PRIME discovery and SOAR confirmation of a very bright symbiotic nova PRIME25aaghjd near the Galactic center

ATel #17426; R. Hamada (UOsaka), K. De (Columbia), D. Suzuki (UOsaka), T. Sumi (UOsaka), A. Idei (UOsaka), S. Makida (UOsaka), T. Nagano (UOsaka), S. Nakayama (UOsaka), R. Ogawa (UOsaka), Y. Okumoto (UOsaka), Y. K. Satoh (Kanto Gakuin U), T. Tamaoki (UOsaka)
on 30 Sep 2025; 04:06 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Kishalay De (kde1@mit.edu)

Tweet

We report the discovery and spectroscopic classification of a very bright NIR transient during the Galactic bulge survey carried out by the PRime-focus Infrared Microlensing Experiment (PRIME). PRIME is a 1.8m telescope with 1.56 square degree FOV (0.5 arcsec/pixel) located in Sutherland, South Africa at the South African Astronomical Observatory (Sumi et al. 2025). PRIME25aaghjd was first detected as a candidate transient generated in our custom image reduction and subtraction pipeline based on the ZOGY algorithm (Zackay et al. 2016, De et al. 2020) at a H-band mag of 8.7 +/- 0.1 mag (in the Vega system) on UT 2025-02-16, and at J2000 coordinates

RA 17:48:14.63
Dec -29:51:18.95

The transient is located ~1.1 degrees away from the Galactic center, with a corresponding integrated line of sight extinction of ~8 mags in V-band (Schalfly et al. 2011). We caution that the first detection of the transient was brighter than the nominal saturation level of the detector, and immediately after the resumption of Galactic bulge 2025 observations; therefore the transient erupted likely before and was brighter than the quoted measurement. The source is coincident with a faint IR source in the archival VVV catalog within ~ 1” with a magnitude of H = 14.1 +/- 0.1 mag. The implied amplitude of the outburst is > 5 mags. Subsequent detections of the source indicate a monotonically fading light curve, decaying to H ~ 14.0 mag by 2025-07-31.

On UT 2025-09-28, we obtained a near-infrared spectrum of the source with the Triplespec spectrograph on the SOAR telescope as part of our Target of Opportunity Program (SOAR 2025B-002; PI: De). The reduced spectrum shows a red continuum peaking in H-band, with broad emission lines of He I, Pa gamma and Pa beta with FWHM ~ 1100 km/s. On top of the continuum, we detect strong CO absorption in the first overtone near 2.29 micron, indicative of a cool red giant spectrum. The combination of broad emission lines, cool giant spectrum and quiescent IR counterpart suggest the source to be a new symbiotic nova (e.g. Mikolajewska 2010, Munari 2024) towards the Galactic center.

We encourage multi-wavelength follow-up of the source. We thank the AEON observers at the SOAR telescope for carrying out these observations.