AstroNote 2025-209

Following AstroNote 2025-208 reporting on the automatic ground- and space-based follow-up of the Type Ia SN 2025qpk earlier this week, we report on a similar case of BTSbot-nearby automated follow-up for the new, likely Type II, SN 2025qtt. We refer the reader to Rehemtulla+25b and AstroNotes 2024-140, 2025-46, and 2025-208 for a detailed description of the BTSbot-nearby automated infant SN follow-up program and prior notable cases of rapid follow-up.

SN 2025qtt (ZTF25abawltx) is located in UGC 11453 (z=0.012839; Springob+05) with a z-independent distance of 38.5 Mpc (Tully+16; distance modulus = 32.93 mag). It was first discovered in Zwicky Transient Facility (ZTF; Bellm+19) data by BTSbot-nearby and reported to TNS automatically on 2025-07-11 at 08:57:58 (all times in UTC). It was detected in ZTF with Milky Way (MW) reddening corrected g- and r-band magnitudes of 17.10 +/- 0.06 mag and 17.48 +/- 0.06 mag, respectively. At the distance of UGC 11453, these imply absolute magnitudes of Mg=-15.83 mag and Mr=-15.45 mag. At that time, BTSbot-nearby triggered a follow-up request to the SED Machine (SEDM; Blagorodnova+18, Rigault+19, Kim+22) and the Ultraviolet/Optical Telescope (UVOT; Roming+05) aboard the Neil Gehrels Swift Observatory (Swift; Gehrels+04). 

Like prior BTSbot-nearby triggers to Swift/UVOT, the trigger was sent using the new urgency 0 mode (Tohuvavohu+24). This enabled Swift observations to start just over 6 minutes after the BTSbot-nearby trigger (measured from the timestamp of the first non-coadded UVOT exposure, 09:04:01). Below we include a photometry table of co-added UVOT detections. These measurements are not host-subtracted but are corrected for reddening due to the MW line-of-sight. The UVOT V-band measurement is subject to very large uncertainties due, in part, to the lack of a template for subtraction, so we exclude the V-band measurement from the photometry table.

We measure a UVW2-g color of -0.237 mag, indicating the transient is very hot. We have requested further Swift observations to monitor the UV evolution of this source.

SEDM began observing SN 2025qtt 25 minutes after the BTSbot-nearby trigger, obtaining gri photometry and a spectrum. The SEDM spectrum, although difficult to interpret due to its low resolution, shows narrow emission features characteristic of a Type II SN with flash ionization, i.e. the H Balmer series, C IV, and a blend of (likely) He II, C III, and N III. A UH88/SNIFS spectrum taken ~4 hours later by Hoogendam et al. provides a higher resolution view of these features and gives further support to these line identifications. Although these features are characteristic of a Type II SN with flash ionization, a Type IIn classification cannot be definitively ruled out at this time. We encourage further spectroscopic follow-up observations to monitor the evolution of these features and finalize the classification.

Swift also observed SN 2025qtt with the X-ray telescope (XRT; Burrows+05) between 0.3 and 10 keV in photon-counting mode. We analyzed these data using the online tools of the UK Swift Team (https://www.swift.ac.uk/user_objects), which employ the software package HEASoft version 6.32 and methods described in Evans+07 and Evans+09. SN 2025qtt was not detected. The 3-sigma count-rate limit is 0.008 s^-1 (0.3-10 keV). Assuming a power-law with a photon index of Gamma=2 and a Galactic neutral hydrogen column density of 1.2e21 cm^-2 (HI4PI+16), the count-rate limit corresponds to an unabsorbed flux of 3.7e-13 erg cm^-2 s^-1 and a luminosity of 6.6e40 erg s^-1 (all between 0.3-10 keV).

BTSbot is hosted in Kowalski (Duev+19), ZTF’s first-party alert broker, and submits triggers using Fritz, ZTF’s SkyPortal instance (Coughlin+23).

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 Award #2407588 and a partnership including Caltech, USA; Caltech/IPAC, USA; University of Maryland, USA; University of California, Berkeley, USA; University of Wisconsin at Milwaukee, 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, and OKC, University of Stockholm, Sweden. Operations are conducted by Caltech's Optical Observatory (COO), Caltech/IPAC, and the University of Washington at Seattle, USA.

SED Machine is based upon work supported by the National Science Foundation under Grant No. 1106171.

The SkyPortal project acknowledges the generous support of The Gordon and Betty Moore Foundation.

Zwicky Transient Facility access for N.R., S.S., and A.A.M. was supported by Northwestern University and the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). N.R., and A.A.M. are supported by DoE award #DE-SC0025599.