Fast optical flares from M dwarfs detected by a one-second-cadence survey with Tomo-e Gozen

Aizawa, Masataka; Kawana, Kojiro; Kashiyama, Kazumi; Ohsawa, Ryou; Kawahara, Hajime; Naokawa, Fumihiro; Tajiri, Tomoyuki; Arima, Noriaki; Jiang, Hanchun; Hartwig, Tilman; Fujisawa, Kotaro; Shigeyama, Toshikazu; Arimatsu, Ko; Doi, Mamoru; Kasuga, Toshihiro; Kobayashi, Naoto; Kondo, Sohei; Mori, Yuki; Okumura, Shin-ichiro; Takita, Satoshi; Sako, Shigeyuki

doi:10.1093/pasj/psac056

Cited by 14 publications

(6 citation statements)

References 63 publications

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“…The spearman coefficient is 𝑟 𝑠 = 0.34, and corresponding 𝑝-value is 0.00011. This result is roughly consistent with that yielded in Aizawa et al (2022), supporting that the decay time of flares is dominated by the radiative cooling of the compressed chromosphere. In the analysis of four giant flares from the TESS observations, Ilin et al (2021) set two parameters (FWHM i and FWHM g ) to represent the impulsive phase and the general phase to decouple 𝑡 1/2 .…”

Section: The Timescale Of the Modelsupporting

confidence: 90%

Minute-cadence Observations of the LAMOST Fields with the TMTS: III. Statistic Study of the Flare Stars from the First Two Years

Liu¹,

J²,

Gu³

et al. 2023

Preprint

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Tsinghua University-Ma Huateng Telescopes for Survey (TMTS) aims to detect fast-evolving transients in the Universe, which has led to the discovery of thousands of short-period variables and eclipsing binaries since 2020. In this paper, we present the observed properties of 125 flare stars identified by the TMTS within the first two years, with an attempt to constrain their eruption physics. As expected, most of these flares were recorded in late-type red stars with 𝐺 BP − 𝐺 RP > 2.0 mag, however, the flares associated with bluer stars tend to be on average more energetic and have broader profiles. The peak flux (𝐹 peak ) of the flare is found to depend strongly on the equivalent duration (ED) of the energy release, i.e., 𝐹 peak ∝ ED 0.72±0.04 , which is consistent with results derived from the Kepler and Evryscope samples. This relation is likely related to the magnetic loop emission, while -for the more popular non-thermal electron heating model -a specific time evolution may be required to generate this relation. We notice that flares produced by hotter stars have a flatter 𝐹 peak ∝ ED relation compared to that from cooler stars. This is related to the statistical discrepancy in light-curve shape of flare events with different colors. In spectra from LAMOST, we find that flare stars have apparently stronger H𝛼 emission than inactive stars, especially at the low temperature end, suggesting that chromospheric activity plays an important role in producing flares. On the other hand, the subclass having frequent flares are found to show H𝛼 emission of similar strength in their spectra to that recorded with only a single flare but similar effective temperature, implying that the chromospheric activity may not be the only trigger for eruptions.

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Section: The Timescale Of the Modelsupporting

confidence: 90%

Minute-cadence Observations of the LAMOST Fields with the TMTS: III. Statistic Study of the Flare Stars from the First Two Years

Liu¹,

J²,

Gu³

et al. 2023

Preprint

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“…Flaring stars are now being routinely discovered in modern time-domain sky surveys like Kepler [80], TESS [81,82], EvryScope [83], NGTS [84], ZTF [85] or Tomo-e Gozen [86] what perform high cadence continuous observations of the fixed sky regions. However, most of these experiments do not provide temporal resolution better than half a minute, or in rare cases-better than a second, and are being performed in a single photometric filter that somehow reduces the scientific content of collected statistical results.…”

Section: Expected Resultsmentioning

confidence: 99%

SAINT (Small Aperture Imaging Network Telescope)—A Wide-Field Telescope Complex for Detecting and Studying Optical Transients at Times from Milliseconds to Years

Beskin,

Biryukov,

Gutaev

et al. 2023

Photonics

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In this paper, we present a project of a multi-channel wide-field optical sky monitoring system with high temporal resolution—Small Aperture Imaging Network Telescope (SAINT)— mostly built from off-the-shelf components and aimed towards searching and studying optical transient phenomena on the shortest time scales. The instrument consists of twelve channels each containing 30 cm (F/1.5) GENON Max objectives mounted on separate ASA DDM100 mounts with pointing speeds up to 50 deg/s. Each channel is equipped with a 4128 × 4104 pixel Andor Balor sCMOS detector and a set of photometric griz filters and linear polarizers. At the heart of every channel is a custom-built reducer-collimator module allowing rapid switching of an effective focal length of the telescope—due to it the system is capable of operating in either wide-field survey or narrow-field follow-up modes. In the first case, the field of view of the instrument is 470 square degrees (39 sq.deg. for a single channel) and the detection limits (5σ level at 5500 Å) are 12.5, 16.5, 19, 21 with exposure times of 20 ms, 1 s, 30 s and 20 min, correspondingly. In the second, follow-up (e.g., upon detection of a transient of interest by either a real-time detection pipeline, or upon receiving an external trigger) regime, all telescopes are oriented towards the single target, and SAINT becomes an equivalent to a monolithic 1-meter telescope, with the field of view reduced to 11′ × 11′, and the exposure times decreased down to 0.6 ms (1684 frames per second). Different channels may then have different filters installed, thus allowing a detailed study—acquiring both color and polarization information—of a target object with the highest possible temporal resolution. The telescopes are located in two pavilions with sliding roofs and are controlled by a cluster of 25 computers that both govern their operation and acquire and store up to 800 terabytes of data every night, also performing its real-time processing using a dedicated fast image subtraction pipeline. Long-term storage of the data will require a petabyte class storage. The operation of SAINT will allow acquiring an unprecedented amount of data on various classes of astrophysical phenomena, from near-Earth to extragalactic ones, while its multi-channel design and the use of commercially available components allows easy expansion of its scale, and thus performance and detection capabilities.

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“…Small flares occur much more frequently than large ones. Based on dimensional arguments and observational data, the rise-time of such flares scales with their energy as µ E t flare rise 3 (Aizawa et al 2022). So-called "superflares," which include an increase in brightness larger than 3 mag, are observed several times a year by very-widefield surveys (Howard et al 2019).…”

Section: Backgrounds To a Blind Searchmentioning

confidence: 99%

Detecting the Early Optical Flashes of Gamma-Ray Bursts with Small Telescope Arrays

Sadeh

2024

ApJ

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We present an observational approach for the independent detection of the early optical emission of long gamma-ray bursts (GRBs). For this purpose, we explore the potential of the Large Array Survey Telescope (LAST). This array of small optical telescopes can be used to scan a wide region of the sky, and to focus on a smaller field of view with increased sensitivity, as needed. The modularity of the array facilitates dynamic scanning of multiple fields, by shifting telescope pointing directions with high cadence. This can significantly increase the effective sky-coverage of a blind survey on short timescales. For events associated with gamma-ray counterparts, the valuable early time data can supplement high-energy observations. Regardless of gamma-ray association, detections can potentially be used to explore various phenomena associated with GRBs, such as orphan afterglows; dirty fireballs; and choked jets. We simulate a sample of GRBs and their respective optical signals at early times. After accounting for dynamic cadence, the light curves are given as input to a machine-learning classifier, used to identify astrophysical transients. We find that, by dedicating half of an LAST array to a blind search, one would expect to independently detect 7–11 GRBs yr–1, corresponding to an approximate intrinsic event rate of 0.12 deg–2 yr–1.

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Fast optical flares from M dwarfs detected by a one-second-cadence survey with Tomo-e Gozen

Cited by 14 publications

References 63 publications

Minute-cadence Observations of the LAMOST Fields with the TMTS: III. Statistic Study of the Flare Stars from the First Two Years

Minute-cadence Observations of the LAMOST Fields with the TMTS: III. Statistic Study of the Flare Stars from the First Two Years

SAINT (Small Aperture Imaging Network Telescope)—A Wide-Field Telescope Complex for Detecting and Studying Optical Transients at Times from Milliseconds to Years

Detecting the Early Optical Flashes of Gamma-Ray Bursts with Small Telescope Arrays

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