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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').
Advanced Search

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.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"
  1. LIGO/Virgo/KAGRA S250827l: Updated Sky localization
  2. The EP-WXT trigger 01709200800 is likely a flaring star
  3. EP250827a: TRT optical observations
  4. EP250827a: BOOTES-7 early optical dectection
  5. EP250827a / GRB 250827A: MASTER-OAFA OT observation
  6. EP250827a: Gemini-South redshift z = 1.613
  7. EP250827a: Global MASTER-Net observations report
  8. EP250827a: Las Cumbres independent detection of the optical counterpart
  9. EP250827a: Gemini-South optical counterpart detection
  10. EP250827a: Einstein Probe detection of an X-ray transient
  11. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  12. Fermi GRB 250826A: Global MASTER-Net observations report
  13. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  14. EP250821a: Gemini GMOS Redshift Confirmation
  15. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  16. Fermi trigger No 777883624: Global MASTER-Net observations report
  17. Fermi Gamma-ray Burst Monitor trigger 777883624/250826283 is not a GRB
  18. GRB 250826A: Fermi GBM Final Real-time Localization
  19. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  20. Fermi GRB 250824B: Global MASTER-Net observations report
  21. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  22. LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
  23. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  24. GRB 250823A: Swift-BAT refined analysis
  25. LIGO/Virgo/KAGRA S250818k: Continued Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  26. GRB 250821B: AstroSat CZTI detection
  27. GRB 250819A: AstroSat CZTI detection
  28. LIGO/Virgo/KAGRA S250818k: FTW Observations Show Continued Reddening of AT 2025ulz
  29. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  30. GRB 250821B: Insight-HXMT detection
  31. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  32. GRB 250823A: Swift-XRT refined Analysis
  33. EP250821a: MeerKAT radio counterpart
  34. EP triggers 01709200706 and 01709200707: GOTO confirmation of flaring stars
  35. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  36. GRB 250824B: Fermi GBM Final Real-time Localization
  37. The EP-WXT trigger 01709200707 is likely a flaring star
  38. GRB 250823A: COLIBRÍ optical observations
  39. The EP-WXT trigger 01709200706 is likely a flaring star
  40. GRB 250823A: SVOM/VT optical observation
  41. GRB 250824A: Fermi GBM Final Real-time Localization
  42. GRB 250823A: Swift/UVOT Detection
  43. GRB 250823A: NOT optical observations
  44. LIGO/Virgo/KAGRA S250818k: CFH/MegaCam follow-up observation for AT2025ulz
  45. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  46. GRB 250823A: Fermi GBM Observation
  47. GRB 250818B: MeerKAT Detection
  48. GRB 250823A: Enhanced Swift-XRT position
  49. GRB 250823A: LCOGT Optical Detection
  50. GRB 250823A: BOOTES6/DPRT early optical detection
  51. GRB 250823A: Liverpool Telescope optical detection
  52. GRB 250823A: Swift detection of a burst
  53. GRB 250823A: Fermi GBM Final Real-time Localization
  54. Swift GRB250823.84: Global MASTER-Net observations report
  55. Konus-Wind detection of GRB 250821B
  56. LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS
  57. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  58. LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
  59. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  60. LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
  61. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  62. LIGO/Virgo/Kagra S250818k: STEP/T80N upper limits on 2025ulz
  63. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  64. GRB 250806A: Gemini observations of host galaxy candidate
  65. IPN triangulation of GRB 250821B (long/bright)
  66. GRB 250821A: Kilonova-Catcher optical upper limits
  67. EP250821a: Swift/XRT counterpart fading
  68. GRB 250812A: SVOM/ECLAIRs refined analysis
  69. GRB 250821A: Swift-BAT refined analysis
  70. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  71. LIGO/Virgo/KAGRA S250818k: NOT optical observations of AT2025ulz
  72. EP250821a: Swift/UVOT further observations.
  73. EP250821a: VLT X-shooter spectroscopic redshift z = 0.577
  74. LIGO/Virgo/KAGRA S250818k: GRAWITA TNG NIR observations of AT2025ulz
  75. GRB 250821A: VLT/FORS2 Optical Observation
  76. GRB 250821A: GECAM-B detection
  77. GRB 250821B: SVOM/GRM observation
  78. EP250821a: SVOM/VT optical observation
  79. Fermi GRB 250821B: Global MASTER-Net observations report
  80. GRB 250821A: NOT z-band upper limit
  81. GRB 250821C: Fermi GBM Final Real-time Localization
  82. GRB 250821A: KAIT optical upper limit
  83. LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
  84. GRB 250821A: Swift-XRT refined Analysis
  85. Swift GRB 250821A: Global MASTER-Net observations report
  86. GRB 250821B: Fermi GBM Detection
  87. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of AT 2025ulz
  88. GRB 250821B: BALROG localization (Fermi Trigger / GRB 250821672)
  89. LIGO/Virgo/KAGRA S250818k : Tautenburg observations, upper limits
  90. GRB 250821B: Fermi GBM Final Localization of a Bright Burst
  91. GRB 250821A: Enhanced Swift-XRT position
  92. GRB 250821A: Swift/UVOT Upper Limits
  93. EP250821a: Rapidly fading optical source detected in Las Cumbres followup
  94. EP250821a: Swift XRT and UVOT counterpart detection
  95. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  96. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  97. GRB 250821A: LCOGT Optical Upper Limits
  98. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  99. LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
  100. GRB 250821A: Prompt enhanced Swift-XRT position

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