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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
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To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

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subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"

8474 results found.

  1. LIGO/Virgo/KAGRA S250912s: 2 counterpart neutrino candidate events from an IceCube neutrino search
  2. EP250908c: tentative VLT/FORS2 redshift z = 2.87
  3. EP250911a: Upper limit from Fermi-GBM Observations
  4. LIGO/Virgo/KAGRA S250912f: Updated Sky localization
  5. LIGO/Virgo/KAGRA S250912f: Identification of a GW compact binary merger candidate
  6. EP250911a: Optical detection with Kinder observations
  7. LIGO/Virgo/KAGRA S250911ac: Updated Sky localization and Source Classification
  8. LIGO/Virgo/KAGRA S250908y: Updated Sky localization
  9. LIGO/Virgo/KAGRA S250911ac: Identification of a GW compact binary merger candidate
  10. GRB 250911A: COLIBRÍ optical counterpart candidate
  11. LIGO/Virgo/KAGRA S250906ca: Updated Sky localization
  12. GRB 250910A: SVOM/VT optical upper limit
  13. EP250908C: GROND observation of the fading optical counterpart
  14. LIGO/Virgo/KAGRA S250910b: Retraction of GW compact binary merger candidate
  15. EP#01709240653: Swift-XRT observations
  16. EP250908b: SVOM/VT optical candidate (Coordinate supplement for GCN 41758)
  17. EP250908b: SVOM/VT optical candidate
  18. LIGO/Virgo/KAGRA S250908y: Identification of a GW compact binary merger candidate
  19. LIGO/Virgo/KAGRA S250906ca: Identification of a GW compact binary merger candidate
  20. IceCube-250905A: Upper limits from a search for additional neutrino events in IceCube
  21. LIGO/Virgo/KAGRA S250830bp: DECam/SOAR GW-MMADS updates
  22. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 2 Candidates
  23. IceCube-250905A - IceCube observation of a high-energy neutrino candidate track-like event
  24. LIGO/Virgo/KAGRA S250904cv: Updated Sky localization
  25. LIGO/Virgo/KAGRA S250904br: Updated Sky localization
  26. GRB 250905A: KAIT optical upper limit
  27. GRB 250905A: Swift detection of a burst
  28. IceCube-Cascade 250903A: Upper limits from a search for additional neutrino events in IceCube
  29. EP250827a and EP250827b: Upper limit from Fermi-GBM Observations
  30. GRB 250904A: Swift detection of a burst
  31. LIGO/Virgo/KAGRA S250904ae: Updated Sky localization
  32. LIGO/Virgo/KAGRA S250904cv: Identification of a GW compact binary merger candidate
  33. GRB 250903A: Swift-XRT observations
  34. EP250903a: Swift-XRT observations
  35. EP250903a: retraction of the LCO candidate, and discovery of the likely counterpart
  36. LIGO/Virgo/KAGRA S250904br: Identification of a GW compact binary merger candidate
  37. LIGO/Virgo/KAGRA S250904ae: Identification of a GW compact binary merger candidate
  38. EP250903a: LCO candidate counterpart discovery
  39. EP/WXT01709201159: GOTO optical follow-up
  40. IceCube-250831A: Upper limits from a search for additional neutrino events in IceCube
  41. LIGO/Virgo/KAGRA S250902av: 1 counterpart neutrino candidate event from an IceCube neutrino search
  42. LIGO/Virgo/KAGRA S250901cb: Updated Sky localization
  43. IceCube-Cascade 250828A: Upper limits from a search for additional neutrino events in IceCube
  44. LIGO/Virgo/KAGRA S250830bp: DECam GW-MMADS candidates
  45. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 1 Candidates
  46. LIGO/Virgo/KAGRA S250901cb: Identification of a GW compact binary merger candidate
  47. EP250831a: NOT optical observations and tentative afterglow candidate
  48. LIGO/Virgo/KAGRA S250830m: Updated Sky localization
  49. LIGO/Virgo/KAGRA S250831cc: Coverage and upper limits from MAXI/GSC observations
  50. IceCube-250831A - IceCube observation of a high-energy neutrino candidate track-like event
  51. GRB 250831A: Swift-XRT counterpart detection
  52. LIGO/Virgo/KAGRA S250830bp: Coverage and upper limits from MAXI/GSC observations
  53. LIGO/Virgo/KAGRA S250830bp: NED Galaxies in the 4-Update Localization Volume
  54. LIGO/Virgo/KAGRA S250830bp: Updated Sky localization, EM Bright Classification, and Source Classification
  55. LIGO/Virgo/KAGRA S250830bp: Identification of a GW compact binary merger candidate
  56. GRB 250830B: Swift ToO observations
  57. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  58. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  59. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  60. EP250828a: Optical counterpart detection with Kinder observations
  61. EP250828a: Liverpool Telescope upper limits
  62. EP250828a: NOT optical counterpart confirmation
  63. EP250828a: SVOM/VT optical candidate
  64. EP250828a: Optical upper limit with Kinder observations
  65. LIGO/Virgo/KAGRA S250827fo: Updated Sky localization
  66. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  67. LIGO/Virgo/KAGRA S250827l: Updated Sky localization
  68. EP250827a: BOOTES-7 early optical dectection
  69. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  70. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  71. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  72. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  73. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  74. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  75. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  76. LIGO/Virgo/KAGRA S250818k: CFH/MegaCam follow-up observation for AT2025ulz
  77. GRB 250823A: Swift detection of a burst
  78. LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS
  79. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  80. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  81. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  82. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  83. GRB 250806A: Gemini observations of host galaxy candidate
  84. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  85. LIGO/Virgo/KAGRA S250818k: GRAWITA TNG NIR observations of AT2025ulz
  86. GRB 250821A: KAIT optical upper limit
  87. LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
  88. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of AT 2025ulz
  89. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  90. LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
  91. GRB 250821A: Swift detection of a burst
  92. LIGO/Virgo/KAGRA S250818k: Multi-band Gemini GMOS Detections
  93. GRB 250818B: Kilonova-Catcher optical afterglow detection
  94. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  95. LIGO/Virgo/KAGRA S250818k: Updated Sky localization and EM Bright Classification
  96. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  97. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  98. LIGO/Virgo/KAGRA S250818k: Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  99. GRB 250818B: Keck redshift of the optical afterglow
  100. LIGO/Virgo/KAGRA S250818t: Updated Sky localization

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