A Survey for Fast Transients in the Fornax Cluster of Galaxies

Rau, A.; Ofek, E. O.; Kulkarni, S. R.; Madore, Barry F.; Pevunova, O.; Ajello, M.

doi:10.1086/589762

Cited by 22 publications

(32 citation statements)

References 34 publications

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“…The dominant population of fast optical transients (FOTs) is flares from Galactic low-mass main sequence stars, particularly M dwarfs (e.g., Kulkarni & Rau 2006;Rau et al 2008;Berger et al 2013). These flares are thought to arise from magnetic reconnection events in convective envelopes.…”

Section: Introductionmentioning

confidence: 99%

iPTF Archival Search for Fast Optical Transients

Kulkarni

Nugent

et al. 2018

ApJL

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There has been speculation about a class of relativistic explosions with an initial Lorentz factor Γ init smaller than that of classical gamma-ray bursts (GRBs). These "dirty fireballs" would lack prompt GRB emission but could be pursued via their optical afterglow, appearing as transients that fade overnight. Here we report a search for such transients (that fade by 5-σ in magnitude overnight) in four years of archival photometric data from the intermediate Palomar Transient Factory (iPTF). Our search criteria yielded 50 candidates. Of these, two were afterglows to GRBs that had been found in dedicated follow-up observations to triggers from the Fermi GRB Monitor. Another (iPTF14yb) was a GRB afterglow discovered serendipitously. Eight were spurious artifacts of reference image subtraction, and one was an asteroid. The remaining 38 candidates have red stellar counterparts in external catalogs. The photometric and spectroscopic properties of the counterparts identify these transients as strong flares from M dwarfs of spectral type M3-M7 at distances of d≈0.15-2.1 kpc; three counterparts were already spectroscopically classified as late-type M stars. With iPTF14yb as the only confirmed relativistic outflow discovered independently of a high-energy trigger, we constrain the all-sky rate of transients that peak at m=18 and fade by Δm=2 mag in Δt=3 hr to be 680 yr 1 -, with a 68% confidence interval of 119 2236 yr 1 --. This implies that the rate of visible dirty fireballs is at most comparable to that of the known population of long-duration GRBs.

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Section: Introductionmentioning

confidence: 99%

iPTF Archival Search for Fast Optical Transients

Kulkarni

Nugent

et al. 2018

ApJL

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“…Many surveys have focused their interest on poorly known objects lying in the gap in the absolute magnitude distribution that separates luminous novae (M R ≥ −10) and faint supernovae (M R ≤ −14) (e.g., Rau et al 2008). Although this gap had been understood to be populated mostly by eruptions of luminous blue variables (LBVs, see Maund et al 2006), it is now evident that new types of explosions may be responsible for the transient events occurring in this luminosity range, from exotic (LBVlike) outbursts of Wolf-Rayet stars (Pastorello et al 2007a) to other long duration transients, such as M85 OT2006-1 (Kulkarni et al 2007;Rau et al 2008;Ofek et al 2008;Pastorello et al 2007b), whose nature remains debated.…”

Section: Introductionmentioning

confidence: 99%

“…Although this gap had been understood to be populated mostly by eruptions of luminous blue variables (LBVs, see Maund et al 2006), it is now evident that new types of explosions may be responsible for the transient events occurring in this luminosity range, from exotic (LBVlike) outbursts of Wolf-Rayet stars (Pastorello et al 2007a) to other long duration transients, such as M85 OT2006-1 (Kulkarni et al 2007;Rau et al 2008;Ofek et al 2008;Pastorello et al 2007b), whose nature remains debated. In this context, a significant impulse to the study of objects in this gap was brought about by the discoveries of two nearby objects, namely SN 2008S in NGC 6946 and the 2008 luminous optical transient in NGC 300 (hereafter NGC 300 OT2008-1).…”

Section: Introductionmentioning

confidence: 99%

VLT spectropolarimetry of the optical transient in NGC 300

Patat¹,

Maund²,

Benetti³

et al. 2010

A&A

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Aims. We study possible signs of asymmetry in the bright optical transient in NGC 300, to obtain independent information about the explosion mechanism, the progenitor star and its circumstellar environment. Methods. Using VLT-FORS1, we obtained low-resolution optical linear spectropolarimetry of NGC 300 OT2008-1 on two epochs, 48 and 55 days after the discovery, covering the spectral range 3600-9330 Å. Results. The data exhibit a continuum polarization at a very significant level. At least two separate components are identified. The first is characterized by both a strong wavelength dependency and a constant position angle (68.6 ± 0.3 degrees), which is parallel to the local spiral arm of the host galaxy. The latter is aligned along a completely different position angle (151.3 ± 0.4). While the former is identified as arising in the interstellar dust associated with NGC 300, the latter is most likely caused by continuum polarization by dust scattering in the circumstellar environment. No line depolarization is detected in correspondence to the most intense emission lines, disfavoring electron scattering as the source of intrinsic polarization. This implies that there is a very small deviation from symmetry in the continuum-forming region. Given the observed level of intrinsic polarization, the transient must be surrounded by a significant amount of dust (≥4 × 10 −5 M ), asymmetrically distributed within a few thousand AU. This probably implies that one or more asymmetric outflow episodes took place during the past history of the progenitor.

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“…The authors provided a summary of the upper limits on extragalactic fast optical transients evolving on ∼0.5 hours timescales until 2013: the upper limits placed by all those surveys ( Fig. 6) confirm that Galactic M-dwarf flares outnumber extragalactic fast transients by a large factor (up to several orders of magnitude, Rau et al 2008). More recent surveys explore similar short-timescale regimes, for example the High Cadence Transient Survey (Förster et al 2016, HiTS).…”

Section: Introductionmentioning

confidence: 87%

“…Bersten et al (2018) present the remarkable discovery of another optical supernova shock breakout, revealing an increase by ∆M V ∼ 0.6 in ∼ 25 minutes and estimated to last ∼ 0.1 day. Other fastcadenced surveys include a monitoring of the Fornax galaxy cluster (Rau et al 2008), and blind surveys such as ROTSE III (Rykoff et al 2005), the Deep Lens Survey (DLS, Becker et al 2004), MASTER (Lipunov et al 2007), and Pi of the Sky (Soko lowski et al 2010). Results from the Pan-STARRS Medium-Deep Survey were reported by Berger et al (2013b).…”

Section: Introductionmentioning

confidence: 99%

Probing the extragalactic fast transient sky at minute time-scales with DECam

Andreoni

Cooke

Webb

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Searches for optical transients are usually performed with a cadence of days to weeks, optimised for supernova discovery. The optical fast transient sky is still largely unexplored, with only a few surveys to date having placed meaningful constraints on the detection of extragalactic transients evolving at sub-hour timescales. Here, we present the results of deep searches for dim, minute-timescale extragalactic fast transients using the Dark Energy Camera, a core facility of our all-wavelength and all-messenger Deeper, Wider, Faster programme. We used continuous 20 s exposures to systematically probe timescales down to 1.17 minutes at magnitude limits g > 23 (AB), detecting hundreds of transient and variable sources. Nine candidates passed our strict criteria on duration and non-stellarity, all of which could be classified as flare stars based on deep multi-band imaging. Searches for fast radio burst and gamma-ray counterparts during simultaneous multi-facility observations yielded no counterparts to the optical transients. Also, no long-term variability was detected with pre-imaging and follow-up observations using the SkyMapper optical telescope. We place upper limits for minute-timescale fast optical transient rates for a range of depths and timescales. Finally, we demonstrate that optical g-band light curve behaviour alone cannot discriminate between confirmed extragalactic fast transients such as prompt GRB flashes and Galactic stellar flares.

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A Survey for Fast Transients in the Fornax Cluster of Galaxies

Cited by 22 publications

References 34 publications

iPTF Archival Search for Fast Optical Transients

iPTF Archival Search for Fast Optical Transients

VLT spectropolarimetry of the optical transient in NGC 300

Probing the extragalactic fast transient sky at minute time-scales with DECam

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