The Radio Properties of Type Ibc Supernovae

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The Radi Prperties f Type Ibc Supernvae Alicia M. Sderberg Caltech Astrnmy, MC 105-24, Pasadena, CA 91106, USA Abstract.

1 The Radi Prperties f Type Ibc Supernvae Alicia M. Sderberg Caltech Astrnmy, MC , Pasadena, CA 91106, USA Abstract. Over the past few years, lng-duratin 7-ray bursts (GRBs), including the subclass f X- ray flashes (XRFs), have been revealed t be a rare variety f Type Ibc supernva (SN Ibc). While all these events result frm the death f massive stars, the electrmagnetic luminsities f GRBs and XRFs exceed thse f rdinary Type Ibc SNe by many rders f magnitude. The bserved diversity f stellar death crrespnds t large variatins in the energy, velcity, and gemetry f the explsin ejecta. Using multi-wavelength (radi, ptical. X-ray) bservatins f the nearest GRBs, XRFs, and SNe Ibc, I shw that while GRBs and XRFs cuple at least -^ 10^^ erg t relativistic material, SNe Ibc typically cuple < 10^^ erg t their fastest (albeit nn-relativistic) utflws. Specifically, I find that less than 3% f lcal SNe Ibc shw any evidence fr assciatin with a GRB r XRF Recently, a new class f GRB s and XRFs has been revealed which are under-luminus in cmparisn with the statistical sample f GRBs. Owing t their faint high-energy emissin, these sub-energetic bursts are nly detectable nearby (z < 0.1) and are likely 10 times mre cmmn than csmlgical GRBs. In cmparisn with lcal SNe Ibc and typical GRBs/XRFs, these explsins are intermediate in terms f bth vlumetric rate and energetics. Yet the essential physical prcess that causes a dying star t prduce a GRB, XRF, r sub-energetic burst, and nt just a SN, remains a crucial pen questin. Prgress requires a detailed understanding f rdinary SNe Ibc which will be faciutated with the launch f wide-field ptical surveys in the near future. Keywrds: Stars: Supemvae PACS: Bw INTRODUCTION The discvery f several gamma-ray bursts (GRBs) and X-ray flashes (XRFs) at z < 0.3 in the last few years has firmly established that GRBs and XRFs are accmpanied by supemvae f Type Ibc (SNe Ibc) (see Wsley and Blm 1 fr a review). While the distributin f GRB/XRF-SN ptical luminsities appears indistinguishable frm that f lcal SNe Ibc [2], spectrscpy reveals unusually brad absrptin lines ("brad-lined", BL) in every case [3]. At ther wavelengths, these explsins are easily distinguished since GRBs and XRFs prduce mildly-relativistic ejecta, which gives rise t strng nnthermal "afterglw" emissin. Radi bservatins are critical in this analysis since they prvide the best calrimetry f the fastest ejecta. Recenfly, we have identified a ppulatin f GRBs/XRFs that are sub-energetic by a factr f'~ 10^ and abut 10 times mre cmmn than typical bursts [4, 5]. Given their under-luminus prmpt energy release, current satellites can nly detect them nearby (z < 0.1). These sub-energetic explsins are intermediate between GRBs/XRFs and lcal SNe Ibc with respect t gamma-ray energy, jet cllimatin, and vlumetric rate, and thus hint at an verall cntinuum. Mtivated by the GRB/XRF-SN cnnectin and the discvery f sub-energetic GRBs, I embarked n a survey f ptically-selected lcal {d < 200 Mpc) SNe Ibc with the CP937, Supernva 1987A: 20 Years After, edited by S. Immler, K. Weiler, and R. McCray 2007 American Institute f Physics /07/$

2 30 - S 20 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I SNe Ibc discvered SNe Ibc with radi data at t < 150 days I VLA Survey Begins J ffl 10 - VLA Dedicatin I I. n n TTTTT HI Year FIGURE 1. The discvery rate f SNe Ibc each year (yellw) is cmpared with the fractin bserved in the radi n timescales less than 150 days (red). Early radi bservatins are crucial fr cnstraining underluminus and/r ff-axis GRBs since they trace the fastest ejecta in the explsin. Since the launch f ur VLA survey nearly every SN Ibc has been bserved n this timescale. Very Large Array (VLA). The gal is t determine the fractin f SNe Ibc that prduce mildly-relativistic ejecta. This survey is well-suited t recgnizing bursts fr which n gamma-ray emissin is detected, either because the jets are pinted away frm ur line-f-sight ("ff-axis") r the emissin is belw the detectin threshlds f current satellites. Since then I have bserved '~ 200 SNe Ibc with the VLA, n timescales f days t years after the explsin. This dedicated effrt has served t characterize in a systematic way the envirnments and ejecta prperties f SNe Ibc fr the first time. Early radi bservatins are crucial fr identifying sub-energetic and/r uncllimated explsins. On the ther hand, late-time radi bservatins are sensitive t jets initially beamed away frm ur line-f-sight. Thrugh this intense VLA prgram, I have established that (i) rughly 15% f SNe Ibc shw detectable radi emissin, (ii) less than '~ 3% shw radi luminsities cmparable t thse bserved fr GRB/XRF afterglws [6, 5], (iii) less than 10% f SNe Ibc harbr typical GRBs pinted away frm ur line-f-sight [7, 8], and (iv) basic ptical prperties (peak luminsity, phtspheric velcities) are nt reliable indicatrs f strng radi emissin and/r relativistic ejecta. 493

3 A LARGE RADIO SURVEY OF SNE IBC: THE SAMPLE Beginning in 2002,1 have btained radi bservatins fr every newly discvered SN Ibc within a maximum distance f '~ 200 Mpc and accessible t the VLA. All targets are drawn frm astrnmical circulars which typically reprt'~ 20 new SNe Ibc each year, f which'~ 90% are accessible t the VLA. Almst all f the reprted SNe Ibc are fund thrugh "targeted" SN search campaigns which mnitr nly the mst luminus lcal galaxies (e.g., RC3 catalg). Upn spectral classificatin, I immediately trigger a VLA Target-f-Opprtunity bservatin resulting in first epch radi bservatins within a few days f discvery. Since mst SNe Ibc are discvered near maximum light, the first epch VLA bservatins crrespnd t days t weeks after the explsin. Fllw-up bservatins fr each SN are scheduled lgarithmically in time since the explsin. I supplement this sample with radi data f SNe Ibc taken befre The majrity f these data were extracted frm the VLA archive and were primarily taken fr radi studies f nearby galaxies, while sme were taken specifically fr SN fllw-up. As a result, the archival data generally prbe significantly later timescales than my VLA survey. This is highlighted in Figure 1 where the discvery rate f SNe Ibc is cmpared with the fractin bserved with the VLA; early bservatins (/ < 150 days) were uncmmn in the years preceding my VLA survey. The cmbined dataset includes all VLA bservatins f lcal SNe Ibc t date. THE RADIO PROPERTIES OF SNE IBC This large sample f radi bservatins are presented in detail in Sderberg [9]. The large majrity f these bservatins were cnducted at 4.86 and/r 8.46 GHz. As shwn in Figure 2, the fractin f SNe Ibc with detectable radi emissin is small, '~ 15%, crrespnding t a ttal f 30 SNe Ibc detected t date. Of thse with psitive detectins, the majrity ('~ 70%) are discvered befre radi maximum with well-cnstrained spectral peaks. As shwn in Figures 2 and 3, the peak radi luminsities span fur rders f magnitude, iv,radi ~ 10^^ 10^" erg s^^ Hz^^ n timescales f 1 t 1000 days. Figure 2 shws that GRB/XRF-SNe are distinguished frm ptically-selected SNe Ibc by their strng, early-peaking radi emissin. As discussed in the next sectin, these prperties can be used as a prxy fr the presence f relativistic ejecta. Nrmalizing by the distance t which each SN culd be detected and the effective mnitring time f the survey, we prduce the radi luminsity functin shwn in Figure 3. Clearly, sub-luminus radi SNe Ibc are the mst cmmn, thugh least ften detected. As discussed in detail in Sderberg [9], I find n evidence fr any crrelatin between basic ptical prperties (peak luminsity, phtspheric velcities) and radi luminsity. This hlds, in particular, fr the fractin f brad-lined SNe Ibc fr which the radi detectin rate is n higher than that bserved fr rdinary SNe Ibc. I therefre emphasize that neither ptical luminsity nr BL spectral features are reliable prxies fr strng radi emissin. 494

1024 10 100 1000 Time Since Explsin (days) 10000 FIGURE 2. T date, 30 lcal (d < 200 Mpc) SNe Ibc have been detected at radi wavelengths, the majrity f which were fund thrugh my dedicated VLA survey.

4 Time Since Explsin (days) FIGURE 2. T date, 30 lcal (d < 200 Mpc) SNe Ibc have been detected at radi wavelengths, the majrity f which were fund thrugh my dedicated VLA survey. Detectins are shwn as clred lightcurves and 3(7 upper limits as inverted grey triangles. GRB-SN 1998bw and XRF-SN 2006aj, als within the maximum distance f this sample, are distinguished by their bright early peaking radi emissin (black). Bth f these events were sub-energetic in cmparisn with typical GRBs (e.g., GRB ; grey) andxrfs (e.g., XRF020903; grey). THE VELOCITY AND ENERGY OF THE FASTEST EJECTA As discussed by Chevalier [10], the radi emissin frm SNe Ibc is prduced as the fastest ejecta shck-accelerate particles in the circumstellar medium (CSM). Turbulence amplifies the magnetic field and the accelerated (relativistic) electrns prduce synchrtrn radiatin which peaks in the radi band just after the explsin. The spectral peak, defined by a lw-frequency turn-ver, is dminated by synchrtrn self-absrptin (SSA) as shwn by ur detailed studies f several SNe Ibc [11, 12]. This is different than the case fr mst Type II SNe which are dminated by external free-free absrptin due t a dense CSM [13]. As shwn by Readhead [14], fr radi surces dminated by SSA the brightness temperature, Zg = c^fy/{2nk0^v^), is cnstrained t 5 x 10^" K, assuming the pstshck energy density is in equipartitin between magnetic fields, eg, and relativistic electrns, e^. With this assumptin, rbust cnstraints n the radius, r, and internal energy f the shcked CSM, it,, are derived [10,15,16]. These quantities scale as simple 495

10 06aj 9Bbw 3 Z ++++t^ I P I I nil H M I nil H l I I MM H M I MM I I I I MM 10^ * I 10-= IQZ5 IQZe lo^'' 1028 1028 103 Radi Luminsity (erg s~' Hz~') FIGURE 3.

5 10 06aj 9Bbw 3 Z ++++t^ I P I I nil H M I nil H l I I MM H M I MM I I I I MM 10^ * I 10-= IQZ5 IQZe lo^'' Radi Luminsity (erg s~' Hz~') FIGURE 3. Tp: The peak radi luminsity distributin fr lcal SNe Ibc peaks near L v ~ IQp-^ erg s^i Hz^i. The peak radi luminsities f GRB-SN 1998bw and XRF-SN2006aj are shwn fr cmparisn (arrws) since they lie within a cmparable distance as the ptically-selected sample. Bttm: The radi luminsity functin f SNe Ibc. Lw luminsity SNe clearly dminate the intrinsic sample, thugh they are rarely bserved since they fall belw the current VLA detectin limits. We emphasize that this analysis includes several biases, including effective mnitring time pre-2002 and efficiency f ptical spectrscpic classificatin. bservables including the peak spectral frequency, Vp, the flux at the spectral peak, fp, and the luminsity distance, d (see Sderberg et al. 11, 12 fr a detailed discussin). Here we adpt the simple mdel f Chevalier and Franssn 16, assuming e^ = e^ = 0.1 which prvides the fllwing relatins: : 4 X \0^^{fplxniyfl^\dlMpc)^'^l^\vpl5 GHz) cm (1) E, = 1.5 X 10'*^((//Mpc)'^(/p/mJy)'*(Vp/5 GHz)"'(r/10^^ cm)"^ erg. (2) We nte that the radius f the emitting material is nly weakly dependent n the energy partitin fractins, while departures frm equipartitin prduce a strng increase the 496

$1030 1039 1028 1 1 < 1 1 1 1 1 1 1 1 1 1 1 1 ^ 1 1 1 1 1 1 1 yi 1 1 : ^\ ^ * -. \ ^ * ^ \ * * ^^Ni) / "^ \. r\\ ^^^fc // ^ ' *%:vr ^3f.M */ 3 J X) K,^ (0 0!$

6 < ^ yi 1 1 : ^\ ^ * -. \ ^ * ^ \ * * ^^Ni) / "^ \. r\\ ^^^fc // ^ ' *%:vr ^3f.M */ 3 J X) K,^ (0 0! [1, 102'^ / / > m/ / f f^ ^' i' 1 / # # ' / '. / ' ' (tp/days)(i/p/5 GHz) FIGURE 4. The peak radi luminsities f all the SNe Ibc detected t date are pltted against the timescale f peak. SNe with well-cnstrained peaks are shwn as black encircled dts while thse where the peak is nt well cnstrained are shwn as black dts with Unes indicating the extraplatin f the radi Ught-curves between the range f typically bserved peak times. GRB-SN 1998bw and XRF-SN 2006aj were als discvered within this vlume and are shwn as grey stars. Dashed lines indicate hw the velcity f the fastest ejecta scales with the bserved spectral parameters. energy. Taken tgether with the bserved peak time, tp, the velcity f the shck is easily estimated frm Equatin 1 and the resulting values are shwn fr these SNe Ibc in Figure 4. SNe with early, bright radi emissin have the fastest ejecta. As shwn in the Figure, f the thirty radi bright SNe Ibc in this sample, the inferred velcities range frm 0.01 t 0.5c, and nne shw the mildly-relativistic ejecta inferred fr GRB- SN 1998bw [15] r XRF-SN 2006aj [5]. Next is a discussin f the explsin energetics. As derived by Chevalier [17], it, is just r^ 20% f the ttal energy (kinetic and internal) f the shcked CSM, which in turn is equal t the kinetic energy f the fastest ejecta. Including this cnversin factr, we find that the kinetic energy f the fastest ejecta, E^:^ ^^ 5Ei, spans 10^^ 10^^ erg fr SNe Ibc, a factr f 10^ t 10^ times less than that traced by the ptical emissin. Finally, we cmpare these ejecta parameters (velcity, kinetic energy) with thse f GRB and XRFs, including the class f sub-energetic bursts (Figure 5). We find evidence f a clear dichtmy between rdinary SNe Ibc and typical GRBs/XRFs: rdinary SNe cuple rughly 10^^ erg t their fastest (but nn-relativistic) ejecta at v '~ 0.15c. 497

1052 - S 10^ - M CD W S 104B 1046 - Ordinary SNe Ibc Nn-relativistic I 1... Sub-energetic GRB-SNe Relativistic I L. 0.01 0.1 1 10 Velcity f the Fastest Ejecta (T/S) FIGURE 5.

7 S 10^ - M CD W S 104B Ordinary SNe Ibc Nn-relativistic I 1... Sub-energetic GRB-SNe Relativistic I L Velcity f the Fastest Ejecta (T/S) FIGURE 5. The kinetic energy and velcity f the fastest ejecta fr radi bright SNe Ibc are cmpared withthsef GRBs,XRFs, and sub-energetic bursts. Ordinary SNe Ibc (red) are distinguished in that they cuple 10^^ erg t nn-relativistic ejecta at v a; 0.15c while GRBs and XRFs (blue) cuple at 10^^ erg t relativistic material (T a; 10). Sub-energetic bursts (black) are intermediate between the tw classes, cupling at least 10^^ erg t mildly-relativistic (T a; 3). Meanwhile, typical GRBs/XRFs cuple 10^^ erg t relativistic jets with F '~ 10. Subenergetic explsins bridge these tw classes, cupling at least 10^^ erg t mildlyrelativistic utflws with r'~ 3. A related questin is whether the bserved radi emissin fr sme SNe Ibc may be suppressed due t viewing angle effects, specifically imprtant in the case f an assciated GRB jet directed away frm ur line-f-sight [18]. In this scenari a rapid increase in radi emissin is expected as the jet decelerates and spreads sideways, eventually crssing ur line-f-sight n a timescale f '~ 1 yr after the explsin. As shwn in Figure 2 and discussed in Sderberg et al. [8], radi bservatins f '~ 70 SNe Ibc talcen between mnths t decades after the explsin reveal n evidence fr assciated GRB jets. Statistically we cnstrain the fractin f SNe Ibc harbring typical GRB jets t be less than 10%. 498

CONCLUSIONS In cnclusin, based n ur large survey f ptically selected lcal SNe Ibc, I find that (i) rughly 15% shw detectable radi emissin, (ii) the peak radi luminsities f SNe Ibc span fur rders f

8 CONCLUSIONS In cnclusin, based n ur large survey f ptically selected lcal SNe Ibc, I find that (i) rughly 15% shw detectable radi emissin, (ii) the peak radi luminsities f SNe Ibc span fur rders f magnitude with peak times between 1 and 1000 days, (iii) the kinetic energy and fastest velcity f these explsins are significantly different frm thse f typical GRBs and XRFs, (iv) cmpared with the sample f sub-energetic GRBs, <^ 3% f SNe Ibc shw ejecta prperties indicative f an engine-driven explsin, and (v) the fractin f SNe Ibc harbring classical GRB jets viewed ff-axis is cnstrained t less than 10%. Despite this prgress, it remains an pen questin why just'~ 1% f SNe Ibc give rise t GRBs r XRFs. A deeper understanding f the prgenitrs f rdinary SNe Ibc will shed light n this issue. With the recent advent f wide-field ptical surveys, SNe Ibc frm "blind" search campaigns will sn dminate new discveries. Any investigatin f the relatin between the large-scale envirnment (hst galaxy characteristics) and ejecta prperties relies n SNe discvered thrugh these unbiased surveys. In particular, hst galaxy metallicity is argued t be a critical parameter as a prxy fr the prgenitr metallicity. Numerical mdels suggest that nly lw metallicity prgenitrs are able t prduce the accretin-disk pwered utflws inferred fr GRBs [19]. Therefre, these mdels predict that engine-driven explsins are unlikely t be hsted in the luminus, high-metallicity galaxies mnitred by targeted SN searches [20]. Lking frward, a radi survey fcused exclusively n the SNe Ibc discvered thrugh blind surveys will directly address and answer these crucial questins. REFERENCES 1. S. E. Wsley, and J. S. Blm, ARA&A 44, (2006). 2. A. M. Sderberg, et al., ApJ 636, (2006). 3. E. Plan, etal. Nature 442, (2006). 4. A. M. Sderberg, et al., Nature 430, (2004). 5. A. M. Sderberg, etal.,nature 442, (2006), 6. E. Berger, S. R. Kulkami, D. A. Frail, and A. M. Sderberg,^;j/ 599, 408^18 (2003). 7. A. M. Sderberg, D. A. Frail, and M. H. Wieringa, ApJL 607, LI 3-L16 (2004). 8. A. M. Sderberg, E. Nakar, E. Berger, and S. R. Kulkami, ApJ 638, (2006). 9. A. M. Sderberg, ^^ (2007), in preparatin. 10. R. A. Chevalier, ^;j/ 499, 810 (1998). 11. A. M. Sderberg, et al, ApJ 621, (2005). 12. A. M. Sderberg, R. A. ChevaUer, S. R. Kulkami, and D. A. Frail, ^pj 651, (2006). 13. K. W. Weiler, N. Panagia, M. J. Mnies, and R. A. Siamek, ARA&A 40, 387^38 (2002). 14. A. C. S. Readhead,^;^/ 426, (1994). 15. S. R. Kulkami, et al. Nature 39?,, (1998). 16. R. A. Chevalier, and C. Franssn, ^;j/ 651, (2006). 17. R. A. Chevalier, ApJ 111, (1983). 18. B. Vaczyn&ki, Acta Astrnmica 51, 1^ (2001). 19. S. E. Wsley, A. Heger, and T A. Weaver, Reviews f Mdem Physics 74, (2002). 20. K. Z. Stanek, et al., Acta Astrnmica 56, (2006). 499

11. DUAL NATURE OF RADIATION AND MATTER

11. DUAL NATURE OF RADIATION AND MATTER Very shrt answer and shrt answer questins 1. Define wrk functin f a metal? The minimum energy required fr an electrn t escape frm the metal surface is called the