We report multicolor optical imaging and polarimetry observations of the afterglow of the first TeV-detected gamma-ray burst (GRB), GRB 190114C, using the RINGO3 and MASTER II polarimeters. Observations begin 31s after the onset of the GRB and continue until ~7000s postburst. The light curves reveal a chromatic break at ~400-500s, with initial temporal decay {alpha}=1.669+/-0.013 flattening to {alpha}~1 postbreak, which we model as a combination of reverse and forward shock components with magnetization parameter R_B_~70. The observed polarization degree decreases from 7.7%+/-1.1% to 2%-4% 52-109s postburst and remains steady at this level for the subsequent ~2000s at a constant position angle. Broadband spectral energy distribution modeling of the afterglow confirms that GRB 190114C is highly obscured (A_v,HG_=1.49+/-0.12mag; N_H,HG_=(9.0+/-0.03)x10^22^cm^-2^). We interpret the measured afterglow polarization as intrinsically low and dominated by dust -in contrast to the P>10% measured previously for other GRB reverse shocks-with a small contribution from polarized prompt photons in the first minute. We test whether first- and higher-order inverse Compton scattering in a magnetized reverse shock can explain the low optical polarization and subteraelectronvolt emission but conclude that neither is explained in the reverse shock inverse Compton model. Instead, the unexpectedly low intrinsic polarization degree in GRB 190114C can be explained if large-scale jet magnetic fields are distorted on timescales prior to reverse shock emission.
We present early-time optical through infrared photometry of the bright Swift gamma-ray burst (GRB) 080607, starting only 6s following the initial trigger in the rest frame. Complemented by our previously published spectroscopy, this high-quality photometric data set allows us to solve for the extinction properties of the redshift 3.036 sightline, giving perhaps the most detailed information to date on the ultraviolet continuum absorption properties of any sightline outside our Local Group.
We present a multi-wavelength analysis of Swift gamma-ray burst GRB 090727, for which optical emission was detected during the prompt {gamma}-ray emission by the 2m autonomous robotic Liverpool Telescope and subsequently monitored for a further two days with the Liverpool and Faulkes Telescopes. Within the context of the standard fireball model, we rule out a reverse shock origin for the early-time optical emission in GRB 090727 and instead conclude that the early-time optical flash likely corresponds to emission from an internal dissipation process. Putting GRB 090727 into a broader observational and theoretical context, we build a sample of 36 {gamma}-ray bursts (GRBs) with contemporaneous early-time optical and {gamma}-ray detections. From these GRBs, we extract a sub-sample of 18 GRBs, which show optical peaks during prompt {gamma}-ray emission, and perform detailed temporal and spectral analysis in {gamma}-ray, X-ray, and optical bands. We find that in most cases early-time optical emission shows sharp and steep behavior, and notice a rich diversity of spectral properties. Using a simple internal shock dissipation model, we show that the emission during prompt GRB phase can occur at very different frequencies via synchrotron radiation. Based on the results obtained from observations and simulation, we conclude that the standard external shock interpretation for early-time optical emission is disfavored in most cases due to sharp peaks ({Delta}t/t<1) and steep rise/decay indices, and that internal dissipation can explain the properties of GRBs with optical peaks during {gamma}-ray emission.
We present optical (g', R_c_, and I_c_) to near-infrared (J) simultaneous photometric observations for a primary transit of GJ3470b, a Uranus-mass transiting planet around a nearby M dwarf, by using the 50cm MITSuME telescope and the 188cm telescope, both at the Okayama Astrophysical Observatory. From these data, we derive the planetary mass, radius, and density as 14.1 +/-1.3M_{Earth}_, 4.32_-0.10_^+0.21^R_{Earth}_, and 0.94+/-0.12g/cm3, respectively, thus confirming the low density that was reported by Demory et al. (2013ApJ...768..154D) based on the Spitzer/IRAC 4.5{mu}m photometry (0.72_-0.12_^+0.13^g/cm3). Although the planetary radius is about 10% smaller than that reported by Demory et al., this difference does not alter their conclusion that the planet possesses a hydrogen-rich envelope whose mass is approximately 10% of the planetary total mass. On the other hand, we find that the planet-to-star radius ratio (R_p_/R_s_) in the J band (0.07577_-0.00075_^+0.00072^) is smaller than that in the I_c_(0.0802+/-0.0013) and 4.5{mu}m (0.07806_-0.00054_^+0.00052^) bands by 5.8%+/-2.0% and 2.9%+/-1.1%, respectively. A plausible explanation for the differences is that the planetary atmospheric opacity varies with wavelength due to absorption and/or scattering by atmospheric molecules. Although the significance of the observed R_p_/R_s_variations is low, if confirmed, this fact would suggest that GJ3470b does not have a thick cloud layer in the atmosphere. This property would offer a wealth of opportunity for future transmission-spectroscopic observations of this planet to search for certain molecular features, such as H_2_O, CH_4_, and CO, without being prevented by clouds.
The mechanisms giving rise to diffuse radio emission in galaxy clusters and, in particular, their connection with cluster mergers are still being debated. We explore the internal dynamics of Abell 2254, which has been shown to host a very clumpy and irregular radio halo. Our analysis is mainly based on redshift data for 128 galaxies acquired at the Telescopio Nazionale Galileo. We combined galaxy velocities and positions to select 110 cluster galaxies and analyze its internal dynamics. We also used new (g', r', i') photometric data acquired at the Isaac Newton Telescope, and (V, i') photometric data available in the Subaru Archive. X-ray data from the XMM-Newton Science Archive were analyzed to study the hot gas component.
We report on our detailed characterization of Earth's second known temporary natural satellite, or minimoon, asteroid 2020CD3. An artificial origin can be ruled out based on its area-to-mass ratio and broadband photometry, which suggest that it is a silicate asteroid belonging to the S or V complex in asteroid taxonomy. The discovery of 2020CD3 allows for the first time a comparison between known minimoons and theoretical models of their expected physical and dynamical properties. The estimated diameter of 1.2_-0.2_^+0.4^m and geocentric capture approximately a decade after the first known minimoon, 2006RH120, are in agreement with theoretical predictions. The capture duration of 2020CD3 of at least 2.7yr is unexpectedly long compared to the simulation average, but it is in agreement with simulated minimoons that have close lunar encounters, providing additional support for the orbital models. 2020CD3's atypical rotation period, significantly longer than theoretical predictions, suggests that our understanding of meter-scale asteroids needs revision. More discoveries and a detailed characterization of the population can be expected with the forthcoming Vera C. Rubin Observatory Legacy Survey of Space and Time.
gri light curves of the low-luminosity AGN NGC 4395
Short Name:
J/ApJ/756/73
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results of broadband photometric reverberation mapping (RM) to measure the radius of the broad-line region, and subsequently the black hole mass (M_BH_), in the nearby, low-luminosity active galactic nuclei NGC 4395. Using the Wise Observatory's 1m telescope equipped with the Sloan Digital Sky Survey g', r', and i' broadband filters, we monitored NGC 4395 for nine consecutive nights and obtained three light curves each with over 250 data points. The g' and r' bands include time variable contributions from H{beta} and H{alpha}, respectively, plus continuum. The i' band is free of broad lines and covers exclusively continuum. We show that by looking for a peak in the difference between the cross-correlation and the auto-correlation functions for all combinations of filters, we can get a reliable estimate of the time lag necessary to compute M_BH_. We measure the time lag for H{alpha} to be 3.6+/-0.8hr, comparable to previous studies using the line-resolved spectroscopic RM method. We argue that this lag implies a black hole mass of M_BH_=(4.9+/-2.6)x10^4^M_{sun}_.
Isolated early-type galaxies are evolving in unusually poor environments for this morphological family, which is typical of cluster inhabitants. We investigate the mechanisms driving the evolution of these galaxies. Several studies indicate that interactions, accretions, and merging episodes leave their signature on the galaxy structure, from the nucleus down to the faint outskirts. We focus on revealing such signatures, if any, in a sample of isolated early-type galaxies, and we quantitatively revise their galaxy classification. We observed 20 (out of 104) isolated early-type galaxies, selected from the AMIGA catalog, with the 4KCCD camera at the Vatican Advanced Technology Telescope (VATT) in the Sloan Digital Sky Survey (SDSS) g and r bands. These are the deepest observations of a sample of isolated early-type galaxies so far: on average, the light profiles reach {mu}_g_~=28.11+/-0.70mag/arcsec^2^ and {mu}_r_~=27.36+/-0,68mag/arcsec^2^. The analysis was performed using the AIDA package, providing point spread function-corrected 2D surface photometry up to the galaxy outskirts. The package provides a model of the 2D galaxy light distribution, which after model subtraction enhances the fine and peculiar structures in the residual image of the galaxies. Our re-classification suggests that the sample is composed of bona fide early-type galaxies spanning from ellipticals to late-S0s galaxies. Most of the surface brightness profiles are best fitted with a bulge plus disc model, suggesting the presence of an underlying disc structure. The residuals obtained after the model subtraction show the nearly ubiquitous presence of fine structures, such as shells, stellar fans, rings, and tails. Shell systems are revealed in about 60% of these galaxies. Because interaction, accretion, and merging events are widely interpreted as the origin of the fans, ripples, shells and tails in galaxies, we suggest that most of these isolated early-type galaxies have experienced such events. Because they are isolated (after 2-3Gyr), these galaxies are the cleanest environment in which to study phenomena connected with events like these.
We continuously monitored the blazar S5 0716+714 in the optical g, r, and i bands from 2017 November 10 to 2019 June 6. The total number of observations is 201 nights including 26973 data points. This is a very large quasi-simultaneous multicolor sample for the blazar. The average time spans and time resolutions are 3.4hr and 2.9min per night, respectively. During the period of observations, the target source in the r band brightens from 14.16m to 12.29m together with five prominent subflares, and then becomes fainter to 14.76m, and again brightens to 12.94m with seven prominent subflares. For the long-term variations, we find a strong flatter-when-brighter (FWB) trend at a low-flux state and then a weak FWB trend at a higher-flux state. A weak FWB trend at a low-flux state and then a strong FWB trend at a higher-flux state are also reported. Most subflares show strong FWB trends, except for two flares with a weak FWB trend. The particle acceleration and cooling mechanisms together with the superposition of the different FWB slopes from the subflares likely explain the optical color behaviors. A scenario of bent jet is discussed.
Compact groups of galaxies provide conditions similar to those experienced by galaxies in the earlier universe. Recent work on compact groups has led to the discovery of a dearth of mid-infrared transition galaxies (MIRTGs) in Infrared Array Camera (3.6-8.0{mu}m) color space as well as at intermediate specific star formation rates. However, we find that in compact groups these MIRTGs have already transitioned to the optical ([g-r]) red sequence. We investigate the optical color-magnitude diagram (CMD) of 99 compact groups containing 348 galaxies and compare the optical CMD with mid-infrared (mid-IR) color space for compact group galaxies. Utilizing redshifts available from Sloan Digital Sky Survey, we identified new galaxy members for four groups. By combining optical and mid-IR data, we obtain information on both the dust and the stellar populations in compact group galaxies. We also compare with more isolated galaxies and galaxies in the Coma Cluster, which reveals that, similar to clusters, compact groups are dominated by optically red galaxies. While we find that compact group transition galaxies lie on the optical red sequence, LVL+SINGS mid-IR transition galaxies span the range of optical colors. The dearth of mid-IR transition galaxies in compact groups may be due to a lack of moderately star-forming low mass galaxies; the relative lack of these galaxies could be due to their relatively small gravitational potential wells. This makes them more susceptible to this dynamic environment, thus causing them to more easily lose gas or be accreted by larger members.
