The Study of X-Ray Flux Variability of M87 Imazawa, Ryo; Fukazawa, Yasushi; Takahashi, Hiromitsu
Astrophysical journal/The Astrophysical journal,
10/2021, Letnik:
919, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract
We searched for a short-term X-ray variability of the M87 core and jet from archival X-ray data with long exposure data taken by the Suzaku, Chandra, and NuSTAR telescopes. We found the ...intraday variability for the Suzaku data obtained in 2006, and for the Chandra core obtained in 2017. The intraday variability suggested a minute emission region about the size of the Schwarzschild radius of the M87 supermassive black hole. Suzaku could not resolve a core and HST-1; however, in 2006, HST-1 was much brighter than the core, and thus, the variability is likely due to the HST-1. Since the photon index in 2006 was 2.38, the emission was possibly synchrotron emission from the local shock region in the HST-1, indicating that the particle acceleration of TeV electrons occurred far away (∼100 pc) from the core. Assuming the fading time to be equal to the synchrotron cooling time, the magnetic field is constrained to be
B
∼ 1.94
δ
1/3
mG. Moreover, the photon index of the core in 2017 was approximately 1.96; thus, the possible emission was from the radiative inefficiency accretion flow of the core or inverse Compton scattering in the jet. Intraday time variability prefers the latter possibility.
Abstract
We present early-phase panchromatic photometric and spectroscopic coverage spanning the far-ultraviolet to near-infrared regime of the nearest hydrogen-rich core-collapse supernova (SN) in ...the last 25 yr, SN 2023ixf. We observe early “flash” features in the optical spectra due to confined dense circumstellar material (CSM). We observe high-ionization absorption lines (Fe
ii
, Mg
ii
) in the ultraviolet spectra from very early on. We also observe a multipeaked emission profile of H
α
in the spectrum beginning at ∼16 days, which indicates ongoing interaction of the SN ejecta with a preexisting 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 yr before the explosion assuming a standard red supergiant wind. The UV spectra are dominated by multiple highly ionized narrow absorption 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 × 10
14
cm (∼45 au) is a result of enhanced mass loss (10
−3.0±0.5
M
⊙
yr
−1
) two decades before the explosion.
Asteroid systems such as binaries and pairs are indicative of the physical properties and dynamical histories of 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 XC15 in 2022 December to investigate its surface properties. The rotation period of 2010 XC15 is possibly a few to several dozen hours and the color indices of 2010 XC15 are derived as g − r = 0.435 ± 0.008, r − i = 0.158 ± 0.017, and r − z = 0.186 ± 0.009 in the Pan-STARRS system. The linear polarization degrees of 2010 XC15 are a few percent at the phase angle range of 58°–114°. We found that 2010 XC15 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 XC15 and 1998 WT24 are of common origin (i.e., an 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 XC15 and 1998 WT24 was transported from the main belt through the ν6 resonance or Hungaria region.
Abstract
Type IIn/Ia-CSM supernovae (SNe IIn/Ia-CSM) are classified by their characteristic spectra, which exhibit narrow hydrogen emission lines originating from 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 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 strong interaction with a confined and aspherical CSM. We performed 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
M
⊙
yr
−1
, and that the total CSM mass is 0.5–4
M
⊙
. The CSM mass can be accommodated by not only a red supergiant (RSG), but also by 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 a variant.
ABSTRACT
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, α = 8.8–32.4°) from 2021 October to 2022 January and found that Phaethon has a minimum polarization degree Pmin = −1.3 ± 0.1 per cent, a polarimetric slope h = 0.22 ± 0.02 per cent deg−1, and an inversion angle α0 = 19.9 ± 0.3°. The derived geometric albedo is pV = 0.11 (in the range of 0.08–0.13). These polarimetric properties are consistent with anhydrous chondrites, contradict hydrous chondrites, and typical cometary nuclei.
Abstract
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 an SN IIb to an SN Ib; ...prominent H
α
seen in the pre-maximum phase diminishes toward the post-maximum phase, while He
i
lines show increasing strength.
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
ii
, as is also supported by the velocity evolution of H
α
. The light-curve evolution is consistent with the canonical stripped-envelope SN subclass but among the slowest. The light curve lacks the initial cooling phase and shows a bright main peak (peak
M
V
= −17.82 ± 0.17 mag), mostly driven by radioactive decay of
56
Ni. The light-curve analysis suggests a thin outer H envelope (
M
env
∼ 0.05
M
⊙
) and a compact progenitor (
R
env
∼ 3
R
⊙
). An interaction-powered synchrotron self-absorption model can reproduce the radio light curves with a mean shock velocity of 0.1
c
. The mass-loss rate is estimated to be in the range of (1.9−2.8) × 10
−5
M
⊙
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.
Abstract
We have performed intensive follow-up observations of a Type IIn/Ia-CSM supernova (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 less than −19.5 mag. The light curves decline slowly with a rate of ∼0.75 mag/100 days. In the late phase (≳300 days), the light curves show accelerated decay (∼1.2 mag/100 days). The optical spectra show prominent hydrogen emission lines and broad features possibly associated with Fe-peak elements. In addition, the H
α
profile exhibits a narrow P-Cygni profile with an absorption minimum of ∼100 km s
−1
. SN 2020uem shows a higher H
α
/H
β
ratio (∼7) than those of SNe IIn, which suggests a denser circumstellar medium (CSM). The NIR spectrum shows the Paschen and Brackett series with a 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
d
) and temperature (
T
d
) are derived to be (
M
d
,
T
d
) ∼ (4−7 × 10
−5
M
⊙
, 1500–1600 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 ∼4650 Å and ∼5900 Å of SNe IIn/Ia-CSM are more suppressed than those of SNe Ia; these lines are possibly contributed, at least partly, by Mg
i
and Na
i
, and may be suppressed by high ionization behind the reverse shock caused by the massive CSM.
Abstract We report the study of a huge optical intraday flare on 2021 November 12 at 2 a.m. UT in the blazar OJ 287. In the binary black hole model, it is associated with an impact of the secondary ...black hole on the accretion disk of the primary. Our multifrequency observing campaign was set up to search for such a signature of the impact based on a prediction made 8 yr earlier. The first I -band results of the flare have already been reported by Kishore et al. (2024). Here we combine these data with our monitoring in the R -band. There is a big change in the R – I spectral index by 1.0 ± 0.1 between the normal background and the flare, suggesting a new component of radiation. The polarization variation during the rise of the flare suggests the same. The limits on the source size place it most reasonably in the jet of the secondary BH. We then ask why we have not seen this phenomenon before. We show that OJ 287 was never before observed with sufficient sensitivity on the night when the flare should have happened according to the binary model. We also study the probability that this flare is just an oversized example of intraday variability using the Krakow data set of intense monitoring between 2015 and 2023. We find that the occurrence of a flare of this size and rapidity is unlikely. In machine-readable Tables 1 and 2, we give the full orbit-linked historical light curve of OJ 287 as well as the dense monitoring sample of Krakow.
Abstract
We study the optical flux and polarization variability of the binary black hole blazar OJ 287 using quasi-simultaneous observations from 2015 to 2023 carried out using telescopes in the USA, ...Japan, Russia, Crimea, and Bulgaria. This is one of the most extensive quasi-simultaneous optical flux and polarization variability studies of OJ 287. OJ 287 showed large amplitude, ∼3.0 mag flux variability, large changes of ∼37% in degree of polarization, and a large swing of ∼215° in the angle of the electric vector of polarization. During the period of observation, several flares in flux were detected. Those flares are correlated with a rapid increase in the degree of polarization and swings in electric vector of polarization angle. A peculiar behavior of anticorrelation between flux and polarization degree, accompanied by a nearly constant polarization angle, was detected from JD 2,458,156 to JD 2,458,292. We briefly discuss some explanations for the flux and polarization variations observed in OJ 287.
We present a summary of the results of the OJ 287 observational campaign, which was carried out during the 2021/2022 observational season. This season is special in the binary model because the major ...axis of the precessing binary happens to lie almost exactly in the plane of the accretion disc of the primary. This leads to pairs of almost identical impacts between the secondary black hole and the accretion disk in 2005 and 2022. In 2005, a special flare called “blue flash” was observed 35 days after the disk impact, which should have also been verifiable in 2022. We did observe a similar flash and were able to obtain more details of its properties. We describe this in the framework of expanding cloud models. In addition, we were able to identify the flare arising exactly at the time of the disc crossing from its photo-polarimetric and gamma-ray properties. This is an important identification, as it directly confirms the orbit model. Moreover, we saw a huge flare that lasted only one day. We may understand this as the lighting up of the jet of the secondary black hole when its Roche lobe is suddenly flooded by the gas from the primary disk. Therefore, this may be the first time we directly observed the secondary black hole in the OJ 287 binary system.
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