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To: stefano@bicar.it
From: atel@astronomerstelegram.org
Subject: ATel 17706, 17707
Message-Id: <20260304070539.F3423288084C@server.astronomerstelegram.org>
Date: Wed, 4 Mar 2026 02:05:39 -0500 (EST)

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Posted: Within the last 24 hours
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ATEL #17706							     ATEL #17706

Title:	MAXI/GSC observation of an outburst onset of a Be/X-ray binary
		pulsar GS 1843+00
Author:	M. Nakajima, H. Negoro (Nihon U.), T. Mihara (RIKEN), M. Sugizaki
		(Kanazawa U.), K. Takagi, H. Nishio (Nihon U.), T. Tamagawa, N. Kawai,
		M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, Y. Kawakubo,
		H. Hiramatsu, Y. Kondo, D. Iijima, A. Yoshida (AGU), Y. Tsuboi, H.
		Sugai, N. Nagashima, Y. Ishihara (Chuo U.), M. Shidatsu, C. Kang,
		T. Nakamoto, M. Uenishi, T. Usuki, S. Yatsuzuka (Ehime U.), I. Takahashi,
		Y. Yatsu (Science Tokyo), S. Nakahira, S. Ueno, H. Tomida, S. Ogawa,
		M. Kurihara (JAXA), Y. Ueda, K. Fujiwara, S. Kobayashi (Kyoto U.),
		M. Yamauchi, M. Nishio, C. Hiraizumi (Miyazaki U.), K. Yamaoka (Nagoya
		U.), W. Iwakiri (Chiba U.), T. Kawamuro (Osaka U.), S. Yamada (Tohoku
		U)
Queries:	nakajima.motoki@nihon-u.ac.jp
Posted:	3 Mar 2026; 13:25 UT
Subjects:X-ray, Binary, Neutron Star, Transient, Pulsar

GS 1843+00 (Ginga 1843+009) is a Be/X-ray binary hosting a 29.5-s X-ray
pulsar (Israel et al. 2001).  This source was discovered by Ginga in 1988
(Makino 1988, IAUc. 4583), and several X-ray outbursts have since been
observed by Ginga, RXTE, Swift, INTEGRAL and MAXI.  Following the major
outburst in 2009 March (ATel #1959, #1973, #1977) and two subsequent minor
outbursts in 2009 November and 2010 March, no significant X-ray activity
has been reported for the past 16 years.

On 2026 February 27 (MJD 61098), MAXI/GSC detected a weak X-ray enhancement
from a position consistent with that of GS 1843+00. The latest MAXI/GSC
public data (https://maxi.riken.jp/v7l3h/J1845+008/index.html) show that
the current brightening began on 2026 February 19 (MJD 61090) and the daily
averaged 2-20 keV flux reached 0.099 &plusmn; 0.016 photons s-1
cm-2 (28 &plusmn; 4 mCrab) on March 1 (MJD 61100). After 16
years of quiescence, we confirm that GS 1843+00 has resumed X-ray activity.

The average flux increase rate over the past 5 days is 0.012 photons s-1
cm-2 day-1 (3 mCrab day-1). The current
brightening behavior resembles that of the previous event observed in 1997
February by RXTE/ASM. If the present outburst follows the evolution of
the previous brightening, it is expected to peak around 2026 March 16 (MJD
61115). Follow-up observations are encouraged to clarify the nature of
this source.

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Password Certification: Motoki Nakajima (nakajima.motoki@nihon-u.ac.jp)
https://www.astronomerstelegram.org/?read=17706
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ATEL #17707							     ATEL #17707

Title:	Fermi J1820-1648: Upper limits from a neutrino search with
		IceCube
Author:	Yuhua Yao (University of Wisconsin-Madison), Justin Vandenbroucke
		(University of Wisconsin-Madison) for the IceCube Collaboration
Queries:	justin.vandenbroucke@wisc.edu
Posted:	3 Mar 2026; 23:31 UT
Subjects:Neutrinos, Nova, Transient

The IceCube Collaboration (http://icecube.wisc.edu/) reports:

IceCube has performed a search for track-like muon neutrino events arriving
from the direction of Fermi J1820-1648, a transient in the Galactic plane,
following reports from Fermi LAT (ATels #17688, #17699), SOAR (ATel #17700)
and other optical observations (ATels #17689,  #17698), as well as SMA
(ATel #17704). We searched in the time range of two weeks (2026-02-04 00:00:00.00
UTC to 2026-02-18 00:00:00.00 UTC), during which IceCube was collecting
good quality data.

For this search, we report a p-value of 1.0 with respect to an atmospheric
background-only hypothesis. We accordingly derive a time-integrated muon-neutrino
flux upper limit for this source of E^2 dN/dE = 0.23 GeV cm^-2 at 90% CL,
under the assumption of an E^-2 power law. 90% of events IceCube would
detect from a source at this declination with an E^-2 spectrum are between
approximately 40 TeV and 20 PeV.

The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector
operating at the geographic South Pole, Antarctica. The IceCube realtime

alert point of contact can be reached at roc@icecube.wisc.edu.

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Password Certification: Justin Vandenbroucke (justin.vandenbroucke@wisc.edu)
https://www.astronomerstelegram.org/?read=17707
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