Person: Berger, Edo
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Berger
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Edo
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Berger, Edo
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Publication An extremely energetic supernova from a very massive star in a dense medium(Springer Science and Business Media LLC, 2020-04-13) Nicholl, Matt; Blanchard, Peter K.; Berger, Edo; Chornock, Ryan; Margutti, Raffaella; Gomez, Sebastian; Lunnan, Ragnhild; Miller, Adam A.; Fong, Wen-fai; Terreran, Giacomo; Vigna-Gómez, Alejandro; Bhirombhakdi, Kornpob; Bieryla, Allyson; Challis, Pete; Laher, Russ R.; Masci, Frank J.; Paterson, KerryPublication The First Vlbi Detection of an Ultracool Dwarf: Implications for the Detectability of Sub-Stellar Companions(IOP Publishing, 2009) Forbrich, Jan; Berger, EdoWe present milliarcsecond-resolution radio very long baseline interferometry (VLBI) observations of the ultracool dwarfs TVLM 513–46546 (M8.5) and 2MASS J00361617+1821104 (L3.5) in an attempt to detect sub-stellar companions via direct imaging or reflex motion. Both objects are known radio emitters with strong evidence for periodic emission on timescales of about 2 and 3 hours, respectively. Using the inner seven VLBA antennas, we detect unresolved emission from TVLM 513–46546 on a scale of 2.5 mas (∼ 50 stellar radii), leading to a direct limit on the radio emission brightness temperature of TB & 4 × 105 K. However, with the higher spatial resolution afforded by the full VLBA we find that the source appears to be marginally and asymmetrically resolved at a low S/N ratio, possibly indicating that TVLM 513–46546 is a binary with a projected separation of ∼ 1 mas (∼ 20 stellar radii). Using the 7-hr baseline of our observation we find no astrometric shift in the position of TVLM 513–46546, with a 3σ limit of about 0.6 mas. This is about 3 times larger than expected for an equal mass companion with a few-hour orbital period. Future monitoring of its position on a range of timescales will provide the required astrometric sensitivity to detect a planetary companion with a mass of ∼ 10 MJ in a & 15 d (& 0.06 AU) orbit, or with a mass of ∼ 2 MJ in an orbit of & 0.5 yr (& 0.3 AU).Publication Cosmological Constraints from Measurements of Type Ia Supernovae Discovered during the First 1.5 yr of the Pan-STARRS1 Survey(IOP Publishing, 2014) Rest, Armin; Scolnic, D.; Foley, R. J.; Huber, M. E.; Chornock, R.; Narayan, Gautham; Tonry, J. L.; Berger, Edo; Soderberg, Alicia; Stubbs, Christopher; Riess, A.; Kirshner, Robert; Smartt, S. J.; Schlafly, E.; Rodney, S.; Botticella, M. T.; Brout, D.; Challis, P.; Czekala, Ian; Drout, Maria Rebecca; Hudson, M. J.; Kotak, R.; Leibler, C.; Lunnan, R; Marion, G. H.; McCrum, M.; Milisavljevic, D.; Pastorello, A.; Sanders, Nathan Edward; Smith, K.; Stafford, E.; Thilker, D.; Valenti, S.; Wood-Vasey, W. M.; Zheng, Z.; Burgett, W. S.; Chambers, K. C.; Denneau, L.; Draper, P. W.; Flewelling, H.; Hodapp, K. W.; Kaiser, N.; Kudritzki, R.-P.; Magnier, E. A.; Metcalfe, N.; Price, P. A.; Sweeney, W.; Wainscoat, R.; Waters, C.We present griz P1 light curves of 146 spectroscopically confirmed Type Ia supernovae (SNe Ia; 0.03 < z < 0.65) discovered during the first 1.5 yr of the Pan-STARRS1 Medium Deep Survey. The Pan-STARRS1 natural photometric system is determined by a combination of on-site measurements of the instrument response function and observations of spectrophotometric standard stars. We find that the systematic uncertainties in the photometric system are currently 1.2% without accounting for the uncertainty in the Hubble Space Telescope Calspec definition of the AB system. A Hubble diagram is constructed with a subset of 113 out of 146 SNe Ia that pass our light curve quality cuts. The cosmological fit to 310 SNe Ia (113 PS1 SNe Ia + 222 light curves from 197 low-z SNe Ia), using only supernovae (SNe) and assuming a constant dark energy equation of state and flatness, yields $w=-1.120^{+0.360}_{-0.206}\hbox{(Stat)} ^{+0.269}_{-0.291}\hbox{(Sys)}$. When combined with BAO+CMB(Planck)+H 0, the analysis yields $\Omega _{\rm M}=0.280^{+0.013}_{-0.012}$ and $w=-1.166^{+0.072}_{-0.069}$ including all identified systematics. The value of w is inconsistent with the cosmological constant value of –1 at the 2.3σ level. Tension endures after removing either the baryon acoustic oscillation (BAO) or the H 0 constraint, though it is strongest when including the H 0 constraint. If we include WMAP9 cosmic microwave background (CMB) constraints instead of those from Planck, we find $w=-1.124^{+0.083}_{-0.065}$, which diminishes the discord to <2σ. We cannot conclude whether the tension with flat ΛCDM is a feature of dark energy, new physics, or a combination of chance and systematic errors. The full Pan-STARRS1 SN sample with ~three times as many SNe should provide more conclusive results.Publication A Search for Fast Optical Transients in the Pan-STARRS1 Medium-Deep Survey: M-Dwarf Flares, Asteroids, Limits on Extragalactic Rates, and Implications for LSST(American Astronomical Society, 2013) Berger, Edo; Leibler, C. N.; Chornock, R; Rest, A.; Foley, R. J.; Soderberg, Alicia; Price, P. A.; Burgett, W. S.; Chambers, K. C.; Flewelling, H.; Huber, M. E.; Magnier, E. A.; Metcalfe, N.; Stubbs, Christopher; Tonry, J. L.We present a search for fast optical transients (τ ~ 0.5 hr-1 day) using repeated observations of the Pan-STARRS1 Medium-Deep Survey (PS1/MDS) fields. Our search takes advantage of the consecutive g P1 r P1 observations (16.5 minutes in each filter), by requiring detections in both bands, with non-detections on preceding and subsequent nights. We identify 19 transients brighter than 22.5 AB mag (S/N gsim 10). Of these, 11 events exhibit quiescent counterparts in the deep PS1/MDS templates that we identify as M4-M9 dwarfs at d ≈ 0.2-1.2 kpc. The remaining eight transients lack quiescent counterparts, exhibit mild but significant astrometric shifts between the g P1 and r P1 images, colors of (g – r)P1 ≈ 0.5-0.8 mag, non-varying light curves, and locations near the ecliptic plane with solar elongations of about 130°, which are all indicative of main-belt asteroids near the stationary point of their orbits. With identifications for all 19 transients, we place an upper limit of R FOT(τ ~ 0.5 hr) lsim 0.12 deg–2 day–1 (95% confidence level) on the sky-projected rate of extragalactic fast transients at lsim 22.5 mag, a factor of 30-50 times lower than previous limits; the limit for a timescale of ~1 day is R FOT lsim 2.4 × 10–3 deg–2 day–1. To convert these sky-projected rates to volumetric rates, we explore the expected peak luminosities of fast optical transients powered by various mechanisms, and find that non-relativistic events are limited to M ≈ –10 to ≈ – 14 mag for a timescale of ~0.5 hr to ~1 day, while relativistic sources (e.g., gamma-ray bursts, magnetar-powered transients) can reach much larger luminosities. The resulting volumetric rates are lsim 13 Mpc–3 yr–1 (M ≈ –10 mag), lsim 0.05 Mpc–3 yr–1 (M ≈ –14 mag), and lsim 10–6 Mpc–3 yr–1 (M ≈ –24 mag), significantly above the nova, supernova, and gamma-ray burst rates, respectively, indicating that much larger surveys are required to provide meaningful constraints. Motivated by the results of our search, we discuss strategies for identifying fast optical transients in the Large Synoptic Survey Telescope main survey, and reach the optimistic conclusion that the veil of foreground contaminants can be lifted with the survey data, without the need for expensive follow-up observations.Publication PS1-10afx at z = 1.388: Pan-STARRS1 Discovery of a New Type of Superluminous Supernova(American Astronomical Society, 2013) Chornock, R; Berger, Edo; Rest, A.; Milisavljevic, Danny; Lunnan, R; Foley, R. J.; Soderberg, Alicia; Smartt, S. J.; Burgasser, A. J.; Challis, Peter; Chomiuk, L.; Czekala, Ian; Drout, Maria Rebecca; Fong, W; Huber, M. E.; Kirshner, Robert; Leibler, C.; McLeod, Brian; Marion, G. H.; Narayan, Gautham; Riess, A. G.; Roth, K. C.; Sanders, Nathan Edward; Scolnic, D.; Smith, K.; Stubbs, Christopher; Tonry, J. L.; Valenti, S.; Burgett, W. S.; Chambers, K. C.; Hodapp, K. W.; Kaiser, N.; Kudritzki, R.-P.; Magnier, E. A.; Price, P. A.We present the Pan-STARRS1 discovery of PS1-10afx, a unique hydrogen-deficient superluminous supernova (SLSN) at redshift z = 1.388. The light curve peaked at z P1 = 21.7 mag, making PS1-10afx comparable to the most luminous known SNe, with Mu = –22.3 mag. Our extensive optical and near-infrared observations indicate that the bolometric light curve of PS1-10afx rose on the unusually fast timescale of ~12 days to the extraordinary peak luminosity of 4.1 × 1044 erg s–1 (M bol = –22.8 mag) and subsequently faded rapidly. Equally important, the spectral energy distribution is unusually red for an SLSN, with a color temperature of ~6800 K near maximum light, in contrast to previous hydrogen-poor SLSNe, which are bright in the ultraviolet (UV). The spectra more closely resemble those of a normal SN Ic than any known SLSN, with a photospheric velocity of ~11, 000 km s–1 and evidence for line blanketing in the rest-frame UV. Despite the fast rise, these parameters imply a very large emitting radius (gsim 5 × 1015 cm). We demonstrate that no existing theoretical model can satisfactorily explain this combination of properties: (1) a nickel-powered light curve cannot match the combination of high peak luminosity with the fast timescale; (2) models powered by the spindown energy of a rapidly rotating magnetar predict significantly hotter and faster ejecta; and (3) models invoking shock breakout through a dense circumstellar medium cannot explain the observed spectra or color evolution. The host galaxy is well detected in pre-explosion imaging with a luminosity near L*, a star formation rate of ~15 M ☉ yr–1, and is fairly massive (~2 × 1010 M ☉), with a stellar population age of ~108 yr, also in contrast to the young dwarf hosts of known hydrogen-poor SLSNe. PS1-10afx is distinct from known examples of SLSNe in its spectra, colors, light-curve shape, and host galaxy properties, suggesting that it resulted from a different channel than other hydrogen-poor SLSNe.Publication High-Precision Radio and Infrared Astrometry of Lspm J1314+1320ab. I. Parallax, Proper Motions, and Limits on Planets(American Astronomical Society, 2016) Forbrich, Jan; Dupuy, Trent J.; Reid, Mark; Berger, Edo; Rizzuto, Aaron; Mann, Andrew W.; Liu, Michael C.; Aller, Kimberly; Kraus, Adam L.We present multi-epoch astrometric radio observations with the Very Long Baseline Array (VLBA) of the young ultracool-dwarf binary LSPM J1314+1320AB . The radio emission comes from the secondary star. Combining the VLBA data with Keck near-infrared adaptive-optics observations of both components, a full astrometric fit of parallax (πabs = 57.975 ± 0.045 mas, corresponding to a distance of d = 17.249 ± 0.013 pc), proper motion (µαcosδ = −247.99 ± 0.10 mas yr−1 , µδ = −183.58 ± 0.22 mas yr−1 ), and orbital motion is obtained. Despite the fact that the two components have nearly identical masses to within ±2%, the secondary’s radio emission exceeds that of the primary by a factor of &30, suggesting a difference in stellar rotation history, which could result in different magnetic field configurations. Alternatively, the emission could be anisotropic and beamed toward us for the secondary but not for the primary. Using only reflex motion, we exclude planets of mass 0.7 to 10 Mjup with orbital periods of 600 to 10 days, respectively. Additionally, we use the full orbital solution of the binary to derive an upper limit for the semi-major axis of 0.23 AU for stable planetary orbits within this system. These limits cover a parameter space that is inaccessible with, and complementary to, near-infrared radial velocity surveys of ultracool dwarfs. Our absolute astrometry will constitute an important test for the astrometric calibration of Gaia.Publication Discovery of an Outflow from Radio Observations of the Tidal Disruption event ASASSN-14li(American Astronomical Society, 2016) Alexander, K. D.; Berger, Edo; Guillochon, J.; Zauderer, B. A.; Williams, PeterWe report the discovery of transient radio emission from the nearby optically-discovered TDE ASASSN-14li (distance of 90 Mpc), making it the first typical TDE detected in the radio, and unambiguously pointing to the formation of a non-relativistic outflow with a kinetic energy of ≈ 4−10×1047 erg, a velocity of ≈ 12, 000 − 36, 000 km s−1 , and a mass of ≈ 3 × 10−5 − 7 × 10−4 M⊙. We show that the outflow was ejected on 2014 August 11–25, in agreement with an independent estimate of the timing of super-Eddington accretion based on the optical, UV, and X-ray observations, and that the ejected mass corresponds to about 1 − 10% of the mass accreted in the super-Eddington phase. The temporal evolution of the radio emission also uncovers the circumnuclear density profile, ρ(R) ∝ R−2.5 on a scale of about 0.01 pc, a scale that cannot be probed via direct measurements even in the nearest SMBHs. Our discovery of radio emission from the nearest well-studied TDE to date, with a radio luminosity lower than all previous limits, indicates that non-relativistic outflows are ubiquitous in TDEs, and that future, more sensitive, radio surveys will uncover similar events.Publication Rapidly-Evolving and Luminous Transients From Pan-Starrs1(IOP Publishing, 2014) Drout, M. R.; Chornock, R.; Soderberg, Alicia; Sanders, Nathan Edward; McKinnon, R.; Rest, A.; Foley, R. J.; Milisavljevic, Danny; Margutti, R.; Berger, Edo; Calkins, M.; Fong, W.; Gezari, S.; Huber, M. E.; Kankare, E.; Kirshner, R. P.; Leibler, C.; Lunnan, R.; Mattila, S.; Marion, G. H.; Narayan, G.; Riess, A. G.; Roth, K. C.; Scolnic, D.; Smartt, S. J.; Tonry, J. L.; Burgett, W. S.; Chambers, K. C.; Hodapp, K. W.; Jedicke, R.; Kaiser, N.; Magnier, E. A.; Metcalfe, N.; Morgan, J. S.; Price, P. A.; Waters, C.In the past decade, several rapidly-evolving transients have been discovered whose timescales and luminosities are not easily explained by traditional supernovae (SN) models. The sample size of these objects has remained small due, at least in part, to the challenges of detecting short timescale transients with traditional survey cadences. Here we present the results from a search within the Pan-STARRS1 Medium Deep Survey (PS1-MDS) for rapidly-evolving and luminous transients. We identify 10 new transients with a time above half-maximum (t1/2) of less than 12 days and −16.5 > M > −20 mag. This increases the number of known events in this region of SN phase space by roughly a factor of three. The median redshift of the PS1-MDS sample is z=0.275 and they all exploded in star forming galaxies. In general, the transients possess faster rise than decline timescale and blue colors at maximum light (gP1 − rP1 . −0.2). Best fit blackbodies reveal photospheric temperatures/radii that expand/cool with time and explosion spectra taken near maximum light are dominated by a blue continuum, consistent with a hot, optically thick, ejecta. We find it difficult to reconcile the short timescale, high peak luminosity (L > 1043 erg s−1), and lack of UV line blanketing observed in many of these transients with an explosion powered mainly by the radioactive decay of 56Ni. Rather, we find that many are consistent with either (1) cooling envelope emission from the explosion of a star with a low-mass extended envelope which ejected very little (<0.03 M⊙) radioactive material, or (2) a shock breakout within a dense, optically thick, wind surrounding the progenitor star. After calculating the detection efficiency for objects with rapid timescales in the PS1-MDS we find a volumetric rate of 4800 − 8000 events yr−1 Gpc−3 (4 − 7% of the core-collapse SN rate at z=0.2).Publication Short-Term Hα Variability in M Dwarfs(IOP Publishing, 2009) Lee, Khee-Gan; Berger, Edo; Knapp, Gillian R.We spectroscopically study the variability of Hα emission in mid- to late-M dwarfs on timescales of ∼ 0.1 − 1 hr as a proxy for magnetic variability. About 80% of our sample exhibits statistically significant variability on the full range of timescales probed by the observations, and with amplitude ratios in the range of ∼ 1.2 − 4. No events with an order of magnitude increase in Hα luminosity were detected, indicating that their rate is . 0.05 hr−1 (95% confidence level). We find a clear increase in variability with later spectral type, despite an overall decrease in Hα “activity” (i.e., LHα/Lbol). For the ensemble of Hα variability events, we find a nearly order of magnitude increase in the number of events from timescales of about 10 to 30 min, followed by a roughly uniform distribution at longer durations. The event amplitudes follow an exponential distribution with a characteristic scale of Max(EW)/Min(EW) − 1 ≈ 0.7. This distribution predicts a low rate of ∼ 10−6 hr−1 for events with Max(EW)/Min(EW) & 10, but serendipitous detections of such events in the past suggests that they represent a different distribution. Finally, we find a possible decline in the amplitude of events with durations of & 0.5 hr, which may point to a typical energy release in Hα events for each spectral type (EHα ∼ LHα × t ∼ const). Longer observations of individual active objects are required to further investigate this possibility. Similarly, a larger sample may shed light on whether Hα variability correlates with properties such as age or rotation velocity.Publication An Ultraviolet–Optical Flare from the Tidal Disruption of a Helium-Rich Stellar Core(Nature Publishing Group, 2012) Gezari, S.; Chornock, R; Rest, A.; Huber, M. E.; Forster, K.; Berger, Edo; Challis, Peter J.; Neill, J. D.; Martin, D. C.; Heckman, T.; Lawrence, A.; Norman, C.; Narayan, Gautham; Foley, R. J.; Marion, G. H.; Scolnic, D.; Chomiuk, Laura; Soderberg, Alicia; Smith, K.; Kirshner, Robert; Riess, A. G.; Smartt, S. J.; Stubbs, Christopher; Tonry, J. L.; Wood-Vasey, W. M.; Burgett, W. S.; Chambers, K. C.; Grav, T.; Heasley, J. N.; Kaiser, N.; Kudritzki, R.-P.; Magnier, E. A.; Morgan, J. S.; Price, P. A.The flare of radiation from the tidal disruption and accretion of a star can be used as a marker for supermassive black holes that otherwise lie dormant and undetected in the centres of distant galaxies1. Previous candidate flares2, 3, 4, 5, 6 have had declining light curves in good agreement with expectations, but with poor constraints on the time of disruption and the type of star disrupted, because the rising emission was not observed. Recently, two ‘relativistic’ candidate tidal disruption events were discovered, each of whose extreme X-ray luminosity and synchrotron radio emission were interpreted as the onset of emission from a relativistic jet7, 8, 9, 10. Here we report a luminous ultraviolet–optical flare from the nuclear region of an inactive galaxy at a redshift of 0.1696. The observed continuum is cooler than expected for a simple accreting debris disk, but the well-sampled rise and decay of the light curve follow the predicted mass accretion rate and can be modelled to determine the time of disruption to an accuracy of two days. The black hole has a mass of about two million solar masses, modulo a factor dependent on the mass and radius of the star disrupted. On the basis of the spectroscopic signature of ionized helium from the unbound debris, we determine that the disrupted star was a helium-rich stellar core.