AstroNote 2025-46

BTSbot-nearby (Rehemtulla+25) is a follow-up program designed to fully autonomously send target-of-opportunity requests for nearby (d<60 Mpc) infant SNe found by BTSbot (Rehemtulla+24) in ZTF (Bellm+19) data. Here, we report on BTSbot-nearby follow-up of four recent SNe (2025ay, 2025mg, 2025oq, 2025aml) with the SED Machine (SEDM; Blagorodnova+18).

SN 2025ay (ZTF25aaaprdb) is a Type Iax at d=51.5 Mpc (Saulder+16). It was first reported to TNS automatically after being identified by BTSbot-nearby on 2025-01-04 at 10:28:43 UT. At that time, BTSbot-nearby triggered a follow-up request to SEDM, which obtained a spectrum 23 minutes later (10:51:49). Due to the low resolution and the proximity of 2025ay to its very bright host, the SEDM spectrum is heavily contaminated by light from the host galaxy. Still, we tentatively detect Si II at ~5,000 km/s, which is consistent with later higher quality spectra.

SN 2025mg (ZTF25aabxywm) is a Type II at d=47.6 Mpc (Tully+13). It was first discovered and reported to TNS by Muñoz-Arancibia et al. on 2025-01-15 at 12:16:55 UT. The following night 2025-01-16, it was identified and triggered on by BTSbot-nearby at 03:05:05. Just six and a half minutes later (03:11:31; ~15 hours after the first TNS report), SEDM began observing 2025mg. The spectrum shows broad Halpha and Hbeta features atop a blue continuum.

SN 2025oq (ZTF25aaccmjq) is a Type Ic at d=35.2 Mpc (Bottinelli+86). It was first discovered and reported to TNS by O’Neill et al. on 2025-01-17 at 06:29:25 UT using data from the GOTO survey. The first report using ZTF data came ~7.5 hours later from Muñoz-Arancibia et al. at 14:08:16. BTSbot-nearby identified and triggered SEDM on 2025oq at 08:20:16 (~6 hours before the first ZTF report), and SEDM began its observation 80 minutes later at 09:40:19. The spectrum does not show any clearly identifiable features, only a blue continuum. 

SN 2025aml (ZTF25aadhlrs) is a Type II at d=43.7 Mpc (Tully+13). It was first reported to TNS automatically after being identified and triggered on by BTSbot-nearby on 2025-01-31 at 03:59:06 UT. The SEDM spectrum was taken ~20 minutes later at 04:19 UT. There is a pipeline issue delaying the spectrum’s reduction, but an LT/SPRAT spectrum shortly afterwards (Wise et al.) shows a blue continuum with narrow He II 4686A emission, suggestive of a young Type II SN.

In all four cases, the spectra triggered by BTSbot-nearby are the earliest available spectra of these targets. The attached figure is an adaptation of Figure 1 of Rehemtulla+25, showing the spectroscopic follow-up latencies of these targets in context. All spectra will be made available on WISeREP. In 2025A, BTSbot-nearby will automatically trigger the SOAR 4-m telescope through a NOIRlab program (PI Rehemtulla).

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

This report is 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 Grant No. AST-2034437 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, Deutsches Elektronen-Synchrotron and Humboldt University, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, Trinity College Dublin, Lawrence Livermore National Laboratories, and IN2P3, France. Operations are conducted by COO, IPAC, and UW.

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