GCN Circular 37739

Jannis Necker (DESY), Robert Stein (Caltech), Simeon Reusch (DESY), Sven Weimann (Ruhr University Bochum), 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: 

As part of the ZTF neutrino follow up program (Stein et al. 2023), we observed the localization region of the neutrino event IceCube-241006A (Zegarelli et. al, GCN 37723
Not found
 
 
) 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 2024-10-08 07:00 UTC, approximately 32.4 hours after event time. We covered 76.0% (1.3 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 candidates by our pipeline, all lying within the 90.0% localization of the skymap.

+--------------------------------------------------------------------------------+
| ZTF Name     | IAU Name  | RA (deg)    | DEC (deg)   | Filter | Mag   | MagErr |
+--------------------------------------------------------------------------------+
| ZTF19accjndb |  -------  | 058.6439041 | +08.5812604 | g      | 20.59 | 0.12    
| ZTF24ablklut |  -------  | 058.2043689 | +08.6628184 | r      | 21.69 | 0.18   |  
+--------------------------------------------------------------------------------+
 

Amongst our candidates, 

ZTF19accjndb was first detected on 2019-09-09, and has a crossmatched detection as WISEA J035434.54+083452.2 at a distance of 0.35". This source is also listed in milliquas (Flesch 2023) as a likely QSO (p=98%). This AGN has been detected previously by ZTF, and does not appear to currently be in an elevated optical state. It had been gradually fading in difference image detections for the past 60 days, and these represent minor fluctations relative to the archival PS1 magnitude of g=18.6 (Chambers et al. 2016). 

ZTF24ablklut was first detected on 2024-10-08. It has a cross-matched detection as WISEA J035249.06+083946.1 at a distance of  0.19". Based on the archival MIR colours of this source (W1-W2=1.0), this object is very likely to be an AGN (Stern et al. 2012). The recent optical detection is very faint in difference imaging, representing a small increase relative to the archival detection in PS1 at r=20.5 (Chambers et al. 2016).

We therefore find no reason to suggest that either ZTF19accjndb/WISEA J035434.54+083452.2 or ZTF24ablklut/WISEA J035249.06+083946.1 are related to the neutrino.

Observations of this field will continue as part of our standard ToO cadence for high-energy neutrinos (Stein et al 2023.).

ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC, USA; WIS, Israel; OKC, Sweden; JSI/UMd, USA; DESY, Germany; TANGO, Taiwan; UW Milwaukee, USA; LANL, USA; TCD, Ireland; IN2P3, France.

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 ).