arXiv subjects

Tatsuya Nakaoka

Publications and source records attributed to Tatsuya Nakaoka.

At least 37 records · Page 2Linked to original sources

arXiv2024

IXPE observation of PKS 2155-304 reveals the most highly polarized blazar

We report the X-ray polarization properties of the high-synchrotron-peaked (HSP) blazar PKS 2155$-$304 based on observations with the Imaging X-ray Polarimetry Explorer (IXPE). We observed the source between Oct 27 and Nov 7, 2023. We also conducted an extensive contemporaneous multiwavelength (MW) campaign. We find that during the first half ($T_1$) of the IXPE pointing, the source exhibited the highest X-ray polarization degree detected for an HSP blazar thus far, (30.7$\pm$2.0)%, which dropped to (15.3$\pm$2.1)% during the second half ($T_2$). The X-ray polarization angle remained stable during the IXPE pointing at 129.4$^\circ$$\pm$1.8$^\circ$ and 125.4$^\circ$$\pm$3.9$^\circ$ during $T_1$ and $T_2$, respectively. Meanwhile, the optical polarization degree remained stable during the IXPE pointing, with average host-galaxy-corrected values of (4.3$\pm$0.7)% and (3.8$\pm$0.9)% during the $T_1$ and $T_2$, respectively. During the IXPE pointing, the optical polarization angle changed achromatically from $\sim$140$^\circ$ to $\sim$90$^\circ$ and back to $\sim$130$^\circ$. Despite several attempts, we only detected (99.7% conf.) the radio polarization once (during $T_2$, at 225.5 GHz): with degree (1.7$\pm$0.4)% and angle 112.5$^\circ$$\pm$5.5$^\circ$. The direction of the broad pc-scale jet is rather ambiguous and has been found to point to the east and south at different epochs; however, on larger scales (> 1.5 pc) the jet points toward the southeast ($\sim$135$^\circ$), similar to all of the MW polarization angles. Moreover, the X-ray to optical polarization degree ratios of $\sim$7 and $\sim$4 during $T_1$ and $T_2$, respectively, are similar to previous IXPE results for several HSP blazars. These findings, combined with the lack of correlation of temporal variability between the MW polarization properties, agree with an energy-stratified shock-acceleration scenario in HSP blazars.

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arXiv2024

Intermediate-luminosity Type IIP SN 2021gmj: a low-energy explosion with signatures of circumstellar material

We present photometric, spectroscopic and polarimetric observations of the intermediate-luminosity Type IIP supernova (SN) 2021gmj from 1 to 386 days after the explosion. The peak absolute V-band magnitude of SN 2021gmj is -15.5 mag, which is fainter than that of normal Type IIP SNe. The spectral evolution of SN 2021gmj resembles that of other sub-luminous supernovae: the optical spectra show narrow P-Cygni profiles, indicating a low expansion velocity. We estimate the progenitor mass to be about 12 Msun from the nebular spectrum and the 56Ni mass to be about 0.02 Msun from the bolometric light curve. We also derive the explosion energy to be about 3 x 10^{50} erg by comparing numerical light curve models with the observed light curves. Polarization in the plateau phase is not very large, suggesting nearly spherical outer envelope. The early photometric observations capture the rapid rise of the light curve, which is likely due to the interaction with a circumstellar material (CSM). The broad emission feature formed by highly-ionized lines on top of a blue continuum in the earliest spectrum gives further indication of the CSM at the vicinity of the progenitor. Our work suggests that a relatively low-mass progenitor of an intermediate-luminosity Type IIP SN can also experience an enhanced mass loss just before the explosion, as suggested for normal Type IIP SNe.

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arXiv2024

Detection of X-ray Polarization from the Blazar 1ES 1959+650 with the Imaging X-ray Polarimetry Explorer

Observations of linear polarization in the 2-8 keV energy range with the Imaging X-ray Polarimetry Explorer (IXPE) explore the magnetic field geometry and dynamics of the regions generating non-thermal radiation in relativistic jets of blazars. These jets, particularly in blazars whose spectral energy distribution peaks at X-ray energies, emit X-rays via synchrotron radiation from high-energy particles within the jet. IXPE observations of the X-ray selected BL Lac-type blazar 1ES 1959+650 in 2022 May 3-4 showed a significant linear polarization degree of $Π_\mathrm{x} = 8.0\% \pm 2.3\%$ at an electric-vector position angle $ψ_\mathrm{x} = 123^\circ \pm 8^\circ$. However, in 2022 June 9-12, only an upper limit of $Π_\mathrm{x} \leq 5.1\%$ could be derived (at the 99% confidence level). The degree of optical polarization at that time $Π_\mathrm{O} \sim 5\%$ is comparable to the X-ray measurement. We investigate possible scenarios for these findings, including temporal and geometrical depolarization effects. Unlike some other X-ray selected BL Lac objects, there is no significant chromatic dependence of the measured polarization in 1ES 1959+650, and its low X-ray polarization may be attributed to turbulence in the jet flow with dynamical timescales shorter than 1 day.

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arXiv2023

Observations of Low and Intermediate Spectral Peak Blazars with the Imaging X-ray Polarimetry Explorer

We present X-ray polarimetry observations from the Imaging X-ray Polarimetry Explorer (IXPE) of three low spectral peak and one intermediate spectral peak blazars, namely 3C 273, 3C 279, 3C 454.3, and S5 0716+714. For none of these objects was IXPE able to detect X-ray polarization at the 3$σ$ level. However, we placed upper limits on the polarization degree at $\sim$10-30\%. The undetected polarizations favor models where the X-ray band is dominated by unpolarized photons upscattered by relativistic electrons in the jets of blazars, although hadronic models are not completely eliminated. We discuss the X-ray polarization upper limits in the context of our contemporaneous multiwavelength polarization campaigns.

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arXiv2023

Magnetic Field Properties inside the Jet of Mrk 421: Multiwavelength Polarimetry Including the Imaging X-ray Polarimetry Explorer

We conducted a polarimetry campaign from radio to X-ray wavelengths of the high-synchrotron-peak (HSP) blazar Mrk 421, including Imaging X-ray Polarimetry Explorer (IXPE) measurements on 2022 December 6-8. We detected X-ray polarization of Mrk 421 with a degree of $Π_{\rm X}$=14$\pm$1$\%$ and an electric-vector position angle $ψ_{\rm X}$=107$\pm$3$^{\circ}$ in the 2-8 keV band. From the time variability analysis, we find a significant episodic variation in $ψ_{\rm X}$. During 7 months from the first IXPE pointing of Mrk 421 in 2022 May, $ψ_{\rm X}$ varied across the range of 0$^{\circ}$ to 180$^{\circ}$, while $Π_{\rm X}$ maintained similar values within $\sim$10-15$\%$. Furthermore, a swing in $ψ_{\rm X}$ in 2022 June was accompanied by simultaneous spectral variations. The results of the multiwavelength polarimetry show that the X-ray polarization degree was generally $\sim$2-3 times greater than that at longer wavelengths, while the polarization angle fluctuated. Additionally, based on radio, infrared, and optical polarimetry, we find that rotation of $ψ$ occurred in the opposite direction with respect to the rotation of $ψ_{\rm X}$ over longer timescales at similar epochs. The polarization behavior observed across multiple wavelengths is consistent with previous IXPE findings for HSP blazars. This result favors the energy-stratified shock model developed to explain variable emission in relativistic jets. The accompanying spectral variation during the $ψ_{\rm X}$ rotation can be explained by a fluctuation in the physical conditions, e.g., in the energy distribution of relativistic electrons. The opposite rotation direction of $ψ$ between the X-ray and longer-wavelength polarization accentuates the conclusion that the X-ray emitting region is spatially separated from that at longer wavelengths.

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arXiv2023

Gamma rays from a reverse shock with turbulent magnetic fields in GRB 180720B

Gamma-ray bursts (GRBs) are the most electromagnetically luminous cosmic explosions. They are powered by collimated streams of plasma (jets) ejected by a newborn stellar-mass black hole or neutron star at relativistic velocities (near the speed of light). Their short-lived (typically tens of seconds) prompt $γ$-ray emission from within the ejecta is followed by long-lived multi-wavelength afterglow emission from the ultra-relativistic forward shock. This shock is driven into the circumburst medium by the GRB ejecta that are in turn decelerated by a mildly-relativistic reverse shock. Forward shock emission was recently detected up to teraelectronvolt-energy $γ$-rays, and such very-high-energy emission was also predicted from the reverse shock. Here we report the detection of optical and gigaelectronvolt-energy $γ$-ray emission from GRB 180720B during the first few hundred seconds, which is explained by synchrotron and inverse-Compton emission from the reverse shock propagating into the ejecta, implying a low-magnetization ejecta. Our optical measurements show a clear transition from the reverse shock to the forward shock driven into the circumburst medium, accompanied by a 90-degree change in the mean polarization angle and fluctuations in the polarization degree and angle. This indicates turbulence with large-scale toroidal and radially-stretched magnetic field structures in the reverse and forward shocks, respectively, which tightly couple to the physics of relativistic shocks and GRB jets -- launching, composition, dissipation and particle acceleration.

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arXiv2023

Photometry and Polarimetry of 2010 XC$_{15}$: Observational Confirmation of E-type Near-Earth Asteroid Pair

Asteroid systems such as binaries and pairs are indicative of physical properties and dynamical histories of the Small Solar System Bodies. Although numerous observational and theoretical studies have been carried out, the formation mechanism of asteroid pairs is still unclear, especially for near-Earth asteroid (NEA) pairs. We conducted a series of optical photometric and polarimetric observations of a small NEA 2010 XC$_{15}$ in 2022 December to investigate its surface properties. The rotation period of 2010 XC$_{15}$ is possibly a few to several dozen hours and color indices of 2010 XC$_{15}$ are derived as $g-r=0.435\pm0.008$, $r-i=0.158\pm0.017$, and $r-z=0.186\pm0.009$ in the Pan-STARRS system. The linear polarization degrees of 2010 XC$_{15}$ are a few percent at the phase angle range of 58$^{\circ}$ to 114$^{\circ}$. We found that 2010 XC$_{15}$ is a rare E-type NEA on the basis of its photometric and polarimetric properties. Taking the similarity of not only physical properties but also dynamical integrals and the rarity of E-type NEAs into account, we suppose that 2010 XC$_{15}$ and 1998 WT$_{24}$ are of common origin (i.e., asteroid pair). These two NEAs are the sixth NEA pair and first E-type NEA pair ever confirmed, possibly formed by rotational fission. We conjecture that the parent body of 2010 XC$_{15}$ and 1998 WT$_{24}$ was transported from the main-belt through the $ν_6$ resonance or Hungaria region.

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arXiv2023

Bridging between type IIb and Ib supernovae: SN IIb 2022crv with a very thin Hydrogen envelope

We present optical, near-infrared, and radio observations of supernova (SN) SN~IIb 2022crv. We show that it retained a very thin H envelope and transitioned from a SN~IIb to a SN~Ib; prominent H$α$ seen in the pre-maximum phase diminishes toward the post-maximum phase, while He {\sc i} lines show increasing strength. \texttt{SYNAPPS} modeling of the early spectra of SN~2022crv suggests that the absorption feature at 6200\,Å is explained by a substantial contribution of H$α$ together with Si {\sc ii}, as is also supported by the velocity evolution of H$α$. The light-curve evolution is consistent with the canonical stripped-envelope supernova subclass but among the slowest. The light curve lacks the initial cooling phase and shows a bright main peak (peak M$_{V}$=$-$17.82$\pm$0.17 mag), mostly driven by radioactive decay of $\rm^{56}$Ni. The light-curve analysis suggests a thin outer H envelope ($M_{\rm env} \sim$0.05 M$_{\odot}$) and a compact progenitor (R$_{\rm env}$ $\sim$3 R$_{\odot}$). An interaction-powered synchrotron self-absorption (SSA) model can reproduce the radio light curves with a mean shock velocity of 0.1c. The mass-loss rate is estimated to be in the range of (1.9$-$2.8) $\times$ 10$^{-5}$ M$_{\odot}$ yr$^{-1}$ for an assumed wind velocity of 1000 km s$^{-1}$, which is on the high end in comparison with other compact SNe~IIb/Ib. SN~2022crv fills a previously unoccupied parameter space of a very compact progenitor, representing a beautiful continuity between the compact and extended progenitor scenario of SNe~IIb/Ib.

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arXiv2023

Far-Ultraviolet to Near-Infrared Observations of SN 2023ixf: A high energy explosion engulfed in complex circumstellar material

We present early-phase panchromatic photometric and spectroscopic coverage spanning far-ultraviolet (FUV) to the near-infrared (NIR) regime of the nearest hydrogen-rich core-collapse supernova in the last 25 years, SN 2023ixf. We observe early 'flash' features in the optical spectra due to a confined dense circumstellar material (CSM). We observe high-ionization absorption lines (FeII, MgII) in the ultraviolet spectra from very early on. We also observe a multi-peaked emission profile of H-alpha in the spectrum beginning ~16 d, which indicates ongoing interaction of the SN ejecta with a pre-existing shell-shaped CSM having an inner radius of ~75 AU and an outer radius of ~140 AU. The shell-shaped CSM is likely a result of enhanced mass loss ~35-65 years before the explosion assuming a standard Red-Supergiant wind. The UV spectra are dominated by multiple highly ionized narrow absorption features and broad emission features from elements such as C, N, O, Si, Fe, and Ni. Based on early light curve models of Type II SNe, we infer that the nearby dense CSM confined to (7+-3)e14cm (~45 AU) is a result of enhanced mass loss (10^{-3.0+-0.5} Msol/yr) two decades before the explosion.

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arXiv2023

X-ray Polarization of BL Lacertae in Outburst

We report the first $> 99\%$ confidence detection of X-ray polarization in BL Lacertae. During a recent X-ray/$γ$-ray outburst, a 287 ksec observation (2022 November 27-30) was taken using the Imaging X-ray Polarimetry Explorer ({\it IXPE}), together with contemporaneous multiwavelength observations from the Neil Gehrels {\it Swift} observatory and {\it XMM-Newton} in soft X-rays (0.3--10~keV), {\it NuSTAR} in hard X-rays (3--70~keV), and optical polarization from the Calar Alto, and Perkins Telescope observatories. Our contemporaneous X-ray data suggest that the {\it IXPE} energy band is at the crossover between the low- and high-frequency blazar emission humps. The source displays significant variability during the observation, and we measure polarization in three separate time bins. Contemporaneous X-ray spectra allow us to determine the relative contribution from each emission hump. We find $>99\%$ confidence X-ray polarization $Π_{2-4{\rm keV}} = 21.7^{+5.6}_{-7.9}\%$ and electric vector polarization angle $ψ_{2-4{\rm keV}} = -28.7 \pm 8.7^{\circ}$ in the time bin with highest estimated synchrotron flux contribution. We discuss possible implications of our observations, including previous {\it IXPE} BL Lacertae pointings, tentatively concluding that synchrotron self-Compton emission dominates over hadronic emission processes during the observed epochs.

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arXiv2023

SN 2018gj: A Short-plateau Type II Supernova with Persistent Blue-shifted H-alpha Emission

We present an extensive, panchromatic photometric (UV, Optical, and NIR) and low-resolution optical spectroscopic coverage of a Type IIP supernova SN 2018gj that occurred on the outskirts of the host galaxy NGC 6217. From the V-band light curve, we estimate the plateau length to be ~ 70 +- 2 d, placing it among the very few well-sampled short plateau supernovae (SNe). With V-band peak absolute magnitude Mv < -17.0 +- 0.1 mag, it falls in the middle of the luminosity distribution of the Type II SNe. The colour evolution is typical to other Type II SNe except for an early elbow-like feature in the evolution of V-R colour owing to its early transition from the plateau to the nebular phase. Using the expanding photospheric method, we present an independent estimate of the distance to SN 2018gj. We report the spectral evolution to be typical of a Type II SNe. However, we see a persistent blue shift in emission lines until the late nebular phase, not ordinarily observed in Type II SNe. The amount of radioactive nickel (56Ni) yield in the explosion was estimated to be 0.026 +- 0.007 Msol. We infer from semi-analytical modelling, nebular spectrum, and 1-D hydrodynamical modelling that the probable progenitor was a red supergiant with a zero-age-main-sequence mass < 13 Msol. In the simulated hydrodynamical model light curves, reproducing the early optical bolometric light curve required an additional radiation source, which could be the interaction with the proximal circumstellar matter (CSM).

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arXiv2023

Discovery of X-ray polarization angle rotation in active galaxy Mrk 421

The magnetic field conditions in astrophysical relativistic jets can be probed by multiwavelength polarimetry, which has been recently extended to X-rays. For example, one can track how the magnetic field changes in the flow of the radiating particles by observing rotations of the electric vector position angle $Ψ$. Here we report the discovery of a $Ψ_{\mathrm x}$ rotation in the X-ray band in the blazar Mrk 421 at an average flux state. Across the 5 days of Imaging X-ray Polarimetry Explorer (IXPE) observations of 4-6 and 7-9 June 2022, $Ψ_{\mathrm x}$ rotated in total by $\geq360^\circ$. Over the two respective date ranges, we find constant, within uncertainties, rotation rates ($80 \pm 9$ and $91 \pm 8 ^\circ/\rm day$) and polarization degrees ($Π_{\mathrm x}=10\%\pm1\%$). Simulations of a random walk of the polarization vector indicate that it is unlikely that such rotation(s) are produced by a stochastic process. The X-ray emitting site does not completely overlap the radio/infrared/optical emission sites, as no similar rotation of $Ψ$ was observed in quasi-simultaneous data at longer wavelengths. We propose that the observed rotation was caused by a helical magnetic structure in the jet, illuminated in the X-rays by a localized shock propagating along this helix. The optically emitting region likely lies in a sheath surrounding an inner spine where the X-ray radiation is released.

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arXiv2023

Multicolor and multi-spot observations of Starlink's Visorsat

This study provides the results of simultaneous multicolor observations for the first Visorsat (STARLINK-1436) and the ordinary Starlink satellite, STARLINK-1113 in the $U$, $B$, $V$, $g'$, $r$, $i$, $R_{\rm C}$, $I_{\rm C}$, $z$, $J$, $H$, and $K_s$ bands to quantitatively investigate the extent to which Visorsat reduces its reflected light. Our results are as follows: (1) in most cases, Virorsat is fainter than STARLINK-1113, and the sunshade on Visorsat, therefore, contributes to the reduction of the reflected sunlight; (2) the magnitude at 550 km altitude (normalized magnitude) of both satellites often reaches the naked-eye limiting magnitude ($<$ 6.0); (3) from a blackbody radiation model of the reflected flux, the peak of the reflected components of both satellites is around the $z$ band; and (4) the albedo of the near infrared range is larger than that of the optical range. Under the assumption that Visorsat and STARLINK-1113 have the same reflectivity, we estimate the covering factor, $C_{\rm f}$, of the sunshade on Visorsat, using the blackbody radiation model: the covering factor ranges from $0.18 \leq C_{\rm f} \leq 0.92$. From the multivariable analysis of the solar phase angle (Sun-target-observer), the normalized magnitude, and the covering factor, the phase angle versus covering factor distribution presents a moderate anti-correlation between them, suggesting that the magnitudes of Visorsat depend not only on the phase angle but also on the orientation of the sunshade along our line of sight. However, the impact on astronomical observations from Visorsat-designed satellites remains serious. Thus, new countermeasures are necessary for the Starlink satellites to further reduce reflected sunlight.

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arXiv2023

SN 2020uem: A Possible Thermonuclear Explosion within A Dense Circumstellar Medium (II) The Properties of The CSM from Polarimetry and Light Curve Modeling

Type IIn/Ia-CSM supernovae (SNe IIn/Ia-CSM) are classified by their characteristic spectra, which exhibit narrow hydrogen emission lines originating from a strong interaction with a circumstellar medium (CSM) together with broad lines of intermediate-mass elements. We performed intensive follow-up observations of SN IIn/Ia-CSM 2020uem, including photometry, spectroscopy, and polarimetry. In this paper, we focus on the results of polarimetry. We performed imaging polarimetry at $66$ days and spectropolarimetry at $103$ days after the discovery. SN 2020uem shows a high continuum polarization of $1.0-1.5\%$ without wavelength dependence. Besides, the polarization degree and position angle keep roughly constant. These results suggest that SN 2020uem is powered by a strong interaction with a confined and aspherical CSM. We performed a simple polarization modeling, based on which we suggest that SN 2020uem has an equatorial-disk/torus CSM. Besides, we performed semi-analytic light-curve modeling and estimated the CSM mass. We revealed that the mass-loss rate in the final few hundred years immediately before the explosion of SN 2020uem is in the range of $0.01 - 0.05 {\rm ~M_{\odot}~yr^{-1}}$, and that the total CSM mass is $0.5-4 {\rm ~M_{\odot}}$. The CSM mass can be accommodated by not only a red supergiant (RSG) but a red giant (RG) or an asymptotic-giant-branch (AGB) star. As a possible progenitor scenario of SN 2020uem, we propose a white-dwarf binary system including an RG, RSG or AGB star, especially a merger scenario via common envelope evolution, i.e., the core-degenerate scenario or its variant.

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arXiv2023

SN 2020uem: A Possible Thermonuclear Explosion within A Dense Circumstellar Medium (I) The Nature of Type IIn/Ia-CSM SNe from Photometry and Spectroscopy

We have performed intensive follow-up observations of a Type IIn/Ia-CSM SN (SN IIn/Ia-CSM), 2020uem, with photometry, spectroscopy, and polarimetry. In this paper, we report on the results of our observations focusing on optical/near-infrared (NIR) photometry and spectroscopy. The maximum V-band magnitude of SN 2020uem is over $-19.5$ mag. The light curves decline slowly with a rate of $\sim 0.75 {\rm ~mag}/100 {\rm ~days}$. In the late phase ($\gtrsim 300$ days), the light curves show accelerated decay ($\sim 1.2 {\rm ~mag}/100 {\rm ~days}$). The optical spectra show prominent hydrogen emission lines and broad features possibly associated with Fe-peak elements. In addition, the $\rm Hα$ profile exhibits a narrow P-Cygni profile with the absorption minimum of $\sim 100 {\rm ~km~s^{-1}}$. SN 2020uem shows a higher $\rm Hα/Hβ$ ratio ($\sim 7$) than those of SNe IIn, which suggests a denser CSM. The NIR spectrum shows the Paschen and Brackett series with continuum excess in the H and Ks bands. We conclude that the NIR excess emission originates from newly-formed carbon dust. The dust mass ($M_{\rm d}$) and temperature ($T_{\rm d}$) are derived to be $(M_{\rm d}, T_{\rm d}) \sim (4-7 \times 10^{-5} {\rm ~M_{\odot}}, 1500-1600 {\rm ~K})$. We discuss the differences and similarities between the observational properties of SNe IIn/Ia-CSM and those of other SNe Ia and interacting SNe. In particular, spectral features around $\sim 4650$ {\text Å} and $\sim 5900$ {\text Å} of SNe IIn/Ia-CSM are more suppressed than those of SNe Ia; these lines are possibly contributed, at least partly, by \ion{Mg}{1}] and \ion{Na}{1}, and may be suppressed by high ionization behind the reverse shock caused by the massive CSM.

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arXiv2022

X-ray Polarization Observations of BL Lacertae

Blazars are a class of jet-dominated active galactic nuclei with a typical double-humped spectral energy distribution. It is of common consensus the Synchrotron emission to be responsible for the low frequency peak, while the origin of the high frequency hump is still debated. The analysis of X-rays and their polarization can provide a valuable tool to understand the physical mechanisms responsible for the origin of high-energy emission of blazars. We report the first observations of BL Lacertae performed with the Imaging X-ray Polarimetry Explorer ({IXPE}), from which an upper limit to the polarization degree $Π_X<$12.6\% was found in the 2-8 keV band. We contemporaneously measured the polarization in radio, infrared, and optical wavelengths. Our multiwavelength polarization analysis disfavors a significant contribution of proton synchrotron radiation to the X-ray emission at these epochs. Instead, it supports a leptonic origin for the X-ray emission in BL Lac.

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arXiv2022

The microvariability and wavelength dependence of polarization degree/angle of BL Lacertae in the outburst 2020 to 2021

We have obtained simultaneous and continuous photo-polarization observations of the blazar BL Lacertae in optical and near-infrared (NIR) bands during a historical outburst from 2020 to 2021. In total, fourteen nights of observations were performed where ten observations show microvariability on timescales of a few minutes to several hours. This suggests a compact emission region, and the timescales are difficult to explain by a one-zone shock-in-jet model. Moreover, we found significant differences in the polarization degree (PD) and angle between optical and NIR bands. Nine nights showed a PD in the optical band that is greater than or equal to that in the NIR band, which can be explained by either a shock-in-jet model or the Turbulent Extreme Multi-Zone (TEMZ) model. On the other hand, five nights showed higher PD in a NIR band than an optical band, which cannot be explained by simple shock-in-jet models nor the simple TEMZ model. The observed timescales and wavelength dependency of the PD and polarization angle suggest the existence of complicated multiple emission regions such as an irregular TEMZ model.

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arXiv2022

(3200) Phaethon Polarimetry in the Negative Branch: New Evidence for the Anhydrous Nature of the DESTINY+ Target Asteroid

We report on the first polarimetric study of (3200) Phaethon, the target of JAXA's DESTINY$^+$ mission, in the negative branch to ensure its anhydrous nature and to derive an accurate geometric albedo. We conducted observations at low phase angles (Sun-target-observer angle, alpha = 8.8-32.4 deg) from 2021 October to 2022 January and found that Phaethon has a minimum polarization degree $P_{min}$ = -1.3 +- 0.1 %, a polarimetric slope h = 0.22 +- 0.02 % deg$^{-1}$, and an inversion angle alpha$_0$ = 19.9 +- 0.3 deg. The derived geometric albedo is $p_V$ = 0.11 (in the range of 0.08-0.13). These polarimetric properties are consistent with anhydrous chondrites, and contradict hydrous chondrites and typical cometary nuclei.

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