The GN-z11-Flash Event Can be a Satellite Glint
aa r X i v : . [ a s t r o - ph . H E ] F e b Draft version February 10, 2021
Preprint typeset using L A TEX style emulateapj v. 12/16/11
THE GN-Z11-FLASH EVENT CAN BE A SATELLITE GLINT
Guy Nir , Eran O. Ofek , and Avishay Gal-Yam Draft version February 10, 2021
ABSTRACTRecently Jiang et al. reported the discovery of a possible short duration transient, detected in a singleimage, spatially associated with a z ∼ galaxy. Jiang et al. and Kahn et al. suggested the transientoriginates from a γ -Ray Burst (GRB), while Padmanabhan & Loeb argued the flash is consistent witha supernova shock breakout event of a 300 M ⊙ population III star. Jiang et al. argued against thepossibility that this event originated from light reflected off a satellite. Here we show that reflectionof sunlight from a high-orbit satellite or a piece of space debris is a valid and reasonable explanation.As shown in recent works, the rate of point-like satellite reflections, brighter than 11th magnitude, is > deg − day − near the equatorial plane. At higher declinations the rate is 5–50 times lower, butstill significant: about four orders of magnitudes higher than the rate estimated for GRBs. Keywords: artificial satellites — galaxies: high-redshift — gamma-ray burst: general INTRODUCTION
Recently Jiang et al. (2020) presented a short durationflash in a MOSFIRE (McLean et al. 2008) K -band spec-trum of a galaxy at redshift z ∼ (Oesch et al. 2016).The galaxy is referred to as GN-z11, and the transient isdesignated GN-z11-flash. The transient specific flux was0.057 mJy in the K -band, and it was visible in a single179 s exposure. Jiang et al. (2020) argue the source ofthe transient was a GRB prompt UV flash. Kann et al.(2020) further showed that the properties of the flash areconsistent with a prompt optical emission from a GRB.Shortly after, Steinhardt et al. (2021) suggested amore probable explanation, by presenting other MOS-FIRE K -band images where flashes are seen, arguingthat the source of these transients were reflections offartificial satellites. In response, Jiang et al. (2021) arguethat such flashes are typical of Low Earth Orbit (LEO)satellites, and that those would not be a viable explana-tion for GN-z11-flash, as it was (a) a point-like objectin the raw image, and (b) observed inside the Earth’sshadow, as seen by satellites up to 4000 km above theground. Jiang et al. (2020) also exclude a high-orbitsatellite as the cause of GN-z11-flash as the observationwas made at a declination of ∼ ◦ .However, both Nir et al. (2020) and Corbett et al.(2020) presented samples of high orbit satellite glints thatcan explain GN-z11-flash. They showed that high orbitsatellites, or space debris, rotating at a period of a fewminutes, can cause O (0 . s ) flashes, that would appear aspoint sources under reasonable seeing conditions. Theseflashes would be indistinguishable from fast astrophysicaltransients in single images. ANALYSIS
To appear point like in a slit image, an object mov-ing at an angular velocity v and angle θ to the slit,under s seeing size, must have a flash shorter than ∆ t . s/ ( v cos θ ) . For GN-z11-flash, we take s = 0 . ′′ , Benoziyo Center for Astrophysics, Weizmann Institute ofScience, 76100 Rehovot, Israel We take s = 0 . ′′ as this was the seeing during the observationof the flash. We take v = 15 ′′ s − for a geosynchronous satellite v = 15 ′′ / s and < θ < ◦ , giving . < ∆ t < . s.Such short glints appear as one- or two-frame flashes,that were fairly common in the sample presented byNir et al. (2020).The rate given by Nir et al. (2020) is 30–40 per day perdeg , or . × – . × per day per sky, for satellitesclose to the equatorial plane. This includes glints of 11thmagnitude or brighter. A 0.1 s duration glint, dilutedby a 179 s exposure, would be seen as having a visualmagnitude ∼ .Such flashes can be seen even at high declination,and can be caused by satellites or space debris fromsatellites launched into high orbits, not necessarily onthe equatorial plane, e.g., Molniya and Tundra orbits.The rate of glints at high declinations was measured byCorbett et al. (2020) that find a rate of ≈ per hourper sky ( . × per day), for flashes close to the Southcelestial pole. That survey was only sensitive to flasheswith peak magnitude brighter than ∼ , so that the rateof fainter glints, similar in brightness to GN-z11-flash,may be higher by an order of magnitude. The rate of GRBs across the entire sky is O (1) per day.This rate is lower than the glint rate by four orders ofmagnitude. If we assume GRBs occur only in galaxies,and narrow the search region only to the surface areacovered by high redshift galaxies (about 1% of the sky )the rate of satellite flashes on top of those galaxies wouldstill be two orders of magnitude higher than the rate ofGRBs. moving directly overhead. The actual transverse velocity could belower if the object is closer to the horizon or if its orbit is eccentricand spends more time at higher declinations, (e.g., Tundra orbits). The rate in the equatorial region found by Nir et al. (2020)is about an order of magnitude larger than that found byCorbett et al. (2020), most likely due to the deeper limiting mag-nitude of the former. This suggests that the rate of glints similarin brightness to GN-z11-flash at high declinations could be ≈ times larger than that given by Corbett et al. (2020). To estimate the angular area that could be associated witha galaxy, we can assume that each galaxy takes up an area ∼ . arcsec , including the size of the galaxy and the width of theseeing. Gardner & Satyapal (2000) estimate the number of galaxiesin the Hubble Deep Field to be on the order of 500 arcmin − , so thetotal sky area covered by galaxies is on the order of a few percent. In addition, Padmanabhan & Loeb (2021) suggestedthat GN-z11-flash is caused by a shock breakout eventin a population III star in GN-z11. However, this, aswell as any physical model, requires the release of about . × erg, in ∼ –35 s, in a narrow band between ∼ and 2000 Å (all numbers given in the rest frame). SUMMARY
A few conclusions based on these recent results are:• Glints can be seen at the position of GN-z11-flash,as high orbit satellites would be above Earth’sshadow at that time and direction.• Short duration flashes from rotating objects cancause flashes shorter than 0.1 s, that would appearpoint-like under . ′′ seeing conditions.• High orbit satellites do have high declination orbits.The rate of glints from such objects is at least . × per day per sky, it is most likely higher byat least an order of magnitude, considering thatfainter glints are more abundant.• The rate of such glints coincident with the area ofdistant galaxies on the sky is on the order of 200per day per sky. Thus we suggest that given the current information, asatellite origin can not be ruled out, and the rate of suchevents is higher than that of GRBs.REFERENCES Corbett, H., Law, N. M., Vasquez Soto, A., et al. 2020, arXive-prints, arXiv:2011.02495. https://arxiv.org/abs/2011.02495
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