Optical follow-up of IceCube-190619A with ZTF
ATel #12879; R. Stein (DESY), A. Franckowiak (DESY), J. van Santen (DESY), L. Rauch (DESY), M. Kowalski (DESY), J. Nordin (HU Berlin), M. M. Kasliwal (Caltech), I. Andreoni (Caltech), T. Ahumada (UMD), M. Coughlin (Caltech), L. P. Singer (NASA GSFC), S. Anand (Caltech)
on 20 Jun 2019; 21:42 UT
Credential Certification: Anna Franckowiak (anna.franckowiak@desy.de)
Subjects: Optical, Neutrinos
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 high-energy neutrino event
IceCube-190619A (see GCN #24854 and https://gcn.gsfc.nasa.gov/notices_amon_g_b/132707_54984442.amon) with the Palomar 48-inch telescope equipped with the 47-square-degree ZTF camera (Bellm et al. 2019, Graham et al. 2019).
We obtained target-of-opportunity observations for two field covering the 90% confidence region, beginning at UT 2019-06-20 10:03 in the g-band filter and UT 2019-06-20 10:26 in the r-band filter (21 hours after the neutrino detection), each with an exposure length of 300s.
The images were processed through the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts (Masci et al. 2019). Candidates were filtered using the AMPEL software package (see Nordin et al. 2019). After rejecting stellar sources (Tachibana and Miller 2018) and moving objects and applying machine learning algorithms (Mahabal et al. 2019), two potential transient or variable objects were detected in both images in spatial coincidence with the neutrino arrival direction.
| ZTF Name |
RA (deg) |
DEC (deg) |
Filt. |
Mag. (g) |
Magerr. (g) |
Mag. (r) |
Magerr. (r) |
| ZTF18actxchc |
346.181678 |
12.202749 |
g |
19.78 |
0.12 |
19.88 |
0.15 |
| ZTF19aaycool |
345.221270 |
10.454273 |
g |
20.31 |
0.19 |
20.34 |
0.14 |
ZTF18actxchc was previously detected with the g-filter on June 4th and June 7th at 20.1 and 20.3 mag, and has since brightened. It was not detected with the r-filter in observations on the same dates, with limiting magnitudes of 20.4 and 20.0, but has a history of variability. ZTF19aaycool was first detected on June 7th at 20.5 mag in g-filter and has no history of variability, though given the magnitude uncertainty it cannot be concluded whether the lightcurve is rising. Further observations will be scheduled to determine whether either of these objects is a potential neutrino source candidate. Given the size of the neutrino error region, the chance coincidence of objects is expected.
The median 5 sigma upper limit for an isolated point source in our images was r > 20.8 and g > 20.4 mag for the observations made on June 20.
Ongoing observations of the area will continue as part of regular survey observations.
ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC, USA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA; DESY, Germany; MOST, Taiwan; UW Milwaukee, USA; LANL USA; Tokyo Tech, Japan; IIT-B, India; IIA, India; LJMU, UK; TTU, USA; and USyd, Australia. ZTF acknowledges the generous support of the NSF under AST MSIP Grant No 1440341. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949. Alert distribution service provided by DIRAC@UW (Patterson et al. 2019). Alert filtering and follow-up coordination is being undertaken by the GROWTH marshal system (Kasliwal et al. 2019).
