18:12Z (4 years ago)
From
Yuhan Yao at Caltech <yyao@astro.caltech.edu>
Yuhan Yao (Caltech), Daniel Perley (LJMU), Anna Ho (UC Berkeley)
We report the discovery of a fast-evolving red transient by the Zwicky Transient Facility (ZTF) public all-sky survey and the Liverpool Telescope (LT).
ZTF21aayokph (AT2021lfa) was discovered at the position (J2000) of:
ra = 12:32:48.725 (188.203019 deg)
dec = -01:29:22.56 (-1.489601 deg)
on 2021 May 4 by ZTF at r=18.60 +/- 0.08 mag (MJD=59338.2325) and g=18.80+/-0.11 mag (MJD=59338.3126). The last upper limits were on 2021 May 2 at g > 20.58 mag (MJD=59336.2569) and r > 20.23 mag (MJD=59336.3110). The rise rate (>0.85 mag/day) of AT2021lfa is therefore very fast. The Galactic extinction towards the direction of AT2021lfa is E(g-r)=0.02. The nearest counterpart in Legacy Survey deep imaging is 2.9 arcsec away (g=24.2 mag, r=23.5 mag).
The high Galactic latitude, red color, and lack of stellar counterpart or bright host galaxy motivated us to trigger follow-up observations.
Multi-band LT imaging at 15.5 hours and 19 hours after the first detection revealed rapid fading (1.9 mag/day in r-band) and colors consistent with a non-thermal SED. At the time of the most recent LT observation (at MJD 59339.04026) we measure r=20.12+/-0.04 mag and g=20.52 +/- 0.04 mag.
We did not identify any GRBs coincident with this position during the time window between the last non-detection and the first detection.
The fast rise, fast decay, red color, and lack of counterpart of AT2021lfa make it a strong candidate afterglow.
ZTF is supported by the National Science Foundation under Grant No. AST-2034437 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, Deutsches Elektronen-Synchrotron and Humboldt University, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, Trinity College Dublin, Lawrence Livermore National Laboratories, and IN2P3, France. Operations are conducted by COO, IPAC, and UW.
GCN Circular 29940
Subject
DDOTI Observations of ZTF21aayokph (AT2021lfa)
Date
2021-05-05T04:29:06Z (4 years ago)
From
Alan M Watson at UNAM <alan@astro.unam.mx>
Alan M. Watson (UNAM), Nat Butler (ASU), Rosa L. Becerra (UNAM), Simone Dichiara
(GSFC/UMD), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Oc��lotl Lopez
(UNAM), Diego Gonzalez (UNAM), Margarita Pereyra (UNAM), Srihari Ravi (ASU), and
Eleonora Troja (GSFC/UMD) report:
We observed ZTF21aayokph (AT2021lfa) (Yao, Perley, & Ho, GCN Circ. 29938) with
the DDOTI wide-field imager at the Observatorio Astron��mico Nacional on Sierra
San Pedro Martir (http://ddoti.astroscu.unam.mx) from 2021-05-05 03:18 to 04:10
UTC and obtained 2700 seconds of exposure in the w filter.
We observed a region covering aproximately 7 degrees in RA and 10 degrees in
declination (about 70 square degrees). We calibrated our images against the
APASS catalog.
We detect a source reported by Yao, Perley, & Ho (GCN Circ. 29938) with an AB
magnitude of w = 20.51 +/- 0.10.
Observations are continuing.
We thank the staff of the Observatorio Astronomico Nacional in San Pedro Martir.
GCN Circular 29941
Subject
RATIR Observations of ZTF21aayokph (AT2021lfa)
Date
2021-05-05T04:31:03Z (4 years ago)
From
Alan M Watson at UNAM <alan@astro.unam.mx>
Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William H.
Lee (UNAM), Michael G. Richer (UNAM), Ori Fox (STScI), J. Xavier Prochaska
(UCSC), Josh Bloom (UCB), Antonino Cucchiara (UVI), Eleonora Troja (GSFC), Owen
Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), Jes��s Gonz��lez (UNAM), Carlos
Rom��n-Z����iga (UNAM), Harvey Moseley (GSFC), John Capone (UMD), V. Zach Golkhou
(U. Wash.), and Vicki Toy (UMD) report:
We observed ZTF21aayokph (AT2021lfa) (Yao, Perley, and Ho, GCN Circ. 29938)
with the Reionization and Transients Infrared Camera (RATIR) on the 1.5m Harold
Johnson Telescope at the Observatorio Astron��mico Nacional on Sierra San Pedro
M��rtir from 2021/05 5.15 to 2021/05 5.18 UTC, obtaining a total of 0.21 hours
exposure in the g, r, Z, Y, J, and H bands and 0.39 hours exposure in the i
band.
We detect the source reported by Yao, Perley, & Ho (GCN Circ. 29938) In
comparison with the SDSS DR9 and 2MASS catalogs, we obtain:
g = 20.85 +/- 0.07
r = 20.48 +/- 0.06
i = 20.06 +/- 0.03
Z = 19.97 +/- 0.07
Y = 20.28 +/- 0.16
J = 20.16 +/- 0.20
H = 18.39 +/- 0.31
These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the source.
Observations are continuing.
We thank the staff of the Observatorio Astron��mico Nacional in San Pedro
M��rtir.
GCN Circular 29945
Subject
ZTF21aayokph (AT2021lfa): Redshift from Gemini South
Date
2021-05-05T14:14:38Z (4 years ago)
From
Yuhan Yao at Caltech <yyao@astro.caltech.edu>
Yuhan Yao (Caltech), Anna Ho (UC Berkeley), Daniel Perley (LJMU)
We observed the candidate afterglow ZTF21aayokph/AT2021lfa (Yao, Perley, and Ho, GCN Circ. 29938) with GMOS-S under our ToO program GS-2021A-Q-124 (PI: Ho). The observation, conducted in the Nod-and-Shuffle mode with a 1 arcsec slit, started at 2021-05-05 04:19:19 UT, corresponding to 22.7 hours after the first ZTF detection.
We obtained 2 x 450 s spectroscopic exposures with the B600 grating and 2 x 450 s exposures with the R400 grating, providing coverage over the range 3620-9540 AA. No flux calibration was performed. The spectrum was reduced using the IRAF package for GMOS.
We clearly identified absorption lines of Mg II 2796 and Mg II 2803 at the redshift of z = 1.063 in the B600 and R400 spectra. Absorption lines from Mg I and Fe II are marginally detected in the spectra at consistent redshift. We therefore identify z=1.063 as the most probable redshift for AT2021lfa, although in practice this is only a lower limit. The lack of a DLA places an upper limit of z < 2.3.
We thank the GMOS-S observing staff for rapidly scheduling and executing our observations, in particular Jeong-Eun Heo.
GCN Circular 29948
Subject
ZTF21aayokph (AT2021lfa): Nanshan/NEXT optical upper limit
Date
2021-05-06T07:59:38Z (4 years ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
S.Y. Fu (NAOC), Z.P. Zhu (NAOC, HUST), X. Liu, D. Xu (NAOC), X. Gao
(Urumqi No.1 Senior High School), J.Z. Liu (XAO) report:
We observed the field of ZTF21aayokph (AT2021lfa) (Yao, Perley, & Ho,
GCN 29938) using the NEXT-0.6m telescope located at Nanshan, Xinjiang,
China. We obtained 6x300 s frames in the Sloan r-band, starting at
19:35:55 UT on 2021-05-05, i.e., ~ 38.02 hr after the ZTF detection in
r-band.
The optical transient is not detected in our stacked image, down to a
limiting magnitude of r ~ 21.2, calibrated with the nearby PanSTARRS field.
GCN Circular 29950
Subject
ZTF21aayokph (AT2021lfa): Assy optical observations
Date
2021-05-06T16:17:11Z (4 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
V. Kim (FAI, Pulkovo Observatory), N. Pankov (HSE, IKI), M. Krugov
(FAI), A. Pozanenko (IKI), S. Belkin (IKI) report on behalf of GRB IKI FuN:
We observed the field of ZTF21aayokph (AT2021lfa) (Yao et al., GCN
29938) with AZT-20 telescope of Assy-Turgen observatory starting on
2021-05-05 (UT) 15:51:00.
We clearly detect the optical transient (Yao et al., GCN 29938; Watson
et al., GCN 29940; Butler et al., GCN 29941; Yao et al., GCN 29945; Fu
et al., GCN 29948).
Preliminary photometry of the optical transient in r',i' - filters is
following
Date UT start t-T0 Exp. Filter OT Err. UL(3sigma)
(mid, days) (s)
2021-05-05 15:51:00 n/a 35*60 r' 21.20 0.06 22.5
2021-05-05 16:40:30 n/a 57*60 i' 20.83 0.06 21.8
The photometry is based on the nearby SDSS-DR12 stars.
We note the same color r'-i'= 0.37 +/- 0.08 of our observations and the
color which can be deduced from RATIR observations r-i = 0.42 +/- 0.07
at ~0.5 days earlier (Butler et al., GCN 29941).
GCN Circular 29952
Subject
Lowell Discovery Telescope Observations of ZTF21aayokph (AT2021lfa)
Date
2021-05-06T17:50:06Z (4 years ago)
From
Brendan O'Connor at UMD <oconnorb@umd.edu>
B. O'Connor (UMD, GWU), S.Dichiara (UMD, NASA-GSFC), E. Troja
(UMD, NASA-GSFC), P. Gatkine (Caltech), J.M. Durbak (UMD), S.B. Cenko
(NASA-GSFC), A. Kutyrev (UMD, NASA-GSFC), S. Veilleux (UMD) report:
We observed the field of ZTF21aayokph (AT2021lfa) reported by (Yao,
Perley, & Ho, GCN Circ. 29938) using the Large Monolithic Imager (LMI)
on the 4.3m Lowell Discovery Telescope (LDT) at Happy Jack, AZ.
Observations started on May 6, 2021 at 05:39:57 UT (about 48 hours after
the initial detection by ZTF) in the SDSS r-band.
We detect the source with magnitude r ~ 21.63 +/- 0.02 AB mag.
Compared to the magnitude determined by Butler et al. (GCN Circ.
29941) the transient faded with temporal index alpha ~ 1.5
in the r-band.
Magnitudes are calibrated against the SDSS catalog and are not
corrected for Galactic extinction.
We thank the staff of the Lowell Discovery Telescope for assistance
with these observations.
GCN Circular 29953
Subject
ZTF21aayokph (AT2021lfa): X-ray Detection with Swift/XRT
Date
2021-05-06T20:31:59Z (4 years ago)
From
Anna Ho at UC Berkeley <annayqho@berkeley.edu>
Anna Ho (UC Berkeley), Yuhan Yao (Caltech), and Daniel Perley (LJMU)
We observed the cosmological fast transient ZTF21aayokph/AT2021lfa (Yao,
Perley, and Ho, GCN Circ. 29938) with Swift/XRT beginning at 2021-05-05
05:32 UT, or 1.0d after the first ZTF detection. In a 5ks exposure, we
detect X-ray emission with a count rate of 0.0084 +/- 0.0015 ct/s. Using
WebPIMMS [1] we estimate [2] that this corresponds to an unabsorbed 0.3-10
keV flux density of 2.9E-13 ergs/cm2/s. At z=1.063 (Yao, Ho, and Perley,
GCN Circ. 29945) this is a luminosity of 1.9E45 erg/s, typical of an X-ray
afterglow of a long-duration GRB at this epoch [3].
We thank the Swift staff for rapidly approving and scheduling our
observations.
[1] https://heasarc.gsfc.nasa.gov/cgi-bin/Tools/w3pimms/w3pimms.pl
[2] Using a hydrogen column density of 2.16E20/cm2 (Willingale, R., et al.
2013, MNRAS, 431, 394) and a power-law index of 2
[3] Evans, P.~A., et al. 2007, AAP, 469, 379
GCN Circular 29954
Subject
ZTF21aayokph (AT2021lfa): Mondy and Koshka observatory optical observations
Date
2021-05-06T20:42:41Z (4 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
N. Pankov (HSE, IKI), S. Belkin (IKI), E. Klunko (ISTP), A. Novichonok
(Petrozavodsk State University, KIAM), A. Pozanenko (IKI), A.
Zhornichenko (KIAM) report on behalf of GRB IKI FuN:
We observed the field of ZTF21aayokph (AT2021lfa) (Yao et al., GCN
29938) with AZT-33IK telescope of Sayan observatory (Mondy) and and
Zeiss-1000 telescope of Koshka observatory (INASAN).
We clearly detect the optical transient (Yao et al., GCN 29938; Watson
et al., GCN 29940; Butler et al., GCN 29941; Yao et al., GCN 29945; Fu
et al., GCN 29948; Kim et al., GCN 29950; O'Connor et al., GCN 29952)
in Mondy observatory and marginally detect it in Koshka observatory.
Preliminary photometry of the optical transient is following
Date UT start Filter Exp. OT Err. UL(3sigma) Telescope
(s)
2021-05-05 14:57:10 R 25*120 20.70 0.07 22.7 AZT-33IK
2021-05-05 17:56:56 R 38*120 21.5 0.4 21.3 Zeiss-1000
The photometry is based on the nearby USNO-B1.0 star
USNO-B1.0_id R2
0884-0227886 14.13
GCN Circular 29959
Subject
ZTF21aayokph (AT2021lfa): MASTER OT detection 3h befor ZTF
Date
2021-05-07T16:23:38Z (4 years ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
V. Lipunov, V.Kornilov, E.Gorbovskoy, I.Gorbunov,P.Balanutsa,V.Vladimirov,A.Kuznetsov,
D. Vlasenko, N.Tiurina, D.Zimnukhov, V.Senik,V.Topolev, A.Chasovnikov, K.Zhirkov, D.Cheryasov (Lomonosov MSU,SAI,PhysicsDepartment),
D. Buckley (South African Astronomical Observatory),
O.A. Gres, N.M. Budnev (Irkutsk State University, API),
R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico FelixAguilar OAFA),
R. Rebolo, M. Serra(The Instituto de Astrofisica de Canarias),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity)
MASTER Global robotic net (MASTER-Net:http://observ.pereplet.ru Lipunov et al.,2010,Advances in Astronomy,2010,30L)
observed 12:32:48.725 -01:29:22.56 in survey mode (several images per night, not sequential, with different centers)
at MASTER-OAFA ~3h befor Zwicky detection (2021-05-04 05:34:39.360UT in TNSTR1478, Yao et al. GCN 29938).
There is optical source detected by MASTER auto-detection system as
MASTER OT J123248.62-012924.5 (sigma ~1")
We have nearest reference images at 2021-05-01 04:49:38UT.
Reduction will be continued.
GCN Circular 29964
Subject
ZTF21aayokph (AT2021lfa): continued Mondy optical observations
Date
2021-05-07T21:58:07Z (4 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
N. Pankov (HSE, IKI), E. Klunko (ISTP), A. Pozanenko (IKI), S. Belkin
(IKI) report on behalf of GRB IKI FuN:
We continued observation of the ZTF21aayokph (AT2021lfa) (Yao et al.,
GCN 29938; Watson et al., GCN 29940; Butler et al., GCN 29941; Yao et
al., GCN 29945; Fu et al., GCN 29948; Kim et al., GCN 29950; O'Connor
et al., GCN 29952; Ho et al., GCN 29953; Pankov et al., GCN 29954;
Lipunov et al., GCN 29959) with AZT-33IK telescope of Sayan observatory
(Mondy).
Preliminary photometry of the optical transient is following
Date UT start Filter Exp. OT Err. UL(3sigma)
(s)
2021-05-06 16:01:16 R 30*120 22.60 0.14 22.9
The photometry is based on the nearby USNO-B1.0 star
USNO-B1.0_id R2
0884-0227886 14.13
GCN Circular 30064
Subject
ZTF21aayokph (AT2021lfa): continued Assy optical observations
Date
2021-05-21T06:58:41Z (4 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
N. Pankov (HSE, IKI), S. Belkin (IKI), V. Kim (FAI, Pulkovo
Observatory), M. Krugov (FAI), A. Pozanenko (IKI), report on behalf of
GRB IKI FuN:
We observed the field of ZTF21aayokph (AT2021lfa) (Yao et al., GCN
29938) with AZT-20 telescope of Assy-Turgen observatory on 2021-05-17
and 2021-05-18.
We still detect the optical transient (Yao et al., GCN 29938; Watson et
al., GCN 29940; Butler et al., GCN 29941; Yao et al., GCN 29945; Fu et
al., GCN 29948; Kim et al., GCN 29950; O'Connor et al., GCN 29952; Ho
et al., GCN 29953; Pankov et al., GCN 29954; Lipunov et al., GCN 29959;
Pankov et al., GCN 29964).
Preliminary photometry of the optical transient is following
Date UT start t-T0 Exp. Filter OT Err. UL(3sigma)
(mid, days) (s)
2021-05-17 16:19:12 n/a 200*60 r' 23.60 0.28 23.9
2021-05-18 15:52:05 n/a 230*60 r' 23.67 0.29 24.0
The photometry is based on the nearby SDSS-DR12 stars.
GCN Circular 30079
Subject
ZTF21aayokph (AT2021lfa): LBT optical observations
Date
2021-05-26T08:07:05Z (4 years ago)
From
Andrea Rossi at INAF <andrea.rossi@inaf.it>
A. Rossi, E. Palazzi, F. Cusano (INAF-OAS) report on behalf of the
GRAWITA collaboration:
We observed the field of ZTF21aayokph/AT2021lfa (Yao et al., GCN 29938)
simultaneously in the r' and z' bands with the LBC imager mounted on LBT
(Mt Graham, AZ, USA). We obtained 20min of imaging on 2021-05-11 and
starting at 6:26 UT, 6 days after the first communication by ZTF.
Observations were performed under good weather conditions with an
average seeing of ~1.1".
We clearly detect the host galaxy at the position of the afterglow and
we preliminary measure the following AB magnitudes
r=23.9+-0.1
z=24.1+-0.2
calibrated against SDSS field stars.
We acknowledge the excellent support from the LBTO and LBT-INAF staff,
particularly A Cardwell, S. Allanson, and D. Paris, in obtaining these
observations.