Time-series and Phasecurve Photometry of Episodically-Active Asteroid (6478) Gault in a Quiescent State Using APO, GROWTH, P200 and ZTF

We observed Episodically Active Asteroid (6478) Gault in 2020 with multiple telescopes in Asia and North America and have found that it is no longer active after its recent outbursts at the end of 2018 and start of 2019. The inactivity during this apparation allowed us to measure the absolute magnitude of Gault of H_r = 14.63 +/- 0.02, G_r = 0.21 +/- 0.02 from our secular phasecurve observations. In addition, we were able to constrain Gault's rotation period using time-series photometric lightcurves taken over 17 hours on multiple days in 2020 August, September and October. The photometric lightcurves have a repeating $\lesssim$0.05 magnitude feature suggesting that (6478) Gault has a rotation period of ~2.5 hours and may have a semi-spherical or top-like shape, much like Near-Earth Asteroids Ryugu and Bennu. The rotation period of ~2.5 hours is near to the expected critical rotation period for an asteroid with the physical properties of (6478) Gault suggesting that its activity observed over multiple epochs is due to surface mass shedding from its fast rotation spun up by the Yarkovsky-O'Keefe-Radzievskii-Paddack effect.

repeating 0.05 magnitude feature suggesting that (6478) Gault has a rotation period of ∼2.5 hours and may have a semi-spherical or top-like shape, much like Near-Earth Asteroids Ryugu and Bennu. The rotation period of ∼2.5 hours is near to the expected critical rotation period for an asteroid with the physical properties of (6478) Gault suggesting that its activity observed over multiple epochs is due to surface mass shedding from its fast rotation spun up by the Yarkovsky-O'Keefe-Radzievskii-Paddack effect.

INTRODUCTION
Active asteroids produce comet-like tails and comae that can be driven by many different types of forces different from comets themselves (Jewitt et al. 2015). While sublimation of water ice is a primary driver for activity in 'typical' comets, the ∼20 known (so far) active asteroids in the Main Belt seem to lose mass via a wider array of physical effects such as collisions (e.g., Snodgrass et al. 2010), rotational instabilities (e.g., Jewitt et al. 2013), and thermal fracture (e.g., Jewitt et al. 2019a). We can assess the physics of a particular active asteroid's activity via observations over long time baselines that assess the object's photometric and morphological development. As more and more active asteroids are discovered, it is vital to continuously monitor these objects and determine the frequency of the various phenomena in the Main Belt.
Main Belt asteroid (6478) Gault (1998 JC 1 ; "Gault" hereafter) has been the subject of wide interest since the discovery in early 2019 of comet tail-like extended emission (Smith et al. 2019). Eventually three tails were noted in January 2019 Jewitt et al. 2019b) on the S-type Phocaea family member (Sanchez et al. 2019), suggesting multiple sporadic outbursts of activity. Ye et al. (2019) assessed the dynamics of the dust seen near Gault and estimated that two outbursts had actually occurred in late 2018. Searches through archival data that serendipitously caught Gault revealed that there had been active episodes in 2013, 2016, and 2017 as well (Chandler et al. 2019).
Many authors have proposed that the cause of Gault's activity is the instability of material on its surface (Hui et al. 2019;Jewitt et al. 2019b;Kleyna et al. 2019;Moreno, F. et al. 2019;Ye et al. 2019) due its rotation being spun up by the the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect (Bottke Jr et al. 2006;Kleyna et al. 2019). A critical observational test of this hypothesis would be to measure the asteroid's rotational period. Unfortunately, due to the dust around the asteroid, the rotational period had not been well constrained as reflected sunlight from dust grains would swamp the signal from the asteroid itself and thus suppress short-term lightcurve variations due to Gault's shape, as indeed Jewitt et al. (2019b) concluded. However there have been published reports of some hints of rotational signatures in lightcurve data. For example, Ivanova et al. (2020) suggest a rotation period of 1.79 hours, Carbognani & Buzzoni (2020) suggest 3.34 hours, Ferrín et al. (2019) have 3.36 hours, and Kleyna et al. (2019) suggest ∼2 hours. In all cases, the lightcurve amplitude was quite small, on the order of just a few hundredths of a magnitude, which would be on the same order of the signal noise. It should also be noted that others (e.g., Moreno, F. et al. 2019) report no variation in photometry over a time span longer than these periods. This very small amplitude demonstrates the challenge of photometrically extracting a rotation period from an active body (see also Bolin & Lisse 2020, for an example).
In this paper we report on several sets of imaging and photometry of Gault obtained in 2019 while it was still active as well as in 2020 when the asteroid appeared to be quiescent (Purdum et al. 2020). These datasets have allowed us to constrain the rotation period of Gault. We also use all of the data to understand the longer-term, secular variations in Gault's activity. In §2 we describe the observations from 2019 and 2020. In §3 we present the photometry, and in §4 we discuss Gault's behavior, spin state, and shape, and summarize the article.

OBSERVATIONS
For our analysis we have made use of both our own, PI-led, pointed observations using several telescope facilities in the GROWTH (Global Relay of Observatories Watching Transients Happen) network (Kasliwal et al. 2019) and other faculties, as well as archival data from the Zwicky Transient Survey (ZTF, Graham et al. 2019;Bellm et al. 2019). Our pointed observations occurred on 17 nights between 2019 January 8 and 2020 October 20, and made use of six telescopes. On 7 of those 17 nights, we were able to have multiple telescopes follow Gault in a coordinated effort. The observations in 2019 showed Gault to still be active, but all such observations in 2020 showed no activity, only a point source (Purdum et al. 2020). The ZTF data are from 89 nights from 2018 November 01 to 2020 October 14. All data in this work have been flat-and bias-corrected since only CCDs were used. Tables 1 and 2 list the technical details  of each telescope and the particulars about each observing run, respectively, while Tables 3 and 4 are the photometric data plotted for this work and the archival ZTF survey, respectively. We describe below each telescope facility used in our work.
2.1. Mount Laguna Observatory 1.0-Meter Telescope Images of Gault were taken with the Mount Laguna Observatory (MLO) 1.0-meter telescope on 2020 June 24 UT, several months after the asteroid was leaving Solar conjunction. 120 images were taken with 30-second exposure times each, culminating 60 minutes of total exposure to measure the morphology of the asteroid.
Later observations were taken of Gault with MLO with an aim to constrain a rotation period. This data was taken between 2020 August 23 UT and 2020 October 20 UT over 6 separate campaigns listed in Table 2. MLO lightcurve images were taken in the Johnson-Cousins R filter with between 165 and 190 separate 120-second exposures.

Lulin One-meter Telescope
The time-series observations of Gault using the Lulin one-meter Telescope (LOT) at the Lulin Observatory, Taiwan, for 2020 August 23 and 24 UT lasted 6.4 hours and 5.2 hours, respectively. The other time span on 2020 September 21 UT and 2020 October 11 UT lasted 6.4 hours and 6.8 hours, respectively. Except for the use of unfiltered CCD observations early in the campaign, all observations are acquired with R-filter and obtained through non-sidereal tracking.

Astrophysics Research Consortium 3.5-meter Telescope
Between 2019 January 8 UT and 2019 June 6 UT we observed Gault over 6 campaigns with the Astrophysics Research Consortium 3.5-meter Telescope (ARC) at Apache Point Observatory before the asteroid headed into Solar conjunction (Table 2)

Palomar Observatory 200-Inch Telescope
On 2020 Aug 27 UT, the Palomar Observatory 200-inch telescope (P200) observed Gault in the r band. The 103 exposures each had an equivalent exposure time of 90 seconds, accumulating in a total of 9,270 seconds with an average seeing of ∼1.5". Observations were made with the Caltech HIgh-speed Multi-color camERA (CHIMERA, Harding et al. 2016). Although CHIMERA observes in two simultaneous optical bands, we only use the r band in this work.

Zwicky Transient Facility using the Palomar 48-Inch Telescope
Images of Gault were taken with the Zwicky Transient Facility (ZTF)  which is mounted on the Palomar Observatory's 48-inch telescope (P48) Dekany et al. 2020). ZTF images are located in the ZTF archive (Masci et al. 2019) and Gault's photometry was measured with a 5" aperture and processed using the ZChecker software . The 30-second exposure time observations were made in the r band and color-corrected using the g − r value of 0.50 ± 0.04 from Ye et al. (2019). Data in Figure 4 between 2018 November 1 UT and 2019 February 10 UT are adapted from Ye et al. (2019). A full list of the ZTF observations starting 2020 April 2 UT and ending 2020 October 14 UT is located in Table 4. The seeing varied between 1.5"-2.5" and the airmasses varied from 1.4 to 2.6 during the span of our observations.

GROWTH-India Telescope
We observed Gault on multiple nights with the 0.7m GROWTH-India telescope (GIT), using the SDSS r filter and an Apogee KAF3200EB camera giving a ∼ 11 × 7.5 field of view. Due to the slow motion of Gault, we used sidereal tracking and took multiple exposures. Data were acquired in 120 sec exposures on 2020 September 21, followed by 180 sec exposures on 2020 October 16 and October 20. Data were downloaded and processed in real time at our data processing machine at IIT Bombay. We calibrated images for processing by applying bias correction and flat-fielding, obtained astrometry solution using offline engine of astrometry.net (Lang et al. 2010) and finally removing cosmic-rays

GROWTH Coordinated Observations
On 2020 September 21 UT, LOT, GIT, MLO, and the Table Mountain Observatory (TMO) 1.0-meter telescope participated in a 20-hour relay of observing Gault for photometric lightcurve variation. MLO started the relay at 2020-09-21 04:24:47 UT (airmass 2.0) and ran continuous observations of 120-second exposure times until 11:35:27 UT (airmass 2.0) the same day, totaling 22800 seconds of exposure time. LOT took over shortly after at 14:26:07 (airmass 1.2) amassing 14130 seconds of 90-second exposures before finishing at 20:29:09 UT (airmass 2.5). GIT observed Gault for roughly 6 hours in 135 images amassing 16,200 seconds of exposure starting from 17:21:31 UT (airmass 1.2), in the middle of the LOT observations, and ending at 23:18:07 UT (airmass 2.5). TMO observed Gault for roughly 4 hours in 225 images amassing 13,500 seconds of exposure starting at 06:36:37 UT (airmass 1.3), in the middle of MLO's observations. Typical seeing for GIT is 2.5" and for TMO is 1.5". We were able to take data with Table  Mountain Observatory despite the degraded conditions caused by a nearby wildfire. Additional coordination among the GROWTH network include MLO-LOT observations on 2020 August 23 and 24 UT and 2020 October 11 UT, TMO-LOT on 2020 September 22 UT, and MLO-GIT on 2020 October 16 and 20 UT.

Active and Inactive states of Gault
Follow-up observations with the ARC 3.5-meter telescope at Apache Point Observatory on 2019 February 25 UT showed evidence for multiple tails. A deep-stack image consisting of 4680 seconds of exposure is shown on the left side of Figure 1. The surface brightness of Gault in this stack is 24.0 mag/sq.arcsec within a 10,000 km aperture. The right side of Figure 1 shows Gault's third tail in a 4320-second deep-stack image from the ARC 3.5-meter telescope on 2019 April 26 UT and the 10,000 km surface brightness was calculated to be 23.8 mag/sq.arcsec. The images were combined in deep, median-stacks centered on Gault and then used to compute the calibrated r-band photometry from comparisons to a similar deep-stacked images of reference stars with Solar colors from the same initial image. We referenced photometry of the reference star from the Pan-STARRS catalog (Chambers et al. 2016).
Both surface brightnesses were brighter than the surface brightness of 25.8 mag/sq.arcsec found when it was inactive in 2020 June by Purdum et al. (2020). Our deep-stack image taken by the P200 in the r band is shown in Figure  2, which lacks cometary features and has a surface brightness of 26.3 mag/sq.arcsec, also dimmer than the surface brightnesses from early 2019. Figure 3 shows Gault's reduced magnitude phasecurve from ZTF data taken between 2017 June 14 UT to 2017 December 2 UT. The reduced magnitude data is described by r − 5 log 10 (r∆) where r and ∆ are the heliocentric and geocentric distances. We can then find the r-band absolute magnitude H r and phase slope parameter G by fitting the reduced magnitudes to the phase function of the form:

Secular Photometry and Updated Absolute Magnitude
where r is the r-band magnitude of Gault taken with a 5 aperture, α is the phase angle of the asteroid at the time of mid-exposure, and Φ 1 and Φ 2 are two basis functions normalized at unity for α = 0 • (Bowell et al. 1989;Muinonen et al. 2010;Pravec et al. 2012). These best fit parameters are H r = 14.631 ± 0.019 and G r = 0.207 ± 0.020 after it had exited Solar conjunction and was no longer active. This is significantly fainter than the value of 14.31 ± 0.01 measured by ZTF when Gault was last seen to be inactive in 2017 ). This could be caused by the change in observing geometry over time creating a different line-of-site projection of Gault's light-scattering cross-section. Using the updated predicted absolute magnitude of Gault with the blue line in Figure 4, we can see the instability in the brightness of Gault over time using 5" aperture photometry. Figure 4 shows the time-series r band ZTF photometry between June and October of 2020. Gault exited Solar conjunction and was observed between 2020 April 02 UT (MJD = 58941) and 2020 October 14 UT (MJD = 59136). Comparing the measured equivalent r-band magnitude of Gault from photometry measured in ZTF observations taken on these dates with the predicted magnitude of Gault based on our measured r-band absolute magnitude of H r = 14.631 ± 0.019 and phase function slope value G = 0.207 ± 0.020, we do not see any significant brightening in the actual magnitude of Gault compared to the predicted magnitudes. This is in contrast to the brightness of Gault in the "active" portion of its lightcurve between 2018 November 01 UT (MJD = 58423) and 2019 February 10 UT (MJD = 58524). Between 2019 February 24 UT (MJD = 58538) and 2019 July 9 UT (MJD = 58673), the measured brightness and predicted brightness begin to become similar suggesting that the enhanced cross-section of Gault caused by dust within its vicinity was beginning to diminish in contrast to the increase in brightness of comets whose brightness are observed to increase with steadily increasing activity as they approach the Sun (Bolin et al. 2020a,b).

Time-Series Lightcurves
While Gault was active in 2019, the ARC 3.5-meter telescope at Apache Point Observatory took short-period lightcurve images, as shown in Figure 5. Much like Figure 6 in Jewitt et al. (2019b), this plot shows little variation in the lightcurve while the asteroid was experiencing activity and producing comet-like features. The variations that do occur in these lightcurves have small-amplitude peaks and are caused by noise consistent with the uncertainty values in their individual differential photometry.  While the asteroid is active, the data do not line up with the predicted magnitude due to dust obscuring the surface of the asteroid. As Gault continued to be dust dominated as it entered Solar conjunction before MJD 58700, the predicted and observed magnitudes started to align again. After exiting Solar conjunction, Gault shows that it aligns with the new predicted values during inactivity. The vertical lines indicate the observation epochs in this work.
The flatness of the lightcurves is noted even as the brightness of Gault began to resemble its predicted brightness based on its pre-activity H r seen in Figure 4. In order to determine the rotational period of Gault after it returned to an inactive state, we obtained coordinated long-term lightcurves on nine separate dates starting in August 2020, with the longest single lightcurve of 19 hours on 2020 September 21 UT. The results are displayed in Figures 6 and 7. Figure 5. 2019 data from the ARC 3.5-meter telescope. The data are organized chronologically from top to bottom and are offset by 0.1 magnitude from each other. The first 3 dates correspond to the epochs in which Gault was active and where the ZTF photometry is brighter than predicted, and the last 3 dates were obtained during the dust-dominated epochs that followed, as seen in Figure 4.
The separate observatories are indicated by color, with MLO as red, LOT as green, P200 as orange, TMO as purple, and GIT as blue. Each lightcurve for each observatory has an additional reference star lightcurve normalized to -0.3 magnitude to show that the reference stars used to calculate the differential photometry of Gault did not vary over time (or if so, not at the same period and amplitude as the asteroid's lightcurves). The reference star lightcurves have small error bars and have not been corrected for airmass or weather effects on their photometry and therefore are curved, but display no strong signs of periodicity.
Each date in Figures 6 and 7 also contain vertical orange lines indicate small-amplitude, periodic peaks in the asteroid lightcurves based on 2.49-hour intervals from an arbitrary t = 0 denoted by the green line in Figure 6. The peaks roughly halfway between the orange lines are denoted with a vertical light-blue line. The peaks repeat roughly every 1.25 -2.5 hours, indicating a possible rotation period around 2.5 hours.
A Lomb-Scargle (Lomb 1976) periodogram was constructed from MLO and LOT data of Gault ranging from August to October of 2020 and is shown along with a folded lightcurve of Gault in Figure 8. The differential photometry technique we used to create the periodogram relied on determining the difference between the brightness of Gault and the comparison stars in the same field of view to acquire the Gault's light curve. The comparison stars we selected depended on the maximum frame width that we used through one run and on the similarity of FWHM (Full Width at Half Maximum) estimated between Gault and the chosen stars. By comparing the reference stars' light curves, some variable stars were ruled out in the photometric analysis. To combine several photometry runs through different nights, the mean values of each run were automatically scaled using an IDL routine that we created. We then searched for significant periodicities using the Lomb-Scargle periodogram functions on the combined light curve data to find the most likely rotation period of Gault. The frequency analysis from the strong peak near ∼ 20 cycles/day in Figure  8 gives a rotation period of ∼1.25 hours, which corresponds to a single-peaked lightcurve. It is natural to assume a double-peaked lightcurve for Gault, which computes to a sidereal rotation period of 2.49 ± 0.07 hours. The uncertainty here of ±0.07 hours is estimated using the bootstrap method (Press et al. 1986) which removed √ N data points from the time series lightcurves and recalculated the period value from the Lomb-Scargle periodogram. This process was repeated 10,000 separate times with the resulting central value of 2.49 hours and a 1 − σ uncertainty estimate of 0.07 hours.   The amplitude of the MLO and LOT lightcurves are low, so it is somewhat difficult to recognize a continuous variation in brightness in the folded version of the lightcurve, as seen on the right in Figure 8.

DISCUSSION AND SUMMARY
The surface brightness profiles taken from deep-stacked images of Gault from the MLO 1.0-meter on 2020 July 21 UT (Purdum et al. 2020) and P200 on 2020 August 27 UT indicate that Gault is no longer active after it appeared to have an outburst of material that caused multiple tails to form starting in October of 2018 . The surface brightness measurements of 25.8 mag/sq.arcsec and 26.3 mag/sq.arcsec, from MLO and Palomar, respectively, are fainter compared to the surface brightness values of Gault from the ARC 3.5-meter Telescope on 2019 February 9 UT, had a measurement of 24 mag/sq.arcsec (Purdum et al. 2020). The fainter measurements in 2020 could mean that Gault no longer has material surrounding it and can be deemed inactive.
Gault's deactivation can also be seen over time in the photometry from ZTF observations of Gault in Figure 4. The activity of Gault is apparent on the left side of the plot with the data being much brighter and more variable than the predicted magnitudes from JPL's HORIZONS ephemeris service 1 . The outbursts for Gault's first two tails were estimated to have occurred on 2018 October 18 ± 5 UT and 2018 December 24 ± 1 UT , which is during the "active" portion of the lightcurve (see Figure 4). The third tail was much dimmer than the first two and so the exact time of initiation is uncertain, but Jewitt et al. (2019b) estimates it to be 2019 February 10 ± 7 UT, right at the time the "active" portion of Figure 4 ends.
After Gault had produced its third tail, the ZTF photometry started to line back up with the predicted magnitudes from JPL's HORIZONS ephemeris service, indicating that the active stage had come to an end. However, this alignment did not last as the photometry from ZTF started to dip below the predicted magnitudes in Figure 4. The misalignment occurred while Gault no longer had tails but was still surrounded by dust, which can skew photometric measurements. The right side of Figure 4, however, shows that Gault's photometry exiting Solar conjunction was more stable than the active stage of the plot, therefore providing more evidence for Gault's inactivity.
Interestingly, Gault no longer aligned with the predicted magnitudes HORIZONS ephemeris service after it had exited Solar conjunction. We found that altering the phase parameter G in Equation 1 from 0.25 to 0.21 and the absolute magnitude H from JPL's HORIZONS' 14.3 to 14.6, re-aligns the photometry in Figure 4. This phenomenon can be attributed to the observing geometry of Gault changing throughout its orbit. The higher absolute magnitude H r in 2019 could be due to pole-on observations, while the equator-on observations would result in a smaller absolute magnitude in 2020.
Photometric lightcurve observations with the ARC 3.5-meter while Gault was still dust-dominated (see Figure 5) in 2019 started to show some variation as the activity on Gault diminished, but the low-amplitude of the variations were not enough to conclude a rotation period. Our observations of Gault in 2020 also produced low-amplitude lightcurves (see Figures 6 and 7), even though it no longer displayed signs of activity. The viewing geometry is also much different for our observations in 2020 than from when it was active in 2019. This means that Gault could have a spherical or top-shaped geometry like Near-Earth Asteroids Ryugu and Bennu (Hirabayashi et al. 2020). It is also worth noting that near-Earth Asteroid (3200) Phaethon was imaged by Arecibo radar observations and was found to have a round, top-like shape when it passed by Earth in December of 2017 (Taylor et al. 2019). At that time, Kim et al. (2018) found Phaethon's peak amplitude was small, ∼0.1 magnitudes, which is somewhat similar to our data in Figures 6 and 7.
Despite the low amplitude in the lightcurves, we did notice periodic small-amplitude peaks and found they are separated by roughly 2.5 hours and plotted vertical orange lines to indicate the estimations. Some peaks occurred at 2.5 hour intervals that split the usual periodic peaks and are marked by dashed, blue lines 1.25 hours in between the orange lines. Several vertical lines in these figures correspond to peaks in the Gault lightcurve and little to no variation in the reference star lightcurve (see August 24, September 21, September 23, October 20 in Figures 6 and 7), which is an indication that the peaks are non-anomalous and are a result of the rotation of the asteroid. The periodogram in Figure 8 shows Gault has a rotation period of 2.49 ± 0.07 hours, assuming the frequency of ∼ 20 cycles/day (∼1.25 hours) corresponds to a double-peaked lightcurve.
With the assumption that Gault is nearly spherical or top-shaped (see Harris et al. (2014) on the determination of an asteroid's shape from its lightcurve), we assume the b/a axial ratio is close to 1-1.3 given its maximum possible lightcurve amplitude of ∼0.1-0.3 as seen in our data and the data from Kleyna et al. (2019) and the relation between b/a and lightcurve amplitude of b/a = 10 0.4∆M from Binzel et al. (1989). The critical breakup period of a strengthless ellipsoid as a function of axial ratio is given by  as where ρ is the density of the ellipsoid and G is the Newtonian gravitational constant. Gault should have a density of roughly equal to 2.2 g/cm 3 (Sanchez et al. 2019;Marsset et al. 2019), consistent with other S-Type asteroids (Carry 2012). Figure 9 presents the critical period with which Gault would start shedding surface material as a function of the axial ratio and density. An orange square labelled in Figure 9 is likely to contain the critical rotation period for an object with Gault's geometry. A rotation period like the one we have found at 2.5 hours seems to be at or near the critical period of Gault and therefore could be the cause of the activity started in 2018. Previous authors have also proposed Gault's activity was caused by rotational instability induced from the YORP effect (Jewitt et al. 2019b;Kleyna et al. 2019;Ferrín et al. 2019). Jewitt et al. (2015) determined that the YORP spin-up timescale for Gault should be roughly 22 Myr, much shorter than the 100 Myr-timescale for the re-orientation of the spin of a ∼4 km asteroid by non-destructive collisions (Farinella et al. 1998). It is therefore possible that Gault may experience rotational fission if it continues to be spun up past its rotational breakup limit (eg., Moreno et al. 2017). Some asteroids are observed to be spinning beyond their rotational limit, but this is typically for asteroids smaller than the kilometer scale (Pravec et al. 2008) to smaller than the meter scale (Bolin et al. 2014; which are held together by cohesive forces (Sánchez & Scheeres 2014). However, it should be noted that examples of km-scale asteroids have been found rotating faster than their critical period (Chang et al. 2017) from fast rotating asteroid searches in wide-field optical surveys (Chang et al. 2016(Chang et al. , 2019. Other causes for activity are somewhat less likely than rotational instability. For instance, unlike Main Asteroid Belt Comets (Jewitt et al. 2015), there are many clues that point away from ice sublimation as the driver for Gault's activity. Since Gault is an S-type and a member of the inner Main Belt Phocaea family, it likely formed inside the snow line and therefore would not experience sublimation (Vernazza & Beck 2016). Additionally, Gault's activity was observed with the ARC 3.5-meter telescope when Gault was located at a heliocentric distance of 2.41 AU on 2019 February 9 UT. When Gault was observed to be inactive by the MLO 1.0-meter telescope on 2020 June 24 UT, it had a heliocentric distance of 2.07 AU, suggesting the shorter distance to perihelion did not drive the activity. Collision events are also unlikely to be the cause for activity due to the multiple epochs of activity occurring in the few months Gault was active. Thermal disintegration is also somewhat unlikely due to Gault's low-eccentricity orbit. Active asteroids with this kind of driver typically have highly eccentric orbits which cause large changes in temperature that lead to fracture (Delbo et al. 2014;Jewitt et al. 2015). Other processes such as Solar radiation pressure are unlikely due to Gault's rotation constantly changing the orientation with respect to the Sun. Therefore we find that Gault's activity was likely driven from rapid rotation at its critical period of 2.5 hours.   (3) Right Ascension at the start of observation; (4) Declination at the start of observation; (5) Heliocentric distance at start of observation; (6) Geocentric distance at start of observation; (7) Phase Angle at start of observation; (8) Filter; (9) in-image seeing of at the start of observation. Note- Table 3 is published in its entirety in the machine-readable format. A portion is shown here for guidance regarding its form and content.