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To: stefano@bicar.it
From: atel@astronomerstelegram.org
Subject: ATel  17274, 17275
Message-Id: <20250707071223.25B39288079F@server.astronomerstelegram.org>
Date: Mon,  7 Jul 2025 03:12:23 -0400 (EDT)

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Posted: Within the last 24 hours
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ATEL #17274							     ATEL #17274

Title:	Detection of bursts from FRB 20250613A down to 300 MHz with
		uGMRT
Author:	Yash Bhusare (NCRA -TIFR, India), Yogesh Maan (NCRA - TIFR),
		Ajay Kumar (NCRA - TIFR), Banshi Lal (NCRA - TIFR), Tarraneh Eftekhari
		(Northwestern University), and Shami Chatterjee (Cornell University)
Queries:	ybhusare@ncra.tifr.res.in
Posted:	6 Jul 2025; 09:10 UT
Subjects:Radio, Fast Radio Burst

Using the upgraded Giant Metrewave Radio Telescope (GMRT), we report the
detection of 10 bursts from repeating fast radio burst FRB 20250613A that
was recently discovered by the ASKAP team (Atel #17257). Observations were
carried out from 2:30 to 5:30 UTC at Band 3 (300 - 500 MHz) on 2025 July
02 and at Band 4 (550 - 750 MHz) on 2025 July 03 (2:30 to 5:30 UTC). The
on-source time was 86 minutes at Band 3 and 123 minutes at Band 4. Filterbank
data were recorded from a phased-array beam and searched using the TransientX
pipeline above a S/N threshold of 8 and at a single DM of 174.6 pc cm^-3
(as reported by the ASKAP team; Atel #17257). A more comprehensive search
using coherently dedispersed and high time resolution data, over a range
of DMs, is currently underway.

In Band 3 observations, we detected six bursts, with the emission in one
of the bursts extending up to the lower edge of the band at 300 MHz. In
Band 4 observations, we detected four bursts. Burst signal-to-noise (S/N)
ratios range from 8 to 22 at Band 3 and from 11 to 44 at Band 4. Using
the measured widths and S/N values from TransientX along with the radiometer
equation, the burst fluences range from 0.5 to 2.5 Jy ms. The measured
pulse-widths range between 1.5 ms and 22.3 ms. We also measured structure-optimised
DMs of 174.72 +/- 0.09 and 174.75 +/- 0.12 pc cm^-3 for the brightest burst
detected in Band 4 and Band 3, respectively, using DM_phase.

Detection of these new bursts shows that the emission from FRB 20250613A
extends to frequencies as low as 300 MHz, and confirms continued activity
of the source. We encourage further multi-frequency monitoring and especially
observations at even lower radio frequencies.

We thank the observatory for prompt scheduling of our observations and
the GMRT staff for their support. The GMRT is operated by the National
Centre for Radio Astrophysics of the Tata Institute of Fundamental Research.

Dynamic spectra of a few bursts: https://drive.google.com/drive/folders/1E3S8_4kvM7bSx7KY2VU9H8bVL1wcjFuC?usp=sharing
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Password Certification: Yogesh Maan (maan@astron.nl)
https://www.astronomerstelegram.org/?read=17274
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ATEL #17275							     ATEL #17275

Title:	Follow up observations of interstellar comet 3I/ATLAS
Author:	M. Minev (IA and NAO, BAS, Bulgaria), A. Kostov (IA and NAO,
		BAS, Bulgaria), A. Mutafov (IA and NAO, BAS, Bulgaria)
Queries:	CorrespondingAuthor&#39;sEmailAddress
Posted:	6 Jul 2025; 21:14 UT
Subjects:Optical, Comet

Following the current alerts from ATel#17263 and ATel#17264 we perform
2 hours of observations of the newly discovered interstellar comet 3I/ATLAS.
The observations were carried out at two of the telescopes of the National
Astronomical Observatory - Rozhen - 1.5m ASA AZ1500 telescope, and 50/70cm
Schmidt telescope. Between 20:50:46 UT and 22:54:36 UT at 2025-07-04 a
set of 275 images in filter R were obtained with the 1.5m ASA AZ1500 telescope,
and 60 more with the 50/70cm Schmidt telescope. Co-adding the images reveal
clearly cometary activity of 3I/ATLAS. The isophote contour map of the
resulted co-added image shows relatively symmetrical shape, with slight
elongation along the axis of the heliocentric velocity vector of the comet.
The outermost contour, which is set at 1 sigma_sky above the sky level
is extended at ~ 42500 km along the X axis (the X axis and the heliocentric
velocity vector is nearly parallel), while along the Y axis, the contour
encompass approximately 38000 km at the comet geocentric distance of 3.4
AU. The step of the contours is 0.05 mag.

This contour map can be found here: https://nao-rozhen.org/kostov/C2025N1_contour_map.jpg

The picture of the 275 co-added images, each one 22s exposure can be found
here: https://nao-rozhen.org/kostov/libra.astro.bas.jpg

Additionally we calculate the R magnitude of the comet to be 17.46 +/-0.02
[mag], and the phase angle corrected Afrho of 413 +/-6 [cm]. The calculations
were done with photometric aperture with radius 3 arcsec, which corresponds
to 3000 km at the comet position.

The research that led to these results was carried out with the help of
infrastructure purchased under the National Roadmap for Scientific Infrastructure,
financially coordinated by the Ministry of Education and Science of the
Republic of Bulgaria. It is also partially supported by Bulgarian Scientific
Research Fund of the Ministry of Education and Science under the grants
KP-06-N78/5 / 2023 and KP-06-H88/5 "Physical properties and chemical composition
of asteroids and comets - a key to increasing our knowledge of the Solar
System origin and evolution."

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