The LHAASO collaboration recently reported the measurement of the gamma-ray spectra of GRB 221009A, which is the brightest burst ever, covering an energy range from 0.3 TeV to about 10 TeV. Based on the observation, we investigate the ALP-photon oscillation effect in the host galaxy of GRB 221009A and the Milky Way. The CL_s method is applied to set constraints on the ALP parameters in this study. Given the uncertain magnetic field configuration in the host galaxy, we use three different models: a homogeneous magnetic field model, a magnetic field model identical to that of the Milky Way, and a model constructed from the HST observations of the host galaxy. We find that the constraints derived using these three host galaxy magnetic field models are comparable. Our results are complementary in the small ALP mass regions compared with other experiments.

Axionlike particles (ALPs) may undergo mixing with photons in the presence of astrophysical magnetic fields, leading to alterations in the observed high energy $\gamma$-ray spectra. In this study, we investigate the ALP-photon oscillation effect using the spectra of the blazar Mrk 421 over 15 observation periods measured by Major Atmospheric Gamma Imaging Cherenkov Telescopes (MAGIC) and Fermi Large Area Telescope (Fermi-LAT). Compared with previous studies, we generate mock data under the ALP hypothesis and employ the ${\mathrm{CL}}_{\mathrm{s}}$ method to set constraints on the ALP parameters. This method is widely utilized in high energy experiments and avoids the exclusion of specific parameter regions where distinguishing between the null and ALP hypotheses is challenging. We find that the ALP-photon coupling $g_{a\gamma }$ is constrained to be smaller than $\sim 2\times {10}^{-11}{\mathrm{GeV}}^{-1}$ for ALP masses ranging from ${10}^{-9}\mathrm{eV}$ to ${10}^{-7}\mathrm{eV}$ at the 95% confidence level. We also present the constraints derived from the TS distribution under the null hypothesis, which is commonly utilized in previous astrophysical ALP studies. Our results reveal that the combined constraints of all the periods obtained from both methods are consistent. However, the ${\mathrm{CL}}_{\mathrm{s}}$ method remains effective in cases where the latter method fails to provide constraints for specific observation periods.

The interaction between axion-like particles (ALPs) and photons induces ALP-photon oscillations in astrophysical magnetic fields, leading to spectral distortions in the γ-ray spectrum of blazars. The primary uncertainty of this phenomenon may originate from the magnetic field within the jet of the blazar. Many studies focus on a simple jet magnetic field model with a toroidal component exerting a predominant influence on regions far from the central region. While many investigations have explored the effects of ALP-photon oscillations using typical parameter values in this model, it is important to recognize that these parameters can be constrained by multi-wavelength observations. In this study, we utilize the high energy γ-ray spectrum of Mrk 421 obtained from MAGIC and Fermi-LAT observations. By employing multi-wavelength fitting with a one-zone synchrotron self-Compton model, we derive the parameters characterizing the simple toroidal balazar jet magnetic field model, and investigate their impacts on the ALP constraints.

Oscillations between axion-like particles (ALPs) and photons in astrophysical magnetic fields can lead to irregularities in the high energy gamma ray spectra of blazars. The magnetic field within the blazar jet plays a crucial role in shaping these effects, with its strength in the emission region being an important parameter determined by multi-wavelength observations. However, the origin of the high energy bump observed in the spectral energy distribution of some blazars is a topic of debate, with both leptonic and hadronic scenarios providing plausible explanations that result in different magnetic field strengths in the emission region. In this study, we investigate the impact of magnetic field configurations on the constraints of ALP parameters. We consider both leptonic and hadronic emission scenarios for the blazar Mrk 501 and derive the corresponding jet magnetic field strengths. Additionally, we explore two jet magnetic field models: one with a toroidal component and the other with helical and tangled components. By analyzing the spectra of Mrk 501 observed by MAGIC and Fermi-LAT from 2017-06-17 to 2019-07-23, which are well-described by both emission scenarios, we derive constraints on the ALP parameters. Our results demonstrate that both the emission scenario and the magnetic field structure play a significant role in deriving these constraints, with the hadronic model leading to much more stringent limits compared to the leptonic model.

Quasar absorption lines are a powerful tool for studying the Universe, enabling us to probe distant gas, dust, and galaxy formation and evolution. However, detecting these lines, particularly Ca ii absorption lines, is a time-consuming and laborious process. Existing deep learning methods are prone to false positives and still require extensive manual verification and parameter measurement. This work presents three multitask convolutional neural network models and identifies the ResNet-CBAM model, which incorporates residual learning and an attention mechanism as the most effective. The results show that the ResNet-CBAM model achieves an accuracy of 99.7% in detecting Ca ii absorbers and excels in predicting critical parameters such as equivalent width and full width at half-maximum, with average correlation coefficients of 0.98 and 0.85, respectively. Furthermore, its remarkable generalization ability significantly improves detection precision on unseen data, rising from 20.3% of the cutting-edge model to 92.6%. In addition, with our numerous optimizations, our method can directly search for nonnormalized data, still achieving an accuracy of 98.6%. This translates to a dramatic reduction in manual inspection workload, paving the way for efficient and automated Ca ii absorber identification. In real-world applications on the Sloan Digital Sky Survey DR7 and DR12, our model successfully rediscovered 321 known Ca ii absorbers while identifying potential candidates in an additional 381 spectra. The codes used in this paper are available on Zenodo at doi:10.5281/zenodo.13953656.

High energy photons traveling through astrophysical magnetic fields have the potential to undergo oscillations with axion-like particles (ALPs), resulting in modifications to the observed photon spectrum. High energy $γ-$ray sources with significant magnetic field strengths provide an ideal setting to investigate this phenomenon. Ton 599, a flat spectrum radio quasar with a magnetic field strength on the order of Gauss in its emission region, presents a promising opportunity for studying ALP-photon oscillations. In this study, we analyze the effects of ALP-photon oscillations on the $γ$-ray spectrum of Ton 599 as observed by Fermi-LAT. Our investigation considers the potential influences of the broad-line region and dusty torus on the $γ-$ray spectrum of Ton 599. We set the constraints on the ALP parameters at the $95\%$ confidence level, and find that the constraints on \(g_{aγ}\) can reach approximately \(2 \times 10^{-12}~\mathrm{GeV}^{-1}\) for \(m_a \sim 10^{9}~\mathrm{eV}\).