The Astronomer's Telegram: Top ATels

For reporting and commenting upon new observations of astronomical transients by the professional astrophysics community.

ATel 18115: Detection of a thermonuclear X-ray burst from XTE J1810-189 with NuSTAR during its October 2026 outburst

We report preliminary timing and spectral results from NuSTAR and Neil Gehrels Swift Observatory/XRT observations of the neutron star low-mass X-ray binary XTE J1810 & minus;189 during its ongoing October 2026 outburst. ...
https://www.astronomerstelegram.org/?read=18115
date: 2026-10-21T19:29:03-00:00
creator: Manoj Mandal, Sachindra Naik, Jaya Chowdhury, Souvik Manik, Sabyasachi Pal, Aman Kaushik, Sudip Bhattacharyya, Andrea Sanna, Gaurava K. Jaisawal

ATel 18114: Betelgeuse 2026 dimming is stopping at magnitude 1.0 at mid October

Betelgeuse is the closest red supergiant, and a first magnitude star, known since antiquity, lying in the constellation of Orion. In 1603 (ATel#16001) it has been classified as the brightest star of Orion by Johannes Bayer (Uranometria, Augusta, 1603) and it is the alpha star in Orion, even if -averagely- its visual magnitude is 0.45 while Rigel (beta Orionis) outshines Betelgeuse with 0.13 mag. ...
https://www.astronomerstelegram.org/?read=18114
date: 2026-10-21T10:30:31-00:00
creator: Costantino Sigismondi, Fabio Mariuzza, Wolfgang Vollmann, Andrea Brucato, Andrea Reguitti

ATel 18113: Spectroscopic Classification of AT 2026abza with the Lick Shane Telescope

We report the classification of AT2026abza from spectroscopic observations with the Kast spectrograph on the Shane telescope obtained on 2026 October 3 UT. ...
https://www.astronomerstelegram.org/?read=18113
date: 2026-10-19T17:18:49-00:00
creator: J. Karcheski, K. C. Patra, R. Kaur, R. J. Foley, H. Abunemeh

ATel 18112: XRISM/Xtend Transient Search (XTS) detected an X-ray flare possibly from 1eRASS J053652.4+211435

XRISM/Xtend Transient Search (XTS) detected an X-ray flare from an X-ray source XRISM J0537+2115 on 2026-10-08 TT. The source position was determined to be (R.A., Dec.) = (84.223, 21.247), with a systematic error of & sim; 40 arcsec. ...
https://www.astronomerstelegram.org/?read=18112
date: 2026-10-19T13:01:26-00:00
creator: A. Yoshimoto, Y. Maeda, T. Hakamata, Y. Kanemaru, A. Miyamoto, Y. Omiya, Y. Uchida, T. Yoneyama, M. Audard, E. Behar, K. Fukushima, K. Hasegawa, H. Iinuma, S. Inoue, Y. Ishihara, N. Ishii, S. Ishiwata, C. Kang, R. Kawada, M. Kikuchi, T. Kiyomoto, T. Kohmura, H. Kuramoto, W. Lee, H. Matsumoto, A. Miyamoto, M. Mizumoto, Y. Motogami, H. Murakami, T. Narita, M. Nobukawa, H. Noda, S. Ogawa, K. Sakamoto, Y. Sakamoto, M. Shidatsu, H. Takahashi, T. Takagi, S. Takatsuka, F. Takisawa, Y. Terada, Y. Terashima, Y. Tsuboi, A. Uchida, H. Uchida, T. Usuki, M. Yoshimoto

ATel 18111: MAXI/GSC detection of an X-ray flares from UX Ari on 2026-10-17 UT

At 07:20 on 2026-10-17 UT, the MAXI/GSC nova alert system triggered on a source at a position consistent with that of the RS CVn star UX Ari. The light curve showed two peaks. ...
https://www.astronomerstelegram.org/?read=18111
date: 2026-10-19T09:55:07-00:00
creator: Y. Ishihara, H. Ogaki, S. Yatsuzuka, T. Mihara, W. Iwakiri, H. Negoro, M. Nakajima, K. Saito, T. Yokoyama, M. Wada, A. Aoyama, M. Ota, T. Tamagawa, N. Kawai, M. Matsuoka, T. Sakamoto, M. Serino, S. Sugita, Y. Kawakubo, H. Hiramatsu, T. Kato, A. Yoshida, Y. Tsuboi, M. Shidatsu, C. Kang, M. Uenishi, T. Usuki, H. Aoe, I. Takahashi, Y. Yatsu, S. Nakahira, S. Ueno, H. Tomida, M. Kurihara, Y. Ueda, K. Fujiwara, S. Kobayashi, M. Yamauchi, M. Nishio, C. Hiraizumi, K. Yamaoka, M. Sugizaki, T. Kawamuro, S. Yamada, S. Ogawa

ATel 18110: Spectroscopic Classification of Astrophysical Transients with KCWI on the Keck II Telescope

We report the classifications of astrophysical transients from spectroscopic observations with the Keck Cosmic Web Imager (KCWI) on the Keck II telescope obtained on 2026 October 15 UT. ...
https://www.astronomerstelegram.org/?read=18110
date: 2026-10-19T00:46:36-00:00
creator: R. Kaur, R. J. Foley, T. Murphey

ATel 18109: uGMRT Radio Detection of the X-ray Binary 4U 1630-47 during 2026 outburst

We report a radio detection of the black hole X-ray binary 4U 1630-47 with the upgraded Giant Metrewave Radio Telescope (uGMRT) on 2026 September 27. The source was observed for approximately 1 hour in Band 4, with an on-source integration time of 17 minutes. ...
https://www.astronomerstelegram.org/?read=18109
date: 2026-10-18T19:41:13-00:00
creator: Sayantan Bhattacharya, Maxime Parra, Jyotirmoy Dey, Sudip Bhattacharyya, Isabella Mariani, Noa Grollimund

ATel 18108: The CSS quasar 3C 138 is still in a very bright optical state

In the last nights the compact steep-spectrum (CSS) quasar 3C 138 (a.k.a. QSO B0518+165, 4FGL J0521.2+1637) at R.A. 80.292 deg, Dec. +16.629 deg (J2000.0) and z=0.759 (Lynds et al. ...
https://www.astronomerstelegram.org/?read=18108
date: 2026-10-17T22:01:58-00:00
creator: Alessandro Marchini ; Leonardo Stiaccini, Gaia Verna, University of Siena - Italy); Giacomo Bonnoli ; Pierfrancesco Basile, Pioltello - Italy)

ATel 18107: Independent Discovery of a Probable Nova in M81, M81N 2026-10a

We report the discovery of a probable nova in M81 on a co-added 3180-s unfiltered CMOS frame taken on 2026 Oct. 15.165 UT with the 0.65-m telescope at Ondrejov under cloudy conditions. ...
https://www.astronomerstelegram.org/?read=18107
date: 2026-10-16T19:23:50-00:00
creator: K. Hornoch, H. Kucakova, A. W. Shafter

ATel 18106: Superhumps in Gaia19bnd: a newly identified SU UMa-type dwarf nova

Based on its long-term light curve, we identified Gaia19bnd/AT 2019dyn as a candidate SU UMa-type dwarf nova. Its outburst activity is characterized by frequent short outbursts and longer, brighter events, likely superoutbursts, lasting approximately 11-13 days. ...
https://www.astronomerstelegram.org/?read=18106
date: 2026-10-16T09:34:20-00:00
creator: D. Yu. Rusanova, A. O. Simon, S. Dufoer, F.-J. Hambsch, S. Kurowski, S. Fisek, S. Otken, A. Popowicz, A. Yu. Korosko, P. J. Mikolajczyk, L. Wyrzykowski, K. Kotysz, W. Ogloza, N. Karaman, J. M. Carrasco, D. Athanasopoulos, K. Vrontaki, E. Gkiokas, J. K.T. Qvam, R. A. Street, A. Pucek, W. Skrobacz, J. Kolar