Low-resolution SALT RSS spectroscopy using grism GR0300 (3900A - 10000A, 1800s) of the recently announced transient AT2022kms (ATLAS2022olj, Tonry et al., 2022TNSTR1404....1T; Smith et al. 2022TNSAN.115....1S; Groot et al., 2022TNSAN.117....1S) in NGC 55, taken at (start time) 03:24:21 UTC; JD = 2459724.64189, shows a moderately blue continuum, superposed with strong emission lines of the Balmer series, and weaker emission features of HeI and FeII. The Balmer H-alpha line shows a total full-width-at-half-maximum (FWHM) of 20.8A, corresponding to 950 km/s. Correcting for instrumental broadening leaves a corrected value of FWHM~740 km/s. Other lines are not-resolved.
The spectrum lacks the [CaII] emission typical for an Intermediate-Luminosity Red Transient (ILRT), ruling out this classification. The spectrum is reminiscent of the confirmed LNR NGC4490-2011OT1 (Pastorello et al., 2019, A&A 625, L8).
The combination of the slow rise in the lightcurve reported by Smith et al. and Groot et al., in combination with the current spectrum, strongly suggests a Luminous Red Nova before merger maximum. We expect the source to further brighten by an additional 3-8 magnitudes on a timescale of weeks. Regular monitoring in all wavebands is strongly encouraged.
Data obtained under the SALT transient program (2021-2-LSP-001). We thank the SALT Operations Team for their fast reaction time to the alert.
| Catalog | Name | Reported RA | Reported DEC | Reported Obj-Type | Reported Redshift | Host Name | Host Redshift | Remarks | TNS RA | TNS DEC | TNS Obj-Type | TNS Redshift |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| TNS | 2022kms [ATLAS22olj] | 00:15:14.619 | -39:13:22.27 | 00:15:14.669 | -39:13:22.47 |