Estimation of the detectability of optical orphan afterglows

Zou, Yuan‐Chuan; Wu, Xue-Feng; Dai, Z. G.

doi:10.1051/0004-6361:20064853

Cited by 30 publications

(29 citation statements)

References 47 publications

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“…Nondetections of OA are in agreement with current theoretical predictions (Totani & Panaitescu 2002;Nakar et al 2002;Zou et al 2007;Rossi et al 2008;Metzger et al 2015). However, these works either extrapolated the properties of a few known GRB afterglows to the orphans (e.g., Totani & Panaitescu 2002) or assumed basic prescriptions for the known GRB population properties or for the afterglow emission model.…”

Section: Introductionsupporting

confidence: 89%

“…Similarly, Zou et al (2007) adopt a set of fixed physical parameters (kinetic energy and micro-physical parameters) and only allow for a possible distribution of θ jet . They predict a rate of 1.3 × 10 −2 deg −2 yr −1 for OAs brighter than R = 20, which is consistent with our findings at the corresponding flux (red solid curve in Fig.…”

Section: Discussionmentioning

confidence: 99%

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Unveiling the population of orphanγ-ray bursts

Ghirlanda

Salvaterra

Campana

et al. 2015

A&A

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Gamma-ray bursts (GRBs) are detectable in the γ-ray band if their jets are oriented toward the observer. However, for each GRB with a typical θ jet , there should be ∼2/θ 2 jet bursts whose emission cone is oriented elsewhere in space. These off-axis bursts can eventually be detected when, due to the deceleration of their relativistic jets, the beaming angle becomes comparable to the viewing angle. Orphan afterglows (OAs) should outnumber the current population of bursts detected in the γ-ray band even if they have not been conclusively observed so far at any frequency. We compute the expected flux of the population of orphan afterglows in the mm, optical, and X-ray bands through a population synthesis code of GRBs and the standard afterglow emission model. We estimate the detection rate of OAs with ongoing and forthcoming surveys. The average duration of OAs as transients above a given limiting flux is derived and described with analytical expressions: in general OAs should appear as daily transients in optical surveys and as monthly/yearly transients in the mm/radio band. We find that ∼2 OA yr −1 could already be detected by Gaia and up to 20 OA yr −1 could be observed by the ZTF survey. A larger number of 50 OA yr −1 should be detected by LSST in the optical band. For the X-ray band, ∼26 OA yr −1 could be detected by the eROSITA. For the large population of OA detectable by LSST, the X-ray and optical follow up of the light curve (for the brightest cases) and/or the extensive follow up of their emission in the mm and radio band could be the key to disentangling their GRB nature from other extragalactic transients of comparable flux density.

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Section: Introductionsupporting

confidence: 89%

Section: Discussionmentioning

confidence: 99%

Unveiling the population of orphanγ-ray bursts

Ghirlanda

Salvaterra

Campana

et al. 2015

A&A

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“…This is due to its unprecedented combination of depth and sky coverage which has been permitted by the large area of MegaCAM, the high throughput of the 3.6 meter CFH Telescope, the organisation of a survey adequate for visible afterglow searches, and by the implementation of dedicated software allowing a quick processing of the images and an efficient search for variable objects. If we compare our observations to theoretical predictions, the assumption that we have detected no afterglow gives an upper limit which is marginally consistent with the (optimistic) prediction of Totani & Panaitescu (2002), and fully consistent with the more pessimistic predictions of Nakar et al (2002), and Zou et al (2006). If we assume that our candidate is a real afterglow we reach a different conclusion: our data are incompatible with the predictions of Nakar et al (2002) and Zou et al (2006) at the 90% confidence level.…”

Section: Constraining Grb Beamingsupporting

confidence: 45%

“…If we compare our observations to theoretical predictions, the assumption that we have detected no afterglow gives an upper limit which is marginally consistent with the (optimistic) prediction of Totani & Panaitescu (2002), and fully consistent with the more pessimistic predictions of Nakar et al (2002), and Zou et al (2006). If we assume that our candidate is a real afterglow we reach a different conclusion: our data are incompatible with the predictions of Nakar et al (2002) and Zou et al (2006) at the 90% confidence level. More importantly, if OT 20050728 is a true GRB afterglow, our work is the first one to provide Table 2. an estimate of the amount of observing time needed to detect a significant number of GRB visible afterglows.…”

Section: Constraining Grb Beamingsupporting

confidence: 45%

Constraining the rate of GRB visible afterglows with the CFHTLS very wide survey

Malacrino¹,

Atteia²,

Boër³

et al. 2008

AIP Conference Proceedings

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Aims. We analyze images of the CFHTLS Very Wide Survey to search for visible orphan afterglows from gamma-ray bursts (GRBs). Methods. We have searched 490 square degrees down to magnitude r'=22.5 for visible transients similar to GRB afterglows. We translate our observations into constraints on the number of GRB visible afterglows in the sky, by measuring the detection efficiency of our search with a simulation reproducing the characteristics of our observational strategy and the properties of on-axis GRB afterglows. Results. We have found only three potential candidates, of which two are most probably variable stars, and one presents similarities to an orphan afterglow. We constrain the number of visible afterglows to be less than 220 down to r'=22.5 in the whole sky at any time. Our observations are marginally consistent with the most optimistic model, which predicts orphan afterglows to be about 10 times more frequent than GRBs. Conclusions. This search has led to the detection of one possible GRB afterglow, and provides the strongest constraints on the rate of GRB visible afterglows as well as an estimation of the observing time required to detect a significant number of GRB afterglows.

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“…Up until today the quest for their discovery has resulted in upper (θ jet ∼ < 22 • Levinson et al 2002) or lower (θ jet ∼ > 0.8 • Soderberg et al 2006b) limits on the GRB opening angles. Some peculiar transients in past surveys could have been genuine OAs both in the optical (Rau et al 2006;Zou et al 2007;Malacrino et al 2007) and radio (for a recent reveiw on blind surveys see Murphy et al 2013) regime, but none have been confirmed so far. The evolution of the OA lightcurve differs from that of a normal afterglow before reaching its peak flux.…”

Section: Pos(aaska14)052mentioning

confidence: 99%

The SKA View of Gamma-Ray Bursts

Burlon¹,

Ghirlanda²,

Horst³

et al. 2015

Proceedings of Advancing Astrophysics With the Square Kilometre Array — PoS(AASKA14)

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Gamma-ray bursts (GRBs) are some of the most extreme events in the Universe. As well as providing a natural laboratory for investigating fundamental physical processes, they might trace the cosmic star formation rate up to extreme redshifts and probe the composition of the intergalactic medium over most of the Universe's history. Radio observations of GRBs play a key part in determining their physical properties, but currently they are largely limited to follow-up observations of γ-ray-detected objects. The SKA will significantly increase our ability to study GRB afterglows, following up several hundred objects in the high frequency bands already in the "early science" implementation of the telescope. SKA1-MID Bands 4 (4 GHz) and 5 (9.2 GHz) will be particularly suited to the detection of these transient phenomena. The SKA will trace the peak of the emission, sampling the thick-to-thin transition of the evolving spectrum, and follow-up the afterglow down to the time the ejecta slow down to non-relativistic speeds. The full SKA will be able to observe the afterglows across the non-relativistic transition, for ∼ 25% of the whole GRB population. This will allow us to get a significant insight into the true energy budget of GRBs, probe their surrounding density profile, and the shock microphysics. The SKA will also be able to routinely detect the elusive "orphan afterglow" emission, from the population of GRBs whose jets are not pointed towards the Earth. We expect that a deep all-sky survey such as SKA1-SUR will see around 300 orphan afterglows every week. We predict these detection to be ∼ > 1000 when the full SKA telescope will be operational.Advancing Astrophysics with the Square Kilometre Array

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Estimation of the detectability of optical orphan afterglows

Cited by 30 publications

References 47 publications

Unveiling the population of orphanγ-ray bursts

Unveiling the population of orphanγ-ray bursts

Constraining the rate of GRB visible afterglows with the CFHTLS very wide survey

The SKA View of Gamma-Ray Bursts

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