Rapid Response Mode observations of GRB 160203A: Looking for fine-structure line variability at <i>z</i> = 3.52

Context.  Gamma-ray bursts are the most energetic known explosions. Although they fade rapidly, they give us the opportunity to measure redshift and important properties of their host galaxies. We report the photometric and spectroscopic study of the Swift GRB 160203A at z = 3.518, and its host galaxy. Fine-structure absorption lines, detected in the afterglow at different epochs, allow us to investigate variability due to the strong fading background source.  Aims.  We obtained two optical to near-infrared spectra of the GRB afterglow with X-shooter on ESO/VLT, 18 minutes and 5.7 hours after the burst, allowing us to investigate temporal changes of fine-structure absorption lines.  Methods.  We measured H I column density log N(HI/cm–2) = 21.75 ± 0.10, and several heavy-element ions along the GRB sightline in the host galaxy, among which Si II, Al II, Al III, C II, Ni II, Si IV, C IV, Zn II and Fe II, and Fe II∗ and Si II∗ fine-structure transitions from energetic levels excited by the afterglow, at the common redshift z = 3.518. We measured [M/H]TOT = –0.78 ± 0.13 and a [Zn/Fe]FIT = 0.69 ± 0.15, representing the total (dust corrected) metallicity and dust depletion, respectively. We detected additional intervening systems along the line of sight at ɀ = 1.03, ɀ = 1.26, ɀ = 1.98, ɀ = 1.99, ɀ = 2.20, and ɀ = 2.83. We could not measure significant variability in the strength of the fine-structure lines throughout all the observations and determined an upper limit for the GRB distance from the absorber of d Results.  GRB 160203A belongs to a growing sample of GRBs with medium resolution spectroscopy, provided by the Swift/X-shooter legacy programme, which enables a detailed investigation of the interstellar medium in high-redshift GRB host galaxies. In particular, this host galaxy shows relatively high metal enrichment and dust depletion already in place when the universe was only 1.8 Gyr old.</p

Correction to: Comparing emission- and absorption-based gas-phase metallicities in GRB host galaxies at <i>z</i> = 2−4 using JWST

This is a correction to: P. Schady and others, Comparing emission- and absorption-based gas-phase metallicities in GRB host galaxies at z = 2−4 using JWST, Monthly Notices of the Royal Astronomical Society, Volume 529, Issue 3, April 2024, Pages 2807–2831, https://doi.org/10.1093/mnras/stae677.We found a mistake in our abstract where we accidentally wrote that the host galaxy of GRB 090323 was at z = 4.7 whereas it is in fact at redshift z = 3.58 based on the NIRSpec emission line spectrum of the host galaxy. The redshift of this GRB host galaxy is correctly reported in the rest of the paper. We also found a bug in our code that produces the [O III] λ5007 surface brightness maps of the host galaxies of GRB 050820A and GRB 150403A (figs 1 and 2 of the original paper) that caused the labelled physical pixel scale to be too small by a factor of ∼1.4. This error only affected the axes shown in the figures and has no implications for the rest of the paper. The corresponding pixel-to-kpc conversions have now been corrected and the updated maps are shown in Figs 1 and 2.</p

GRB 221009A: Discovery of an Exceptionally Rare Nearby and Energetic Gamma-Ray Burst

We report the discovery of the unusually bright long-duration gamma-ray burst (GRB), GRB 221009A, as observed by the Neil Gehrels Swift Observatory (Swift), Monitor of All-sky X-ray Image, and Neutron Star Interior Composition Explorer Mission. This energetic GRB was located relatively nearby (z = 0.151), allowing for sustained observations of the afterglow. The large X-ray luminosity and low Galactic latitude (b = 4.°3) make GRB 221009A a powerful probe of dust in the Milky Way. Using echo tomography, we map the line-of-sight dust distribution and find evidence for significant column densities at large distances (≳10 kpc). We present analysis of the light curves and spectra at X-ray and UV-optical wavelengths, and find that the X-ray afterglow of GRB 221009A is more than an order of magnitude brighter at T 0 + 4.5 ks than that from any previous GRB observed by Swift. In its rest frame, GRB 221009A is at the high end of the afterglow luminosity distribution, but not uniquely so. In a simulation of randomly generated bursts, only 1 in 104 long GRBs were as energetic as GRB 221009A; such a large E γ,iso implies a narrow jet structure, but the afterglow light curve is inconsistent with simple top-hat jet models. Using the sample of Swift GRBs with redshifts, we estimate that GRBs as energetic and nearby as GRB 221009A occur at a rate of ≲1 per 1000 yr—making this a truly remarkable opportunity unlikely to be repeated in our lifetime

The first JWST spectrum of a GRB afterglow: No bright supernova in observations of the brightest GRB of all time, GRB 221009A

International audienceWe present JWST and Hubble Space Telescope (HST) observations of the afterglow of GRB 221009A, the brightest gamma-ray burst (GRB) ever observed. Observations obtained with NIRSPEC (0.6-5.5 micron) and MIRI (5-12 micron) 12 days after the burst are the first mid-IR spectroscopy performed for a GRB. Assuming the underlying slope is that of a single power-law, we obtain $\beta \approx 0.35$ and $A_V = 4.9$, in excess of the notional Galactic value. This is suggestive of extinction above the notional Galactic value, possibly due to patchy extinction within the Milky Way or dust in the GRB host galaxy. It further implies that the X-ray and optical/IR regimes are not on the same branch of the synchrotron spectrum of the afterglow. If the cooling break lies between the X-ray and optical/IR, then the temporal declines would only match for a post jet break, ISM medium and electron index with $p<2$. The shape of the JWST spectrum is near-identical in the optical/nIR to X-shooter spectroscopy obtained at 0.5 days and to later time observations with HST. The lack of spectral evolution suggests the SNe is either substantially fainter or bluer than SN~1998bw. Our {\em HST} observations also reveal a disc-like host galaxy, viewed close to edge-on that further complicates the isolation of any supernova component. The host galaxy appears rather typical amongst long-GRB hosts and suggests that the extreme properties of GRB 221009A are not directly tied to its galaxy-scale environment

Fires in the deep: The luminosity distribution of early-time gamma-ray-burst afterglows in light of the Gamow Explorer sensitivity requirements

Context. Gamma-ray bursts (GRBs) are ideal probes of the Universe at high redshift (ɀ), pinpointing the locations of the earliest star-forming galaxies and providing bright backlights with simple featureless power-law spectra that can be used to spectrally fingerprint the intergalactic medium and host galaxy during the period of reionization. Future missions such as Gamow Explorer (hereafter Gamow) are being proposed to unlock this potential by increasing the rate of identification of high-ɀ (ɀ > 5) GRBs in order to rapidly trigger observations from 6 to 10 m ground telescopes, the James Webb Space Telescope (JWST), and the upcoming Extremely Large Telescopes (ELTs). Aims. Gamow was proposed to the NASA 2021 Medium-Class Explorer (MIDEX) program as a fast-slewing satellite featuring a wide-field lobster-eye X-ray telescope (LEXT) to detect and localize GRBs with arcminute accuracy, and a narrow-field multi-channel photo-ɀ infrared telescope (PIRT) to measure their photometric redshifts for > 80% of the LEXT detections using the Lyman-α dropout technique. We use a large sample of observed GRB afterglows to derive the PIRT sensitivity requirement. Methods. We compiled a complete sample of GRB optical–near-infrared (optical-NIR) afterglows from 2008 to 2021, adding a total of 66 new afterglows to our earlier sample, including all known high-ɀ GRB afterglows. This sample is expanded with over 2837 unpublished data points for 40 of these GRBs. We performed full light-curve and spectral-energy-distribution analyses of these after-glows to derive their true luminosity at very early times. We compared the high-ɀ sample to the comparison sample at lower redshifts. For all the light curves, where possible, we determined the brightness at the time of the initial finding chart of Gamow, at different high redshifts and in different NIR bands. This was validated using a theoretical approach to predicting the afterglow brightness. We then followed the evolution of the luminosity to predict requirements for ground- and space-based follow-up. Finally, we discuss the potential biases between known GRB afterglow samples and those to be detected by Gamow. Results. We find that the luminosity distribution of high-ɀ GRB afterglows is comparable to those at lower redshift, and we therefore are able to use the afterglows of lower-ɀ GRBs as proxies for those at high ɀ. We find that a PIRT sensitivity of 15 µJy (21 mag AB) in a 500 s exposure simultaneously in five NIR bands within 1000 s of the GRB trigger will meet the Gamow mission requirements. Depending on the ɀ and NIR band, we find that between 75% and 85% of all afterglows at ɀ > 5 will be recovered by Gamow at 5σ detection significance, allowing the determination of a robust photo-ɀ. As a check for possible observational biases and selection effects, we compared the results with those obtained through population-synthesis models, and find them to be consistent. Conclusions. Gamow and other high-ɀ GRB missions will be capable of using a relatively modest 0.3 m onboard NIR photo-ɀ telescope to rapidly identify and report high-ɀ GRBs for further follow-up by larger facilities, opening a new window onto the era of reionization and the high-redshift Universe.</p

A very luminous jet from the disruption of a star by a massive black hole

Tidal disruption events (TDEs) are bursts of electromagnetic energy that are released when supermassive black holes at the centres of galaxies violently disrupt a star that passes too close1. TDEs provide a window through which to study accretion onto supermassive black holes; in some rare cases, this accretion leads to launching of a relativistic jet2–9, but the necessary conditions are not fully understood. The best-studied jetted TDE so far is Swift J1644+57, which was discovered in γ-rays, but was too obscured by dust to be seen at optical wavelengths. Here we report the optical detection of AT2022cmc, a rapidly fading source at cosmological distance (redshift z = 1.19325) the unique light curve of which transitioned into a luminous plateau within days. Observations of a bright counterpart at other wavelengths, including X-ray, submillimetre and radio, supports the interpretation of AT2022cmc as a jetted TDE containing a synchrotron ‘afterglow’, probably launched by a supermassive black hole with spin greater than approximately 0.3. Using four years of Zwicky Transient Facility10 survey data, we calculate a rate of 0.02−0.01+0.04 per gigapascals cubed per year for on-axis jetted TDEs on the basis of the luminous, fast-fading red component, thus providing a measurement complementary to the rates derived from X-ray and radio observations11. Correcting for the beaming angle effects, this rate confirms that approximately 1 per cent of TDEs have relativistic jets. Optical surveys can use AT2022cmc as a prototype to unveil a population of jetted TDEs