AstroNote 2025-208

BTSbot-nearby (Rehemtulla+25) is a follow-up program designed to autonomously send time-of-opportunity (ToO) requests for nearby (d<~60 Mpc) infant supernovae (SNe) found by BTSbot (Rehemtulla+24) in ZTF (Bellm+19) data.

SN 2025qpk (ZTF25abadtsx) is a Type Ia in UGC 11622 (z=0.01377, d~61 Mpc; Theureau+17). It was first reported to TNS automatically after being identified by BTSbot-nearby on 2025-07-07 at 06:26:15 UTC. At that time, BTSbot-nearby triggered a follow-up request to the SED Machine (SEDM; Blagorodnova+18) and the Ultraviolet/Optical Telescope (UVOT; Roming+05) aboard the Neil Gehrels Swift Observatory (Swift; Gehrels+04). SEDM began observing SN 2025qpk 20 minutes later, obtaining gri photometry and a spectrum. The UVOT request was sent using the new urgency 0 mode (Tohuvavohu+24), meaning no manual validation of the trigger was necessary before it was sent to the spacecraft for execution. This novel functionality enabled extremely low-latency UV follow-up; space-based observations occurred only 59 minutes after the BTSbot-nearby trigger from the ground.

The SEDM spectrum shows features standard to normal Type Ia SNe, including Si II and S II. We estimate the velocity of the Si II 6355 A feature to ~22,000 km/s. The Ca II near-infrared triplet is marginally visible at a similar velocity. Using Next Generation SuperFit (NGSF; Goldwasser+22) with the redshift fixed to that of the host galaxy, we find a match to SN 2011fe at a phase of 16.7 d before peak (see the attached image). The low resolution of the SEDM spectrum limits what can be learned, so we encourage further follow-up observations.

The reduced UVOT images reveal there is little-to-no SN flux present in the UV (see the attached image with the SN position marked by the red circle). Host subtraction in the UV is not currently possible as there are no prior UVOT images of this field, however, we will obtain UV template images after the SN has faded to perform subtraction and recover SN flux measurements from these images. We have requested further Swift observations to monitor the UV light curve over the next three days.

Swift also observed SN 2025qpk 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 2025qpk was not detected. The 3-sigma count-rate limit is 0.005 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 5.1e20 cm^-2 (HI4PI+16), the count-rate limit corresponds to an unabsorbed flux of 1.9e-13 erg cm^-2 s^-1 and a luminosity of 8.2e40 erg s^-1 (all between 0.3-10 keV).

The discovery and follow-up of SN 2025qpk is a pioneering demonstration of a fully autonomous system – in part, enabled by AI tools – which is capable of commanding observatories on the ground and in space. This system is built on a myriad of infrastructure innovations, particularly those by the teams maintaining and improving Swift and SkyPortal. We believe similar workflows will hold a critical place in the coming Rubin and Roman eras of time-domain astronomy, particularly in the study of young and rapidly evolving transients such as infant SNe. BTSbot-nearby will continue automatically triggering SEDM, Swift/UVOT and other facilities for new infant SN discoveries; starting in 2025B, BTSbot-nearby will also trigger rapid ToOs to Gemini-N/GMOS.

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.