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To: stefano@bicar.it
From: atel@astronomerstelegram.org
Subject: ATel 17473, 17474, 17475
Message-Id: <20251105071737.E2D2628808AB@server.astronomerstelegram.org>
Date: Wed, 5 Nov 2025 02:17:37 -0500 (EST)

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Posted: Within the last 24 hours
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ATEL #17473							     ATEL #17473

Title:	Detection of 1665/1667 MHz OH absorption in 3I/ATLAS
Author:	D. J. Pisano (University of Cape Town), Oleg M. Smirnov (Rhodes
		University &amp; SARAO), Mykola Ivchenko (KTH), Lorenz Roth (KTH),
		Sarah Buchner (SARAO)
Queries:	o.smirnov@ru.ac.za
Posted:	4 Nov 2025; 10:28 UT
Subjects:Radio, Comet

We observed 3I/ATLAS with MeerKAT on 24 October 2025 from UTC 05:17:16-08:29:37,
using the L-band receivers and the NE54M (1.633 kHz channel width) correlator
mode, reaching an rms sensitivity of 1.5 mJy/beam in a 0.3 km/s channel
with a beam size of 40”. Angular separation from the Sun at time of observation
was 3.76 degrees. OH absorption was detected in both the 1665 MHz and 1667
MHz lines.  Gaussian fits to the two lines yielded peak fluxes of -8.4+/-3.1
mJy and -14.2+/-3.4 mJy at -15.59+/-0.16 km/s and -15.65+/-0.17 km/s for
the two lines, respectively. The FWHMs were 0.88+/-0.37 km/s and 1.26+/-0.40
km/s. The integrated fluxes over the two lines are -7.9+/-2.9 mJy km/s
and -19.1+/-5.2 mJy km/s.  The absorption features are consistent with
the expected OH level population due to the heliocentric velocity of the
comet. The detection of OH on 24 October 2025 contrasts with the MeerKAT
non-detection of these lines on 20 September 2025 from 14:36:54-15:39:25
UTC (rms noise of 3 mJy/beam) and 28 September 2025 from 10:00:26-16:55:53
UTC (rms noise of 1 mJy/beam).

The MeerKAT telescope is operated by the South African Radio Astronomy
Observatory, which is a facility of the National Research Foundation, an
agency of the Department of Science, Technology and Innovation. DJP and
OS greatly acknowledge support from the South African Research Chairs Initiative
of the Department of Science, Technology and Innovation and the National
Research Foundation.

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Password Certification: Oleg Smirnov (o.smirnov@ru.ac.za)
https://www.astronomerstelegram.org/?read=17473
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ATEL #17474							     ATEL #17474

Title:	An X-ray upper limit towards CHIME J1634+44 in a radio-active
		state, from Chandra follow-up
Author:	Mason Ng (McGill University; Trottier Space Institute at McGill
		University) for the CHIME/FRB/Pulsar Collaborations
Queries:	mason.ng@mcgill.ca
Posted:	4 Nov 2025; 15:06 UT
Subjects:Radio, X-ray, Transient

CHIME J1634+44 is a long-period radio transient that has recently entered
another radio-active bursting phase (ATels #17434, #17440).

We observed J1634+44 with the ACIS-S instrument aboard Chandra via a DDT
observation for approximately 10 ks, between 2025/10/28 20:18 and 2025/10/28
23:44 (TT). We present results from a preliminary analysis at this point,
and will report detailed analysis in a forthcoming publication.

We do not detect a significant source at (or near) the known source coordinates
at the 3&sigma; level using CIAO/wavdetect. Thus, we derived a preliminary
3&sigma; upper limit on the 0.5-7.0 keV unabsorbed flux of 2.8 &times;
10-15 erg/s/cm2 using the aprates, aplimits, and
modelflux tools in CIAO. This assumes a fiducial power law spectrum with
NH = 0.075 &times; 1022 cm-2 (Dong et
al., 2025, ApJ, 988L, 29) and &Gamma; = 1.7. At a distance of d = 3 kpc,
this corresponds to an upper limit on the 0.5-7 keV luminosity of 3.1 &times;
1030 erg/s.

We thank the Chandra team for promptly scheduling this observation.

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Password Certification: Mason Ng (masonng@mit.edu)
https://www.astronomerstelegram.org/?read=17474
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ATEL #17475							     ATEL #17475

Title:	Spectroscopic Classifications with the SNIFS spectrograph on
		the UH88-inch Telescope
Author:	A. Bridges, Y. Cheng, A. Coffey, A. Gilbert, O. Kangwai (UH
		Hilo), C. Angus (Queen’s University Belfast), W. B. Hoogendam, D.
		O. Jones, M. Kong (IfA, UH Manoa)
Queries:	dojones@hawaii.edu
Posted:	4 Nov 2025; 17:52 UT
Subjects:Supernovae

We report the following classifications from spectroscopic observations
with the SNIFS spectrograph on the UH88 telescope, obtained on 2025 Nov
2 UT through the SCAT survey (Tucker et al. 2022). The targets were supplied
by ATLAS (Tonry et al. 2018) and ZTF (Bellm et al. 2019) and classified
by students in the UH Hilo Stellar Physics Lab course. The classifications
were performed with SNID (Blondin & Tonry, 2007).

Name         | IAU Name   | RA (J2000)  | Dec (J2000)  | z       | Type
| Notes 
ATLAS25nju   | AT2025abva | 22:33:42.67 | -43:41:37.30 | 0.036   | Ia 
| (1) 
ATLAS25ndj   | AT2025abgq | 22:37:02.36 | -18:59:22.08 | 0.04881 | Ia 
| (2) 
ATLAS25nlw   | AT2025abyc | 02:44:25.31 | -24:34:08.58 | 0.02    | II 
| (3) 
ZTF25abzrrhe | AT2025abmd | 04:04:53.45 | +12:40:55.19 | 0.03451 | II 
| (4)

Notes: 
When the redshift is given to 3 decimal places or less, it is derived from
the SN spectrum. Otherwise, the redshift is determined from the host galaxy.

(1) We measure a Si II velocity of -11,900 km/s.  SNID matches are consistent
with a phase slightly before maximum light. 
(2) We measure a Si II velocity of -12,800 km/s using the NED redshift
of 0.04881.  SNID indicates a phase near maximum light. 
(3) Blue continuum with evidence for H-alpha at the approximate, best-fit
SNID redshift of 0.02. 
(4) The listed redshift is from NED.  Blue continuum is present with evidence
for broadened H alpha.

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Password Certification: David Jones (david.jones@ucsc.edu)
https://www.astronomerstelegram.org/?read=17475
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