Gaia22alz (ATel)
Slowest classical nova ever observed and early premaximum spectra were obtained.
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============================================================================== ATEL #15355 ATEL #15355
Title: Intriguing developments in the slowly rising Galactic optical transient Gaia22alz (AT2022bpq) Author: E. Aydi, K. V. Sokolovsky, J. Strader, L. Chomiuk, A. Kawash (MSU), J. Brink, D. A. H. Buckley (SAAO/UCT), M. Orio (UoW/INAF), J. Mikolajewska (NCAC), K. Z. Stanek, C. S. Kochanek (OSU), and B. J. Shappee (Univ. of Hawaii) Queries: aydielia@msu.edu Posted: 29 Apr 2022; 21:18 UT Subjects:Optical, Ultra-Violet, X-ray, Binary, Cataclysmic Variable, Nova, Star, Transient, Variables
We report on multi-wavelength follow up of the slowly rising Galactic optical transient Gaia22alz (AT2022bpq), which was discovered by Gaia on 2022-02-04.2UT (https://www.wis-tns.org/object/2022bpq). Earlier follow up by Brink et al. (ATel #15270) on 2022-03-11 reported optical spectra dominated by emission lines of Balmer, He II, He I, and C IV, characterized by a FWHM of around 400-500 km/s. Based on photometry from the All-Sky Automated Survey for SNe (ASAS-SN; Shappee et al. 2014, ApJ, 788, 48S and Kochanek et al. 2017PASP, 129, 4502) the transient, which started around 2022-01-25, is still rising slowly and reached a magnitude g = 13.1 on 2022-04-29 (see below a link to the latest ASAS-SN light curve). In archival data from the Dark Energy Camera Plane Survey (DECaPS; Schlafly 2018, ApJs 234, 39) the source has a pre-outburst magnitude g = 18.9, implying a current outburst amplitude of 5.8 mag.
We have obtained a series of low-, medium-, and high-resolution optical spectra on 2022-03-15, 04-03, 04-09, 04-10, 04-14, and 04-21 using the Goodman spectrograph (Clemens et al. 2004, SPIE, 5492, 331) on the 4.1-m SOAR telescope (Cerro Pachon, Chile) and the High Resolution Spectrograph (HRS; Crause et al. 2014, Proc. SPIE, 91476) mounted on the 11-m Southern African Large Telescope as part of the SALT Large Science Program on Transients. The spectrum obtained on 2022-03-15 showed similar features to the ones reported in Brink et al. (ATel #15270). However, from 2022-04-03 onwards, the spectra showed dramatic changes with the He II and C IV emission lines fading considerably, and the Balmer and He I lines developing prominent P Cygni absorption profiles at blueshifted velocities of 1700-1800 km/s, indicating the presence of an optically thick outflow. The spectra at this stage resemble those of classical novae before optical peak, but further follow up are required to determine the nature of this event. The slowly rising light curve and the spectral changes make this an interesting transient and multi-wavelength follow up are highly encouraged.
Based on the absorption by diffuse interstellar bands (DIBs) and the empirical relations from Friedman et al. 2011 (ApJ 727, 33), we derive E(B-V) = 1.5 mag and Av = 4.65 mag, assuming Rv = 3.1. This is higher than the estimate of Av = 3.472 mag from the Schlafly et al. (2011, ApJ 737, 1035) Galactic reddening maps.
The Neil Gehrels Swift Observatory observed Gaia22alz for 0.7ks on 2022-04-20.53 (JD 2459690.03). Swift/XRT detected no X-ray source at the position of the nova with an upper limit of 0.003 +/-0.002 cts/s. Assuming emission by a kT= 2 keV thermal plasma and an HI column density of 76.10x10^20 cm^-2 (Kalberla et al. 2005 A&A, 440, 775) this translates to an unabsorbed 0.3-10.0 keV flux limit of 7x10^-13 ergs/cm^2/s. An ultraviolet source is detected at the position of the transient by Swift/UVOT with UVW2 magnitude = 15.01 +- 0.03 (Vega system).
The ASAS-SN sky patrol light curve can be found here: https://asas-sn.osu.edu/sky-patrol/coordinate/cef95f4e-66e7-4a2b-ad65-608ca3...
This ATel is based on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of MCTIC/LNA, the U.S. NSF's NOAO, UNC, and MSU. We also acknowledge ESA Gaia, DPAC and the Photometric Science Alerts Team (<a href="http://gsaweb.ast.cam.ac.uk/alerts">http://gsaweb.ast.cam.ac.uk/alerts</a>).
We thank the Neil Gehrels Swift Observatory team and PI, Brad Cenko, for rapid scheduling these ToO observations.
The Dark Energy Camera Plane Survey (DECaPS; NOAO Proposal ID 2016A-0323 and 2016B-0279, PI: D. Finkbeiner) includes data obtained at the Blanco telescope, Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory (NOAO).
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