A multiwavelength study of Swift GRB 060111B constraining the origin of its prompt optical emission

The BL Lac object 3C 66A was the target of an intensive multiwavelength monitoring campaign organized in 2003–2004. During the campaign, its spectral energy distribution (SED) was measured and flux measurements from radio to X-ray frequencies as well as upper limits in the very high energy (VHE) γ-ray regime were obtained. Here, we reproduce the SED and optical spectral variability pattern observed during our multiwavelength campaign using a time-dependent leptonic jet model. Our model could successfully simulate the observed SED and optical light curves and predict an intrinsic cutoff value for the VHE γ-ray emission at ~4 GeV implying the effect of the optical depth due to the intergalactic infrared background radiation (IIBR) to be negligible. Also, the contribution of external Comptonization (EIC), due to the presence of a broad-line region (BLR), in the emission of γ-ray photons could be significant early-on when the emission region is very close to the central engine but as it travels farther out, the production mechanism of hard X-ray and γ-ray photons becomes dominated by synchrotron self-Compton mechanism (SSC).

The BL Lac object 3C 66A was the target of an intensive multiwavelength monitoring campaign organized in 2003–2004. During the campaign, its spectral energy distribution (SED) was measured and flux measurements from radio to X-ray frequencies as well as upper limits in the very high energy (VHE) γ-ray regime were obtained. Here, we reproduce the SED and optical spectral variability pattern observed during our multiwavelength campaign using a time-dependent leptonic jet model. Our model could successfully simulate the observed SED and optical light curves and predict an intrinsic cutoff value for the VHE γ-ray emission at ~4 GeV implying the effect of the optical depth due to the intergalactic infrared background radiation (IIBR) to be negligible. Also, the contribution of external Comptonization (EIC), due to the presence of a broad-line region (BLR), in the emission of γ-ray photons could be significant early-on when the emission region is very close to the central engine but as it travels farther out, the production mechanism of hard X-ray and γ-ray photons becomes dominated by synchrotron self-Compton mechanism (SSC).

We present optical and near-infrared (NIR) photometry of 28 gamma-ray bursts (GRBs) detected by the \textit{Swift} satellite and rapidly observed by the Reionization and Transients Infrared/Optical (RATIR) camera. We compare the optical flux at fiducial times of 5.5 and 11 hours after the high-energy trigger to that in the X-ray regime to quantify optical darkness. 46$\pm$9 per cent (13/28) of all bursts in our sample and 55$\pm$10 per cent (13/26) of long GRBs are optically dark, which is statistically consistently with previous studies. Fitting RATIR optical and NIR spectral energy distributions (SEDs) of 19 GRBs, most (6/7) optically dark GRBs either occur at high-redshift ($z>4.5$) or have a high dust content in their host galaxies ($A_{\rm V} > 0.3$). Performing K-S tests, we compare the RATIR sample to those previously presented in the literature, finding our distributions of redshift, optical darkness, host dust extinction and X-ray derived column density to be consistent. The one reported discrepancy is with host galaxy dust content in the BAT6 sample, which appears inconsistent with our sample and other previous literature. Comparing X-ray derived host galaxy hydrogen column densities to host galaxy dust extinction, we find that GRBs tend to occur in host galaxies with a higher metal-to-dust ratio than our own Galaxy, more akin to the Large and Small Magellanic Clouds. Finally, to mitigate time evolution of optical darkness, we measure $\beta_{\rm OX,rest}$ at a fixed rest frame time, $t_{\rm rest}=1.5$ hours and fixed rest frame energies in the X-ray and optical regimes. Choosing to evaluate optical flux at $\lambda_{\rm rest}=0.25~\mu$m, we remove high-redshift as a source of optical darkness, demonstrating that optical darkness must result from either high-redshift, dust content in the host galaxy along the GRB sight line, or a combination of the two.

Astronomy & Astrophysics manuscript no. (will be inserted by hand later) arXiv:astro-ph/0504050v1 3 Apr 2005 A possible bright blue SN in the afterglow of GRB 020305 ⋆ J. Gorosabel 1,2 , J.P.U. Fynbo 3 , A. Fruchter 2 , A. Levan 4 , J. Hjorth 3 , P. Nugent 5 , A.J. Castro-Tirado 1 , J.M. Castro Cer´on 2,3 , J. Rhoads 2 , D. Bersier 2 , and I. Burud 2 Instituto de Astrof´isica de Andaluc´ia (IAA-CSIC), P.O. Box 03004, E-18080 Granada, Spain Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Kobenhavn O, Denmark Department of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK Lawrence Berkeley National Laboratory, MS 50-F, 1 Cyclotron Road, Berkeley, CA 94720, USA Received ; accepted Abstract. We report on ground-based and HST(+STIS) imaging of the afterglow and host galaxy of the Gamma-Ray Burst (GRB) of March 5 2002. The GRB occurred in a R = 25.17 ± 0.14 galaxy, which apparently is part of an interacting system. The lightcurve of the optical afterglow shows a rebrightening, or at least a plateau, 12–16 days after the gamma-ray event. U BV RIK ′ multi-band imaging of the afterglow ∼12 days after the GRB reveals a blue spectral energy distribution (SED). The SED is consistent with a power-law with a spectral index of β = −0.63 ± 0.16, but there is tentative evidence for deviations away from a power-law. Unfortunately, a spectroscopic redshift has not been secured for GRB 020305. From the SED we impose a redshift upper limit of z . 2.8, hence excluding the pseudo redshift of 4.6 reported for this burst. We discuss the possibilities for explaining the lightcurve, SED and host galaxy properties for GRB 020305. The most natural interpretation of the lightcurve and the SED is an associated supernova (SN). Our data can not precisely determine the redshift of the GRB. The most favoured explanation is a low redshift (z ∼ 0.2) SN, but a higher redshift (z & 0.5) SN can not be excluded. We also discuss less likely scenarios not based on SNe, like a burst occurring in a z = 2.5 galaxy with an extinction curve similar to that of the Milky Way. Key words. gamma rays: bursts – techniques: photometric 1. Introduction For long duration GRBs the relation with supernovae (SNe) became firmly established with the discovery of the type Ic su- pernova SN 2003dh associated with GRB 030329 (Stanek et al. 2003; Hjorth et al. 2003). This result lends strong support to the collapsar model (Woosley 1993), but a SN is also an ingredient in other models (e.g. Dado et al. 2003; Fryer & Heger 2004). However, the associated SNe follow a broad distribution of op- tical luminosities (Zeh et al. 2004). Furthermore the connection of GRBs with SNe of other types than Ic can not be excluded, motivated by the two possible associations of GRBs and II type SNe (SN 1997cy, Germany et al. 2000; SN 1999E, Rigon et al. 2003). Therefore, the afterglow lightcurves and SEDs around the SN peak are far from being described by an universal SN template. In this study we present ground and space-based opti- cal observations of GRB 020305 carried out from 11.5 to 321.2 days after the burst. Send offprint requests to: J. Gorosabel Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden. Correspondence to: jgu@iaa.es GRB 020305 was localised by the HETE-II satellite on March 5.4968 UT (Ricker et al. 2002). The high-energy emis- sion as seen by the Interplanetary network (IPN) consisted in two broad pulses, with a total GRB duration of ∼280s (Hurley et al. 2002), placing it in the long-soft burst category. Price et al. (2002) reported the presence of a transient optical source in the HETE-II/IPN error box in images taken ∼20 hours after the GRB. Further imaging confirmed the fading behaviour of the candidate (Lee et al. 2002; Ohyama et al. 2002). The paper is structured as follows: Sect. 2 details the ob- servations and the data reduction, Sect. 3 reports the results on the SED, lightcurve and host galaxy, Sect. 4 discusses several interpretations of the results, and finally Sect. 5 draws the con- clusions of this study. 2. Observations and data reduction 2.1. NOT observations We observed the field of GRB 020305 from the ground with the 2.56-m Nordic Optical Telescope (NOT) on 2002 March 16.95–22.18 UT, i.e. 11.45–16.68 days after the GRB. The in- strument used was the Andaluc´ia Faint Object Spectrograph (ALFOSC) equipped with a 2048 2 pixel Loral CCD having a

The BL Lac object 3C 66A was observed in an extensive multiwavelength monitoring campaign (the Whole Earth Blazar Telescope [WEBT] campaign) from 2003 July until 2004 April. The spectral energy distribution (SED) was measured over the entire electromagnetic spectrum, with flux measurements from radio to X-ray frequencies and upper limits in the very high energy (VHE) γ-ray regime. Here we use a time-dependent leptonic jet model to reproduce the SED and optical spectral variability observed during our multiwavelength campaign. Our model simulations could successfully reproduce the observed SED and optical light curves and predict an intrinsic cutoff value for the VHE γ-ray emission at ~4 GeV. The effect of the optical depth due to the intergalactic infrared background radiation (IIBR) on the peak of the high-energy component of 3C 66A was found to be negligible. Also, the presence of a broad-line region (BLR) in the case of 3C 66A may play an important role in the emission of γ-ray photons when the emission region is very close to the central engine, but farther out, the production mechanism of hard X-ray and γ-ray photons becomes rapidly dominated by synchrotron self-Compton emission. We further discuss the possibility of an observable X-ray spectral variability pattern. The simulated results do not predict observable hysteresis patterns in the optical or soft X-ray regimes for major flares on multiday timescales.

We develop a model of early Gamma-Ray Burst (GRB) afterglows with dominant X-ray contribution from the reverse shock (RS) propagating in highly relativistic (Lorentz factor γ w ∼ 106) magnetized wind of a long-lasting central engine. The model reproduces, in a fairly natural way, the overall trends and yet allows for variations in the temporal and spectral evolution of early optical and X-ray afterglows. The high energy and the optical synchrotron emission from the RS particles occurs in the fast cooling regime; the resulting synchrotron power L s is a large fraction of the wind luminosity, (L w and σ w are wind power and magnetization). Thus, plateaus—parts of afterglow light curves that show slowly decreasing spectral power—are a natural consequence of the RS emission. Contribution from the forward shock (FS) is negligible in the X-rays, but in the optical both FS and RS contribute similarly: FS optical emission is in the slow cooling regime, producing smooth components, while RS optical emission is in the fast cooling regime, and thus can both produce optical plateaus and account for fast optical variability correlated with the X-rays, e.g., due to changes in the wind properties. We discuss how the RS emission in the X-rays and combined FS and RS emission in the optical can explain many puzzling properties of early GRB afterglows.

We present extensive radio and millimeter observations of the unusually bright GRB 130427A at z=0.340, spanning 0.67 to 12 days after the burst. Taken in conjunction with detailed multi-band UV, optical, NIR, and X-ray observations we find that the broad-band afterglow emission is composed of distinct reverse shock and forward shock contributions. The reverse shock emission dominates in the radio/millimeter and at <0.1 days in the UV/optical/NIR, while the forward shock emission dominates in the X-rays and at >0.1 days in the UV/optical/NIR. We further find that the optical and X-ray data require a Wind circumburst environment, pointing to a massive star progenitor. Using the combined forward and reverse shock emission we find that the parameters of the burst are an isotropic kinetic energy of E_Kiso~2e53 erg, a mass loss rate of Mdot~3e-8 Msun/yr (for a wind velocity of 1,000 km/s), and a Lorentz factor at the deceleration time of Gamma(200s)~130. Due to the low density and large isotropic energy, the absence of a jet break to ~15 days places only a weak constraint on the opening angle of theta_j>2.5 deg, and therefore a total energy of E_gamma+E_K>1.2e51 erg, similar to other GRBs. The reverse shock emission is detectable in this burst due to the low circumburst density, which leads to a slow cooling shock. We speculate that this is a required property for the detectability of reverse shocks in the radio and millimeter bands. Following on GRB 130427A as a benchmark event, observations of future GRBs with the exquisite sensitivity of VLA and ALMA, coupled with detailed modeling of the reverse and forward shock contributions will test this hypothesis.

We study the morphology of gamma-ray burst (GRB) afterglows viewed off-axis using a simplified analytical model. We consider steep jets, which are expected to be the most common type. These jets, characterized by steep lateral gradients in energy and Lorentz factor, produce highly beamed emission. The observed signal is dominated by their minimum visible angle at any given time. Consequently, the afterglow morphology depends on when this angle begins to decrease, revealing the inner regions of the jet. Depending on whether this decrease occurs before, at, or after the reverse shock crosses the ejecta, three distinct classes of light curves emerge. In the first scenario, the de-beamed emission can produce a rapidly rising signal even prior to the reverse shock crossing. This is expected in GRBs with long duration, low energy, dense circumburst media, or combinations thereof. In some cases, the ejecta shell can be considered as effectively thick in the inner regions and effectively thin in the outer regions. For forward shocks, the temporal slopes in both regimes are identical, which makes it hard to detect the transition. Reverse shocks, however, have distinct temporal slopes, allowing potential detection of the transition in light curves if their emission surpasses that of the forward shock. The characteristic synchrotron frequency of de-beamed emission evolves independently of jet structure for forward shocks but depends on the lateral energy and Lorentz factor gradients for the reverse shock, with slower evolution for steep energy and shallow Lorentz factor gradients.

We present JHKL' photometry of a complete sample of steep-spectrum radio-loud quasars from the revised 3CR catalogue in the redshift range 0.65 < z < 1.20. After correcting for contributions from emission lines and the host galaxies, we investigate their spectral energy distributions (SEDs) around 1 micron. About 75% of the quasars are tightly grouped in the plane of optical spectral index, alpha_lo, versus near-infrared spectral index, alpha_hi, with the median value of alpha_lo close to the canonical value, and the median alpha_hi slightly flatter. We conclude that the fraction of moderately-obscured, red quasars decreases with increasing radio power, in accordance with the `receding torus' model which can also explain the relatively flat median near-infrared spectra of the 3CR quasars. Two of the red quasars have inverted infrared spectral indices, and we suggest that their unusual SEDs might result from a combination of dust-scattered and transmitted quasar light.

We perform a detailed study on the dynamics of a relativistic blast wave with\nthe presence of a long-lived reverse shock (RS). Although a short-lived RS has\nbeen widely considered, the RS is believed to be long-lived as a consequence of\na stratification expected on the ejecta Lorentz factors. The existence of a\nlong-lived RS makes the forward shock (FS) dynamics to deviate from a\nself-similar Blandford-McKee solution. Employing the "mechanical model" that\ncorrectly incorporates the energy conservation, we present an accurate solution\nfor both the FS and RS dynamics. We conduct a sophisticated calculation of the\nafterglow emission. Adopting a Lagrangian description of the blast wave, we\nkeep track of an adiabatic evolution of numerous shells between the FS and RS.\nAn evolution of the electron spectrum is also followed individually for every\nshell. We then find the FS and RS light curves by integrating over the entire\nFS and RS shocked regions, respectively. In particular, we make use of an\nanalytic expression for observed spectral flux, which we derive here in terms\nof an observed frequency and observer time. Exploring a total of 20 different\nejecta stratifications, we explain in detail how a stratified ejecta affects\nits blast wave dynamics and afterglow light curves. We show that, while the FS\nlight curves are not sensitive to the ejecta stratifications, the RS light\ncurves exhibit much richer features, including steep declines, plateaus, bumps,\nre-brightenings, and a variety of temporal decay indices. These distinctive RS\nfeatures may be observable if the RS has higher values of the micophysics\nparameters than the FS. We discuss possible applications of our results in\nunderstanding the GRB afterglow data.\n

Multiwavelength properties of blazars

The investigation of supernova remnants (SNRs) across the electromagnetic spectrum from radio up to very high energy gamma‐rays can serve as a test of the particle acceleration and touches on one of the unresolved problems of modern astrophysics, namely the origin of cosmic rays and the Galaxy's contribution to the overall cosmic ray spectrum. The multiwavelength observations of Cas A SNR demonstrated that structure and spectral features have clear signs of young SNRs and its overall properties make this object the best target to test a hypothesis of cosmic ray origin in SNRs. Studies of Cas A at very high energies by SHALON telescope showed the location of TeV gamma‐ray emission region relative to the position of reveres shock. Also, the spectral energy distribution was obtained at high and very high energies. To describe the spectral and structural features of this SNR viewed in non‐thermal emission, two approaches involving reverse and also both reverse and forward shocks to the mechanism of diffusive shock acceleration of cosmic rays in Cas A were applied. It is demonstrated that the observational properties of Cas A are well reproduced by the hadronic model with significant contribution of both the forward and reverse shocks in the generation of broadband emission. Calculation results suggest that the very high efficiency of particle acceleration in Cas A, which value is up to 25% of the supernova explosion energy with energy of accelerated particles not exceeding of eV. Whereas, the forward shock model predicts the spectral characteristics of the TeV‐gamma‐emission corresponding to ones detected at 800 GeV–40 TeV that are the evidence of acceleration of the hadronic cosmic rays in shells of SNRs up to eV

view Abstract Citations (20) References (53) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Optical Photometry of the X-Ray Novae GU MUS(=NOVA MUSCAE 1991) and V518 Per (=GRO J0422+32) King, N. L. ; Harrison, T. E. ; McNamara, B. J. Abstract We present UBVRI photometry of the x-ray novae GU Mus and V518 Per. We compare the temporal evolution of the optical and x-ray emission of these two objects to that of the prototype black hole x-ray nova system V616 Mon, and find that the outbursts of all three systems exhibited similar behavior, but on slightly different time scales. We calculate decline rates for the light curves and delay times between primary and secondary x-ray maxima. Fits to the optical and ultraviolet spectral energy distributions (SEDs) of GU Mus and the optical energy distribution of VS 18 Per were made using reddened continuum power-law models (Fv∝v∝, and a two-component hot blackbody+steady-state (geometrically thin) accretion disk model. We found that the SEDs of GU Mus following primary outburst are equally well fit by either a power-law model with index α∼0.7, or a two-component accretion disk+35 000 K blackbody model. Following the secondary outburst of GU Mus, the SED is best fitted by a power-law model with index α∼0.2. Sixteen months following the main outburst of GU Mus, the SED is consistent with that of K5/7 V. We use this fit to derive a lower limit distance of 4 kpc to GU Mus. The SEDs of V518 Per are best fit by a range of power-law models where the spectral index a changes from ∼-0.4 to ∼-0.1 within 227 days following x-ray maximum. Publication: The Astronomical Journal Pub Date: April 1996 DOI: 10.1086/117907 Bibcode: 1996AJ....111.1675K Keywords: X-RAYS: BURSTS; NOVAE; STARS: INDIVIDUAL: GU MUS; STARS: INDIVIDUAL: V518 PER full text sources ADS | data products SIMBAD (4)

In a survey with Chandra and HST of a sample of 17 radio sources with bright radio jets (16 powerful FR II and one nearby FR I), we detected X-ray and optical emission from a number of radio hot spots and lobes. Six hot spots on the near sides of powerful FR II galaxies (as determined from the jet asymmetry) were detected at X-rays, while none were detected on the far side, suggesting that high-energy emission from hot spots is anisotropic. In the nearby FR I galaxy 0836+299 (the only FR I in our sample) both hot spots are detected in X-rays, in agreement with the symmetric radio morphology. In the latter case the spectral energy distributions (SEDs) of both hot spots can be modeled from radio to X-rays with synchrotron emission from a single power-law energy distribution of electrons with Lorentz factors up to ~2 × 107. For the six hot spots of powerful FR II galaxies the X-ray flux lies above the extrapolation from the radio-to-optical continuum. Modeling the SEDs with a one-zone synchrotron self-Compton model, we find that equipartition is strongly violated, with the particle energy density dominating over the magnetic field one by 1-2 orders of magnitude. We discuss alternatives to this simple model, concluding that a viable alternative is that the X-ray emission is produced in the still-relativistic (Doppler factor δ = 3-6) terminal part of the jet by inverse Compton (IC) scattering on the CMB or synchrotron photons emitted by plasma flowing with a small velocity. X-ray emission from some of the lobes is detected on the side opposite to the jet, suggesting the possible relevance of back-scattered central radiation in providing seed photons for the IC process.

In the fireball model, it is more physically realistic that gamma-ray burst (GRB) ejecta have a range of bulk Lorentz factors (assuming M α −S). The low Lorentz factor part of the ejecta will catch up with the high Lorentz factor part when the latter is decelerated by the surrounding medium to a comparable Lorentz factor. Such a process will develop a long-lasting weak reverse shock until the whole ejecta are shocked. Meanwhile, the forward shocked materials are gradually supplied with energy from the ejecta that are catching-up, and thus the temporal decay of the forward shock emission will be slower than that without an energy supply. However, the reverse shock may be strong. Here, we extend the standard reverse-forward shock model to the case of radially nonuniform ejecta. We show that this process can be classified into two cases: the thick shell case and the thin shell case. In the thin shell case, the reverse shock is weak and the temporal scaling law of the afterglow is the same as that in Sari & Mészáros (2000). However, in the thick shell case, the reverse shock is strong and thus its emission dominates the afterglow in the high energy band. Our results also show slower decaying behavior of the afterglow due to the energy supply by low Lorentz factor materials, which may help the understanding of the plateau observed in the early optical and X-ray afterglows.