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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"

32492 results found.

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

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