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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"

32494 results found.

  1. GRB 250823A: SVOM/VT optical observation
  2. GRB 250823A: Swift/UVOT Detection
  3. GRB 250823A: NOT optical observations
  4. LIGO/Virgo/KAGRA S250818k: CFH/MegaCam follow-up observation for AT2025ulz
  5. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  6. GRB 250823A: Fermi GBM Observation
  7. GRB 250818B: MeerKAT Detection
  8. GRB 250823A: LCOGT Optical Detection
  9. GRB 250823A: BOOTES6/DPRT early optical detection
  10. GRB 250823A: Liverpool Telescope optical detection
  11. Konus-Wind detection of GRB 250821B
  12. LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS
  13. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  14. LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
  15. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  16. LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
  17. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  18. LIGO/Virgo/Kagra S250818k: STEP/T80N upper limits on 2025ulz
  19. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  20. GRB 250806A: Gemini observations of host galaxy candidate
  21. IPN triangulation of GRB 250821B (long/bright)
  22. GRB 250821A: Kilonova-Catcher optical upper limits
  23. EP250821a: Swift/XRT counterpart fading
  24. GRB 250812A: SVOM/ECLAIRs refined analysis
  25. GRB 250821A: Swift-BAT refined analysis
  26. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  27. LIGO/Virgo/KAGRA S250818k: NOT optical observations of AT2025ulz
  28. EP250821a: Swift/UVOT further observations.
  29. EP250821a: VLT X-shooter spectroscopic redshift z = 0.577
  30. LIGO/Virgo/KAGRA S250818k: GRAWITA TNG NIR observations of AT2025ulz
  31. GRB 250821A: VLT/FORS2 Optical Observation
  32. GRB 250821A: GECAM-B detection
  33. GRB 250821B: SVOM/GRM observation
  34. EP250821a: SVOM/VT optical observation
  35. Fermi GRB 250821B: Global MASTER-Net observations report
  36. GRB 250821A: NOT z-band upper limit
  37. GRB 250821A: KAIT optical upper limit
  38. LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
  39. Swift GRB 250821A: Global MASTER-Net observations report
  40. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of AT 2025ulz
  41. LIGO/Virgo/KAGRA S250818k : Tautenburg observations, upper limits
  42. GRB 250821A: Swift/UVOT Upper Limits
  43. EP250821a: Rapidly fading optical source detected in Las Cumbres followup
  44. EP250821a: Swift XRT and UVOT counterpart detection
  45. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  46. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  47. GRB 250821A: LCOGT Optical Upper Limits
  48. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  49. LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
  50. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  51. LIGO/Virgo/KAGRA S250818k: EP/FXT observation of AT 2025ulz
  52. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  53. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  54. GRB 250818B: 10 GHz VLA detection
  55. LIGO/Virgo/KAGRA S250818k: Pan-STARRS grizy-band imaging and photometry of AT2025ulz
  56. LIGO/Virgo/KAGRA S250818k: Swift observations of AT 2025ulz
  57. LIGO/Virgo/KAGRA S250818k: Multi-band Gemini GMOS Detections
  58. LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
  59. GRB 250814A: Swift/UVOT Upper Limits
  60. GRB 250813B: Swift/UVOT Upper Limit
  61. IPN triangulation of GRB 250816A (short)
  62. IPN triangulation of GRB 250814C (short)
  63. IPN triangulation of GRB 250804B (short)
  64. GRB 250818B: FTW optical and NIR observations show reddening of the counterpart
  65. GRB 250818B: Kilonova-Catcher optical afterglow detection
  66. LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
  67. GRB 250818B: Liverpool Telescope optical detections
  68. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  69. LIGO/Virgo/KAGRA S250818k: Updated Sky localization and EM Bright Classification
  70. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  71. GRB 250818A: AstroSat CZTI detection
  72. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  73. LIGO/Virgo/KAGRA S250818k: Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  74. GRB 250818B: Swift/UVOT Detection
  75. LIGO/Virgo/KAGRA S250818k: FTW Fast reddening of AT 2025ulz
  76. GRB 250818B: optical afterglow detection with Lesedi (GOTO25fzq)
  77. GRB 250818B: TRT Optical Observation
  78. Fermi GRB 250816A: Global MASTER-Net observations report
  79. GRB 250818B: SAO RAS optical observations
  80. Swift GRB 250818A: Global MASTER-Net observations report
  81. GRB 250818B: NOT optical observations
  82. GRB 250818B: EP-FXT counterpart detection
  83. GRB 250818A: Swift-BAT refined analysis
  84. LIGO/Virgo/KAGRA S250818k: FTW optical and NIR observations of AT 2025ulz
  85. GRB 250818B: Keck redshift of the optical afterglow
  86. GRB 250818B: KAIT optical observations
  87. GRB 250818A: Swift/UVOT Upper Limits
  88. LIGO/Virgo/KAGRA S250818t: Updated Sky localization
  89. GRB 250813B: SVOM/ECLAIRs refined analysis
  90. GRB 250818A: Fermi GBM Observation
  91. GRB 250818B: SVOM/VT optical observation
  92. GRB 250814A: Further GRAWITA TNG NIR observations
  93. GRB 250818B: Swift-XRT afterglow detection
  94. GRB 250818B: GOTO optical counterpart candidate
  95. GRB 250818B: SVOM detection of a short burst
  96. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  97. sb25081602: Swift-XRT observations
  98. GRB 250816A: SVOM/GRM observation of a short burst
  99. Fermi GRB 250814B: Global MASTER-Net observations report
  100. GRB 250814A: Swift-BAT refined analysis

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