IceCube-210210A
GCN Circular 29454
Subject
IceCube-210210A: IceCube observation of a high-energy neutrino candidate event
Date
2021-02-10T14:42:58Z (4 years ago)
From
Cristina Lagunas Gualda at DESY <cristina.lagunas@desy.de>
The IceCube Collaboration (http://icecube.wisc.edu/) reports:
On 21/02/10 at 11:53:55.65 UT IceCube detected a track-like event with a high probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_GOLD alert stream. The average astrophysical neutrino purity for Gold alerts is 50%. This alert has an estimated false alarm rate of 0.464 events per year due to atmospheric backgrounds. The IceCube detector was in a normal operating state at the time of detection.
After the initial automated alert (https://gcn.gsfc.nasa.gov/notices_amon_g_b/134979_17138286.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:
Date: 21/02/10
Time: 11:53:55.65 UT
RA: 206.06 (+ 1.40 - 0.95 deg 90% PSF containment) J2000
Dec: 4.78 (+ 0.62 - 0.56 deg 90% PSF containment) J2000
We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino.
There is one Fermi-LAT 4FGL source inside the 90% localization region, 4FGL J1342.7+0505, located at RA 205.69 deg and Dec 5.09 deg (J2000), at a distance of 0.49 degrees from the best-fit location.
The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc@icecube.wisc.edu
GCN Circular 29461
Subject
IceCube-210210A: Two Candidate Counterparts from the Zwicky Transient Facility
Date
2021-02-10T16:59:54Z (4 years ago)
From
Simeon Reusch at DESY <simeon.reusch@desy.de>
Simeon Reusch (DESY), Sven Weimann (Ruhr University Bochum), Robert Stein (DESY), Micheal Coughlin (UMN) and Anna Franckowiak (DESY/Ruhr University Bochum) report,
On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations:
We observed the localization region of the neutrino event IceCube-210210A (Lagunas et. al, GCN 29454) with the Palomar 48-inch telescope, equipped with the 47 square degree ZTF camera (Bellm et al. 2019, Graham et al. 2019). We started observations in the g- and r-band beginning at 2021-02-10 12:07 UTC, approximately 0.2 hours after event time. We covered 2.1 sq deg, corresponding to 78.6% of the reported localization region. This estimate accounts for chip gaps. Each exposure was 300s with a typical depth of 21.0 mag.
The images were processed in real-time through the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts (Masci et al. 2019). AMPEL (Nordin et al. 2019, Stein et al. 2020) was used to search the alerts database for candidates. We reject stellar sources (Tachibana and Miller 2018) and moving objects, and apply machine learning algorithms (Mahabal et al. 2019). We are left with two high-significance transient candidates from our pipeline, both lying within the 90.0% localization of the skymap.
+---------------------------------------------------------------------------------+
| ZTF Name | IAU Name | RA (deg) | DEC (deg) | Filter | Mag | MagErr |
+---------------------------------------------------------------------------------+
| ZTF21aajxjrv | AT2021clu | 206.9855020 | +05.3138660 | r | 21.03 | 0.13 |
| ZTF21aajxjry | AT2021clv | 207.3743696 | +04.9786236 | r | 21.47 | 0.19 |
+---------------------------------------------------------------------------------+
Both candidates are possible transients, with no prior detections, that have not yet been spectroscopically classified. Additional target-of-opportunity observations with ZTF are planned for 2021-02-11 as part of our neutrino follow-up program (Stein et al. 2020).
Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. 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.
GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949.
Alert distribution service provided by DIRAC@UW (Patterson et al. 2019).
Alert database searches are done by AMPEL (Nordin et al. 2019).
Alert filtering is performed with the AMPEL Follow-up Pipeline (Stein et al. 2020).
GCN Circular 29463
Subject
IceCube-210210A: No counterpart candidates in INTEGRAL SPI-ACS and IBIS prompt observation
Date
2021-02-10T17:25:55Z (4 years ago)
From
Volodymyr Savchenko at ISDC,U of Geneve <savchenk@in2p3.fr>
V. Savchenko, C. Ferrigno (ISDC/UniGE, Switzerland)
J. Rodi (IAPS-Roma, Italy)
A. Coleiro (APC, France)
S. Mereghetti (INAF IASF-Milano, Italy)
on behalf of the INTEGRAL multi-messenger collaboration:
https://www.astro.unige.ch/cdci/integral-multimessenger-collaboration
Using combination of INTEGRAL all-sky detectors (following [1]):
SPI/ACS, IBIS/Veto, and IBIS we have performed a search for a prompt
gamma-ray counterpart of IceCube-210210A (GCN 29454).
At the time of the event (2021-02-10 11:53:55 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The peak of the event
localization probability was at an angle of 121 deg with respect to
the spacecraft pointing axis. This orientation implies strongly
suppressed (2.7% of optimal) response of ISGRI, somewhat suppressed
(54% of optimal) response of IBIS/Veto, and somewhat suppressed (48%
of optimal) response of SPI-ACS.
The background within +/-300 seconds around the event was very stable
(excess variance 1.1).
We have performed a search for any impulsive events in INTEGRAL SPI-
ACS (as described in [2]), IBIS, and IBIS/Veto data.
We do not detect any significant counterparts and estimate a 3-sigma
upper limit on the 75-2000 keV fluence of 3.6e-07 erg/cm^2 (within the
50% probability containment region of the source localization) for a
burst lasting less than 1 s with a characteristic short GRB spectrum
(an exponentially cut off power law with alpha=-0.5 and Ep=600 keV)
occurring at any time in the interval within 300 s around T0. For a
typical long GRB spectrum (Band function with alpha=-1, beta=-2.5, and
Ep=300 keV), the derived peak flux upper limit is ~3.2e-07 (9.4e-08)
erg/cm^2/s at 1 s (8 s) time scale in 75-2000 keV energy range.
We report for completeness and in order of FAP, all excesses
identified in the search region. We find: 1 possibly associated
excess:
T-T0 | scale | S/N | flux ( x 1e-06 erg/cm2/s) | FAP
-44.5 | 2.7 | 4.1 | 3.13 +/- 0.767 +/- 1.1 | 0.0487
2 likely background excesses:
T-T0 | scale | S/N | flux ( x 1e-06 erg/cm2/s) | FAP
19.7 | 0.15 | 3.6 | 1.15 +/- 0.329 +/- 0.405 | 0.734
78.6 | 0.6 | 3.6 | 0.555 +/- 0.163 +/- 0.196 | 0.789
Note that FAP estimates (especially at timescales above 2s) may be
possibly further affected by enhanced non-stationary local background
noise. This list excludes any excesses for which FAP is close to
unity.
All results quoted are preliminary.
This circular is an official product of the INTEGRAL Multi-Messenger
team.
[1] Savchenko et al. 2017, A&A 603, A46
[2] Savchenko et al. 2012, A&A 541A, 122S
GCN Circular 29464
Subject
IceCube-210210A: Upper limits from Fermi-GBM Observations
Date
2021-02-10T18:34:54Z (4 years ago)
From
Christian Malacaria at NASA-MSFC/USRA <cmalacaria@usra.edu>
C. Malacaria (NASA-MSFC/USRA) reports on behalf of the Fermi-GBM Team:
For the IceCube high-energy neutrino candidate event 210210A (GCN 29454),
at the event time Fermi-GBM was observing the reported neutrino location at:
RA: 206.06 (+1.40 -0.95 deg 90% PSF containment) J2000
Dec: 4.78 (+0.62 -0.56 deg 90% PSF containment) J2000
There was no Fermi-GBM onboard trigger around the event time of the
neutrino candidate. An automated, blind search for short gamma-ray bursts
below the onboard triggering threshold in Fermi-GBM also identified no
counterpart candidates. The GBM targeted search, the most sensitive,
coherent search for GRB-like signals, was run from +/-30 s around the
neutrino candidate time. From this search, no significant signal was found
related to IceCube-210210A.
We set upper limits on impulsive gamma-ray emission. Using the
representative soft, normal, and hard GRB-like templates
(arXiv:1612.02395), we report the following 3 sigma flux upper limits over
10-1000 keV (in units of 10^-7 erg/s/cm^2):
Timescale soft norm hard
--------------------------------------
0.128 s: 8.5 12. 21.
1.024 s: 2.7 3.4 6.3
8.192 s: 1.1 1.6 3.4
GCN Circular 29473
Subject
Fermi-LAT Gamma-ray Observations of IceCube-210210A
Date
2021-02-11T09:21:35Z (4 years ago)
From
Simone Garrappa at DESY <simone.garrappa@desy.de>
S. Garrappa (DESY-Zeuthen), S. Buson (Univ. of Wuerzburg), C. C. Cheung
(NRL) on behalf of the Fermi-LAT collaboration:
We report an analysis of observations of the vicinity of the high-energy
IC210210A neutrino event (GCN 29454) with all-sky survey data from the
Large Area Telescope (LAT), on board the Fermi Gamma-ray Space
Telescope. The IceCube event was detected on 2021-02-10 at 11:53:55.65
UT (T0) with J2000 position RA = 206.06 (+1.40, -0.95) deg, Decl. = 4.78
(+0.62, -0.56) deg (90% PSF containment). One cataloged >100 MeV
gamma-ray source is located within the 90% IC200210A localization
region. This is 4FGL J1342.7+0505 (4FGL, The Fermi-LAT collaboration
2020, ApJS, 247, 33), associated with 4C +05.57 (Pilkington and Scott
1965, MmRAS, 69, 183), a.k.a., PKS 1340+05 (Bolton et al. 1975 Aust.J.
Phys. Astrophys. SuppL, No. 34, 1), at redshift z = 0.13663 (Hewett and
Wild, 2010, MNRAS, 405, 2302). PKS 1340+05 has been classified
spectroscopically as a BL Lac (BL Lac galaxy-dominated, de Menezes et al
2019, A&A 630, A55) and broad-line radio galaxy (Grandi 1983, MNRAS,
204, 691). Based on a preliminary analysis of the LAT data over the
timescales of 1-day and 1-month prior to T0, this object is not
significantly detected (> 5 sigma).
We searched for intermediate (days to years) timescale emission from a
new gamma-ray transient source. Preliminary analysis indicates no
significant (> 5 sigma) new excess emission (> 100 MeV) at the IC210210A
best-fit position. Assuming a power-law spectrum (photon index = 2.0
fixed) for a point source at the IC210210A best-fit position, the >100
MeV flux upper limit (95% confidence) is < 6.1e-10 ph cm^-2 s^-1 for
~12-years (2008-08-04 to 2021-02-10 UTC), and < 9.8e-9 (< 1e-7) ph cm^-2
s^-1 for a 1-month (1-day) integration time before T0.
Since Fermi normally operates in an all-sky scanning mode, regular
monitoring of this source will continue. For these observations the
Fermi-LAT contact persons are S. Garrappa (simone.garrappa at desy.de)
and S. Buson (sara.buson at uni-wuerzburg.de).
The Fermi-LAT is a pair conversion telescope designed to cover the
energy band from 20 MeV to greater than 300 GeV. It is the product of an
international collaboration between NASA and DOE in the U.S. and many
scientific institutions across France, Italy, Japan and Sweden.
GCN Circular 29475
Subject
IceCube-210210A: No neutrino counterpart in ANTARES
Date
2021-02-11T12:47:34Z (4 years ago)
From
Antoine Kouchner at ANTARES Collaboration <kouchner@apc.in2p3.fr>
Alexis Coleiro (APC/Universite de Paris) and Damien Dornic (CPPM/CNRS) on behalf of the ANTARES Collaboration.
Using data from the ANTARES detector, we have performed a follow-up analysis of the recently reported single track-like event IceCube-210210A (GCN #29454 <https://gcn.gsfc.nasa.gov/gcn3/29454.gcn3>). The reconstructed origin was -18 degrees below the horizon for ANTARES.
No up-going muon neutrino candidate events were recorded within 90% error box of the IceCube event during a +/- 1h time-window centered on the IceCube event time, and over which the potential source remained visible all time. This leads to a preliminary 90% confidence level upper limit on the muon-neutrino fluence from a point source of 16 GeV.cm^-2 over the energy range 3.5 TeV - 3.7 PeV (the range corresponding to 5-95% of the detectable flux) for an E^-2 power-law spectrum, and 40 GeV.cm^-2 (680 GeV - 355 TeV) for an E^-2.5 spectrum. A search over an extended time window of +/- 1 day has also yielded no detection (50% visibility).
ANTARES <http://antares.in2p3.fr/> is the largest undersea neutrino detector (Mediterranean Sea) and it is primarily sensitive to astrophysical neutrinos in the TeV-PeV energy range. At 10 TeV, the median angular resolution for muon neutrinos is about 0.5 degrees. In the range 1-100 TeV ANTARES has a competitive sensitivity to this position in the sky.
GCN Circular 29480
Subject
Swift-XRT observations of IceCube-210210A
Date
2021-02-11T16:37:49Z (4 years ago)
From
Timothee Gregoire at Penn State <tmg5746@psu.edu>
A. Keivani (Columbia U.), J.P. Osborne (U. Leicester), F. Krauss (PSU),
T. Gregoire (PSU), P.A. Evans (U. Leicester), J.A. Kennea (PSU),
H. A. Ayala Solares (PSU), D.F. Cowen (PSU), J. DeLaunay (PSU) and D. B. Fox (PSU) report:
Swift observed the field of IceCube 210210A (GCN Circ. 29454) between 14:14:46 on February 10, 2021
and 00:03:08 on February 11, 2021. Due to a technical problem only two pointings were done with a
radius of 0.2 degrees each, one centered on the event position and one centered on 4FGL J1342.7+0505.
A total of 7.5 ks of cleaned photon counting (PC) mode data was collected.
We found 6 X-ray sources, as detailed below. These sources are either known or unknown but with
count rate consistent with the previous non-detections. We therefore do not
claim any of them as the likely counterpart to IceCube 210210A.
Source 5 is coincident with the best position of the assumed optical counterpart to 4FGL J1342.7+0505 reported by SIMBAD. Its count-rate in our follow up data is 2.6 (+/-0.3) x 10^-2 ct s^-1. This source has previously been observed by Swift on 2009 August 29 and is in the 2SXPS catalogue (2SXPS J134243.1+050425) with a count-rate of 2.5 (+/-1.1) x 10^-2 ct s^-1. This is consitent with our new measurement.
The 3-sigma upper limit in the field was in the range 2-3 x 10^-3 ct/sec.
The detected sources were:
Source no: 1
RA (J2000): 206.11779 [degrees] = 13h 44m 28.27s
Dec (J2000): +4.8410 [degrees] = +04d 50' 27.7"
Error: +2.8 [arcsec, 90% conf. radius]
Count rate (0.3-10 keV): 1.4 (+0.3, -0.3) x 10^-2 ct s-1
Flux (0.3-10 keV): 5.8 (+1.2, -1.1) x 10^-13 erg cm-2 s-1
Note: This is 6" from the SIMBAD object 1RXS J134428.3+045027
Source no: 2
RA (J2000): 206.07773 [degrees] = 13h 44m 18.65s
Dec (J2000): +4.7588 [degrees] = +04d 45' 31.5"
Error: +4.7 [arcsec, 90% conf. radius]
Count rate (0.3-10 keV): 3.6 (+1.3, -1.1) x 10^-3 ct s-1
Flux (0.3-10 keV): 1.5 (+0.6, -0.5) x 10^-13 erg cm-2 s-1
Source no: 3
RA (J2000): 205.52674 [degrees] = 13h 42m 06.42s
Dec (J2000): +5.0902 [degrees] = +05d 05' 24.6"
Error: +3.7 [arcsec, 90% conf. radius]
Count rate (0.3-10 keV): 2.3 (+/-0.3) x 10^-2 ct s-1
Flux (0.3-10 keV): 9.7 (+1.4, -1.3) x 10^-13 erg cm-2 s-1
Note: This is 2.4" from the SIMBAD object 2E 3124
Source no: 4
RA (J2000): 205.55271 [degrees] = 13h 42m 12.65s
Dec (J2000): +5.1739 [degrees] = +05d 10' 26.1"
Error: +6.1 [arcsec, 90% conf. radius]
Count rate (0.3-10 keV): 2.3 (+1.3, -1.0) x 10^-3 ct s-1
Flux (0.3-10 keV): 1.0 (+0.5, -0.4) x 10^-13 erg cm-2 s-1
Source no: 5
RA (J2000): 205.68170 [degrees] = 13h 42m 43.61s
Dec (J2000): +5.0754 [degrees] = +05d 04' 31.3"
Error: +2.5 [arcsec, 90% conf. radius]
Count rate (0.3-10 keV): 2.6 (+/-0.3) x 10^-2 ct s-1
Flux (0.3-10 keV): 1.11 (+0.15, -0.14) x 10^-12 erg cm-2 s-1
Source no: 6
RA (J2000): 205.74168 [degrees] = 13h 42m 58.00s
Dec (J2000): +5.0609 [degrees] = +05d 03' 39.4"
Error: +7.6 [arcsec, 90% conf. radius]
Count rate (0.3-10 keV): 2.8 (+1.3, -1.0) x 10^-3 ct s-1
Flux (0.3-10 keV): 1.2 (+0.5, -0.4) x 10^-13 erg cm-2 s-1
Note: This is 2.9" from the SIMBAD object BD+05 2790.
GCN Circular 29493
Subject
IceCube-210210A: Upper limits from a search for additional neutrino events in IceCube
Date
2021-02-12T15:39:03Z (4 years ago)
From
Alex Pizzuto at ICECUBE/U of Wisconsin <pizzuto@wisc.edu>
The IceCube Collaboration (http://icecube.wisc.edu/) reports:
IceCube has performed a search for additional track-like muon neutrino events arriving
from the direction of IceCube-210210A (https://gcn.gsfc.nasa.gov/gcn3/29454.gcn3) in a time
range of 2 days centered on the alert event time (2021-02-09 11:53:55.65 UTC to 2021-02-11 11:53:55.65 UTC) during which IceCube was collecting good quality data. Excluding the
event that prompted the alert, four additional track-like events are found in spatial coincidence
with the 90% containment region of IceCube-210210A. We find that these data are consistent with atmospheric background expectations, with a p-value of 1.0. We accordingly derive a time-integrated muon-neutrino flux upper limit at the alert position of E^2 dN/dE = 3.0 x 10^-5 TeV cm^-2 at 90% CL, under the assumption of an E^-2 power law. 90% of events IceCube would detect from a source at this declination with an E^-2 spectrum are approximately between 1 TeV and 5 PeV.
A subsequent search was performed to include the month of data prior to the alert event (2021-01-11 11:53:55.65 UTC to 2021-02-11 11:53:55.65 UTC). In this case, we report a p-value of 1.0, consistent with no significant excess of track-like events, and a corresponding time-integrated muon-neutrino flux upper limit assuming an E^-2 spectrum (E^2 dN/dE) of
4.4 x 10^-5 TeV cm^-2 at the 90% CL.
The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc@icecube.wisc.edu<mailto:roc@icecube.wisc.edu>.
GCN Circular 29501
Subject
IceCube-210210A: Four Candidate Optical Counterparts from DECam Observations
Date
2021-02-13T05:00:26Z (4 years ago)
From
Robert Morgan at U. of Wisconsin-Madison <robert.morgan@wisc.edu>
Robert Morgan (U of Wisconsin-Madison), Alyssa Garcia (U of Michigan), Alex Drlica-Wagner (Fermilab), Kathy Vivas (NOIRLab), Ken Herner (Fermilab), Keith Bechtol (U of Wisconsin-Madison), Kyoungsoo Lee (Purdue U), Eric Gawiser (Rutgers U), Yi-Kuan Chiang (Ohio State U), and Hwihyun Kim (NOIRLab) report:
We triggered the Dark Energy Camera (DECam) at Cerro Tololo Inter-American Observatory in Chile on the localization area of the GOLD neutrino event detected by IceCube (IceCube-210210A, GCN 29454). Observations took place on 2021-02-11 at 09:00 UT (approximately 21 hours after the alert) and on 2021-02-12 at 09:00 UT in the gri bands, using 150 second exposures, and reaching 10-sigma limiting magnitudes of approximately 23 mag. Each night, the 75.1% of the 90% localization area was covered by DECam. We reduced the DECam images using the DESGW difference imaging pipeline (Herner et al. 2020), using pre-existing DECaLS images as templates.
We required that candidate counterparts are (1) not found in GAIA DR3, (2) detected on both nights in the same filter by Source Extractor with 1 of the detections also passing a machine learning artifact detection program (autoscan, Goldstein et. al 2015), (3) not found in a spatial-temporal look-up in the Minor Planet Center or Near Earth Object Catalog, (4) not ruled out as an artifact by visual inspection.
We find four optical counterpart candidates:
| NAME | TNS (IAU) | RA | DEC | HOST |
| DESNU-a-893025 | AT2021ctp | 206.361822 | 4.602091 | PSO J206.3618+04.6020 |
| DESNU-b-892671 | AT2021ctq | 206.453649 | 4.329346 | PSO J206.4539+04.3285 |
| DESNU-c-893197 | AT2021ctr | 205.841861 | 3.960848 | PSO J205.8419+03.9613 |
| DESNU-d-891087 | AT2021cts | 206.437552 | 4.011537 | PSO J206.4375+04.0115 |
With photometry:
| NAME | MJD_NITE_1 | MAG_NITE_1 | MJD_NITE_2 | MAG_NITE_2 | FILTER |
| DESNU-a-893025 | 59256.379 | 22.98 | 59257.373 | 22.89 | r |
| DESNU-b-892671 | 59256.381 | 22.81 | 59257.375 | 23.10 | i |
| DESNU-c-893197 | 59256.379 | 21.69 | 59257.373 | 21.69 | r |
| DESNU-d-891087 | 59256.375 | 23.30 | 59257.367 | 23.07 | g |
Notes:
- DESNU-c-893197 is bright enough for most spectroscopic instruments to target and is well separated from the host
- DESNU-a-893025 and DESNU-d-891087 are both faint and coincident with the host center, but characterization is still encouraged
- DESNU-b-892671 is well separated from the host
We also report the detection of and photometry for the one of the candidates detected by ZTF (GCN 29461). The second candidate detected by ZTF was outside the field of view of DECam in these observations.
| TNS (IAU) | MJD_NITE_1 | MAG_NITE_1 | MJD_NITE_2 | MAG_NITE_2 | FILTER |
| AT2021clu | 59256.379 | 20.77 | 59257.373 | 20.78 | r |
We will continue to monitor these candidates with DECam over the next 3 weeks, as well as the 90% localization area of IceCube-210210A. Spectroscopic characterization of all above candidates, and / or a spectroscopic redshift of the host is encouraged. The TNS reports for these candidates contain DECam discovery images in the Comments section.
GCN Circular 29519
Subject
IceCube-210210A: Two Additional Optical Candidate Counterparts Found by DECam
Date
2021-02-17T19:42:49Z (4 years ago)
From
Robert Morgan at U. of Wisconsin-Madison <robert.morgan@wisc.edu>
Robert Morgan (U of Wisconsin-Madison), Alyssa Garcia (U of Michigan), Alex Drlica-Wagner (Fermilab), Kathy Vivas (NOIRLab), Ken Herner (Fermilab), Keith Bechtol (U of Wisconsin-Madison), Kyoungsoo Lee (Purdue U), Eric Gawiser (Rutgers U), Yi-Kuan Chiang (Ohio State U), Hwihyun Kim (NOIRLab), and Yujin Yang (KASI) report:
We expand on the DECam follow-up of IceCube-210210A (GCN 29461) presented in GCN 29501. We collected an additional epoch of gri observations on 2021-02-15 at 09:00 UT using 150 second exposures and reaching 10-sigma limiting magnitudes of approximately 23 mag. Approximately 75.1% of the 90% localization area was covered by DECam. We reduced the DECam images using the DESGW difference imaging pipeline (Herner et al. 2020), using pre-existing DECaLS and Blink images as templates.
We required that candidate counterparts are (1) not found in GAIA DR3, (2) detected on two nights in the same filter by Source Extractor with 1 of the detections also passing a machine learning artifact detection program (autoscan, Goldstein et. al 2015), (3) not found in a spatial-temporal look-up in the Minor Planet Center or Near Earth Object Catalog, (4) not ruled out as an artifact by visual inspection.
Previously (in GCN 29501) we reported four optical counterpart candidates (AT2021ctp, AT2021ctq, AT2021ctr, and AT2021cts). AT2021ctp shows no temporal evolution in our recent observing epoch and we no longer consider it to be a candidate counterpart. We also find two additional candidate counterparts:
| NAME | TNS (IAU) | RA | DEC | HOST |
| DESNU-e-892577 | AT2021dcz | 206.769807 | 4.089444 | PSO J206.7696+04.0897 |
| DESNU-f-893888 | AT2021ddb | 206.257085 | 4.321923 | PSO J206.2572+04.3211 |
With recent photometry:
| NAME | MJD_NITE_3 | MAG_NITE_3 | FILTER |
| DESNU-e-892577 | 59260.368 | 23.24 | i |
| DESNU-f-893888 | 59260.359 | 23.16 | g |
Notes:
- DESNU-e-892577 showed an initial rise in brightness on the first two nights after IceCube-210210A and is now fading, making a strong case for temporal coincidence with the neutrino.
We will continue to monitor the five total DECam candidates (AT2021ctq, AT2021ctr, AT2021cts, AT2021dcz, and AT2021ddb) as well as one ZTF candidate (AT2021clu) over the next 2 weeks, as well as the 90% localization area of IceCube-210210A. Spectroscopic characterization of all above candidates, and / or a spectroscopic redshift of the host is encouraged. The TNS reports for these candidates contain DECam discovery images in the Comments section.