Multi-band Observations Research Articles

Revealing the Progenitor of SN 2021zby through Analysis of the TESS Shock-cooling Light Curve

We present early observations and analysis of the double-peaked Type IIb supernova (SN IIb) SN 2021zby. TESS captured the prominent early shock-cooling peak of SN 2021zby within the first ∼10 days after explosion with a 30 minute cadence. We present optical and near-infrared spectral series of SN 2021zby, including three spectra during the shock-cooling phase. Using a multiband model fit, we find that the inferred properties of its progenitor are consistent with a red supergiant or yellow supergiant, with an envelope mass of ∼0.30–0.65 M ⊙ and an envelope radius of ∼120–300 R ⊙. These inferred progenitor properties are similar to those of other SNe IIb with a double-peaked feature, such as SNe 1993J, 2011dh, 2016gkg, and 2017jgh. This study further validates the importance of the high cadence and early coverage in resolving the shape of the shock-cooling light curve, while the multiband observations, particularly UV, are also necessary to fully constrain the progenitor properties.

A black widow population dissection through HiPERCAM multiband light-curve modelling

ABSTRACT Black widows are extreme millisecond pulsar binaries where the pulsar wind ablates their low-mass companion stars. In the optical range, their light curves vary periodically due to the high irradiation and tidal distortion of the companion, which allows us to infer the binary parameters. We present simultaneous multiband observations obtained with the HIPERCAM instrument at the 10.4-m GTC telescope for six of these systems. The combination of this five-band (us,gs, rs, is, zs) fast photometer with the world’s largest optical telescope enables us to inspect the light curve range near minima. We present the first light curve for PSR J1641+8049, as well as attain a significant increase in signal to noise and cadence compared with previous publications for the remaining five targets: PSR J0023+0923, PSR J0251+2606, PSR J0636+5129, PSR J0952−0607, and PSR J1544+4937. We report on the results of the light-curve modelling with the Icarus code for all six systems, which reveals some of the hottest and densest companion stars known. We compare the parameters derived with the limited but steadily growing black widow population for which optical modelling is available. We find some expected correlations, such as that between the companion star mean density and the orbital period of the system, which can be attributed to the high number of Roche-lobe filling companions. On the other hand, the positive correlation between the orbital inclination and the irradiation temperature of the companion is puzzling. We propose such a correlation would arise if pulsars with magnetic axis orthogonal to their spin axis are capable of irradiating their companions to a higher degree.

Testing primordial black hole and measuring the Hubble constant with multiband gravitational-wave observations

There exist two kinds of stochastic gravitational-wave backgrounds associated with the primordial curvature perturbations. One is called induced gravitational wave due to the nonlinear coupling of curvature perturbations to tensor perturbations, while the other is produced by coalescences of binary primordial black holes formed when the large amplitude curvature perturbations reenter the horizon in the radiation dominant era. In this paper we find a quite useful relation for the peak frequencies of these two stochastic gravitational-wave backgrounds. This relation can not only offer a smoking-gun criterion for the existence of primordial black holes, but also provide a method for measuring the Hubble constant H 0 by multiband observations of the stochastic gravitational-wave backgrounds.

Adaptive Smoothing with Ambiguity Fixation for GNSS Post-Processing

We propose a complete post-processing solution for GNSS (global navigation satellite system) positioning leveraging linear-regression Kalman filtering methods, employed in a Rauch-Tung-Striebel (RTS) smoothing context, where the model parameters are adapted in an expectation maximization (EM) framework. In particular, we (i) discuss the effects of using different moment approximations in the smoother; (ii) demonstrate that it is advantageous to fixate the integer ambiguities on the smoothing posterior; and (iii) show that the proposed method is viable for a wide range of GNSS measurement models, including single difference, double difference, and ionosphere-free combinations of the multi-band GNSS observations.

Investigating the radiative properties of LHAASO J1908 + 0621

ABSTRACT LHAASO J1908+0621 has recently been detected as a source emitting γ-rays with energies above 100 TeV, and multiband observations show that a break around 1 TeV appears in the γ-ray spectrum. We have reanalysed the GeV γ-ray properties of the 100-TeV source using 14 years of data recorded by the Fermi Large Area Telescope (Fermi-LAT). The spectrum in the energy range range 30–500 GeV has an index of 1.50 ± 0.26, which is much smaller than that detected in TeV γ-rays. Additionally, the radiation properties of this source are investigated based on a one-zone time-dependent model. In the model, LHAASO J1908+0621 is associated with a pulsar wind nebula (PWN) powered by the pulsar PSR J1907 + 0602. High-energy particles composed of electrons and positrons are injected into the nebula. Multiband non-thermal emission is produced via synchrotron radiation and inverse Compton scattering (ICS). Taking the effect of radiative energy losses and adiabatic cooling into account, the spectral energy distribution from a model with a broken power law for the distribution of the injected particles can explain the fluxes detected in the γ-ray bands. The results support the idea that LHAASO J1908 + 0621 originates from the PWN powered by PSR J1907 + 0602, and γ-rays with energy above 100 TeV are produced by electrons/positrons in the nebula via ICS.

Chromatic optical polarization of BL Lac: while faint and bright

ABSTRACT Due to the first results on astrophysical X-ray polarization provided by IXPE observatory, the interest in wavelength-dependent synchrotron polarization of BL Lac-type objects increases. This paper presents the results of multiband optical observations of the well-known blazar named BL Lac (z = 0.069) in polarized light. It was shown that the object’s emission, regardless of its phase of activity, is characterized by the intraday variability of brightness and polarization with changes occurring on a time-scale of up to 1.5 h without any stable oscillation period. Polarimetric observations in the different optical bands show that the degree and angle of polarization of the blazar depend on the wavelength, and the maximum chromatism, as well as the maximum observed polarization degree, was detected during the minimum brightness state; during the flare state, the polarization chromatism changed along with the flux gradient on the time-scale of an hour. Qualitatively, such behaviour can be described by the shock-in-jet model, yet the chromatism amplitude and its rapid changes differ significantly from the model predictions and challenge the numerical calculations.

Photometric Confirmation and Characterization of the Ennomos Collisional Family in the Jupiter Trojans

Collisional families offer a unique window into the interior composition of asteroid populations. Previous dynamical studies of the Jupiter Trojans have uncovered a handful of potential collisional families, two of which have been subsequently confirmed through spectral characterization. In this paper, we present new multiband photometric observations of the proposed Ennomos family and derive precise g − i colors of 75 candidate family members. While the majority of the targets have visible colors that are indistinguishable from background objects, we identify 13 objects with closely grouped dynamical properties that have significantly bluer colors. We determine that the true Ennomos collisional family is tightly confined to and , and the majority of its confirmed members have near-solar spectral slopes, including some of the bluest objects hitherto discovered in the Trojan population. The property of distinctly neutral colors that is shared by both the Ennomos family and the previously characterized Eurybates family indicates that the spectral properties of freshly exposed surfaces in the Jupiter region are markedly different than the surfaces of uncollided Trojans. This implies that the processes of ice sublimation and space weathering at 5.2 au yield a distinct regolith chemistry from the primordial environment within which the Trojans were initially accreted. It also suggests that the Trojans were emplaced in their present-day location from elsewhere sometime after the initial population formed, which is a key prediction of recent dynamical instability models of solar system evolution.

A long-duration gamma-ray burst with a peculiar origin.

It is generally believed that long-duration gamma-ray bursts (GRBs) are associated with massive star core collapse1, whereas short-duration GRBs are associated with mergers of compact star binaries2. However, growing observations3-6 have suggested that oddball GRBs do exist, and several criteria (prompt emission properties, supernova/kilonova associations and host galaxy properties) rather than burst duration only are needed to classify GRBs physically7. A previously reported long-duration burst, GRB 060614 (ref. 3), could be viewed as a short GRB with extended emission if it were observed at a larger distance8 and was associated with a kilonova-like feature9. As a result, it belongs to the type I (compact star merger) GRB category and is probably of binary neutron star (NS) merger origin. Here we report a peculiar long-duration burst, GRB 211211A, whose prompt emission properties in many aspects differ from all known type I GRBs, yet its multiband observations suggest a non-massive-star origin. In particular, substantial excess emission in both optical and near-infrared wavelengths has been discovered (see also ref. 10), which resembles kilonova emission, as observed in some type I GRBs. These observations point towards a new progenitor type of GRBs. A scenario invoking a white dwarf (WD)-NS merger with a post-merger magnetar engine provides a self-consistent interpretation for all the observations, including prompt gamma rays, early X-ray afterglow, as well as the engine-fed11,12 kilonova emission.

The radial profile of dust grain size in the protoplanetary disc of DS Tau

ABSTRACT How do dust grains in protoplanetary discs overcome rapid radial drift and grow from micron size particles to planets is not well understood. The key is to search for evidence of dust accumulation and growth as a function of radius in the disc. We investigate the radial profile of grain size in the DS Tau disc by fitting multiband ALMA observations with self-consistent radiative transfer models. The best-fit grain sizes range from centimeters in the inner disc down to ${\sim }\, 30\, \mu {\rm m}$ in the outer regions. Such an inside-out decreasing tendency is consistent with theories of dust evolution. Based on the best-fit model, we find that dust of ${\sim }\, 2$ Jupiter masses has been depleted within the gap. By taking the gas-to-dust mass ratio into account, the lost mass is enough to form the 3.5 Jupiter mass planet inferred by literature hydrodynamic simulations. Moreover, our modelling also indicates that at the interface region between the gap and the ring, the grain size profile shows a discontinuity, with its amplitude dependent on the dust model adopted in the radiative transfer analysis. Future multiwavelength observations at higher angular resolutions are required to better constrain the grain size and its variation in the vicinity of disc substructures.

Detectability and parameter estimation of GWTC-3 events with LISA

Multiband observations of coalescing stellar-mass black holes binaries could deliver valuable information on the formation of those sources and potential deviations from General Relativity. Some of these binaries might be first detected by the space-based detector LISA and, then, several years later, observed with ground-based detectors. Due to large uncertainties in astrophysical models, it is hard to predict the population of such binaries that LISA could observe. In this work, we assess the ability of LISA to detect the events of the third catalogue of gravitational wave sources released by the LIGO/Virgo/KAGRA collaboration. We consider the possibility of directly detecting the source with LISA and performing archival searches in the LISA data stream, after the event has been observed with ground-based detectors. We also assess how much could LISA improve the determination of source parameters. We find that it is not guaranteed that any event other than GW150914 would have been detected. Nevertheless, if any event is detected by LISA, even with a very low signal-to-noise ratio, the measurement of source parameters would improve by combining observations of LISA and ground based detectors, in particular for the chirp mass.

MUPHOTEN: A MUlti-band PHOtometry Tool for TElescope Network

The early and complete temporal characterization of optical, fast, transient sources requires continuous and multiband observations over different timescales (hours to months). For time-domain astronomy, using several telescopes to analyze single objects is the usual method, allowing the acquisition of highly sampled light curves. Taking a series of images each night helps to construct an uninterrupted chain of observations with a high cadence and low duty cycle. Speed is paramount, especially at early times, in order to capture early features in the light curve that help determine the nature of the observed transients and assess their astrophysical properties. However, the problem of rapidly extracting source properties (temporal and color evolution) with a heterogeneous data set remains. Consequently, we present Muphoten, a general and fast-computation photometric pipeline able to address these constraints. It is suitable for extracting transient brightness over multitelescope and multiband networks to create a single homogeneous photometric time series. We show the performance of Muphoten with observations of the optical transient SN 2018cow (from 2018 June to 2018 July), monitored by the GRANDMA network and with the publicly available data of the Liverpool Telescope.

Short GRB Host Galaxies. I. Photometric and Spectroscopic Catalogs, Host Associations, and Galactocentric Offsets

We present a comprehensive optical and near-infrared census of the fields of 90 short gamma-ray bursts (GRBs) discovered in 2005–2021, constituting all short GRBs for which host galaxy associations are feasible (≈60% of the total Swift short GRB population). We contribute 274 new multi-band imaging observations across 58 distinct GRBs and 26 spectra of their host galaxies. Supplemented by literature and archival survey data, the catalog contains 542 photometric and 42 spectroscopic data sets. The photometric catalog reaches 3σ depths of ≳24–27 mag and ≳23–26 mag for the optical and near-infrared bands, respectively. We identify host galaxies for 84 bursts, in which the most robust associations make up 56% (50/90) of events, while only a small fraction, 6.7%, have inconclusive host associations. Based on new spectroscopy, we determine 18 host spectroscopic redshifts with a range of z ≈ 0.15–1.5 and find that ≈23%–41% of Swift short GRBs originate from z > 1. We also present the galactocentric offset catalog for 84 short GRBs. Taking into account the large range of individual measurement uncertainties, we find a median of projected offset of ≈7.7 kpc, for which the bursts with the most robust associations have a smaller median of ≈4.8 kpc. Our catalog captures more high-redshift and low-luminosity hosts, and more highly offset bursts than previously found, thereby diversifying the population of known short GRB hosts and properties. In terms of locations and host luminosities, the populations of short GRBs with and without detectable extended emission are statistically indistinguishable. This suggests that they arise from the same progenitors, or from multiple progenitors, which form and evolve in similar environments. All of the data products are available on the Broadband Repository for Investigating Gamma-Ray Burst Host Traits website.

Photometric studies on the host galaxies of gamma-ray bursts using 3.6m Devasthal optical telescope

In this article, we present multi-band photometric observations and analysis of the host galaxies for a sample of five interesting gamma-ray bursts (GRBs) observed using the 3.6m Devasthal Optical Telescope (DOT) and the back-end instruments. The host galaxy observations of GRBs provide unique opportunities to estimate the stellar mass, ages, star-formation rates, and other vital properties of the burst environments and hence progenitors. We performed a detailed spectral energy distribution (SED) modeling of the five host galaxies using an advanced tool called Prospector, a stellar population synthesis model. Furthermore, we compared the results with a larger sample of well-studied host galaxies of GRBs, supernovae, and normal star-forming galaxies. Our SED modeling suggests that GRB 130603B, GRB 140102A, GRB 190829A, and GRB 200826A have massive host galaxies with high star formation rates (SFRs). On the other hand, a supernovae-connected GRB 030329 has a rare low-mass galaxy with a low star formation rate. We also find that GRB 190829A has the highest (in our sample) amount of visual dust extinction and gas in its local environment of the host, suggesting that the observed very high energy emission from this burst might have a unique local environment. Broadly, the five GRBs in our sample satisfy the typical correlations between host galaxies parameters and these physical parameters are more common to normal star-forming galaxies at the high-redshift Universe. Our results also demonstrate the capabilities of 3.6m DOT and the back-end instruments for the deeper photometric studies of the host galaxies of energetic transients such as GRBs, supernovae, and other transients in the long run.

Probing the speed of gravity with LVK, LISA, and joint observations

Theories of dark energy that affect the speed of gravitational waves c_{textrm{GW}} on cosmological scales naturally lead to a frequency-dependent transition of that speed close to the LIGO/Virgo/KAGRA (LVK) band. While observations such as GW170817 assure us that c_{textrm{GW}} is extremely close to the speed of light in the LVK band, a frequency-dependent transition below the LVK band is a smoking-gun signal for large classes of dynamical dark energy theories. Here we discuss (1) how the remnants of such a transition can be constrained with observations in the LVK band, (2) what signatures are associated with such a transition in the LISA band, and (3) how joint observations in the LVK and LISA bands allow us to place tight constraints on this transition and the underlying theories. We find that deviations of c_{textrm{GW}} can be constrained down to a level of sim 10^{-17} in the LVK and LISA bands even for mild frequency-dependence, much stronger than existing bounds for frequency-independent c_{textrm{GW}}ne c. We use the strain data from GW170817 to bound the deviation of c_{textrm{GW}} to be less than 10^{-17} at 100 Hz and less than 10^{-18} at 500 Hz. We also identify a particularly interesting type of transition in between the LVK and LISA bands and show how multi-band observations can constrain this further. Finally, we discuss what these current and forecasted constraints imply for the underlying dark energy theories.

Are the Magnetic Field Directions of Surrounding Loops a Key Parameter for Confining a Solar Filament Eruption?

Using high-resolution Hα data from the 1 m New Vacuum Solar Telescope, combined with multiband Atmospheric Imaging Assembly extreme ultraviolet observations and Helioseismic and Magnetic Imager light-of-sight magnetograms from the Solar Dynamical Observatory, we study a quiet-Sun filament eruption on 2019 November 1. During the erupting process, the filament was blocked by at least three sets of surrounding loops (L1–L3). The magnetic field direction of L2 is opposite to that of the top segment of the erupting filament. While the top segment contacted L2, a current sheet formed between L2 and the top segment. Then, magnetic reconnection took place, resulting in the destruction of L2 and the filament. On the other hand, the magnetic field direction of L1 is the same as that of the left leg of the erupting filament, and that of L3 is the same as that of the right leg. The left leg expanded eastward and met L1, then it stopped. The right leg expanded westward and collided with L3. It rebounded and finally stopped at the interaction region. These observations imply that the magnetic field directions of the surrounding magnetic structures are a key parameter for confining a filament eruption. While the field direction of a surrounding structure is the same as that of an eruptive filament, the filament is confined.

GRB Afterglow of the Sub-relativistic Materials with Energy Injection

Sub-relativistic materials launched during the merger of binary compact objects and the core collapse of massive stars acquire velocity structures when expanding in a stratified environment. The remnant (either a spinning magnetized neutron star (NS) or a central black hole) from the compact object or core collapse could additionally inject energy into the afterglow via spin-down luminosity or/and by accreting fallback material, producing a refreshed shock, modifying the dynamics, and leading to rich radiation signatures at distinct timescales and energy bands with contrasting intensities. We derive the synchrotron light curves evolving in a stratified environment when a power-law velocity distribution parameterizes the energy of the shock, and the remnant continuously injects energy into the blast wave. As the most relevant case, we describe the latest multiwavelength afterglow observations (≳900 days) of the GW170817/GRB 170817A event via a synchrotron afterglow model with energy injection of a sub-relativistic material. The features of the remnant and the synchrotron emission of the sub-relativistic material are consistent with a spinning magnetized NS and the faster blue kilonova afterglow, respectively. Using the multiband observations of some short bursts with evidence of kilonovae, we provide constraints on the expected afterglow emission.

LAMOST MRS-N Observation of the W80 Region

The spectral observations and analysis for the W80 region are presented by using the data of Medium-Resolution Spectroscopic Survey of Nebulae (MRS-N) with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). A total of 2982 high-quality nebular spectra have been obtained in the 20 square degree field of view which covers the W80 complex, and the largest sample of spectral data has been established for the first time. The relative intensities, radial velocities (RVs), and full widths at half maximum (FWHMs) are measured with the high spectral resolution of LAMOST MRS-N, for Hα λ6563 Å, [N ii] λλ6548 Å, 6584 Å, and [S ii] λλ6716 Å, 6731 Å emission lines. In the field of view of the whole W80 region, the strongest line emissions are found to be consistent with the bright nebulae NGC 7000, IC 5070, and LBN 391, and weak line emissions also exist in the Middle Region, where no bright nebulae are detected by the wide-band optical observations. The large-scale spectral observations of the W80 region reveal the systematic spatial variations of RVs and FWHMs, and several unique structural features. A “curved feature” to the east of NGC 7000, and a “jet feature” to the west of LBN 391 are detected to be showing larger RVs. A “wider FWHM region” is identified in the eastern part of NGC 7000. The variations of [S ii]/Hα ratios display a gradient from southwest to northeast in the NGC 7000 region, and manifest a ring shape around the “W80 bubble” ionized by an O-type star in L935. Further spectral and multi-band observations are guaranteed to investigate in detail the structural features.

Multiband Detection of Repeating FRB 20180916B

We present a multiband study of FRB 20180916B, a repeating source with a 16.3 day periodicity. We report the detection of four, one, and seven bursts from observations spanning 3 days using the upgraded Giant Metrewave Radio Telescope (300–500 MHz), the Canadian Hydrogen Intensity Mapping Experiment (400–800 MHz) and the Green Bank Telescope (600–1000 MHz), respectively. We report the first ever detection of the source in the 800–1000 MHz range along with one of the widest instantaneous bandwidth detections (200 MHz) at lower frequencies. We identify 30 μs wide structures in one of the bursts at 800 MHz, making it the lowest frequency detection of such structures for this fast radio burst thus far. There is also a clear indication of high activity of the source at a higher frequency during earlier phases of the activity cycle. We identify a gradual decrease in the rotation measure over two years and no significant variations in the dispersion measure. We derive useful conclusions about progenitor scenarios, energy distribution, emission mechanisms, and variation of the downward drift rate of emission with frequency. Our results reinforce that multiband observations are an effective approach to study repeaters, and even one-off events, to better understand their varying activity and spectral anomalies.

X-ray pulsar HD 49798: a contracting white dwarf with a debris disk?

HD 49798/RX J0648.0C4418 is a peculiar binary including a hot subdwarf of O spectral type and a compact companion in a 1.55 day orbit. Based on the steady spin period derivative Ṗ = (−2.17 ± 0.01) × 10−15 s s−1 , the compact object was thought to be a contracting young white dwarf (WD). However, the X-ray luminosity produced by the wind accretion of the massive WD is one order of magnitude smaller than the observed value. In this work, we propose an alternative model to account for the observed X-ray luminosity. If the WD were surrounded by a debris disk, the accretion from the debris disk could produce the observed X-ray luminosity and X-ray pulses. Based on the time-varying accretion rate model, the current mass of the debris disk is constrained to 3.9 × 10−6 M⊙. The accretion torque exerted by such a debris disk can only influence the spin evolution of the WD in the early stages, and its affect is obviously smaller than that caused by the contraction of the WD in the current stage. According to accretion theory, the magnetic field of the WD is constrained to ∼(0.7−7) × 104 G. The calculated conventional polar cap radius of the WD is larger than the observed emitting-zone radius, which probably originates from the existence of strong and small-scale local magnetic field in the polar cap surface. We expect that further multiband observations of this source could help us to confirm or rule out the existence of a debris disk.

Polarization, polarizing efficiency, and grain alignment towards the direction of the cluster NGC 2345

ABSTRACT We have investigated the grain alignment and dust properties towards the direction of the cluster NGC 2345 using the multiband optical polarimetric observations. For the majority of the stars, the observed polarization is found to be due to the interstellar medium with average values of maximum polarization and wavelength corresponding to it as 1.55 per cent and 0.58 $\mu$m, respectively. This reveals a similar size distribution of dust grains to that in the general interstellar medium in the direction of NGC 2345. Alteration of dust properties near the distance of 1.2 kpc towards the direction of NGC 2345 has been noticed. The dust grains located beyond this distance are found to be aligned with the Galactic magnetic field, whereas a dispersion in the orientation of the dust grains lying in the foreground of this distance is found. Polarizing efficiency of grains in this direction is found to be close to the average efficiency for our Galaxy. The decreased grain size along with the increased polarizing efficiency towards the core region of the cluster indicates the local radiation field is higher within the cluster, which is responsible for the increased alignment efficiency of small grains. The wavelength of maximum polarization (associated with the average size of aligned grains) is also found to increase with extinction and reduces with the increase in polarizing efficiency, which can be explained by the radiative torque alignment mechanism.