arXiv subjects

N. Pankov

Publications and source records attributed to N. Pankov.

3 recordsLinked to original sources

arXiv2026

Earliest simultaneous multi-color optical observations of GRB 230328B: from 41 seconds to the host-galaxy identification

We present a multiwavelength study of the long-duration gamma-ray burst GRB 230328B, combining prompt gamma-ray observations with exceptionally early simultaneous optical photometry and extensive X-ray, radio, and host-galaxy follow-up. NUTTELA- TAO began simultaneous g'r'i' observations only 41 s after the Swift/BAT trigger, corresponding to approximately 16 s in the rest frame for the adopted host-galaxy photometric redshift of z_phot = 1.54+-0.06. Unlike sequential multiband measurements, these observations provide an instantaneous optical spectral slope without temporal-interpolation uncertainties. The early optical continuum remains statistically consistent with a constant slope from approximately 10^2 to 7*10^3 s, providing no evidence for rapid dust destruction. The absence of significant color evolution across the pronounced optical rebrightening at approximately 4*10^3 s demonstrates that it is achromatic and favours a dynamical rather than spectral origin. Broadband modelling shows that the optical, X-ray, and radio evolution can be broadly explained by forward-shock emission with late energy injection, although alternative scenarios cannot be excluded. The red optical continuum is consistent with substantial line-of-sight extinction in a massive, dusty host galaxy. Late-time observations are insufficient to constrain a typical GRB-associated supernova at the adopted redshift. GRB 230328B therefore provides a benchmark for connecting the earliest simultaneous optical colors with afterglow dynamics and the host environment of a representative long GRB.

astro-ph.HE↗

arXiv2026

GOTO identification and broadband modelling of the counterpart to the SVOM GRB 250818B

Rapid localisation and follow-up of gamma-ray bursts (GRBs) increasingly rely on low-latency triggers from new missions coupled to wide-field robotic optical facilities. We present the discovery and multi-wavelength follow-up of GRB 250818B, detected by the Space Variable Objects Monitor (SVOM) and localised optically by the Gravitational-wave Optical Transient Observer (GOTO). We compile and homogenise X-ray, optical/NIR, and radio data to build broadband light curves and spectral energy distributions. The afterglow is unusually luminous for a nominal short GRB, lying on the bright end of the short-GRB population in X-rays and optical and among the most luminous high-redshift short-GRB afterglows in the radio. MeerKAT detects the source at 3.1 GHz, while ALMA provides deep higher-frequency limits. Keck/LRIS spectroscopy shows continuum and metal absorption (Fe II, Mg II, Mg I), giving $z=1.216$. Synchrotron forward-shock modelling favours a constant-density medium and strongly prefers refreshed (energy-injection) emission, well described by a two-component jet with $E_{K,iso} \sim 4\times10^{52}$ erg, $n_0 \sim 3.6$ cm$^{-3}$, $\theta_j \simeq 0.10$ rad ($\sim 5.7$ deg), and $p \simeq 1.64$. The host association is ambiguous: the nearest LS DR10 galaxy candidate ($r_{AB} \sim 24.7$) is offset by $\sim 4$ arcsec ($\sim 34$ kpc) with chance-alignment probability $P_{cc} \sim 0.2$, and current imaging does not exclude a fainter, near-coincident host. SED fitting of the candidate host suggests a low-mass galaxy. GRB 250818B highlights the power of rapid wide-field counterpart identification in the SVOM era, while host-association uncertainty can still limit offset-based interpretation.

astro-ph.HE↗

arXiv2019

Normalization of polarized spectral contours for high-accuracy magnetic field measurements

Designed at the Crimean Astrophysical Observatory the SL-method of stellar magnetic field measurement is based on the calculation of the distance between the centers of gravity of the left and right circularly polarized components of the spectral line. The SL-method is free from the limitations of the LSD-method, namely its requirement for weak magnetic fields, weak spectral lines, the same shape of polarized profiles. Also, this method is free from model limitations of the PCA, NDD and ZCD methods also. The SL-method involves the calculation of the magnetic field using individual spectral lines and the subsequent formation of uniform arrays of the magnetic field measurements. The formation of the arrays is based on different criteria, e.g. using spectral lines of a chemical element, assumption of the same physical conditions in the areas of the spectral line formation, a statistically significant difference between the values of the magnetic field calculated from different arrays of spectral lines etc. If there are several arrays of spectral lines, it is necessary to obtain normalized polarized profiles using predetermined parameters for each array: the magnitude of the field, wavelength for normalization, Lande factor and the central residual intensity of the line. In this paper, we present a method of normalization of polarized profiles based on the dependence of the residual intensity of the observed polarized profiles on their central residual intensity (COntour Algorithm of the Line Approximation: COALA). The SL and COALA methods strong depend on the signal-to-noise ratio and a number of used unblended spectral lines. In this work the application of the proposed method is demonstrated for synthetic polarized spectra and for circularly polarized spectra of the yellow subgiant $β$ Aql (Sp G8 IV) obtained on 2014 October 06.

astro-ph.SR↗