arXiv subjects

D. Alexander Kann

Publications and source records attributed to D. Alexander Kann.

17 recordsLinked to original sources

arXiv2024

Unveiling the Multifaceted GRB 200613A: Prompt Emission Dynamics, Afterglow Evolution, and the Host Galaxy's Properties

We present our optical observations and multi-wavelength analysis of the GRB\,200613A detected by \texttt{Fermi} satellite. Time-resolved spectral analysis of the prompt $γ$-ray emission was conducted utilizing the Bayesian block method to determine statistically optimal time bins. Based on the Bayesian Information Criterion (BIC), the data generally favor the Band+Blackbody (short as BB) model. We speculate that the main Band component comes from the Blandford-Znajek mechanism, while the additional BB component comes from the neutrino annihilation process. The BB component becomes significant for a low-spin, high-accretion rate black hole central engine, as evidenced by our model comparison with the data. The afterglow light curve exhibits typical power-law decay, and its behavior can be explained by the collision between the ejecta and constant interstellar medium (ISM). Model fitting yields the following parameters: $E_{K,iso} = (2.04^{+11.8}_{-1.50})\times 10^{53}$ erg, $Γ_0=354^{+578}_{-217}$, $p=2.09^{+0.02}_{-0.03}$, $n_{18}=(2.04^{+9.71}_{-1.87})\times 10^{2}$ cm$^{-3}$, $θ_j=24.0^{+6.50}_{-5.54}$ degree, $ε_e=1.66^{+4.09}_{-1.39})\times 10^{-1}$ and $ε_B=(7.76^{+48.5}_{-5.9})\times 10^{-6}$. In addition, we employed the public Python package \texttt{Prospector} perform a spectral energy distribution (SED) modeling of the host galaxy. The results suggest that the host galaxy is a massive galaxy ($\log(M_\ast / M_\odot)=11.75^{+0.10}_{-0.09}$) with moderate star formation rate ($\mbox{SFR}=22.58^{+13.63}_{-7.22} M_{\odot}$/yr). This SFR is consistent with the SFR of $\sim 34.2 M_{\odot}$ yr$^{-1}$ derived from the [OII] emission line in the observed spectrum.

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arXiv2024

GRB 221009A, The BOAT

GRB 221009A has been referred to as the Brightest Of All Time (the BOAT). We investigate the veracity of this statement by comparing it with a half century of prompt gamma-ray burst observations. This burst is the brightest ever detected by the measures of peak flux and fluence. Unexpectedly, GRB 221009A has the highest isotropic-equivalent total energy ever identified, while the peak luminosity is at the $\sim99$th percentile of the known distribution. We explore how such a burst can be powered and discuss potential implications for ultra-long and high-redshift gamma-ray bursts. By geometric extrapolation of the total fluence and peak flux distributions GRB 221009A appears to be a once in 10,000 year event. Thus, while it almost certainly not the BOAT over all of cosmic history, it may be the brightest gamma-ray burst since human civilization began.

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arXiv2023

A Cosmological Fireball with Sixteen-Percent Gamma-Ray Radiative Efficiency

Gamma-ray bursts (GRBs) are the most powerful explosions in the universe. How efficiently the jet converts its energy to radiation is a long-standing problem and it is poorly constrained. The standard model invokes a relativistic fireball with a bright photosphere emission component. A definitive diagnosis of GRB radiation components and measurement of GRB radiative efficiency require prompt emission and afterglow data with high-resolution and wide-band coverage in time and energy. Here we report a comprehensive temporal and spectral analysis of the TeV-emitting bright GRB 190114C. Its fluence is one of the highest of all GRBs detected so far, which allows us to perform a high-resolution study of the prompt emission spectral properties and their temporal evolution down to a timescale of about 0.1 s. We observe that each of the initial pulses has a thermal component contributing $\sim20\%$ of the total energy, the corresponding temperature and the inferred Lorentz factor of the photosphere evolve following broken power-law shapes. From the observation of the non-thermal spectra and the light curve, the onset of afterglow corresponding to the deceleration of the fireball is considered at $\sim 6$~s. By incorporating the thermal and the non-thermal observations, as well as the photosphere and the synchrotron radiative mechanisms, we can directly derive the fireball energy budget with little dependence on hypothetical parameters and to measure a $\sim 16\%$ radiative efficiency for this GRB. With the fireball energy budget derived, the afterglow microphysics parameters can also be constrained directly from the data.

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arXiv2022

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

Tidal disruption events (TDEs) are bursts of electromagnetic energy released when supermassive black holes (SMBHs) at the centers of galaxies violently disrupt a star that passes too close. TDEs provide a new window to study accretion onto SMBHs; in some rare cases, this accretion leads to launching of a relativistic jet, but the necessary conditions are not fully understood. The best studied jetted TDE to date is Swift J1644+57, which was discovered in gamma-rays, but was too obscured by dust to be seen at optical wavelengths. Here we report the optical discovery of AT2022cmc, a rapidly fading source at cosmological distance (redshift z=1.19325) whose unique lightcurve transitioned into a luminous plateau within days. Observations of a bright counterpart at other wavelengths, including X-rays, sub-millimeter, and radio, supports the interpretation of AT2022cmc as a jetted TDE containing a synchrotron "afterglow", likely launched by a SMBH with spin $a \gtrsim 0.3$. Using 4 years of Zwicky Transient Facility (ZTF) survey data, we calculate a rate of $0.02 ^{+ 0.04 }_{- 0.01 }$ Gpc$^{-3}$ yr$^{-1}$ for on-axis jetted TDEs based on the luminous, fast-fading red component, thus providing a measurement complementary to the rates derived from X-ray and radio observations. Correcting for the beaming angle effects, this rate confirms that about 1% of TDEs have relativistic jets. Optical surveys can use AT2022cmc as a prototype to unveil a population of jetted TDEs.

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arXiv2022

Inhomogeneous Jets from Neutron Star Mergers: One Jet to Rule them all

Using the resultant profiles from 3D hydrodynamic simulations of relativistic jets interacting with neutron star merger wind ejecta, we show how the inhomogeneity of energy and velocity {across the jet surface profile} can alter the observed afterglow lightcurve. We find that the peak afterglow flux depends sensitively on the observer's line-of-sight, not only via the jet inclination but also through the jet rotation: for an observer viewing the afterglow within the GRB-bright jet core, we find a peak flux variability on the order $<0.5$ dex through rotational orientation and $<1.3$ dex for the polar inclination. An observed afterglow's peak flux can be used to infer the jet kinetic energy, and where a top-hat jet is assumed, we find the range of inferred jet kinetic energies for our various model afterglow lightcurves (with fixed model parameters), covers $\sim 1/3$ of the observed short GRB population. Additionally, we present an analytic jet structure function that includes physically motivated parameter uncertainties due to variability through the rotation of the source. % An approximation for the change in collimation due to the merger ejecta mass is included and we show that by considering the observed range of merger ejecta masses from short GRB kilonova candidates, a population of merger jets with a fixed intrinsic jet energy is capable of explaining the observed broad diversity seen in short GRB afterglows.

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arXiv2022

Cosmological Fast Optical Transients with the Zwicky Transient Facility: A Search for Dirty Fireballs

Dirty fireballs are a hypothesized class of relativistic massive-star explosions with an initial Lorentz factor $Γ_\mathrm{init}$ below the $Γ_\mathrm{init}\sim100$ required to produce a long-duration gamma-ray burst (LGRB), but which could still produce optical emission resembling LGRB afterglows. Here we present the results of a search for on-axis optical afterglows using the Zwicky Transient Facility (ZTF). Our search yielded seven optical transients that resemble on-axis LGRB afterglows in terms of their red colors ($g-r>0$ mag), faint host galaxy ($r>23$ mag), and rapid fading ($dr/dt>1$ mag/day). Spectroscopy of the transient emission within a few days of discovery established cosmological distances ($z=0.876$ to $z=2.9$) for six events, tripling the number of afterglows with redshift measurements discovered by optical surveys without a $γ$-ray trigger. Upon a retrospective search, four events (ZTF20abbiixp/AT2020kym, ZTF21aagwbjr/AT2021buv, ZTF21aakruew/AT2021cwd, ZTF21abfmpwn/AT2021qbd) turned out to have a likely associated LGRB (GRB200524A, GRB210204A, GRB210212B, GRB210610B), while three did not (ZTF20aajnksq/AT2020blt, ZTF21aaeyldq/AT2021any, ZTF21aayokph/AT2021lfa). Our search revealed no definitive new class of events: the simplest explanation for the apparently "orphan" events is that they were regular LGRBs missed by high-energy satellites due to detector sensitivity and duty cycle, although it is possible that they were intrinsically faint in $γ$-rays or viewed slightly off-axis. We rule out a scenario in which dirty fireballs have a similar energy per solid angle to LGRBs and are an order of magnitude more common. In addition, we set the first direct constraint on the ratio of the opening angles of the material producing $γ$-rays and the material producing early optical afterglow emission, finding that they must be comparable.

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arXiv2021

GRB jet structure and the jet break

We investigate the shape of the jet break in within-beam gamma-ray burst (GRB) optical afterglows for various lateral jet structure profiles. We consider cases with and without lateral spreading and a range of inclinations within the jet core half-opening angle, $θ_c$. We fit model and observed afterglow lightcurves with a smoothly-broken power-law function with a free-parameter $κ$ that describes the sharpness of the break. We find that the jet break is sharper ($κ$ is greater) when lateral spreading is included than in the absence of lateral spreading. For profiles with a sharp-edged core, the sharpness parameter has a broad range of $0.1\lesssimκ\lesssim4.6$, whereas profiles with a smooth-edged core have a narrower range of $0.1\lesssimκ\lesssim2.2$ when models both with and without lateral spreading are included. For sharp-edged jets, the jet break sharpness depends strongly on the inclination of the system within $θ_c$, whereas for smooth-edged jets, $κ$ is more strongly dependent on the size of $θ_c$. Using a sample of 20 GRBs we find nine candidate smooth-edged jet structures and eight candidate sharp-edged jet structures, while the remaining three are consistent with either. The shape of the jet break, as measured by the sharpness parameter $κ$, can be used as an initial check for the presence of lateral structure in within-beam GRBs where the afterglow is well-sampled at and around the jet-break time.

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arXiv2021

GRB 191016A: A Long Gamma-Ray Burst Detected by TESS

The TESS exoplanet-hunting mission detected the rising and decaying optical afterglow of GRB 191016A, a long Gamma-Ray Burst (GRB) detected by Swift-BAT but without prompt XRT or UVOT follow-up due to proximity to the moon. The afterglow has a late peak at least 1000 seconds after the BAT trigger, with a brightest-detected TESS datapoint at 2589.7 s post-trigger. The burst was not detected by Fermi-LAT, but was detected by Fermi-GBM without triggering, possibly due to the gradual nature of rising light curve. Using ground-based photometry, we estimate a photometric redshift of $z_\mathrm{phot} = 3.29\pm{0.40}$. Combined with the high-energy emission and optical peak time derived from TESS, estimates of the bulk Lorentz factor $Γ_\mathrm{BL}$ range from $90-133$. The burst is relatively bright, with a peak optical magnitude in ground-based follow-up of $R=15.1$ mag. Using published distributions of GRB afterglows and considering the TESS sensitivity and sampling, we estimate that TESS is likely to detect $\sim1$ GRB afterglow per year above its magnitude limit.

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arXiv2020

The Exotic Type Ic Broad-Lined Supernova SN 2018gep: Blurring the Line Between Supernovae and Fast Optical Transients

In the last decade a number of rapidly evolving transients have been discovered that are not easily explained by traditional supernovae models. We present optical and UV data on onee such object, SN 2018gep, that displayed a fast rise with a mostly featureless blue continuum around maximum light, and evolved to develop broad features more typical of a SN Ic-bl while retaining significant amounts of blue flux throughout its observations. The blue excess is most evident in its near-UV flux that is over 4 magnitudes brighter than other stripped envelope supernovae, but also visible in optical g$-$r colors at early times. Its fast rise time of $t_{\rm rise,V} \lesssim 6.2 \pm 0.8$ days puts it squarely in the emerging class of Fast Evolving Luminous Transients, or Fast Blue Optical Transients. With a peak absolute magnitude of M$_r=-19.49 \pm 0.23 $ mag it is on the extreme end of both the rise time and peak magnitude distribution for SNe Ic-bl. Only one other SN Ic-bl has similar properties, iPTF16asu, for which less of the important early time and UV data have been obtained. We show that the objects SNe 2018gep and iPTF16asu have similar photometric and spectroscopic properties and that they overall share many similarities with both SNe Ic-bl and Fast Evolving Transients. We obtain IFU observations of the SN 2018gep host galaxy and derive a number of properties for it. We show that the derived host galaxy properties for both SN 2018gep and iPTF16asu are overall consistent with the SNe Ic-bl and GRB/SNe sample while being on the extreme edge of the observed Fast Evolving Transient sample. These photometric observations are consistent with a simple SN Ic-bl model that has an additional form of energy injection at early times that drives the observed rapid, blue rise, and we speculate that this additional power source may extrapolate to the broader Fast Evolving Transient sample.

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arXiv2015

A very luminous magnetar-powered supernova associated with an ultra-long gamma-ray burst

A new class of ultra-long duration (>10,000 s) gamma-ray bursts has recently been suggested. They may originate in the explosion of stars with much larger radii than normal long gamma-ray bursts or in the tidal disruptions of a star. No clear supernova had yet been associated with an ultra-long gamma-ray burst. Here we report that a supernova (2011kl) was associated with the ultra-long duration burst 111209A, at z=0.677. This supernova is more than 3 times more luminous than type Ic supernovae associated with long gamma-ray bursts, and its spectrum is distinctly different. The continuum slope resembles those of super-luminous supernovae, but extends farther down into the rest-frame ultra-violet implying a low metal content. The light curve evolves much more rapidly than super-luminous supernovae. The combination of high luminosity and low metal-line opacity cannot be reconciled with typical type Ic supernovae, but can be reproduced by a model where extra energy is injected by a strongly magnetized neutron star (a magnetar), which has also been proposed as the explanation for super-luminous supernovae.

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arXiv2015

Gamma-Ray Bursts Trace UV Metrics of Star Formation over 3 < z < 5

We present the first uniform treatment of long duration gamma-ray burst (GRB) host galaxy detections and upper limits over the redshift range 3 -15.6 mag, and with extrapolations of the assumed Schechter-type LF well beyond this range. We review proposed astrophysical and observational biases for our sample, and find they are for the most part minimal. We therefore conclude, as the simplest interpretation of our results, that GRBs successfully trace UV metrics of cosmic star formation over the range 3<z<5. Our findings suggest GRBs are providing an accurate picture of star formation processes from z ~3 out to the highest redshifts.

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arXiv2015

How Bad/Good Are the External Forward Shock Afterglow Models of Gamma-Ray Bursts?

The external forward shock (EFS) models have been the standard paradigm to interpret the broad-band afterglow data of gamma-ray bursts (GRBs). One prediction of the models is that some afterglow temporal breaks at different energy bands should be achromatic. Observations in the Swift era have revealed chromatic afterglow behaviors at least in some GRBs, casting doubts on the EFS origin of GRB afterglows. In this paper, we perform a systematic study to address the question: how bad/good are the external forward shock models? Our sample includes 85 GRBs well-monitored X-ray and optical lightcurves. Based on how well the data abide by the EFS models, we categorize them as: Gold sample: (Grade I and II) include 45/85 GRBs. They show evidence of, or are consistent with having, an achromatic break. The temporal/spectral behaviors in each afterglow segment are consistent with the predictions (closure relations) of the EFS models. Silver sample: (Grade III and IV) include 37/85 GRBs. They are also consistent with having an achromatic break, even though one or more afterglow segments do not comply with the closure relations. Bad sample: (Grade V), 3/85 shows direct evidence of chromatic behaviors, suggesting that the EFS models are inconsistent with the data. These are included in the Bad sample. We further perform statistical analyses of various observational properties ($α$, $β$, $t_b$ and model parameters (energy injection index q, p, $θ_j$, $η_γ$, etc) of the GRBs in the Gold Sample, and derive constraints on the magnetization parameter $ε_B$ in the EFS. Overall, we conclude that the simplest EFS models can account for the multi-wavelength afterglow data of at least half of the GRBs. When more advanced modeling (e.g., long-lasting reverse shock, structured jets) is invoked, up to $>90 \%$ of the afterglows may be interpreted within the framework of the ESF models.

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arXiv2015

iPTF14yb: The First Discovery of a GRB Afterglow Independent of a High-Energy Trigger

We report here the discovery by the Intermediate Palomar Transient Factory (iPTF) of iPTF14yb, a luminous ($M_{r}\approx-27.8$ mag), cosmological (redshift 1.9733), rapidly fading optical transient. We demonstrate, based on probabilistic arguments and a comparison with the broader population, that iPTF14yb is the optical afterglow of the long-duration gamma-ray burst GRB 140226A. This marks the first unambiguous discovery of a GRB afterglow prior to (and thus entirely independent of) an associated high-energy trigger. We estimate the rate of iPTF14yb-like sources (i.e., cosmologically distant relativistic explosions) based on iPTF observations, inferring an all-sky value of $\Re_{\mathrm{rel}}=610$ yr$^{-1}$ (68% confidence interval of 110-2000 yr$^{-1}$). Our derived rate is consistent (within the large uncertainty) with the all-sky rate of on-axis GRBs derived by the Swift satellite. Finally, we briefly discuss the implications of the nondetection to date of bona fide "orphan" afterglows (i.e., those lacking detectable high-energy emission) on GRB beaming and the degree of baryon loading in these relativistic jets.

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arXiv2011

The Fast Evolution of SN 2010bh associated with XRF 100316D

(...) Since 1998, only half a dozen spectroscopically confirmed associations have been discovered and XRF 100316D associated with the type-Ic SN 2010bh at z = 0.059 is among the latest. We began observations with GROND 12 hours after the GRB trigger and continued until 80 days after the burst. GROND provided excellent photometric data in six filter bands covering a wavelength range from approx. 350 to 1800 nm, significantly expanding the pre-existing data set for this event. Combining GROND and Swift data, the early broad-band SED is modelled with a blackbody and afterglow component attenuated by dust and gas absorption. The best-fit SED models imply moderate reddening along the line of sight through the host galaxy (A_V = 1.2 \pm 0.1 mag). The temperature and radius evolution of the thermal component are analysed and combined with earlier measurements available from the literature. This reveals a cooling envelope at an apparent initial radius of 7 \times 10^11 cm, which is compatible with a dense wind surrounding a Wolf-Rayet star. Multicolour templates of SN 1998bw are fitted to the SN to directly compare the light-curve properties. This shows that SN 2010bh is ~65% as bright as SN 1998bw. Reaching maximum brightness at ~8 days after the burst in the blue bands, SN 2010bh proves to be the most rapidly evolving GRB-SNe to date. Finally, a two-component parametrised model is fitted to the quasi-bolometric light curve, which delivers physical parameters of the explosion. This yields M_Ni = 0.21 \pm 0.03 M\bigodot and M_ej = 2.6 \pm 0.2 M\bigodot, typical of values within the GRB-SN population. The kinetic energy is 2.4 \pm 0.7 \times 10^52 erg, which is making this SN the second most energetic GRB-SN after SN 1998bw. This supernova has one of the earliest peaks ever recorded and thereafter fades more rapidly than other GRB-SNe, hypernovae, or typical type-Ic SNe. (...)

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arXiv2009

Discerning the physical origins of cosmological Gamma-ray bursts based on multiple observational criteria: the cases of z=6.7 GRB 080913, z=8.3 GRB 090423, and some short/hard GRBs

(Abridged) The two high-redshift gamma-ray bursts, GRB 080913 at z=6.7 and GRB 090423 at z=8.3, recently detected by Swift appear as intrinsically short, hard GRBs. They could have been recognized by BATSE as short/hard GRBs should they have occurred at z <= 1. We perform a more thorough investigation on two physically distinct types (Type I/II) of cosmological GRBs and their observational characteristics. We reiterate the definitions of Type I/II GRBs and review the observational criteria and their physical motivations. Contrary to the traditional approach of assigning the physical category based on the gamma-ray properties (duration, hardness, and spectral lag), we take an alternative approach to define the Type I and Type II Gold Samples using several criteria that are more directly related to the GRB progenitors, and study the properties of the two Gold Samples and compare them with the traditional long/soft and short/hard samples. We find that the Type II Gold Sample reasonably tracks the long/soft population, although it includes several intrinsically short (shorter than 1s in the rest frame) GRBs. The Type I Gold Sample only has 5 GRBs, 4 of which are not strictly short but have extended emission. Other short/hard GRBs detected in the Swift era represent the BATSE short/hard sample well, but it is unclear whether all of them belong to Type I. We suggest that some (probably even most) high-luminosity short/hard GRBs instead belong to Type II. We suggest that GRB 080913 and GRB 090423 are more likely Type II events. We re-emphasize the importance of invoking multiple observational criteria, and cautiously propose an operational procedure to infer the physical origin of a given GRB with available multiple observational criteria, with various caveats laid out.

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arXiv2008

The Rapidly Flaring Afterglow of the Very Bright and Energetic GRB 070125

We report on multi-wavelength observations, ranging from the X-ray to radio wave bands, of the IPN-localized gamma-ray burst GRB 070125. Spectroscopic observations reveal the presence of absorption lines due to O I, Si II, and C IV, implying a likely redshift of z = 1.547. The well-sampled light curves, in particular from 0.5 to 4 days after the burst, suggest a jet break at 3.7 days, corresponding to a jet opening angle of ~7.0 degrees, and implying an intrinsic GRB energy in the 1 - 10,000 keV band of around E = (6.3 - 6.9)x 10^(51) erg (based on the fluences measured by the gamma-ray detectors of the IPN network). GRB 070125 is among the brightest afterglows observed to date. The spectral energy distribution implies a host extinction of Av < 0.9 mag. Two rebrightening episodes are observed, one with excellent time coverage, showing an increase in flux of 56% in ~8000 seconds. The evolution of the afterglow light curve is achromatic at all times. Late-time observations of the afterglow do not show evidence for emission from an underlying host galaxy or supernova. Any host galaxy would be subluminous, consistent with current GRB host-galaxy samples. Evidence for strong Mg II absorption features is not found, which is perhaps surprising in view of the relatively high redshift of this burst and the high likelihood for such features along GRB-selected lines of sight.

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arXiv2007

Spatially resolved properties of the GRB 060505 host: implications for the nature of the progenitor

GRB 060505 was the first well-observed nearby possible long-duration GRB that had no associated supernova. Here we present spatially resolved spectra of the host galaxy of GRB 060505, an Sbc spiral, at redshift z=0.0889. The GRB occurred inside a star-forming region in the northern spiral arm at 6.5 kpc from the center. From the position of the emission lines, we determine a maximum rotational velocity for the galaxy of v~212km/s corresponding to a mass of 1.14x10^11 M_solar within 11 kpc from the center. By fitting single-age spectral synthesis models to the stellar continuum, we derive a very young age for the GRB site, confirmed by photometric and Halpha line measurements, of around 6 Myr which corresponds to the lifetime of a 32 M_solar star. The metallicity derived from several emission line measurements is lowest at the GRB site with 1/5 Z_solar but roughly solar in the rest of the galaxy. Using the 2dF galaxy redshift survey we can locate the host galaxy in its large scale (Mpc) environment. The galaxy lies in the foreground of a filamentary overdensity extending south west from the galaxy cluster Abell 3837 at z=0.0896. The properties of the GRB site are similar to those found for other long-duration GRB host galaxies with high specific star formation rate and low metallicity, which is an indication that GRB 060505 originated from a young massive star that died without making a supernova.

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