GCN Circular 45099
Subject
IceCube-260704A: No candidates from the Zwicky Transient Facility
Event
Date
2026-07-07T10:32:00Z (3 days ago)
From
Robert David Stein at JSI <rdstein@umd.edu>
Via
Web form
Akshay Eranhalodi (DESY), Robert Stein (JSI), Cristobal Zilleruelo Cañas (DESY), Jannis Necker (Leiden University), and Anna Franckowiak (Ruhr University Bochum) report,
On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations:
As part of the ZTF neutrino follow up program (Stein et al. 2023), we observed the localization region of the neutrino event IceCube-260704A (Zegarelli et. al, GCN 45075) 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 2026-07-04 07:25 UTC, approximately 0.1 hours after event time. We covered 98.4% (0.8 sq deg) 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. 2021) 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 the following high-significance transient candidate by our pipeline, lying within the 90.0% localization of the skymap:
+--------------------------------------------------------------------------------+
| ZTF Name | IAU Name | RA (deg) | DEC (deg) | Filter | Mag | MagErr |
+--------------------------------------------------------------------------------+
| ZTF19ablafcb | ------- | 320.5248614 | +34.5149697 | g | 21.09 | 0.20 |
+--------------------------------------------------------------------------------+
ZTF19ablafcb was first detected by ZTF on 2019-07-31. It is located at a galactic latitude of -10.94 degrees. Based on its WISE colours (W1-W2=0.6), historical optical variability in ZTF data, and nuclear location, it is likely that the source is an AGN. The source is clearly visible in archival PS1 imaging, and the source does not appear to be significantly flaring relative to this baseline. We therefore find no temporal evidence to suggest that the AGN is associated to the high-energy neutrino.
We do not select the AGN WISEA J212302.62+340634.2, which was observed by Adami et al. (GCN 45085). This is expected, given that the source was reported to not be flaring. Our ZTF ToO program only targets AGN which are undergoing flares coincident with the detection of neutrinos.
ZTF and GROWTH are worldwide collaborations comprising Caltech/IPAC, USA; University of Maryland, USA; University of California, Berkeley, USA; Cornell University, USA; Drexel University, USA; University of North Carolina at Chapel Hill, USA; Institute of Science and Technology, Austria; National Central University, Taiwan; OKC, Sweden; DZA, Germany.
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 nuztf (Stein et al. 2021, https://github.com/desy-multimessenger/nuztf).