Browsing by Subject "radio-emission"

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Discovery Of A Cosmological, Relativistic Outburst Via Its Rapidly Fading Optical Emission
(2013-06) Cenko, S. Bradley; Kulkarni, S. R.; Horesh, Assaf; Corsi, Alessandra; Fox, Derek B.; Carpenter, John; Frail, Dale A.; Nugent, Peter E.; Perley, Daniel A.; Gruber, D.; Gal-Yam, Avishay; Groot, Paul J.; Hallinan, G.; Ofek, Eran O.; Rau, Arne; MacLeod, Chelsea L.; Miller, Adam A.; Bloom, Joshua S.; Filippenko, Alexei V.; Kasliwal, Mansi M.; Law, Nicholas M.; Morgan, Adam N.; Polishook, David; Poznanski, Dovi; Quimby, Robert M.; Sesar, Branimir; Shen, Ken J.; Silverman, Jeffrey M.; Sternberg, Assaf; Silverman, Jeffrey M.
We report the discovery by the Palomar Transient Factory (PTF) of the transient source PTF11agg, which is distinguished by three primary characteristics: (1) bright (R-peak = 18.3mag), rapidly fading (Delta R = 4mag in Delta t = 2 days) optical transient emission; (2) a faint (R = 26.2 +/- 0.2mag), blue (g' - R = 0.17 +/- 0.29 mag) quiescent optical counterpart; and (3) an associated year-long, scintillating radio transient. We argue that these observed properties are inconsistent with any known class of Galactic transients (flare stars, X-ray binaries, dwarf novae), and instead suggest a cosmological origin. The detection of incoherent radio emission at such distances implies a large emitting region, from which we infer the presence of relativistic ejecta. The observed properties are all consistent with the population of long-duration gamma-ray bursts (GRBs), marking the first time such an outburst has been discovered in the distant universe independent of a high-energy trigger. We searched for possible high-energy counterparts to PTF11agg, but found no evidence for associated prompt emission. We therefore consider three possible scenarios to account for a GRB-like afterglow without a high-energy counterpart: an "untriggered" GRB (lack of satellite coverage), an "orphan" afterglow (viewing-angle effects), and a "dirty fireball" (suppressed high-energy emission). The observed optical and radio light curves appear inconsistent with even the most basic predictions for off-axis afterglow models. The simplest explanation, then, is that PTF11agg is a normal, on-axis long-duration GRB for which the associated high-energy emission was simply missed. However, we have calculated the likelihood of such a serendipitous discovery by PTF and find that it is quite small (approximate to 2.6%). While not definitive, we nonetheless speculate that PTF11agg may represent a new, more common (>4 times the on-axis GRB rate at 90% confidence) class of relativistic outbursts lacking associated high-energy emission. If so, such sources will be uncovered in large numbers by future wide-field optical and radio transient surveys.
Dust And The Type II-Plateau Supernova 2004dj
(2011-05) Meikle, W. P. S.; Kotak, R.; Farrah, D.; Mattila, S.; Van Dyk, S. D.; Andersen, A. C.; Fesen, R.; Filippenko, Alexei V.; Foley, Ryan J.; Fransson, C.; Gerardy, C. L.; Hoflich, Peter A.; Lundqvist, P.; Pozzo, M.; Sollerman, Jesper; Wheeler, J. Craig; heeler, J. Craig
We present mid-infrared (MIR) spectroscopy of a Type II-plateau supernova, SN 2004dj, obtained with the Spitzer Space Telescope, spanning 106-1393 days after explosion. MIR photometry plus optical/near-IR observations are also reported. An early-time MIR excess is attributed to emission from non-silicate dust formed within a cool dense shell (CDS). Most of the CDS dust condensed between 50 days and 165 days, reaching a mass of 0.3 x 10(-5) M-circle dot. Throughout the observations, much of the longer wavelength (> 10 mu m) part of the continuum is explained as an IR echo from interstellar dust. The MIR excess strengthened at later times. We show that this was due to thermal emission from warm, non-silicate dust formed in the ejecta. Using optical/near-IR line profiles and the MIR continua, we show that the dust was distributed as a disk whose radius appeared to be shrinking slowly. The disk radius may correspond to a grain destruction zone caused by a reverse shock which also heated the dust. The dust-disk lay nearly face-on, had high opacities in the optical/near-IR regions, but remained optically thin in the MIR over much of the period studied. Assuming a uniform dust density, the ejecta dust mass by 996 days was (0.5 +/- 0.1) x 10(-4) M-circle dot and exceeded 10(-4) M-circle dot by 1393 days. For a dust density rising toward the center the limit is higher. Nevertheless, this study suggests that the amount of freshly synthesized dust in the SN 2004dj ejecta is consistent with that found from previous studies and adds further weight to the claim that such events could not have been major contributors to the cosmic dust budget.
M• − σRelation For Intermediate-Mass Black Holes In Globular Clusters
(2013-07) Lutzgendorf, N.; Kissler-Patig, M.; Neumayer, N.; Baumgardt, H.; Noyola, E.; de Zeeuw, P. T.; Gebhardt, K.; Jalali, B.; Feldmeier, A.; Gebhardt, K.
Context. For galaxies hosting supermassive black holes (SMBHs), it has been observed that the mass of the central black hole (M center dot) tightly correlates with the effective or central velocity dispersion (s) of the host galaxy. The origin of this M center dot - sigma scaling relation is assumed to lie in the merging history of the galaxies, but many open questions about its origin and the behavior in different mass ranges still need to be addressed. Aims. The goal of this work is to study the black-hole scaling relations for low black-hole masses, where the regime of intermediatemass black holes (IMBHs) in globular clusters (GCs) is entered. Methods. We collected all existing reports of dynamical black-hole measurements in GCs, providing black-hole masses or upper limits for 14 candidates. We plotted the black-hole masses versus different cluster parameters including total mass, velocity dispersion, concentration, and half-mass radius. We searched for trends and tested the correlations to quantify their significance using a set of different statistical approaches. For correlations with a high significance we performed a linear fit, accounting for uncertainties and upper limits. Results. We find a clear correlation between the mass of the IMBH and the velocity dispersion of the GC. As expected, the total mass of the GC then also correlates with the mass of the IMBH. While the slope of the M center dot - sigma correlation differs strongly from the one observed for SMBHs, the other scaling relations M center dot - M-tot, and M center dot - L are similar to the correlations in galaxies. Significant correlations of black-hole mass with other cluster properties were not found in the present sample.
M• − σRelation For Intermediate-Mass Black Holes In Globular Clusters
(2013-07) Lutzgendorf, N.; Kissler-Patig, M.; Neumayer, N.; Baumgardt, H.; Noyola, E.; de Zeeuw, P. T.; Gebhardt, K.; Jalali, B.; Feldmeier, A.; Gebhardt, K.
Context. For galaxies hosting supermassive black holes (SMBHs), it has been observed that the mass of the central black hole (M center dot) tightly correlates with the effective or central velocity dispersion (s) of the host galaxy. The origin of this M center dot - sigma scaling relation is assumed to lie in the merging history of the galaxies, but many open questions about its origin and the behavior in different mass ranges still need to be addressed. Aims. The goal of this work is to study the black-hole scaling relations for low black-hole masses, where the regime of intermediatemass black holes (IMBHs) in globular clusters (GCs) is entered. Methods. We collected all existing reports of dynamical black-hole measurements in GCs, providing black-hole masses or upper limits for 14 candidates. We plotted the black-hole masses versus different cluster parameters including total mass, velocity dispersion, concentration, and half-mass radius. We searched for trends and tested the correlations to quantify their significance using a set of different statistical approaches. For correlations with a high significance we performed a linear fit, accounting for uncertainties and upper limits. Results. We find a clear correlation between the mass of the IMBH and the velocity dispersion of the GC. As expected, the total mass of the GC then also correlates with the mass of the IMBH. While the slope of the M center dot - sigma correlation differs strongly from the one observed for SMBHs, the other scaling relations M center dot - M-tot, and M center dot - L are similar to the correlations in galaxies. Significant correlations of black-hole mass with other cluster properties were not found in the present sample.
Two-fluid temperature-dependent relativistic waves in magnetized streaming pair plasmas
(2010-02) Soto-Chavez, A. R.; Mahajan, S. M.; Hazeltine, R. D.; Soto-Chavez, A. R.; Mahajan, S. M.; Hazeltine, R. D.
A relativistic two-fluid temperature-dependent approach for a streaming magnetized pair plasma is considered. Such a scenario corresponds to secondary plasmas created at the polar caps of pulsar magnetospheres. In the model the generalized vorticity rather than the magnetic field is frozen into the fluid. For parallel propagation four transverse modes are found. Two are electromagnetic plasma modes which at high temperature become light waves. The remaining two are Alfveacutenic modes split into a fast and slow mode. The slow mode is cyclotron two-stream unstable at large wavelengths and is always subluminous. We find that the instability cannot be suppressed by temperature effects in the limit of large (finite) magnetic field. The fast Alfveacuten mode can be superluminous only at large wavelengths, however it is always subluminous at high temperatures. In this incompressible approximation only the ordinary mode is present for perpendicular propagation. For oblique propagation the dispersion relation is studied for finite and large strong magnetic fields and the results are qualitatively described.