J/A+A/691/A181 ELEPHANT Hostless AstroNomical Transients (Pessi+, 2024)
ELEPHANT: ExtragaLactic alErt Pipeline for Hostless AstroNomical Transients.
Pessi P.J., Durgesh R., Nakazono L., Hayes E.E., Oliveira R.A.P.,
Ishida E.E.O., Moitinho A., Krone-Martins A., Moews B., de Souza R.S.,
Beck R., Kuhn M.A., Nowak K., Vaughan S. (for the COIN collaboration)
<Astron. Astrophys. 691, A181 (2024)>
=2024A&A...691A.181P 2024A&A...691A.181P (SIMBAD/NED BibCode)
ADC_Keywords: Transient ; Photometry, classification
Keywords: methods: data analysis - methods: statistical -
astronomical databases: miscellaneous - stars: general
Abstract:
Transient astronomical events that exhibit no discernible association
with a host galaxy are commonly referred to as hostless. These rare
phenomena can offer unique insights into the properties and evolution
of stars and galaxies. However, the sheer number of transients
captured by contemporary high-cadence astronomical surveys renders the
manual identification of all potential hostless transients
impractical. Therefore, creating a systematic identification tool is
crucial for studying these elusive events.
We present the ExtragaLactic alErt Pipeline for Hostless AstroNomical
Transients (ELEPHANT), a framework for filtering hostless transients
in astronomical data streams. It was designed to process alerts from
the Zwicky Transient Facility (ZTF) presented in the Fink broker;
however, its underlying concept can be applied to other data sources.
We used Fink to access all the ZTF alerts produced between January
2022 and December 2023, selecting alerts associated with extragalactic
transients reported in SIMBAD or TNS, as well as those classified as
supernovae (SNe) or kilonovae (KNe) by the machine learning (ML)
classifiers within the broker. We then processed the associated stamps
using a sequence of image analysis techniques to retrieve hostless
candidates.
We find that less than 2% of all analyzed transients are potentially
hostless. Among them, only around 10 percent have a spectroscopic
class reported on TNS, with type Ia SNe being the most common class,
followed by superluminous SNe. In particular, among the hostless
candidates retrieved by our pipeline, there is SN 2018ibb, which has
been proposed to be a pair instability SN candidate, and SN 2022ann,
one of only five known SNe Icn. When no class is reported on TNS, the
dominant classes are quasi-stellar object (QSO) and SN candidates,
with the former obtained from SIMBAD and the latter inferred using the
Fink ML classifier.
ELEPHANT represents an effective strategy to filter extragalactic
events within large and complex astronomical alert streams. There are
many applications for which this pipeline will be useful, ranging from
transient selection for follow-up to studies of transient
environments. The results presented here demonstrate the feasibility
of developing specially crafted pipelines that enable a variety of
scientific studies based on large-scale surveys.
Description:
The events in these tables are the hostless candidates selected by
ELEPHANT in the Fink alert stream.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 133 154 Hostless candidates with spectral class in TNS
tabled1.dat 66 1409 Hostless candidates without spectral class in TNS
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- IAUname Official IAU name
12- 23 A12 --- ZTFname ZTF internal name
25- 26 I2 h RAh Right Ascencion (J2000)
28- 29 I2 min RAm Right Ascencion (J2000)
31- 35 F5.2 s RAs Right Ascencion (J2000)
37 A1 --- DE- Declination sign (J2000)
38- 39 I2 deg DEd Declination (J2000)
41- 42 I2 arcmin DEm Declination (J2000)
44- 48 F5.2 arcsec DEs Declination (J2000)
50- 63 A14 --- Class Spectroscopic classification
65 A1 --- Confirmed [xv] Confirmation of lack of obvious host (1)
67-133 A67 --- Comments Comments
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Note (1): Flag as follows:
v = indicates that no host was visually identified and thus the event is
confirmed to be a hostless candidate
x = indicates that a host association was visually found
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Byte-by-byte Description of file: tabled1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- IAUname Official IAU name
12- 23 A12 --- ZTFname ZTF internal name
25- 26 I2 h RAh Right Ascencion (J2000)
28- 29 I2 min RAm Right Ascencion (J2000)
31- 35 F5.2 s RAs Right Ascencion (J2000)
37 A1 --- DE- Declination sign (J2000)
38- 39 I2 deg DEd Declination (J2000)
41- 42 I2 arcmin DEm Declination (J2000)
44- 48 F5.2 arcsec DEs Declination (J2000)
50- 66 A17 --- Class Machine learning assigned classification
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Acknowledgements:
Priscila Jael Pessi, priscila.pessi(at)astro.su.se
We thank Julien Peloton for assistance in retrieving data from Fink.
We thank the referee for the valuable revision. P.J.P. acknowledges
support from the European Research Council (ERC) under the European
Union's Horizon Europe research and innovation program (grant
agreement No. 10104229 - TransPIre). EEH is supported by a Gates
Cambridge Scholarship (#OPP1144). This work is a result of the COIN
Residence Program #7, held in Lisbon, Portugal, from 9 to 16 September
2023 and supported by the Portuguese Fundacao para a Ciencia e a
Tecnologia (FCT) through the Strategic Programme UIDP/FIS/00099/2020
and UIDB/FIS/00099/2020 for CENTRA. The Cosmostatistics Initiative
(COIN, https://cosmostatistics-initiative.org/) is an international
network of researchers whose goal is to foster interdisciplinarity
inspired by astronomy. This research has made use of the IMBAD
database, operated at CDS, Strasbourg, France. This work made use of
the Fink community broker resources. Fink is supported by LSST-France
and CNRS/IN2P3. This research has made use of "Aladin sky atlas"
developed at CDS, Strasbourg Observatory, France. This work made use
of Astropy (http://www.astropy.org) a community-developed core Python
package and an ecosystem of tools and resources for astronomy (Astropy
Collaboration et al. 2013, 2018, 2022).
(End) Patricia Vannier [CDS] 17-Oct-2024