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To: stefano@bicar.it
From: atel@astronomerstelegram.org
Subject: ATel  17957, 17958, 17959
Message-Id: <20260812070809.9601D28808DD@server.astronomerstelegram.org>
Date: Wed, 12 Aug 2026 03:08:09 -0400 (EDT)

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Posted: Within the last 24 hours
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ATEL #17957							     ATEL #17957

Title:	LHAASO-WCDA Detection of Strong TeV Flaring Activity from the
		Radio Galaxy NGC 1275
Author:	Guangman Xiang (IHEP),Shicong Hu(IHEP), Min Zha (IHEP), Zhiguo
		Yao (IHEP), Jianeng Zhou (SHAO) and Yi Xing (SHAO) report on behalf
		of the LHAASO Collaboration
Queries:	gmxiang@ihep.ac.cn
Posted:	11 Aug 2026; 14:11 UT
Subjects:Gamma Ray, TeV, VHE, AGN

We report the detection of very-high-energy (VHE, E > 100 GeV) gamma-ray
emission from the radio galaxy NGC 1275 (3C 84,z = 0.017) with the Large
High Altitude Air Shower Observatory (LHAASO) - Water Cherenkov Detector
Array (WCDA).

Recent Fermi-LAT observations have revealed enhanced gamma-ray flaring
activity from this object (ATel #17937, #17943), and the source is presently
in an exceptionally bright optical state (ATel #17955).

The VHE flaring activity was detected by the LHAASO-WCDA real-time alert
system. During the time window MJD 61261.81-61262.15, a preliminary analysis
yields an excess at the radio position of NGC 1275 with TS = 74.7 (~7.8
sigma). The preliminary observed spectrum in the ~0.4-7.5 TeV range is
well described by a power law with photon index 2.98 +/- 0.17 (statistical
errors only), corresponding to an integral flux above 1 TeV of ~ 0.6 Crab
units.

Given the current high flux state of NGC 1275 across the gamma-ray, VHE,
and optical bands, multi-wavelength follow-up observations are strongly
encouraged.

LHAASO is a multi-purpose Extensive Air Shower (EAS) array designed to
detect air showers induced by gamma rays and cosmic rays from sub-TeV energies
to above 1 PeV.

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Password Certification: Guangman Xiang (gmxiang@ihep.ac.cn)
https://www.astronomerstelegram.org/?read=17957
==============================================================================
ATEL #17958							     ATEL #17958

Title:	MAXI/GSC detection of an X-ray outburst from GK Per
Author:	T. Mihara (RIKEN), H. Negoro, M. Nakajima, K. Saito, T. Yokoyama,
		M. Wada (Nihon U.),  T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T.
		Sakamoto, M. Serino, S. Sugita, Y. Kawakubo, H. Hiramatsu, A. Yoshida
		(AGU),  Y. Tsuboi, Y. Ishihara, H. Ogaki (Chuo U.), M. Shidatsu, C.
		Kang, M. Uenishi, T. Usuki, S. Yatsuzuka, H. Aoe (Ehime U.), I. Takahashi,
		Y. Yatsu (Science Tokyo),  S. Nakahira, S. Ueno, H. Tomida, M. Kurihara
		(JAXA), Y. Ueda, K. Fujiwara, S. Kobayashi (Kyoto U.), M. Yamauchi,
		M. Nishio, C. Hiraizumi (Miyazaki U.),  K. Yamaoka (Nagoya U.), M.
		Sugizaki (Kanazawa U.), W. Iwakiri (Chiba U.), T. Kawamuro (Osaka
		U.), S. Yamada (Tohoku U), S. Ogawa (TUS)
Queries:	tmihara@riken.jp
Posted:	11 Aug 2026; 23:46 UT
Subjects:X-ray, Binary, Cataclysmic Variable, Nova, Transient

The MAXI/GSC nova alert system triggered on an X-ray brightening from a
position consistent with the white dwarf binary GK Per (intermediate polar
and dwarf nova) 
on 2026 August 9 (MJD 61261) 08:23 UT. The one-day-averaged flux was 40
&plusmn; 10 mCrab in 4-10 keV of 8 good scans between August 8 10:43 -
August 9 8:23 UT. 
Prior to this trigger, the source kept no detection by the MAXI/GSC since
2026 August 2 (MJD 61254). 
Before that, it was 
no detection in 2026 May 21 (MJD 61181) - July 4 (MJD 61225), and 
lack of observation in July 5 (MJD 61226) - August 1 (MJD 61253).

Note that the AAVSO V-band data started to brighten on 2026 July 7 (61228
MJD), and reached 2.5 magnitude brighter state on August 11 (MJD 61263)
than the quiescent.

Multi-wavelength follow-up observations are encouraged.

The latest X-ray light-curve can be checked at

MAXI HP ( https://maxi.riken.jp/pubdata/v7.7l/J0331+439/index.html ).

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Password Certification: Tatehiro Mihara (mihara@crab.riken.jp)
https://www.astronomerstelegram.org/?read=17958
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ATEL #17959							     ATEL #17959

Title:	OHP/MISTRAL optical spectroscopic followup of NGC1275
Author:	Christophe Adami (LAM/Pytheas/AMU), Emeric LeFloc&#39;h (CEA/Irfu)
		report on behalf of a larger collaboration:
Queries:	christophe.adami@lam.fr
Posted:	12 Aug 2026; 03:40 UT
Subjects:Optical, AGN

Following the recent alerts given in ATel#17937, #17943, #17955 and #17957
describing the exceptional bright state of NGC1275, we observed this galaxy
using the T193cm telescope at Observatoire de Haute-Provence (France) with
the MISTRAL spectro-imager.

We first made a 5 minutes image of NGC1275 in i'-band, starting at 20260812_002945UT.
No new sources was visible as compared to the PanStarrs i-band image. We
then made a 1h spectroscopic exposure (3x20min) on the core of NGC1275
(with a North-South orientation of the slit and an aperture of 2.5arcsec,
similar to the seeing) starting at 20260812_0033UT and ending at 20260812_0135UT.
We compared this spectrum with the public NED-available other spectra in
the same wavelength range.

In a preliminar analysis, we detect the same strong emission lines as e.g.
Oxygen and Balmer lines. A few more weak lines seem to appear (observed
e.g. at 6502, 6527, 6534, 6540, 6740, 6918, 6972A) without being clearly
identified to elements present in http://astronomy.nmsu.edu/drewski/tableofemissionlines.html.

The Hgamma emission line also appears broader in the MISTRAL data as compared
to older spectra. The main difference, however, is the now stronger HBeta
(stronger than e.g. [OIII]b), and a new large wing toward the blue part
of the line extending over ~100A when we compare our spectrum more specifically
with the NED 2009 public spectrum (TNG/LRS).

We encourage other optical observations to confirm these apparent changes.

We acknowledge the excellent support from Observatoire de Haute-Provence
and in particular Yoann Larralde Erasun.

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Password Certification: Christophe Adami (christophe.adami@lam.fr)
https://www.astronomerstelegram.org/?read=17959
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