- GCN Circular #29305
A. Y. Q. Ho (UC Berkeley), D. A. Perley (LJMU), Y. Yao (Caltech), and I.
Andreoni (Caltech) report on behalf of the Zwicky Transient Facility
collaboration:
The Zwicky Transient Facility (ZTF; ATel #11266) reports the discovery
last night of ZTF21aaeyldq (AT2021any), a rapidly fading optical
transient located at:
08:15:15.34 -05:52:01.2 (J2000)
123.813909 -5.867007 (J2000)
and detected as part of the high-cadence partnership survey by a filter
designed to find fast transients (Ho et al. 2020, ApJ, 905, 2).
The source was discovered on UT 2021-01-16T06:59:45.6 at r=17.9 mag,
only 22 minutes after the last non-detection (limiting mag r~20.28). Two
additional r-band observations over the next 3.3 hours revealed rapid
fading by 2 magnitudes. No counterpart is visible in deep Legacy Survey
pre-imaging (>24 mag; Dey et al. 2019, ApJ, 157, 5).
The color of the transient is moderately red (g-r~0.3 mag). While the
source is close to the Galactic plane (+16 deg), extinction along the
line of sight is low (E(g-r)~0.07 mag; Schlafly et al. 2011, ApJ, 737, 2).
We urge additional multi-band photometry to establish the rate of fading
and color of this transient.
ZTF is a project led by PI S. R. Kulkarni at Caltech (see ATEL #11266),
and includes IPAC; WIS, Israel; OKC, Sweden; JSI/UMd, USA; UW,USA; DESY,
Germany; NRC, Taiwan; UW Milwaukee, USA and LANL USA. ZTF acknowledges
the generous support of the NSF under AST MSIP Grant No 1440341. Alert
distribution service provided by DIRAC@UW. Alert filtering is done with
Kowalski (Duev et al. 2019), the GROWTH marshal system (supported by NSF
PIRE grant 1545949), and by Fritz (van der Walt et al. 2019, Duev et al.
2019, Kasliwal et al. 2019).
- GCN Circular #29307
A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), D. A. Kann
(HETH/IAA-CSIC), D. A. Perley (LJMU), C. C. Thoene (HETH), M. Blazek, J.
F. Agui Fernandez (both HETH/IAA-CSIC), and R. Scarpa (GTC) report:
We observed the fast-fading hostless transient ZTF21aaeyldq (Ho et al.,
GCN #29305) with OSIRIS at the 10.4m Gran Telescopio Canarias (Roque de
los Muchachos Observatory, La Palma, Canary Islands, Spain), starting at
2021-01-16 23:35:54.359 UT (16.60 hours after the first optical
detection). The source is clearly detected. We obtained a 60 s r'-band
finder image and 4 x 900 s spectroscopy with the R1000B grism.
For the image starting at 2021-01-16 23:27:09.671 (0.68604 days after
the first optical detection), we measure r' = 21.64 +/- 0.03 (AB mag)
vs. a nearby SDSS star.
The spectrum shows a clear continuum over the full spectral range with
many strong absorption lines. We identify these lines as Ly-alpha, SII,
OI, SiII, SiIV, CII, CIV, FeII, AlII, and AlIII, at a mean redshift of z
= 2.514. We identify this as the redshift of the transient. Coupled with
the rapid decay, the moderately red color (Ho et al., GCN #29305) and
the lack of any broad spectral features, we also identify this transient
as a GRB afterglow for which no high-energy trigger has been reported
yet.
- GCN Circular #29308
Amit Kumar (ARIES), Shashi B. Pandey (ARIES), Rahul Gupta (ARIES), Dimple
(ARIES), Ankur Ghosh (ARIES), Amar Aryan (ARIES), Brajesh Kumar (ARIES),
and Kuntal Misra (ARIES) report:
We observed the ZTF discovered fast-fading hostless transient ZTF21aaeyldq
(Ho et al., GCN 29305) using the 4Kx4K CCD Imager (Pandey et al. 2018,
2018BSRSL..87...42P) mounted at the axial port of the 3.6m Devasthal
Optical Telescope of ARIES Nainital. The transient has been identified as a
GRB afterglow at z = 2.514 by Postigo et al. GCN 29307.
The observations were started on 2021-01-16 at 22:15:12.980 UT (~15.258
hours after the detection). We observed two images with an exposure time of
300 seconds each in Bessel R and I bands. At the position reported by Ho et
al., GCN 29305, we detect an uncatalogued source in both R and I bands.
The observed R-band magnitude is as follows:
Date UT start T-T0 (hours) Exp. Filter OT (mag) Err
------------------------------------------------------------------------------------------------
2021-01-16 22:15:12.980 15.258 1*300 R 21.04 0.06
The quoted magnitude is calibrated with the nearby USNO-B1 stars and not
corrected for the Galactic and Host extinction in the direction of the
burst.
3.6m Devasthal Optical Telescope (DOT) is a recently commissioned facility
in the Northern Himalayan region of India (long:79 41 04E, lat:29 21 40N,
alt:2540m) owned and operated by the Aryabhatta Research Institute of
Observational Sciences (ARIES), Nainital (https://www.aries.res.in).
Authors of this GCN circular thankfully acknowledge consistent support from
the technical staff members to run and maintain the 3.6m DOT.
This circular may be cited.
- GCN Circular #29309
Tomas Ahumada (UMD), John Della Costa(SDSU), Brad Cenko (NASA GSFC), and
Robert Quimby (SDSU):
We imaged the position of ZTF21aaeyldq (Ho et al., GCN 29305), a ZTF
discovered fast-fading transient with the Large Monolithic Imager (LMI)
mounted at the 4.3m Lowell Discovery Telescope, starting at 2021-01-17
07:59:33 UT.
We acquired three 180 sec exposures in the i-band and reduced them
following standard procedures. Our image shows a clear source at the
position reported by Ho et al. We calibrated the flux against SDSS sources
in the field and derived a magnitude of 22.1 +- 0.2 mag. The magnitude we
report is not extinction corrected.
We thank the LDT staff, particularly Stephen Levine and Amanda Bosh for
their assistance.
- GCN Circular #29310
Z.P. Zhu (NAOC, HUST), J. P. U. Fynbo (DAWN/NBI), D. A. Perley (LJMU),
S.Y. Fu, D. Xu (NAOC) report on behalf of a larger collaboration:
We observed the field of ZTF21aaeyldq/AT2021any (Ho et al., GCN 29305)
using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC
camera. We did photometry in the Sloan g-/r-/i- filters, and the source,
presumably an orphan GRB afterglow (e.g., A. de Ugarte Postigo et al.,
GCN 29307), is clearly detected in each of our images.
Preliminary photometry of the source is as follows:
T_start(UT) Tmid-T0(day) Exptime(s) Filter Mag MagErr
2021-01-17T02:18:24 0.812 5x300 sdss-g 22.28 0.05
2021-01-17T02:45:53 0.831 5x300 sdss-r 21.86 0.04
2021-01-17T03:13:26 0.850 5x300 sdss-i 21.65 0.03
T0 is 06:59:45.6 UT on 2021-01-16, first ZTF detection of ZTF21aaeyldq,
and calibrated with nearby Pan-STARRS stars.
- GCN Circular #29312
Y.-D. Hu, E. Fernandez-Garcia, A.J. Castro-Tirado, M.D. Caballero-Garcia, M.A. Castro-Tirado (IAA-CSIC), R.P. Hedrosa, I. Hermelo, I. Vico (CAHA) on behalf of a larger collaboration, report:
Following the detection of ZTF21aaeyldq (AT2021any) by the Zwicky Transient Facility (ZTF; Ho et al., GCNC 29305), we triggered the 2.2m CAHA telescope in Almeria (Spain) equipped with CAFOS. BVRI images were gathered starting on Jan 17, 00:02 UT (17.04 hours after first optical detection). Second epoch BVRI images were taken starting at 04:08 UT. The optical counterpart is clearly detected at the ZTF position (Ho et al., GCNC 29305, de Ugarte Postigo et al., GCN 29307, Kumar et al., GCNC 29308, Ahumada et al., GCNC 29309 and Zhu et al., GCNC 29310). We measure a first epoch R-band magnitude (non-extinction corrected) of R = 21.27+-0.13 mag at 00:15 UT, calibrated with the nearby stars present in the USNO-B1.0 catalog.
We thank the staff at CAHA observatory for their excellent support.
- GCN Circular #29313
A. Y. Q. Ho (UC Berkeley) reports on behalf of the Zwicky Transient
Facility collaboration:
We obtained a target-of-opportunity observation of ZTF21aaeyldq/AT2021any
(Ho et al., GCN 29305) with the Neil Gehrels Swift Observatory starting at
UT 2021-01-17 (02h29), which is 0.81d after the first optical detection. We
detected X-ray emission at the transient position with a count rate 0.0067
ct/s. Assuming a neutral hydrogen column density n_H = 8.12E20/cm2
(Willingale et al. 2013) and a power-law spectrum with photon index 2, the
unabsorbed flux is 2.9E-13 erg/cm^2/s. At z=2.514 (A. de Ugarte Postigo et
al., GCN 29307) the luminosity is 1.5E46 erg/s, typical of GRB afterglows
at this epoch.
Further monitoring is planned, and we thank the Swift team for rapidly
scheduling and executing our observations.
- GCN Circular #29316
Michael Coughlin (UMN) and Tomas Ahumada (UMD):
We imaged the position of the fast fading ZTF source ZTF21aaeyldq (Ho et
al., GCN 29305), with the the Kitt Peak Electron Multiplying CCD (EMCCD)
demonstrator (KPED) mounted at the 2.1m Kitt Peak Telescope, starting at
2021-01-17 06:59:49 UT.
We acquired thirty 10 sec exposures in the g- and r-bands, stacked them,
and reduced them following standard procedures. After calibrating the flux
against PS1 sources in the field, we do not see the source reported by Ho
et al. down to a limit of g > 20.1 mag and r > 19.9.
- GCN Circular #29321
D. A. Kann (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/IAA-CSIC,
DARK/NBI), C. C. Thoene (HETH), M. Blazek, J. F. Agui Fernandez (both
HETH/IAA-CSIC), and J. I. Vico Linares (CAHA) report:
We observed the position of the GRB-less afterglow ZTF21aaeyldq (Ho et
al., GCN #29305; de Ugarte Postigo et al., GCN #29307) with CAFOS at the
2.2m telescope at Calar Alto, Almeria, Spain, in the Rc band. We
obtained 10 x 360 s exposures, centered at 1.74430 days after the
transient discovery, under fair conditions but mediocre seeing.
The afterglow (Kumar et al., GCNs #29308; Ahumada et al., GCN #29309;
Zhu et al., GCN #29310; Hu et al., GCN #29312) is clearly detected. We
measure Rc = 22.89 +/- 0.12 mag. (AB mag, vs. the same SDSS star as in
our GTC observation, GCN #29307 converted to Rc following the Lupton
transformations, then transformed back to AB mag).
We take data from Ho et al., GCN #29305; de Ugarte Postigo et al., GCN
#29307; and Zhu et al., GCN #29310 (all in r'), and here assume a
trigger time 22 minutes before the discovery (at the last
non-detection). We find this data is fit well with a single power-law, a
straight decay slope alpha ~ 0.91 +/- 0.02. The magnitude we report now
lies slightly (0.3 mag) below the extrapolation of the afterglow decay.
Further observations are needed to determine whether this represents a
jet break.
- GCN Circular #29327
A. Rossi, E. Palazzi (INAF-OAS) reports on behalf of the GRAWITA
collaboration:
We observed the field of ZTF21aaeyldq (Ho et al., GCN 29305)
simultaneously the J and H bands with the LUCI near-infrared imager and
spectrograph mounted on the Large Binocular Telescope (LBT, Mt Graham,
AZ, USA). Observations were obtained on 2021-01-17 at the UT 06:35:00
(midtime), i.e. ~1 day after the first ZTF detection, for a total of 15
min of on-source exposure time in each band under not very good sky
conditions (seeing=1.4").
We detect the transient (de Ugarte-Postigo GCN#29307, Kumar et al., GCNs
#29308; Ahumada et al., GCN #29309; Zhu et al., GCN #29310; Hu et al.,
GCN #29312, Kann et al., GCN #29321) in both J and H-band images, and we
measure the following AB magnitudes:
J=21.62+-0.20
H=21.36+-0.24
calibrated against 2MASS field stars.
We acknowledge the excellent support from the LBTO and LBT-INAF staff,
particularly A. Cardwell and D. Paris, in obtaining these observations.
- GCN Circular #29330
A. Nicuesa Guelbenzu (TLS Tautenburg), A. Rau (MPE Garching),
and S. Klose (TLS Tautenburg) report:
We observed the field of ZTF21aaeyldq/AT2021any (Ho et al., GCN 29305)
with GROND mounted at the 2.2m MPG telescope at the ESO La Silla
Observatory (Chile).
Observations were performed during three epochs. The data were
calibrated against SDSS stars in the field.
In the g' band we measure the following AB magnitudes:
dt/days mag
1.82415 23.39 +/- 0.11
2.02104 23.47 +/- 0.06
2.87115 23.84 +/- 0.09.
Following Kann et al. (GCN 29321), here we assumed a GRB trigger time
22 minutes before the discovery image (Ho et al., GCN 29305), i.e., at
JD 2459230.77622.
Based on these three epochs, we measure a decay slope of 0.94 +/-
0.05, in agreement with Kann et al. (GCN 29321). There is no evidence
for an underlying host galaxy.
The transient was not detected in the NIR bands.
We thank Sam Kim (PUC) for performing the observations and all people,
in particular P. Eigenthaler, R. Lechaume, A. Hempel, M. Hempel,
T. Schweyer, A. González, involved in bringing GROND back online after
its shutdown due to the Covid 19 pandemia in early 2020.
- GCN Circular #29340
H. M. Antia, Tilak Katoch, Parag Shah and Dhiraj Dedhia
TIFR, Mumbai, India.
Analysis of AstroSat LAXPC data showed the detection of a long
GRB 210116. The light curve showed a peak profile triggered at
T0 = 05h 53m 33s UT on 16 Jan 2021. The light curve showed a peak
profile with T90 = 9 sec. The measured peak count rate above the
background associated with the burst is 867 +/- 37 cts/s in
LAXPC10 and 773 +/- 31 cts/s in LAXPC20 at T0+4 sec. The total
counts in the peak are 3219 +/- 85 cts in LAXPC10 and 2683 +/- 68
in LAXPC 20.
Both LAXPC instruments (LAXPC10 and LAXPC20) have registered this
burst profile in the light curve. For LAXPC20 the nominal energy
range is 3-100 keV, but due to lower gain in LAXPC10 the energy
range is about 30-400 keV.
The background subtracted light curve with 1 sec time-bin is
available at the web-site:
https://www.tifr.res.in/~astrosat_laxpc/grb210116lc.jpg
LAXPC was built by TIFR in collaboration with the Indian Space
Research Organisation. The Indian Space Research Organisation
funded, managed and facilitated the project.
- GCN Circular #29342
D. Nadella (NITK), G. Waratkar (IITB), A. Vibhute (IUCAA), S. Gupta
(IUCAA), P. Sawant (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (IUCAA), A.
R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat
CZTI collaboration:
Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al, 2020,
arxiv:2011.07067) showed detection of a bright long GRB 210116A, which was
also detected by AstroSat LAXPC (GCN #29340).
The source was clearly detected in the 20-200 keV energy range. The light
curve showed a single strong peak at 2021-01-16 05:53:37.500 UT, in all
four quadrants of CZTI. Quadrant D was noisy, and we exclude it from
further analysis. The measured peak count rate associated with the burst is
781 (+54, -60) cts/s above the background in the combined data of three
quadrants (out of four), with a total of 3156 (+232, -222) cts. The local
mean background count rate was 395 (+3, -3) cts/s. Using cumulative rates,
we measure a T90 of 9.5 (+4.1, -1.8) s.
It was also clearly detected in the CsI anticoincidence (Veto) detector in
the 100-500 keV energy range. The light curve showed a single strong peak
of emission in all four quadrants, with the strongest peak consistent with
the above timing. The measured peak count rate is 3039 (+131, -62) cts/s
above the background in the combined Veto data of four quadrants, with a
total of 13614 (+475, -578) cts. The local mean background count rate was
1842 (+6, -6) cts/s. We measure a T90 of 8.8 (+1.7, -1.0) s from the
cumulative Veto light curve.
CZTI GRB detections are reported regularly on the payload site at
http://astrosat.iucaa.in/czti/?q=grb. CZTI is built by a TIFR-led
consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC and
PRL. The Indian Space Research Organisation funded, managed and facilitated
the project.
- GCN Circular #29343
D. A. Perley (LJMU), Anna Y. Q. Ho (Berkeley), Y. Yao (Caltech), and R.
A. Perley (NRAO) report:
We obtained observations with the Very Large Array of ZTF21aaeyldq
(AT2021any; Ho et al., GCN 29305) at a mean frequency of 10 GHz between
04:50 and 05:50 UT on 2021-01-21, approximately 4.95 days after the ZTF
discovery observation.
A source is clearly detected at a position consistent with that of the
optical transient. The flux density at this time is approximately 90
microJy.
We thank the VLA staff for rapidly scheduling and executing these
observations.
- GCN Circular #29344
D. A. Kann (HETH/IAA-CSIC), A. Nicuesa Guelbenzu (TLS Tautenburg), A. de
Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), C. C. Thoene (HETH), M.
Blazek, J. F. Agui Fernandez (both HETH/IAA-CSIC), A. Rau (MPE
Garching), S. Klose (TLS Tautenburg), and J. I. Vico Linares (CAHA)
report:
We obtained further observations of the GRB-less afterglow
ZTF21aaeyldq/AT2021any (Ho et al., GCN #29305; de Ugarte Postigo et al.,
GCN #29307) with CAFOS at the 2.2m telescope at Calar Alto, Almeria,
Spain, in the Rc band at 2.8 days post-discovery, and with GROND mounted
at the 2.2m MPG telescope at the ESO La Silla Observatory (Chile) at 3.9
days after the trigger. The afterglow is clearly detected in each
stacked image.
Further to the observations and analysis described in Kann et al. (GCN
#29321, with data from Ho et al., GCN #29305; de Ugarte Postigo et al.,
GCN #29307; and Zhu et al., GCN #29310) and Nicuesa Guelbenzu et al.
(GCN #29330), we fit the combined data set, also leaving the host-galaxy
magnitudes free, as the GROND data shows a characteristic flattening.
We find that a single power-law fit does not describe the data well
(chi^2/d.o.f. = 3.7), overestimating the CAHA data and not fitting the
curvature seen in the GROND data. However, a broken power-law fit yields
a significantly improved result (chi^2/d.o.f. = 0.12) with fit
parameters alpha_1 = 0.95 +/- 0.03, alpha_2 = 2.30 +/- 0.76 and t_b =
0.82 +/- 0.08 days. This fit may be improved or modified with further
data/observations, but the break signature is clear. It therefore
confirms the initial suggestion of Kann et al. (GCN #29321). This is a
typical feature in GRB afterglows and a further indicator that the
nature of this transient is a GRB afterglow.
Ho et al., GCN #29305, report the first detection at
2021-01-16T06:59:45.6, and a deep non-detection 22 minutes earlier.
Antia et al., GCN #29340, and Nadella et al., GCN #29342, report the
detection of a bright GRB 210116A with AstroSat LAXPC and CZTI at ~05:53
UR on the same day, about 44 minutes before the ZTF non-detection.
Judging from typical GRB afterglow behavior, this makes it unlikely that
the two events are associated with each other but does not rule it out.
An IPN localization of GRB 210116A could confirm or rule out the
association.
- GCN Circular #29364
Ankur Ghosh (ARIES), Dimple (ARIES), Amit Kumar (ARIES), Rahul Gupta
(ARIES), Kuntal Misra (ARIES) and Shashi B. Pandey (ARIES) report:
We obtained further observations of the ZTF21aaeyldq/AT2021any (Ho et
al. GCN #29305, de Ugarte Postigo et al. GCN #29307, Kumar et al. #GCN
29308) with 4K x 4K CCD Imager mounted on 3.6m Devasthal Optical
Telescope (DOT) at Devasthal observatory of ARIES, India, in r-band
at 9.41 days after discovery. We acquired a consecutive set of 12
images with an exposure time of 300 seconds each. We do not detect any
optical counterpart upto a magnitude limit of 23.98 in the stacked
image. The limit do agree with the decay index reported by Kann et al.
GCN #29344.
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